90 l98 is loses power
07-23-2014, 07:35 PM
#1
Racer
Thread Starter
90 l98 is loses power
I know a lot of this has been addressed in the past and I have read a lot of it. I am trying to understand why my L98 won't run right. Had fuel injectors cleaned and new timing chain installed to correct problem of surging at idle and almost no power on WOT. Have new fuel pump and sock; new knock sensor everything else is supposed to be good. After timing chain installed picked a bad engine knock and still had surging and no power. IACV was loose, fixed that; don't know if ECM is throwing codes. Most of the major gaskets have been replaced. Now after all that...cold engine car starts right up; runs fine for 10 miles or so and then starts to stumble and gradually lose power until it will not downshift into passing gear when I push on the gas even up to WOT. It just does nothing but miss, sputter and stumble. I did notice that someone had plugged the MAP vacuum line; hooked this up and the knock stopped but rest of problems continued. If I keep driving and try hard acceleration, the temp gauge bounces back and forth between 210 - 260 but none of the normal, obvious signs of overheating. In this condition it also started leaking oil and burning off on the exhaust. I am at my wits end. Any suggestions please. BTW: engine has 101K miles, does not burn oil had no problems prior to this. I drive (at least did) it drive five times a week. thanks.
07-23-2014, 10:29 PM
#3
Instructor
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Location: NW Arkansas - usually winter in FL
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Hi Tom – understand you frustrations, been there and done that a few times myself.
Anyway, not trying to be a smart-*** or anything like that but it takes only three things for an engine to run. They are fuel, spark and compression. I seriously doubt if compression is disappearing so that leaves only fuel and spark.
My recommendation has always been to diagnose a problem first instead of just tossing parts at it. Guess what I’m trying to say is it might be prudent to try and diagnose the situation when the problem is in attendance.
This is what I would do – certainly others will suggest a different approach.
One easy way to check for fuel is to connect a fuel pressure gauge and then tape it to the outside of the windshield. It’s not wise to have a mechanical fuel pressure gauge inside the car because of the fire hazard – have seen a few cars catch fire because of leaks and blown hoses and the resulting burns are very painful indeed. Anyway, if the pressures are where they should be, the fuel delivery system is doing what it should be and the problem is lying elsewhere.
Connect a voltmeter to the battery + side of the injectors, drive the car until it acts up and then see if the voltage there is close to battery voltage – about 13.20 volts or thereabouts. If the voltage is ok when the engine begins to do it’s stumble thing, then the situation is farther downstream – like Mr Willis says, defective ECU or something inside the distributor.
To do a simple check of the injectors, what I have done in the past is take an LED and attach a couple of long wires to it. Use alligator clamps and then connect one end of the wire to the battery positive and the other wire end to the injector harness that goes to the ECU. This will be the ground side of the injector. Make sure to install a two amp fuse near the end of the wire which connects to the battery +, no sense in starting a fire here. Now, every time the ECU grounds the injector, the LED will then illuminate – it will pulse each time the ECU grounds the injectors. As long as the illumination blinks are consistent, then the ECU is grounding the injectors, as it should. The extremely low current draw of an LED will have no adverse effect on the ECU or any other system. The injectors are energized (opened and fuel flows) when the ECU grounds them. The amount of fuel delivered is controlled by the length of time the ECU is grounding the injector circuit thereby holding it open and allowing fuel to flow.
This is sort of like building your own “noid light” but with this one you can see what is happening while driving the car. It a good investment to make since it will cost less than five bucks, can be used as a normal test light and will last several lifetimes too.
That leaves spark and this might be where the problem is. Any coil can check out ok when cold but they can develop internal shorts and shorts-to-ground as the temperatures increase. This holds true of any type of coil anywhere and will become more pronounced as the voltage and current flow through the coil increases. Same holds true for electronic components, might be OK when cold but do crazy things when they get hot hence the ICU inside the distributor might be defective. Same for the ECU it self.
You can use your home made “noid light” above to check some of the ignition system too. Connections to the battery + are the same and then just connect the other wire to the coil ground – if you can somehow get at it inside the HEI distributor – might be tough (in all practicality might be easier just to replace the ICU and be done with it!). Anyway, if your noid is then flashing and it is consistent, then in all likelihood, the primary ignition system – low voltage side - is doing its job. The secondary high voltage side is usually quite easy – just look at the distributor cap, rotor and wires for any damage. Also, use the FSM and make sure the distributor is properly indexed – i.e., it is installed correctly with respect to the distributor drive gear on the camshaft. Being off only one tooth can cause all kinds of problems as the secondary voltage begins to arc and dance all around the inside of the cap instead of going where it should. Usually this happens when cold too. Not familiar with an Opti so best if others chime in to help you with that.
Several years ago, I did witness a crazy situation where the battery + feed somewhere was making contact with the O2 sensor output wire that goes to the ECU. Since the ECU was then seeing a high voltage output from the O2 sensor, thereby thinking the engine was pig rich, it leaned out the fuel mixture to its full range of authority – to the point where the engine would barely run. It would begin to stumble and miss as you describe.
Anyhow my guess is your problem is either fuel or spark and I’m leaning toward spark or electronic engine controls. Since the engine operates satisfactorly when cold, that tells me that all major mechanical components of your car are ok.
On thing caught my attention and that is your temp gauge is running all over the place. Cannot say for sure but usually these weird electrical things result from faulty ground paths as much as anything else. Any chance that when doing all these repairs on the car that a ground wire was disconnected and then never hooked up again? Just a thought.
Sorry for the rant, I do get a little (a lot??) over analytical at times – but am always curious to see what is going on instead of just shotgunning the damn thing! LOL! Hope I’ve helped out a little – if not finding the problem itself, then stimulating the brain a little and perhaps giving some direction.
Good luck to you – you will find it and when you do, the reasoning behind the malfunction will become crystal clear.
Please get back and tell us what you find.
Jake -
Anyway, not trying to be a smart-*** or anything like that but it takes only three things for an engine to run. They are fuel, spark and compression. I seriously doubt if compression is disappearing so that leaves only fuel and spark.
My recommendation has always been to diagnose a problem first instead of just tossing parts at it. Guess what I’m trying to say is it might be prudent to try and diagnose the situation when the problem is in attendance.
This is what I would do – certainly others will suggest a different approach.
One easy way to check for fuel is to connect a fuel pressure gauge and then tape it to the outside of the windshield. It’s not wise to have a mechanical fuel pressure gauge inside the car because of the fire hazard – have seen a few cars catch fire because of leaks and blown hoses and the resulting burns are very painful indeed. Anyway, if the pressures are where they should be, the fuel delivery system is doing what it should be and the problem is lying elsewhere.
Connect a voltmeter to the battery + side of the injectors, drive the car until it acts up and then see if the voltage there is close to battery voltage – about 13.20 volts or thereabouts. If the voltage is ok when the engine begins to do it’s stumble thing, then the situation is farther downstream – like Mr Willis says, defective ECU or something inside the distributor.
To do a simple check of the injectors, what I have done in the past is take an LED and attach a couple of long wires to it. Use alligator clamps and then connect one end of the wire to the battery positive and the other wire end to the injector harness that goes to the ECU. This will be the ground side of the injector. Make sure to install a two amp fuse near the end of the wire which connects to the battery +, no sense in starting a fire here. Now, every time the ECU grounds the injector, the LED will then illuminate – it will pulse each time the ECU grounds the injectors. As long as the illumination blinks are consistent, then the ECU is grounding the injectors, as it should. The extremely low current draw of an LED will have no adverse effect on the ECU or any other system. The injectors are energized (opened and fuel flows) when the ECU grounds them. The amount of fuel delivered is controlled by the length of time the ECU is grounding the injector circuit thereby holding it open and allowing fuel to flow.
This is sort of like building your own “noid light” but with this one you can see what is happening while driving the car. It a good investment to make since it will cost less than five bucks, can be used as a normal test light and will last several lifetimes too.
That leaves spark and this might be where the problem is. Any coil can check out ok when cold but they can develop internal shorts and shorts-to-ground as the temperatures increase. This holds true of any type of coil anywhere and will become more pronounced as the voltage and current flow through the coil increases. Same holds true for electronic components, might be OK when cold but do crazy things when they get hot hence the ICU inside the distributor might be defective. Same for the ECU it self.
You can use your home made “noid light” above to check some of the ignition system too. Connections to the battery + are the same and then just connect the other wire to the coil ground – if you can somehow get at it inside the HEI distributor – might be tough (in all practicality might be easier just to replace the ICU and be done with it!). Anyway, if your noid is then flashing and it is consistent, then in all likelihood, the primary ignition system – low voltage side - is doing its job. The secondary high voltage side is usually quite easy – just look at the distributor cap, rotor and wires for any damage. Also, use the FSM and make sure the distributor is properly indexed – i.e., it is installed correctly with respect to the distributor drive gear on the camshaft. Being off only one tooth can cause all kinds of problems as the secondary voltage begins to arc and dance all around the inside of the cap instead of going where it should. Usually this happens when cold too. Not familiar with an Opti so best if others chime in to help you with that.
Several years ago, I did witness a crazy situation where the battery + feed somewhere was making contact with the O2 sensor output wire that goes to the ECU. Since the ECU was then seeing a high voltage output from the O2 sensor, thereby thinking the engine was pig rich, it leaned out the fuel mixture to its full range of authority – to the point where the engine would barely run. It would begin to stumble and miss as you describe.
Anyhow my guess is your problem is either fuel or spark and I’m leaning toward spark or electronic engine controls. Since the engine operates satisfactorly when cold, that tells me that all major mechanical components of your car are ok.
On thing caught my attention and that is your temp gauge is running all over the place. Cannot say for sure but usually these weird electrical things result from faulty ground paths as much as anything else. Any chance that when doing all these repairs on the car that a ground wire was disconnected and then never hooked up again? Just a thought.
Sorry for the rant, I do get a little (a lot??) over analytical at times – but am always curious to see what is going on instead of just shotgunning the damn thing! LOL! Hope I’ve helped out a little – if not finding the problem itself, then stimulating the brain a little and perhaps giving some direction.
Good luck to you – you will find it and when you do, the reasoning behind the malfunction will become crystal clear.
Please get back and tell us what you find.
Jake -
07-24-2014, 12:13 AM
#4
Racer
Thread Starter
Hi Tom – understand you frustrations, been there and done that a few times myself.
Anyway, not trying to be a smart-*** or anything like that but it takes only three things for an engine to run. They are fuel, spark and compression. I seriously doubt if compression is disappearing so that leaves only fuel and spark.
My recommendation has always been to diagnose a problem first instead of just tossing parts at it. Guess what I’m trying to say is it might be prudent to try and diagnose the situation when the problem is in attendance.
This is what I would do – certainly others will suggest a different approach.
One easy way to check for fuel is to connect a fuel pressure gauge and then tape it to the outside of the windshield. It’s not wise to have a mechanical fuel pressure gauge inside the car because of the fire hazard – have seen a few cars catch fire because of leaks and blown hoses and the resulting burns are very painful indeed. Anyway, if the pressures are where they should be, the fuel delivery system is doing what it should be and the problem is lying elsewhere.
Connect a voltmeter to the battery + side of the injectors, drive the car until it acts up and then see if the voltage there is close to battery voltage – about 13.20 volts or thereabouts. If the voltage is ok when the engine begins to do it’s stumble thing, then the situation is farther downstream – like Mr Willis says, defective ECU or something inside the distributor.
To do a simple check of the injectors, what I have done in the past is take an LED and attach a couple of long wires to it. Use alligator clamps and then connect one end of the wire to the battery positive and the other wire end to the injector harness that goes to the ECU. This will be the ground side of the injector. Make sure to install a two amp fuse near the end of the wire which connects to the battery +, no sense in starting a fire here. Now, every time the ECU grounds the injector, the LED will then illuminate – it will pulse each time the ECU grounds the injectors. As long as the illumination blinks are consistent, then the ECU is grounding the injectors, as it should. The extremely low current draw of an LED will have no adverse effect on the ECU or any other system. The injectors are energized (opened and fuel flows) when the ECU grounds them. The amount of fuel delivered is controlled by the length of time the ECU is grounding the injector circuit thereby holding it open and allowing fuel to flow.
This is sort of like building your own “noid light” but with this one you can see what is happening while driving the car. It a good investment to make since it will cost less than five bucks, can be used as a normal test light and will last several lifetimes too.
That leaves spark and this might be where the problem is. Any coil can check out ok when cold but they can develop internal shorts and shorts-to-ground as the temperatures increase. This holds true of any type of coil anywhere and will become more pronounced as the voltage and current flow through the coil increases. Same holds true for electronic components, might be OK when cold but do crazy things when they get hot hence the ICU inside the distributor might be defective. Same for the ECU it self.
You can use your home made “noid light” above to check some of the ignition system too. Connections to the battery + are the same and then just connect the other wire to the coil ground – if you can somehow get at it inside the HEI distributor – might be tough (in all practicality might be easier just to replace the ICU and be done with it!). Anyway, if your noid is then flashing and it is consistent, then in all likelihood, the primary ignition system – low voltage side - is doing its job. The secondary high voltage side is usually quite easy – just look at the distributor cap, rotor and wires for any damage. Also, use the FSM and make sure the distributor is properly indexed – i.e., it is installed correctly with respect to the distributor drive gear on the camshaft. Being off only one tooth can cause all kinds of problems as the secondary voltage begins to arc and dance all around the inside of the cap instead of going where it should. Usually this happens when cold too. Not familiar with an Opti so best if others chime in to help you with that.
Several years ago, I did witness a crazy situation where the battery + feed somewhere was making contact with the O2 sensor output wire that goes to the ECU. Since the ECU was then seeing a high voltage output from the O2 sensor, thereby thinking the engine was pig rich, it leaned out the fuel mixture to its full range of authority – to the point where the engine would barely run. It would begin to stumble and miss as you describe.
Anyhow my guess is your problem is either fuel or spark and I’m leaning toward spark or electronic engine controls. Since the engine operates satisfactorly when cold, that tells me that all major mechanical components of your car are ok.
On thing caught my attention and that is your temp gauge is running all over the place. Cannot say for sure but usually these weird electrical things result from faulty ground paths as much as anything else. Any chance that when doing all these repairs on the car that a ground wire was disconnected and then never hooked up again? Just a thought.
Sorry for the rant, I do get a little (a lot??) over analytical at times – but am always curious to see what is going on instead of just shotgunning the damn thing! LOL! Hope I’ve helped out a little – if not finding the problem itself, then stimulating the brain a little and perhaps giving some direction.
Good luck to you – you will find it and when you do, the reasoning behind the malfunction will become crystal clear.
Please get back and tell us what you find.
Jake -
Anyway, not trying to be a smart-*** or anything like that but it takes only three things for an engine to run. They are fuel, spark and compression. I seriously doubt if compression is disappearing so that leaves only fuel and spark.
My recommendation has always been to diagnose a problem first instead of just tossing parts at it. Guess what I’m trying to say is it might be prudent to try and diagnose the situation when the problem is in attendance.
This is what I would do – certainly others will suggest a different approach.
One easy way to check for fuel is to connect a fuel pressure gauge and then tape it to the outside of the windshield. It’s not wise to have a mechanical fuel pressure gauge inside the car because of the fire hazard – have seen a few cars catch fire because of leaks and blown hoses and the resulting burns are very painful indeed. Anyway, if the pressures are where they should be, the fuel delivery system is doing what it should be and the problem is lying elsewhere.
Connect a voltmeter to the battery + side of the injectors, drive the car until it acts up and then see if the voltage there is close to battery voltage – about 13.20 volts or thereabouts. If the voltage is ok when the engine begins to do it’s stumble thing, then the situation is farther downstream – like Mr Willis says, defective ECU or something inside the distributor.
To do a simple check of the injectors, what I have done in the past is take an LED and attach a couple of long wires to it. Use alligator clamps and then connect one end of the wire to the battery positive and the other wire end to the injector harness that goes to the ECU. This will be the ground side of the injector. Make sure to install a two amp fuse near the end of the wire which connects to the battery +, no sense in starting a fire here. Now, every time the ECU grounds the injector, the LED will then illuminate – it will pulse each time the ECU grounds the injectors. As long as the illumination blinks are consistent, then the ECU is grounding the injectors, as it should. The extremely low current draw of an LED will have no adverse effect on the ECU or any other system. The injectors are energized (opened and fuel flows) when the ECU grounds them. The amount of fuel delivered is controlled by the length of time the ECU is grounding the injector circuit thereby holding it open and allowing fuel to flow.
This is sort of like building your own “noid light” but with this one you can see what is happening while driving the car. It a good investment to make since it will cost less than five bucks, can be used as a normal test light and will last several lifetimes too.
That leaves spark and this might be where the problem is. Any coil can check out ok when cold but they can develop internal shorts and shorts-to-ground as the temperatures increase. This holds true of any type of coil anywhere and will become more pronounced as the voltage and current flow through the coil increases. Same holds true for electronic components, might be OK when cold but do crazy things when they get hot hence the ICU inside the distributor might be defective. Same for the ECU it self.
You can use your home made “noid light” above to check some of the ignition system too. Connections to the battery + are the same and then just connect the other wire to the coil ground – if you can somehow get at it inside the HEI distributor – might be tough (in all practicality might be easier just to replace the ICU and be done with it!). Anyway, if your noid is then flashing and it is consistent, then in all likelihood, the primary ignition system – low voltage side - is doing its job. The secondary high voltage side is usually quite easy – just look at the distributor cap, rotor and wires for any damage. Also, use the FSM and make sure the distributor is properly indexed – i.e., it is installed correctly with respect to the distributor drive gear on the camshaft. Being off only one tooth can cause all kinds of problems as the secondary voltage begins to arc and dance all around the inside of the cap instead of going where it should. Usually this happens when cold too. Not familiar with an Opti so best if others chime in to help you with that.
Several years ago, I did witness a crazy situation where the battery + feed somewhere was making contact with the O2 sensor output wire that goes to the ECU. Since the ECU was then seeing a high voltage output from the O2 sensor, thereby thinking the engine was pig rich, it leaned out the fuel mixture to its full range of authority – to the point where the engine would barely run. It would begin to stumble and miss as you describe.
Anyhow my guess is your problem is either fuel or spark and I’m leaning toward spark or electronic engine controls. Since the engine operates satisfactorly when cold, that tells me that all major mechanical components of your car are ok.
On thing caught my attention and that is your temp gauge is running all over the place. Cannot say for sure but usually these weird electrical things result from faulty ground paths as much as anything else. Any chance that when doing all these repairs on the car that a ground wire was disconnected and then never hooked up again? Just a thought.
Sorry for the rant, I do get a little (a lot??) over analytical at times – but am always curious to see what is going on instead of just shotgunning the damn thing! LOL! Hope I’ve helped out a little – if not finding the problem itself, then stimulating the brain a little and perhaps giving some direction.
Good luck to you – you will find it and when you do, the reasoning behind the malfunction will become crystal clear.
Please get back and tell us what you find.
Jake -
07-24-2014, 07:39 AM
#5
I suggest the first thing you should do is set timing. Too far advanced will cause an intake backfire, not enough advance will cause an exhaust backfire.
And when it is not timed properly, the symptoms you are describing can definitely happen. If he didn't unplug the EST wire to set timing, he probably set your base timing to -14° instead of 6°. I believe idle timing advance should be 20.04°.
Also, retarded timing can cause overheating.
And when it is not timed properly, the symptoms you are describing can definitely happen. If he didn't unplug the EST wire to set timing, he probably set your base timing to -14° instead of 6°. I believe idle timing advance should be 20.04°.
Also, retarded timing can cause overheating.
07-24-2014, 10:58 PM
#6
Melting Slicks
The very first thing I would do know what you have already done is to check fo a cluged exhaust you have all the signs of this including the high temps. There are several ways to test them but I like the vacume methoid. hook a vacume gauge up and note the vacume it should be around 20 of so then raise the rpms to about 3500 to 4000 hold it at this point steady. While you are increasing the rpms the vacum will drop once you hold it at 3500 or 4000 steady it should recover to close to where it was at idle if it does not you know something is a wrong you can also take a peak under the car and see if the cats are red. another thing that is offen forgotton is fuel quality take the shreader valve out of the test port for the pressure gauge slide a rubber house over the fitting and into a glass bottle rurn the key to run and off a few times to get some fuel into the bottle then take a look at it does the fuel look good? but I would do the exhaust test before anything else
07-25-2014, 03:34 PM
#7
Instructor
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Location: NW Arkansas - usually winter in FL
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If your engine runs ok for 5-10 minutes, then mechanically your car is fine. Seems like you have a temperature or time related issue and those almost always are fuel or electrical in origin.
Any chance you have a fuel tank that's not venting? That would be evident in the fuel pressure when the situation is happening -
Jake -
Any chance you have a fuel tank that's not venting? That would be evident in the fuel pressure when the situation is happening -
Jake -
07-25-2014, 07:54 PM
#8
Safety Car
Dang Jake that is one helluva write up! I am going to buy an LCD and alligator clips!
Youve gotten some great advice. The heat factor makes me think its the ICM. It could be any of the suggested things but my money is on the ICM. The heat grease usually is pretty gone after 25 years. They arent that expensive, I would replace it
Good luck!
Edit: And buy some heat grease!
Youve gotten some great advice. The heat factor makes me think its the ICM. It could be any of the suggested things but my money is on the ICM. The heat grease usually is pretty gone after 25 years. They arent that expensive, I would replace it
Good luck!
Edit: And buy some heat grease!
07-25-2014, 08:01 PM
#9
Team Owner
Pro Mechanic
that the symptoms align w/an ICM, possibly. And when it is not timed properly, the symptoms you are describing can definitely happen. If he didn't unplug the EST wire to set timing, he probably set your base timing to -14° instead of 6°. I believe idle timing advance should be 20.04°.
Also, retarded timing can cause overheating.
Also, retarded timing can cause overheating.
runs fine for 10 miles or so and then starts to stumble and gradually lose power
Last edited by Tom400CFI; 07-27-2014 at 01:30 PM.
07-26-2014, 06:37 AM
#10
Drifting
heat cuuses electrical problems. Check the coil and all of distributor. Follow all instructions by GM
07-26-2014, 11:51 AM
#11
Racer
Thread Starter
Lots of good advice from all of you. You said suspect the ICM - do you mean ECM or the computer?
I think the one constant through all of the comments and suggestions is a heat related problem - i.e. at full operating temp - runs fine when cold. I do suspect the coil and will change that out - it is 24 years old.
The work mentioned so far has been done by a professional shop without professional results. I will not mention their name at this point. I initially took the car in to fix a surge at idle (TPS adjustment?) and no power (flat on acceleration but not missing and transmission not slipping). In the past, I would have done this work myself but at 70 years old and the 100 degree heat I passed on that. Against my better judgment, I agreed to cleaning the injectors - that is when the knocking and missing problems started and then was told the timing was jumping all place so the timing chain must be worn. Again, against my better judgment, I agreed. Problem just got worse. Then at my insistence they redid diagnostics and replaced the knock sensor and found the IACS "loose". Some improvement on the knocking. Then I noticed the vacuum tube to the MAP was disconnected and plugged. Fixing that stopped the engine knock but still have the problem mentioned above.
So I will change out the coil and see what happens.
I think the one constant through all of the comments and suggestions is a heat related problem - i.e. at full operating temp - runs fine when cold. I do suspect the coil and will change that out - it is 24 years old.
The work mentioned so far has been done by a professional shop without professional results. I will not mention their name at this point. I initially took the car in to fix a surge at idle (TPS adjustment?) and no power (flat on acceleration but not missing and transmission not slipping). In the past, I would have done this work myself but at 70 years old and the 100 degree heat I passed on that. Against my better judgment, I agreed to cleaning the injectors - that is when the knocking and missing problems started and then was told the timing was jumping all place so the timing chain must be worn. Again, against my better judgment, I agreed. Problem just got worse. Then at my insistence they redid diagnostics and replaced the knock sensor and found the IACS "loose". Some improvement on the knocking. Then I noticed the vacuum tube to the MAP was disconnected and plugged. Fixing that stopped the engine knock but still have the problem mentioned above.
So I will change out the coil and see what happens.
07-26-2014, 01:30 PM
#12
Team Owner
Pro Mechanic
07-26-2014, 03:06 PM
#13
Racer
Thread Starter
Duh...I knew that. However, I did not think of that. Very interesting point. Several years ago, I was dyno testing my '78 pace car with a bored and stroked 400 small block and at WOT it starting acting similar to the way my '90 is now. The '78 was a neat car - show winner and fast. 409 ci small block, big cam, 750 EB, 700-4 auto, 4-11 rear end, fiberglass rear spring, front coil springs shortened. that was a neat car. My buddy Chad bought it and is still winning trophies. Oh well back to '90. I will keep you posted.
07-27-2014, 01:15 PM
#14
Heel & Toe
Member Since: Jan 2013
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I know a lot of this has been addressed in the past and I have read a lot of it. I am trying to understand why my L98 won't run right. Had fuel injectors cleaned and new timing chain installed to correct problem of surging at idle and almost no power on WOT. Have new fuel pump and sock; new knock sensor everything else is supposed to be good. After timing chain installed picked a bad engine knock and still had surging and no power. IACV was loose, fixed that; don't know if ECM is throwing codes. Most of the major gaskets have been replaced. Now after all that...cold engine car starts right up; runs fine for 10 miles or so and then starts to stumble and gradually lose power until it will not downshift into passing gear when I push on the gas even up to WOT. It just does nothing but miss, sputter and stumble. I did notice that someone had plugged the MAP vacuum line; hooked this up and the knock stopped but rest of problems continued. If I keep driving and try hard acceleration, the temp gauge bounces back and forth between 210 - 260 but none of the normal, obvious signs of overheating. In this condition it also started leaking oil and burning off on the exhaust. I am at my wits end. Any suggestions please. BTW: engine has 101K miles, does not burn oil had no problems prior to this. I drive (at least did) it drive five times a week. thanks.
Tom - I noticed your thread shortly after I posted mine. Your problem is identical to mine. So far the MAF sensor, EGR and temp. sensor have been replaced with no correction. Runs well cold, goes south when warmed up. I'll be bringing it to another mechanic soon who specializes in Corvettes. Should he be able to find the problem and fix it I'll send you a note to see if that helps. If you resolve the problem please pass along what you've done.
08-04-2014, 09:33 PM
#16
Racer
Thread Starter
Ok. Put in new coil and ICM. Did not correct problems. I was thinking that the missing, sputtering, overheating, etc, was only happening after the engine had been running at operating temp for 30 - 45 minutes. I went out and drove it hard (at least I tried to) after it was at normal operating temp. When I pushed it to the floor my nightmares came back. Now I have a base line for the problem...at normal operating temp the problem is there---this should indicate it is not a engine temp activated problem. Well I took the Vette to my buddy in Whitesboro TX today - he is one of the best! We had discussed the problem a few days earlier. He wanted to bet me it was the injectors - then I remembered some conversations we had several years ago on the stock injectors. The stock injectors hate ethanol! Ethanol eats the covering on the wire coil around the injector and they short out. About 30 minutes after I left his shop, I got a call from him - only two of the injectors ohmed out within specs; two were bad and the other four were very shaky. He order new Bosch 24# pintel injectors. There may be other problems after he installs the new injectors but I doubt it. The second response in this post said to ohm out the injectors. I "thought" they were ok. Oh well, Keep you posted.
08-04-2014, 09:37 PM
#17
Racer
Thread Starter
OH BTW. Since the injectors are bad or shaky, it is a good chance the cats are now bad (they are 24 years old)...certain they will go in the trash.
08-04-2014, 10:31 PM
#18
Melting Slicks
m am still amized with your issuses you have yet to have the exhaust tested for possible clugging esp when it is more or less a 50 dollar test at most i know you do not know me any yes with all that everyone says you could run test forever so you have to pick and choose. But with out tocuhing a book i can promise this with your issues the first test would be fuel quanty and quality then exhaust
08-04-2014, 10:37 PM
#19
Racer
Thread Starter
Hooked 073. I did not want to believe it was a fuel problem or blocked exhaust. But it looks like you and a couple others are right. We will all know in a couple of days...stay tuned. Anyway my 100K mile '90 Festival Car will have all the new parts it needs to go another 100K. My '07 Monty 20th Century Muscle Cars/LG Motorsports/Lingenfelter powered is nice but the '90 has great looks and a pedigree.
