My Father in laws 1994 Z28 Camaro with an LT1 has an interesting issue. Yesterday as he was driving it started really bogging down so she shut it down and parked. when I got there It would fire up but idle terribly. I gave it gas and it would load up and backfire through the exhaust and not get above 2000 rpm. She was shooting flame out the exhaust so I know it was over fueling or not firing. Then as soon as the computer sensed a code she cleaned up and is drivable. Not full power but definitely plenty to drive around with.

Of course being a 1994 NO ONE in town has a reader I can pull the codes with. I am sure that in Closed loop there a sensor or something that is telling it to either over fuel or cut the ignition WAY back, then when it reverts back to open loop (when the SES light comes on) She runs decent using the base fuel table.

Any ideas what sensor may cause the overfueling? O2? TPS? MAF?

I suppose I could use my multi meter to test each one.

Ideas? I am at a loss on this one.

 

Save yourself some time and get a scanner. You can find alternate scan solutions using a laptop and cable in the computer/diaganostic/tuning forum.

 

This is the second thread where you have resisted the suggestion that you scan it with available FREE software. In the first case, probably would have saved you a lot of time, and would have shown up the codes for the failing Opti.

I realize this is not your personal car, and you don't want the trouble of downloading the software as indicated in the previous thread, so you might suggest to your F-I-L that he download the software and get a cable.

https://www.camaroz28.com/forums/lt1...t-help-877657/

 

Injuneer, It wasn't the download, Its the connector. I actually ordered it on Friday. I will know exactly what is wrong come Wednesday.....Pending shipping! I figure he is going to keep calling me when it breaks so I may as well save myself the headache......

 

ITs saying its the High resolution signal from the optispark......

Pretty cool program!

 

That would indicate a problem with the optical cam position sensor in the Opti, or the harness wire from the Opti to the PCM. Check the connectors on both ends of the short Opti harness between the gray connector on the bracket on the passenger side of the intake manifold and the Opti. Look in particular for a blue-green corrosion on the Opti end, or damaged pins. Check the insulation on the wire as well, after 20 years we are starting to see bare spots on the wiring. Replacement short harnesses are available, if that is the problem.

When the PCM sees that the high resolution pulse signal has gone missing, it stops using it and relies totally on the low resolution signal. That will result in slightly less accurate ignition and injector timing, but nothing you would notice.

 

After more testing, and watching as the car did it, It was showing a low resolution signal corruption also. I did an ohm test on all of the wires and they seems good in the harness, I got a new harness with a GM Opti anyhow. I am putting it all back together today. I decided to replace the spark plug wires also. They were TERRIBLE! #7 was nearly burnt through from the manifold. What a pain on the passenger side! I still cant get #2 back on. Any suggestions?

 

The only low res signal is DTC 16, for complete loss of the low res signal. When that happens, the PCM shuts down the fuel system, and the engine won't start/run. If you have the code and the engine is still running, it is a "stored" code, not an active code. That code will set during cranking - the engine does not have to be running. Also does not turn on the SES light.

As far as #2, did you remove the alternator?

 

Codes 16 (low res signal) and 36 (high res signal) are related, in that the low res signal test depends on the existance and timing of the high res signal, and the high res signal test depends on the existance and timing of the low res signal. In other words, each is compared with the other. If there are common faults affecting both signals like an intermittent power or ground connection, causing the loss of pulses or the addition of extra pulses, they can fail either or both.
While troubleshooting a failed Opti for another forum member, I found that the normal current to power it was about .02 amps (20 milliamps) at 12v. An intermittent 12v connection at the most upstream circuit board (with the sensors) was causing similar results. I was able to tap in various locations near or atop the sensor electronics circuit board and witness the drop in supply current to zero. The cause was found to be a loose/broken solder connection at the pin connecting to 12v.

 

When I took it off, I got it right away.

As far as fixing it, I replaced the Opti with a GM unit, and all the spark plug wires. #8 was nearly burnt through from the manifold. I spent more time routing wires than I did on the opti.

The thing is running like a raped ape now. IF it does do it again, now I have the software so that will be very helpful.

 

I think this was the EXACT issue.