92lt1 runs like crap

grumpyvette · May 16, 2014

Rick said:
Hi,
It's been a while, but I hope some of you can help me out! My 92 LT1 is running terrible. History is below. I did a search regarding my problem, but could not find any concrete info to help! I apologize in advance as this is going to be a bit long!

Ok, so my 92 LT1 has been giving me problems for a while now. Car has around 58,000 miles on it. I had changed the opti, plugs, wires, coil, and H2O pump at around 35,000 miles. Drove home from work one night...50 miles...and it was running great. Shut it off for about 1/2 hour, got back in and the exhaust note had become horrible....yes just like that! The car ran, but felt very low on power. Burping and backfiring out of the exhaust. Shaking when accelerating. It sounded ok when idling.

So, I did some trail and error mechanics, after talking with some guys and getting some codes.....changed the TPS, driver's catalytic convertor, driver's O2. Still no luck. Changed the fuel filter, no dice.

The car still running horrible. Note: It would come "back to life" for small spurts and seem fine....only to revert to bad in a few minutes. Did the fuel pressure tests, etc from the factory service manual and decided the pump wasn't a problem. Held pressure after turning key off.

Had a mechanic I know take a look and scan it. (He's not an LT1 expert). He determined that cylinders 2 and 4 weren't firing. He did a compression test and he said they were fine. He advised that it might be the opti.

Codes pulled PRIOR to new opti, plugs, wires, an coil....

43 knock sensor circuit

45 Bank 1 (left front) heated oxygen sensor #1 circuit (rich exhaust indicated)

63 Bank 2 (Rt front) heated oxygen sensor #1 circuit (open circuit)

64 Bank 2 (Rt Front) heated oxygen sensor #1 circuit lean exhaust indicated)

So, this past weekend, I bit the expensive bullet and changed the opti, plugs, wires, and coil AGAIN! The car started up nice....and idled nice (prior to water pump install). Seemed smooth, so I was hopeful. Got it all back together and took her for a spin. TERRIBLE! It was lacking power again, sounded terrible, and shaking horribly. Got home and she was around 180-200 degrees. Let her idle. The car was literally rocking all over the place visibly. It seemed to be "surging or skipping", and I could smell oil...and some smoke was coming from behind the motor.

CODE 15 pulled....after the new opti,etc...

I took some OhM readings from the injectors last night..
1 - 12 ohms
2 - NO reading at all
3 - 4
4 -12
5 - 12
6 - 12
7 - 4
8 - 12

Also....I started it, and it sounded healthy. It got progressively worse as it heated up. I pulled the injector wires off one by one. The driver's side changed the idle when pulled. The passenger side made no difference when pulled. I also touched a screwdriver to each injector while it was running and I could feel pulsing in ALL of them.

Lastly, I used propane to check for vacuum leaks. Found none.

Sorry for the long post!

Thanks,
-Rick

as usual you need too break the problem down too and isolate it too the related sub systems of ignition, compression,engine fuel and air delivery, engine mechanical, engine electrical,exhaust system,and engine cooling, obviously engine sensors and electrical and engine grounds, to do that will require the correct year matching shop manual, a few tools, a multi meter, fuel pressure gauge, vacuum gauge,compression tester, from what you posted,the symptoms strongly suggest a clogged exhaust ,and defective injectors and possibly oxygen sensors, well it appears that injectors 2-3-7 are defective , or clogged, you might try getting the whole set cleaned or replaced along with any OXYGEN sensors and yes those injectors may have caused the OXYGEN SENSORS, subjected to overly rich fuel air bath,conditions to have burned out or failed resulting in the cats becoming partly clogged also, thus restricting the exhaust flow, so the cats may need to be replaced, so check the exhaust back pressure, on both sides it should be under 3psi even when you reve the engine.
low rpm, like idle produces far less exhaust gases back pressure so it may idle but as rpms increase back pressure caused it to choke.
you might try swapping those three strongly suspected defective injectors from current locations with three known to be good after pouring in a can of injector cleaner in the tank in the faint hope that they clean up, but at least you can retest and see if the problem stays at the location or moves with the injector that helps diagnose the issue, but the bad oxygen sensors and clogged cats will still cause it to run like crap until that's corrected if what I strongly suspect is true. obviously testing and use of a multi meter,and shop manual and vacuum/pressure gauge would be useful, testing back pressure between the shorty header and catalytic converter to confirm a restrictive exhaust would be useful as would confirming the oxygen sensors malfunction
without testing you simply guessing
never guess, deal in verified FACTS!
guessing is a waste of time
think logically, isolate and test
yes IM aware some guys would rather dig out their eye with a red hot fork than to read links, but if you take the time to actually research the problem and isolate and test you,ll soon find the answers
well the first thing you do is pull trouble codes
and it would help if you purchased a shop manual.

92lt1 runs like crap

grumpyvette

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