bobharb

My 1990, L98 coupe 6 Speed (95,000miles) is experiencing the following. When started cold she starts quickly with no unusual sounds. First few miles also good, with normal performance. Problem starts as she warms up, starts running rough with a jerking feeling in any gear at lo RPM or when backing off the accelerator. When she is fully warmed up the “running rough” is more pronounced and a loud clanking sound emanates from the engine compartment, compression also feels reduced . At a stop she shakes, sounds and feels like trying to stall and the sound from the engine is like a bucket of bolts on the loose. If I engage the AC, the nose is more pronounced and starts earlier in the cycle, remove the load from the AC and noise and shake remain. When I shut the engine down and try to re-start, right away, it will crank but not start. Wait 10-15min. and she starts just fine but the hesitation and clanking are still present.
Help with a diagnosis and a repair path is appreciated.
Bob

pablocruise

Try removing the serpentine belt and running the engine for a little bit.
That would remove the A/C, alt, power steering, smog pump, and water pump from the equation.

Does the car have catalytic converters?
Might be plugged/breaking apart.

milsurpman

When your engine has a dead miss. The dual mass flywheel will rattle clank and make quite a racket. I have a feeling that when your engine is hot you have a few injectors shorting out causing a dead miss. Ohm your injectors when hot. Any under 11 ohms require replacement.

bobharb

Thanks, I'll follow-up this weekend

bobharb

I" remove the belt this weekend. It has the original Cat Converter.

bobharb

I checked the first 5 injectors when hot and all read 0.00. Tried to start and engine turned over but did not catch (but does when it cools). Based on you input, it seems they should all be replaced. One final question before I get a new set. Could there be anything else in the chain from battery to plugs that could be a contributor or cause of this problem?
Thank you for your help.
Bobhttps://www.corvetteforum.com/forums/images/smilies/thumbsup.gif

RandyJ75

I have basicly the same car as you, and believe me, the problems you cite are the fuel injectors. Do a search on Sam Lam, member here who did a great writeup on changing out the injectors. Then contact FIC injsctors, they have a great deal on injectors, and may have the O ring set you will need to rebuilt the fuel rail. Post back w/ any questions.

Randy

bobharb

Thanks Randy. I check out FCI.
My Vette has original everything and leaking valv covers to boot(burning expensive Synth oil). Can you list what else I should replace (plugs etc)while I'm at this?.

Sweet 90

with Randy, my '90 as well did some of the same things as yours.
I put the Bosh III's in; huge difference. If you have 95K on original plugs,wires,rotor and cap I don't think it would be a bad idea to change them out. You should also check your fuel pressure just to make sure everything is up to snuff when you install your new injectors

Jim

RandyJ75

Changing the valve cover gaskets is alot more work, as you need to remove the A/C compressor and the bracket that it mounts to. I would be sure that they are really leaking, I thought mine were, but it turned out to be the seal on the distributor.
As far as what else to do on your engine, plugs, wires, cap, new coil and maybe even a new module are a great idea. Be perpared to do a good cleaning of the throttle body (make sure to use Throttle body cleaner, not carb cleaner) and the plenum. This is a good time to remove the AIR system, and the ERG, if you want; or, you could replace the ERG valve, and check all of the vacuum hoses, and don't forget to do the throttle body bypass.

Let me know if you have any other questions.

Randy