(1990) L98 starting, idle, hesitation issue...
04-09-2014, 11:44 AM
#1
Race Director
Thread Starter
(1990) L98 starting, idle, hesitation issue...
(starting a new thread based on the L98. the original thread was based on a 1995 LT1 and was almost a year old)
same problem here, but mine is on an L98 (1990 vintage). recently, because of a rear china wall oil leak, i've gone through, and replaced, repaired, or serviced just about everything - new (delco FR5LS) plugs, (taylor 8mm silicone) wires, (accell) cap and rotor, new delco EGR valve, new delco PCV, new pressure regulator diaphragm, rebuilt fuel rails, rebuilt bosch3's from FIC, cleaned and serviced the throttle body, and although not significant to this, a new 180 stat and radiator hoses and cooling fans and fel-pro gaskets. ignition timing is set at factory 6 degrees.
so here's the issue. I have to first crank on the engine for 2 or 3 seconds, and when I hit the key for a second time it starts immediately. idle is a bit rough, but not excessively rough. I get the same hesitation when pulling out from a stop sign or red light, in fact, I have described it the same way - "almost feels like a bad accelerator pump (on a carbureted engine)." during a, steady state, cruise, the thing seems to run just fine, but I can, somewhat, feel a slight, very slight pulsing - a SOTP thing. acceleration, passing, etc, seems fine. idle speed seems fairly smooth, just a bit rough. my gut feeling is it might be a injector issue - ??? I've done a visual inspection on the vacuum lines, and everything looks good. I did not have any issues before the "leak" repair.
my problem - recently, I've moved, and a box of test equipment (fuel pressure gauge, vacuum gauge, TPS test harness, spark tester, is missing. it's around here somewhere, I just can't find it. the first thing I want to do is check the fuel pressure. I can hear the fuel pump for about 2 seconds when I first turn on the key, so I've eliminated a pump relay thing. BTW, injector resistance is 15 +/-.4 ohms, w/ 15.0 being average.
so, based on what I've said, any comments pertaining to the L98. inputs are welcome, since it might help me with troubleshooting and/or something I've overlooked... TIA
Interesting I came across this thread for I am having the same problem. A slight hesitation on takeoff if just going easy and normal. I do not have a miss-fire or any roughness as I would describe it. Don’t really feel it is I do a hard take off. Almost feels like a bad accelerator pump. Have not really chased the problem hard yet.
However during the course of time and for other reasons this is what I have done to the car but with no improvement.
Opti, air filter, clean throttle body, clean MAF resistor wires and IAC plunger and seat.
I have checked the fuel pressure many time but not recently and not while driving (gauge on window). My next course of action will be to replace the fuel filter as I am due anyway. If that does not help I will then measure the fuel pressure while driving. It feels like a insufficient fuel problem to me and not ignition. However the fuel trim and BLM numbers are always right near 128.
I never really considered the injectors but will put it on my list of possibilities. I will probably look at the resistance numbers anyway, cant hurt.
However during the course of time and for other reasons this is what I have done to the car but with no improvement.
Opti, air filter, clean throttle body, clean MAF resistor wires and IAC plunger and seat.
I have checked the fuel pressure many time but not recently and not while driving (gauge on window). My next course of action will be to replace the fuel filter as I am due anyway. If that does not help I will then measure the fuel pressure while driving. It feels like a insufficient fuel problem to me and not ignition. However the fuel trim and BLM numbers are always right near 128.
I never really considered the injectors but will put it on my list of possibilities. I will probably look at the resistance numbers anyway, cant hurt.
so here's the issue. I have to first crank on the engine for 2 or 3 seconds, and when I hit the key for a second time it starts immediately. idle is a bit rough, but not excessively rough. I get the same hesitation when pulling out from a stop sign or red light, in fact, I have described it the same way - "almost feels like a bad accelerator pump (on a carbureted engine)." during a, steady state, cruise, the thing seems to run just fine, but I can, somewhat, feel a slight, very slight pulsing - a SOTP thing. acceleration, passing, etc, seems fine. idle speed seems fairly smooth, just a bit rough. my gut feeling is it might be a injector issue - ??? I've done a visual inspection on the vacuum lines, and everything looks good. I did not have any issues before the "leak" repair.
my problem - recently, I've moved, and a box of test equipment (fuel pressure gauge, vacuum gauge, TPS test harness, spark tester, is missing. it's around here somewhere, I just can't find it. the first thing I want to do is check the fuel pressure. I can hear the fuel pump for about 2 seconds when I first turn on the key, so I've eliminated a pump relay thing. BTW, injector resistance is 15 +/-.4 ohms, w/ 15.0 being average.
so, based on what I've said, any comments pertaining to the L98. inputs are welcome, since it might help me with troubleshooting and/or something I've overlooked... TIA
Last edited by Joe C; 04-09-2014 at 11:56 AM.
04-09-2014, 12:02 PM
#2
Drifting
If you were sold Bosch yellow 280-155-700's you possibly have a lean condition. Datalog, and or scan the vehicle for blm counts. I've personally tested this injector and found blm counts as high as 160. Modifying my flowrate to 20 lbs helped. Typically a off idle lean bog is the first complaint.
04-09-2014, 12:51 PM
#3
Safety Car
Member Since: Jan 2004
Location: Northern California
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Check the fuel pressure...
Sounds like the fuel pump is weak which is why it takes a few seconds to start. After the 2-3 seconds of cranking, the fuel pressure builds up and the engine is able to start but, runs rough because the fuel pressure is still weak.
Also, check the TPS voltage and IAC valve.
.
Sounds like the fuel pump is weak which is why it takes a few seconds to start. After the 2-3 seconds of cranking, the fuel pressure builds up and the engine is able to start but, runs rough because the fuel pressure is still weak.
Also, check the TPS voltage and IAC valve.
.
Last edited by GKK; 04-09-2014 at 12:56 PM.
04-09-2014, 03:04 PM
#4
Race Director
Thread Starter
Check the fuel pressure...
Sounds like the fuel pump is weak which is why it takes a few seconds to start. After the 2-3 seconds of cranking, the fuel pressure builds up and the engine is able to start but, runs rough because the fuel pressure is still weak.
Also, check the TPS voltage and IAC valve.
.
Sounds like the fuel pump is weak which is why it takes a few seconds to start. After the 2-3 seconds of cranking, the fuel pressure builds up and the engine is able to start but, runs rough because the fuel pressure is still weak.
Also, check the TPS voltage and IAC valve.
.
on the weak fuel pump thing, but the condition DID NOT exist prior to all that was done. a fuel pressure test and diagnostics top agenda. I do have the the bosch 280-155-700's, so that may be the issue. my gut feeling - it is an injector issue, but until I start some testing, I'm just guessing. thanks for the replys (so far)...
Last edited by Joe C; 04-09-2014 at 03:07 PM.
04-09-2014, 05:16 PM
#5
Safety Car
Member Since: Jan 2004
Location: Northern California
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Also, since you stated you just repaired the China wall leak, check over all your work and make sure you reconnected all the vacuum hoses and sensors correctly. You might have missed something...
Egr solenoid line under the throttle body, brake booster line behind the plenum, AIT sensor under the plenum etc...
Egr solenoid line under the throttle body, brake booster line behind the plenum, AIT sensor under the plenum etc...
04-09-2014, 07:06 PM
#6
Burning Brakes
You have probably looked thru the "symptoms" section of FSM. you have a "hard start" and a hesitation issue, sound like.
I don't see it as a "lack of fuel" issue. if it were too lean to takeoff it should not improve at higher rpm. I have the Bosch 3 yellow injectors and never had any issue.
you can watch your timing inputs with a light -with the EST wire connected- to see what the timing does as you accelerate.
Once, I left the EST disconnected, and the hesitation was noticeable -of course I got the SES light, but would not have, if the EST was connected. it is a way to verify that the ICM and ECM are advancing spark.
the book mentions the "ignition reference" low or bad connection, the blk/red wire on the dist, as a cause of hesitation.
I would disconnect MAP to see the reaction, also to verify that you get the code set. my 91 has a non adjustable TPS, not sure about yours, but I would also disconnect that sensor to watch for a reaction. I know the TPS does not always set a code.
also, the "clear flood" method at first start might eliminate a leaking inj causing a rich condition. I have heard complaints about the Bosch running rich at start-up, but mine are OK.
My suspicion is that the dis-assembly of the engine has caused this, as you probably suspect. That still leaves a lot of components to consider!
joe
I don't see it as a "lack of fuel" issue. if it were too lean to takeoff it should not improve at higher rpm. I have the Bosch 3 yellow injectors and never had any issue.
you can watch your timing inputs with a light -with the EST wire connected- to see what the timing does as you accelerate.
Once, I left the EST disconnected, and the hesitation was noticeable -of course I got the SES light, but would not have, if the EST was connected. it is a way to verify that the ICM and ECM are advancing spark.
the book mentions the "ignition reference" low or bad connection, the blk/red wire on the dist, as a cause of hesitation.
I would disconnect MAP to see the reaction, also to verify that you get the code set. my 91 has a non adjustable TPS, not sure about yours, but I would also disconnect that sensor to watch for a reaction. I know the TPS does not always set a code.
also, the "clear flood" method at first start might eliminate a leaking inj causing a rich condition. I have heard complaints about the Bosch running rich at start-up, but mine are OK.
My suspicion is that the dis-assembly of the engine has caused this, as you probably suspect. That still leaves a lot of components to consider!
joe
04-09-2014, 09:55 PM
#7
Le Mans Master
In addition to the information in the first post, one of the first things I checked (and many times) was the TPS. I uses a Tech1 and the action was smooth and correct all thru the range. I also checked everything I could read on a Tech 1 as I drove around several times and nothing was out of the ordinary. I have a reference sheet of normal measurements I made many years ago for a comparison.
I should have some time to ohm the injectors and check fuel pressure in the next few days which should not take long. Need a window of time to do the filter.
I should have some time to ohm the injectors and check fuel pressure in the next few days which should not take long. Need a window of time to do the filter.