marlar98

I'm making progress with getting to know my recently purchased 94 Camaro z28. I've changed her oil after seafoam treatment, cleaned the MAF, which has the screen removed, added the missing K&N air filter to the cold air intake, Seafoamed the top end of the engine and reconnected the Scanmaster LT1 to it. I was able to pull a few error codes with the scanmaster. I'm waiting for my ALDL cable to arrive so I can further look into the workings of the engine. The following codes came from the scanmaster.

42 - Ignition control circuit, short or grounded

44- Bank 1 (left) O2 sensor, lean

51 - EEPROM program error (really concerned about this one from everything I've been reading)

84 - (M6) Skip shift solenoid circuit

91 - Skip shift lamp circuit.

Thanks to Fred, (Injuneer) I at least know what the codes are and the definition of the codes, but what do they mean I need to do to correct them? I mentioned before the car runs rich which I'm thinking is due to the O2 sensor being no good on (shows a constant 146 reading on the scanmaster and should constantly fluctuate if I'm not mistaken). Any help you guys can provide will be much appreciated. Thanks

Injuneer

The link I gave to the 94 factory service manual is very useful with regard to codes. Volume 2 has a 2-page description and logic tree analysis of each of the codes.

Pull the "PCM BAT" fuse at the end of the dash for 30 seconds. Your codes can be either active or stored. Clearing them this way will let you observe whether they reset, and how quickly.

DTC 42 has to be a "stored" (in history) code. If it was "active" the engine would not be running. When active, the PCM disables the fuel system. The code does not turn on the SES light. I guess they figure if the engine won't run, it will be obvious a code it set and you will check. Has the engine ever randomly stalled on you, or has it failed to start?

DTC 44 indicates the Bank 1 (left/drivers side) O2 sensor was reading lean (below 200 mV) for at least 50 seconds. When the PCM sees "lean" it richens the mixture. If it's a "true" lean, fine. If it's a "false" lean, it's going to run excessively rich. Possible causes (limiting to things that affect only one side of the engine, not both):

-Faulty O2 sensor or sensor wires
-Lean injector(s) - sticking closed, or dirty
-Exhaust leaks before the O2 sensor. The fast moving exhaust educts air into the leak, and causes a false lean reading at the sensor.

One way to check this is to swap the O2 sensors side-to-side and see if the DTC moves to Bank 2 (DTC 64) indicating a fault with the sensor, or stays on Bank 1 indicating a wiring problem or one of the other problems listed above. And, use the ScanMaster to read the O2 sensor.

DTC 51 indicates a checksum error in the PCM, which may be set by an EEPROM failure. But PCM failures are very rare. This is why you need to clear the codes and see if they come back. The full-time display on the ScanMaster makes your life easy in this respect.

DTC 84 Is your trans auto - 3-2 control solenoid circuit; or manual - skip-shift solenoid circuit? Would appear to be manual, since you also have DTC 91. The skip-shift solenoid is on the drivers side of the trans, and under certain part throttle conditions, prevents you from shifting directly from 1st to 2nd gear. GM did this to meet fuel economy requirements. The first thing everyone with a manual trans does is unplug the solenoid. This defeats the annoying skip-shift feature, and sets a code. In 94/95 this code does not turn on the SES light. And there are no impacts from this code being set. You can eliminate the code by getting a 2 Kohm resistor, and pushing the wire ends into the harness connector, and taping it up.



DTC 91 - Appears someone removed the bulb or snipped the wire to the indicator light on the dash that tells you when skip-shift is active.

marlar98

[QUOTE=Injuneer;6980439]

DTC 42 has to be a "stored" (in history) code. If it was "active" the engine would not be running. When active, the PCM disables the fuel system. The code does not turn on the SES light. I guess they figure if the engine won't run, it will be obvious a code it set and you will check. Has the engine ever randomly stalled on you, or has it failed to start?

I've never had a problem with the car starting. The SES light isn't on, but will come on after 10-15 minutes.

DTC 44 indicates the Bank 1 (left/drivers side) O2 sensor was reading lean (below 200 mV) for at least 50 seconds. When the PCM sees "lean" it richens the mixture. If it's a "true" lean, fine. If it's a "false" lean, it's going to run excessively rich. Possible causes (limiting to things that affect only one side of the engine, not both):

-Faulty O2 sensor or sensor wires
-Lean injector(s) - sticking closed, or dirty
-Exhaust leaks before the O2 sensor. The fast moving exhaust educts air into the leak, and causes a false lean reading at the sensor.

One way to check this is to swap the O2 sensors side-to-side and see if the DTC moves to Bank 2 (DTC 64) indicating a fault with the sensor, or stays on Bank 1 indicating a wiring problem or one of the other problems listed above. And, use the ScanMaster to read the O2 sensor.

I kind of figured the O2 sensor is bad since it has a standard reading of 146 when the engine is running. If I understand correctly, the reading should fluctuate rapidly like it shows on the Bank other O2 sensor on the Scanmaster, but I will check for exhaust leaks and injectors as well.


Thanks for all of your help!

Injuneer

If you have a static O2 sensor reading, its either the sensor or a shorted wire. An open circuit will show about 450 mV. That is the voltage the PCM applies to a sensor to make it work.

marlar98

This would explain why it's running rich I wouldn't it? I'm not familiar with tuning cars with all the electronics connected so forgive me for my ignorance.

marlar98

Just a quick update, pulled the PCM BAT fuse for a few minutes, and put it back to clear the codes. Drove around for about 30 min. Only codes that came back was 44 and the two transmission codes which I'm not too worried about it. Running rich, obviously. I'm going to replace the O2 sensor this weekend. Use only AC Delco heated O2 sensor, right?

Injuneer

Yes, AC Delco or Delphi. But why not try swapping them side-to-side to verify the source of the problem?

marlar98

Quick update of sorts, I haven't had a chance to track down the issue of my car running rich. I now have a starter issue. Starter just clicks rapidly when turning the ignition. I had the battery verified by two different stores and checked out good. So now I gotta figure out that issue before moving to the other issue. If it's the starter, which it sounds like it is, I'll test the O2 sensors. I've ordered the header gaskets (Felpro 1406) just I case as well. There seems to be a ticking sound which could be a blown header gasket which would why the O2 sensor is reading lean.

Fun stuff, lol!

Injuneer

Check for corrosion on the battery terminals, and the starter terminal. Check the cables at the battery for corrosion creeping into the wire strands.

marlar98

The battery cables look fairly new at the terminals. I'm sure the issue is the starter or the cable at the starter end. Thing is, I hate getting under cars. Always have, lol

marlar98

UPDATE:

I had both O2 sensors replaced and the car runs SO MUCH better! No error codes except DTC 13 which is the right O2 sensor in open loop. Any idea what this could be with new AC Delco O2 sensor.

Injuneer

Did you clear the codes by pulling the "PCM BAT" fuse for 30 seconds? What does your Scanmaster show as the sensor reading? See post #4, above.

DTC 13 is not for "open loop". It's for an open circuit. Wiring or sensor problem. Again, swap the O2 sensors side to side. If the code moves to the opposite side, it's a sensor problem. If the code stays on the right side it's a wiring problem.

The open circuit will prevent the PCM from going into closed loop.

marlar98

I cleared the codes and 13 came back again with an SES light. The scanmaster is reading 445 and blips to 449 sporadically.

Both O2 sensors were replaced with AC Delco sensors. Might be an issue with the wiring somewhere. I'll have to check that out.

Injuneer

I explained twice how to do do that.