I hope the LT1 experts can help. First a little background. My brother put an LT1 out of an F-body into a Chevy truck using Painless harness and an OBD1 PCM from some guy in Texas. The engine has no emmission equipment, has headers, true duals, and is Speed Density.

A few months ago the engine started running bad. Really rich on the passenger side bank of the engine. He swapped injectors side to side and spark plugs after checking for any obvious problems. No change. Finally after disconnecting the exhaust (taking the oxy sensor with it) the engine smoothed out. He then reinstalled the exhaust and swapping the oxy sensors, the engine seemed fine, until recently.

Now it is doing it again. Same problem. Runs so rich he can smell gas out of the mufflers. Hooked it up to a Snap-On scanner. No codes and all sensors seem to read ok (except for the Oxy sensors which are erratic due to what we think is gas coating the passenger side sensor).

Anyone with any ideas to look into? Is this some thing that is common with LT1 and someone has seen it before? We have checked the wiring between the PCM and oxy sensors and all injectors and checked OK (no cuts and no shorts to ground). He has replaced the oxy sensors. He tried to narrow it down to one cylinder, and disconnected the injector, but still has same problem. We are beginning to suspect a mechanical issue such as a bent or stuck valve. Thanks in advance for any help.

 

If you swapped messed up oxy sensors from one side to another -- how does that even try to fix the problem? It would just have moved it to the drivers side. You check that the MAS and all that good stuff?

 

Yes we hoped the problem would move to other side. No dice. Same problem on the passenger side. Engine setup to run on Speed Density.

 

Could a bad OptiSaprk cause problems on one side of the engine and not the other? Could the spark be not hot enough or correct timing to burn all of the fuel on the passenger side of the engine?

 

Technically, that is a possibility. What about the wires? Stock?

 

Wires have been replaced (only a year or so). Plugs are not that old, either.

 

The typical causes of one side of the engine running rich include exhaust leaks before the O2 sensors, or a misfire on that bank. Check for exhaust leaks, check for misfires on the passenger side.

Since you are running speed-density, can we assum the LT1 is out of a 1993? Or have you just removed the MAF and let the PCM default to S-D? If its from a 93, you have single-wire O2 sensors, not the 4-wire heated sensors. Erratic sensor operation can result from inadequate sensor temperature, if you have the sensor too far away from the engine - typical with long-tube headers. Many people with 93's convert to heated sensors.

Finally, when you say "the Oxy sensors which are erratic ".... do you mean the sensor mV readings are sticking in one position occasionally, or do you simply mean they are jumping all over the place, ranging from 1xx-9xx mVs all the time? The "sticking" would be a problem, the "jumping all over" is normal. Or is it a case of th O2 sensors only responding correctly under heavy load - see comment above about unheated O2 sensors.

 

Thanks for both of the replys. The engine is a 95 converted to speed density (the person that sold him the PCM said that is "the best" way to go). Erratic readings from the O2 sensors was the way it was described to me, so not really sure.

The good news of the day is that he found the problem. Turns out the wire to the #4 injector had found a sharp screw and was grounding itself, so the injector was basically firing all of the time. This explained the intermittent issue. Everytime he disturbed part of the harness, the problem disapeared for awhile until the wire settled back down on the screw.

Thanks again, James.

 

I would start with the optispark, I have had lots of problems with opti's. My car started running really rich before my opti finally went out, it was running so rich on the passenger side the plugs would be wet with fuel when I removed them. I would try replacing it first, I know they are not cheap but get one from Oreilly's and it will have a lifetime warranty and you won't have to worry about the opti again.