Bodageta1995

So, I have a 89 L98 Automatic with 101,000 miles. Dad has owned since 96, I have it now. I've had it about 1yr and drove it for a while but it always had a rough idle and wouldn't pass emissions (Rich Condition, High CO). Bought a Scan cable and software and troubleshooted about 3 months ago and after about 3 hours idling mostly, it started dying on me..bogging, sparkknocking and I barely got it home. So, I changed the spark plugs/wires (dad had replaced cap and rotor recently). Dad had someone change the #6 and #8 fuel injectors before I got it as the engine stopped running. I have NO trouble codes.

So, here are my issues/symptoms

Problem, slightly rough Idle and bogs enough to kill the engine if you open the throttle abruptly or get above around 2800 rpms.

What I know/did:

1) I replaced plugs and wires - didn't fix it..possibly slight smoother idle. Note, #8 black sooty like rich. Note I recently checked the new plugs and the #8 and #6 were black and sooty after just idling again.

2) Fuel Pressure gage check..ran about 39psi, went up if rpms increased...so OK.

3) Vacuum Gage hooked to Brake Booster..only around -12psi (should be more like 25~30) (assuming my cheap new gage is accurate)..causes questions..have looked for a vacuum leak with carb cleaner - none found yet..could be there or not but I cant find it..want a smoke machine..need to make a cheap one I guess. Note the Vacuum gage is a steady hand.

4) So, I ran a compression check (wondering of the engine was worn out due to the low vacuum gage readings)..each cylinder is 152~155psi except for #1 which read 145. I squirted oil in and little to no change in pressures. So all seem ok.

5) So, the obvious thing to me was that maybe a precat was clogged causing the low vacuum readings and the engine to stall at higher rpms. (note, only the precats remain - main cat was removed years ago). Today I hooked the pressure gage to the Air Tube on each manifold with the check valve removed..should be less than 1/5 psi at idle and 3psi at 2000 rpm..basically seems like zero at all.

6) I also closed off the PCV valve and checked for vacuum at my dipstick tube which should be zero and it was (didnt' think this out be read it somewhere).

So, my gut feel from working on engines in the past (before Fuel Injection) would be the EGR valve, except for the low vacuum and blackish #8 and #6 plugs. One other thing. The Right side temps with a laser temp gun read much hotter on the right side than the left. Left is only around 130F at idle and right is more like 350F. #8 is about 390 deg F while 4/6 is about 250 and the ones on the left side 1,3,5,7 read around 130F (seems might low) As for the precats, the one on the left reads about 120 or so F after about 5 minutes of idle while the Right reads more like 400F but 300F on the exit (which i think means its not working..but again it shouldn't be plugged based on the pressure readings..looks like the LH side isn't working either and maybe was gutted at some point?

So, I'm kind of at a loss. I'm wondering if who ever replaced the #8 and #6 fuel injectors used to high flow rate (pounds) and thats why they are rich. Not sure how to tell. I want to replace all injectors at some point but money is tight so Im just trying to get it to run first.

So, Low Vacuum, rough idle and bogs at higher rpm and exhaust temps highest at #8 (note that is also where the egr tube mounts so that could be normal or could be that the EGR is open..but EGR shouldn't cause low vacuum???

Ideas please. I don't own a vacuum pump to pump the EGR but may need to buy one. I do have a Factor Service manual. I would think it wouldn't be the EGR as I have low engine vacuum (or my new gage is no good)..or maybe I have two seperate issues. I could have a vacuum leak I cant find and also and EGR issue. Supposedly you can push on the EGR diaphram and or feel it's movement but I cant get my hand in there (how do you do that)?

I'm rambling but I'm at a loss. I need to get this thing going as Fall top down weather is here and next year I plan to go the Corvette Museum Anniversay Caravan (was in the one in 1994 with a buddy when they opened). As for the high temps I assume it's a rich condition or EGR issue with the tube? I used to be an automotive engineer with a major manufacturer and we ran some rich tests with the cat converter and they would glow cherry red.

I'm about to get out my software and go at it again. I've enjoyed learning about the Tuned Port Injection..pretty neat system but I'm stumped on this one..

Ideas? Enjoy the fall if you have a running Corvette, top down/t tops off etc..take someone you love for a ride. I have a 5 year old daugter waiting for a ride in ours (someday again I hope).

Ricky
Newnan Georgia

Bodageta1995

Oh, I also hooked in an Noid Light for all injector locations and got a flash at each.

hooked073

hook vacume gauge to a vacume port. get reading at idle. then increase rpms to about 3200 and hold it steady. as you increase rpms vacume will drop as you hold seady at 3200 the vacume should climp back up to real close to your readings at idle. If it does not you have something cluged. I like this methoid of testing over what you did it is woth a try

Bodageta1995

Thanks hooked 073, I'll give it a try. I've had it idleing trying to get my ALDL software to work and after it was hot it seem to bog and die now at around 1200 rpms. I'll let it cool and try again..has a lot of similarities to something clogged but cant figure out what..or find the vacuum leak. Could be my new plugs are fouling..who knows. I'll feed back the info after I give it a try.

hooked073

Also did you replace the fuel filter?

l98tpi

Need to check the injectors that were replaced, they may be a different flow rate injector than the stock injectors. If you do change injectors to higher flow rate injectors you will need to get the chip/ecm retuned.

Bodageta1995

Only 2 injectors were changed. I'm assuming I need to pull them out to see the flow rate. I think it's stamped on the bottom. I hooked up a vacuum gage and tried to hit 3200 rpm. I had to take it slow to get there... on the way the vaccum would go way down, near zero when it would "bog" and then sometimes the rpms would pick back up but when you would get over 3000 rpm rougly, it would start to bog/die..almost like starving for fuel. Maybe I should hook up the fuel gage again and see if the pressure is good when it's bogging? I did note that after it ran for a while (maybe after it got hot) it would bogg maybe as low a 1000rpm and die..let it sit for about 30 minutes and could get 3000 rpm again if I took it slow to get there. I'm guessing if I have the correct fuel pressure then the fuel filter isn't the problem - agree? It's one of the tougher things to find I've worked on (troubleshooting). I do appreciate the help from all. It's nice to get input as I know a lot of "car guys" but they are old school and not into the fuel injected stuff. A vacuum gage says a lot though and the -15 max seems to indicate a problem. I did check the input to the EGR valve which is a "ported vacuum" not manifold and I need -7 vaccuum minimum per the FSM. I got 10..so I figure my gage is in the ballpark. -15 indicates an issue I think that I shouldn't overlook. Only 2 fuel injectors were changed and I'm thinking they may be missmatched. If I can get the thing not to die then I will put in a rebuilt set from FIC soon. I don't think 2 injectors would cause the engine to die at higher RPM..then again maybe they could. I unplugged one and saw little difference. On kind of strange thing is that when I pull off the vacuum hose going to the brake booster the engine speeds up? Maybe thats' normal but I assume the opposite. Its back in the garage until I get more tools/thoughts/etc. Thanks for the help..I'll take more ideas you have them. Low Maniford Vacuum, Rich and Dies at around 3000rpm and maybe 1000 if hot..but actually you can stop it an it will start back and then get maybe 3000 again.the 1000 die is a random thing.

Bodageta1995

From an old school way of thinking..what if my spark is too weak. Is there any way to tell? it runs a timing light just fine...weak coil is what I mean. I ohm checked the coil and it checked ok. I wish I knew an old school mechanic that was top dog using the old "sun" machine to look at spark signatures at varying RPM's. 3 key things I guess, Fuel, Air and Spark. One or more are giving me fits. Vacuum gage says its the Air I guess..Temp gun on exhausts says it's Fuel (hot temps, unless excess air is causing them)..Spark..don't know..seem all have spark. I tried pulling each plug one by one but couldn't make out much change in RPM..its really wierd..slightly rough idle..I also pulled the #8Fuel Injector Wire Plug and saw little change. I need to try that on the other cylinders for comparison..expected big changes. Maybe the fuel curve/computer compensates for things like that to a point? Seemed to change and then smooth back.

hooked073

one thing to think about and the reason I asked if you replaced the filter is you can still have pressure with a reduced flow IE cluged filter.

hooked073

can you get it to a steady 2000 rmps and see what the vacume ready is??

aklim

Spark plug tester? They sell them. That or get a new plug and ground the threads and connect the terminal to the plug wire while the car is running and see the flame? If it is blue, great. Yellow, you have a problem.

kenmohr

do an ohms check on injectors

Bodageta1995

At 2000 rpms, the vacuum is -12(or 12 if you already think of vacuum as negative).

MrWillys

The injectors used in 89 were prone to problems. If two have been replaced you can assume the others are going bad too. Replace injectors just as a service like an oil change and see if you notice improvement. Get a Bosch type injector this time, and not a Multec.

aklim

I would check what the 2 have been replaced with. If you replaced with Bosch and the other 6 are Multec units, will they work well together? Not sure why anyone replaces 2 injectors on a higher mileage car.

muzikmanwi

Don't know if you thought about a plugged catalytic converter or not but it would certainly cause those problems.

Bodageta1995

I pulled off the check valves at the air lines in each of the exhaust manifolds and saw no pressure build definitely nothing of 3psi idle or otherwise so I'm thinking my exhaust/converters aren't clogged.

leesvet

You do not EVER replace 2 fuel injectors on GAS engines. Diesel, yes, GAS, No, never.
Because...

gas is soooooooooo much more precise and critical to the air/fuel ratio being constantly managed as it constantly changes due to changing demand.

Have you Ohms tested the injectors?
IIWM, I wouldn't waste my time. I'd just order a set of B-III's and be done with it.

While you wait on UPS, pull the o2 sensor (if you can) and test for a plugged cat. \Read your FSM for the procedure. If you DO NOT have a FSM, then you will continue to throw parts and not solve the problem that's going to be quite simple. The FSM has detailed flow charts to follow that cover ANY possible condition and all possible solutions.
Good luck.

Its the injectors and/or inj system harness.

Bodageta1995

So, I finally found something meaningful. I made a homemade smoke machine (gallon can, battery powered pump from an old blow up air mattress and hooked it to the brake booster hose I figured if I'm only getting about 12 in hg vacuum and since my compression check was good that a vaccum leak should be the focus. I used wood chips from my smoker..the mesquete smelled really good (by I digress)..anyhow...quickly had a lot of smoke coming from my throttle body area. I had previously put on a latex glove, to cap and monitor pressure build, where the MAF goes..so I took off that section of the intake plastic duct and capped the throttle body with a latex glove..still getting a lot of smoke there. I've pulled off the two significant sized hoses on the passenger side and capped them to give visibility and I'm still getting smoke. It's dang hard to tell where it's coming from though. It looks like its most likely from the throttle shaft on both the LH and RH sides..maybe its' worn. I'm still looking. I'm guessing no smoke should be coming out??? Has anyone done this. It's hard for me to think a leak in the shaft of the plates could cause such a reduction in engine vacuum but maybe it is? should b 23 or so it's 12??? It's after my mass airflow sensor so maybe thats the deal..maybe it even gets worse if the throttle is opened and thats causing my bogg...kind of like a four barrel quadrajet with secondary throttle plates that open too soon. Anyhow that is where I'm at..been working on this for about 4 months or more..missed the summer top down..dont want to miss the nice fall weather. Has anyone else had a vacuum leak at their throttle shaft bore? I'm going to go smoke it again and try to see exactly where but it's tough to see exactly..was/am still hoping to find a vacuum line for an easy fix or even just put on new gaskets. I did tighten the four bolts and it didn't help. I also wonder about the IAC..if it were to be cracked or anything might it leak..and others have worked on this car in the recent past before I got it..should it need a gasket and maybe it wasnt' reinstalled? Any thoughts would be appreciated. I still never replaced the fuel filter as I just cant see how that could be my problem when I get good pressure at the gauge in the fuel rail, even when revving high enough to bog and kill the engine. Last Sat, I started it up and got to about 4800 rpm in park before it would bog and want to die..of course I could let off and it would keep running..seems as it gets hotter the bog rpm drops.

I really want to get this thing roadworthy.

Thanks!

Bodageta1995

So, the mesquite wood apparently has made me pretty hungry while working on the Corvette today. Taking a little break for a bite to eat. Assuming I have a worn shaft. I've done some internet searches and I don't see any OEM type units available except for and ebay guy who uses the name "xtreme-fi". His units are rebuilt and 52mm. I'm guessing thats an overbore.

Will the 52mm have any negative impacts on my totally stock 1989 L98?

Does anyone know of any sources for parts other than used. I figure the used ones are probably worn too or partially. I hate to spend the money and find it's not my issue but I'm getting smoke with the smoke machine and I still "think" thats where its coming from on both sides.

I wiggled my throttle shaft and it moves maybe 0.001 ~0.002 (as a guess). I'm not sure if thats normal or not..thats an up down movement with my hand..its not much movement at all.but maybe not much is too much. It's not like it's loose and floppy.