Hi everyone,

My name is Mikko and I'm brand new to the forum.
This will be my first post as I am getting desperate for help with my car. I am hoping that some of you more experineced people could help me troubleshoot my vehicle.

I have a 1994 Chevrolet Camaro Z28 - (5.7L LT1 - 4L60E). The car is pretty much stock and the only non stock parts that I am aware of are the K&N Air intake and an MSD Box (Currently disconnected and running on stock coil).

The car has been developing a ton of issues, most of which are intermittent and are starting to drive me crazy. I will list below the symptoms that I am getting and the issues that I am aware of.

- Thermostat seems to sometimes be stuck open? Temperatures often won't rise above 1/4 of the gage. Fans come on as soon as I start the car.
- Lack of power when accelerating. Seems better when accelerating from a full stop rather than after slowing down on the highway. Lack of power below 2K RPM.
- Misfiring when accelerating. Quiet pops from the exhaust and slight twitching (this is a new symptom).
- Smell of gasoline fumes in the cabin. This happens when I have to press on the throttle and the car won't accelerate properly.
- Twitching RPM at idle. The RPM sometimes starts ramping up and down and the car will twitch. This mostly happens at idle but can also sometimes be noticed when driving. Oil pressure needle also twitches.
- Sometimes has trouble starting.
- No AC/HVAC (I haven't even bothered looking into this yet)

I am aware the transmission is having some issues. It wasn't shifting recently and it was a failed shift solenoid. It was replaced and it's been better since but I am not convinced.

Here are a list of parts that I know have been replaced:

- Fuel pump.
- Fuel Filter.
- Purge Solenoid.
- MAP Sensor
- Air Filter
- TPS Sensor
- Distributor Cap
- Ignition Coil (Some mechanic thought the MSD could be faulty)

Parts that I am replacing next when I get a chance.

- Belt
- Idle tensioner
- IAC (Idle Air Control Valve)
- Thermostat / Thermostat housing / Gasket

Sometimes the car seems to be driving okay without any issues. Sometimes I am gettin some or all of the above symptoms at the same time.
I have had very little luck with local mechanics helping me diagnose these issues, most of them have complained about the computer being a 1994 so they can't read it (ridiculous?!).

I have downloaded the SCAN 9495 software and built my own OBD-1 to USB cable which is working great btw (THANKS GUYS!!). I am now able to get to my DTC codes through the data logs.
But I am getting so many codes most of which seem to be very random so I have a hard time figuring out the problem. And I rarely get the same code twice! Could some of you guys help me decipher these datalogs?
My wild inexperienced guess from the codes that I am getting is that I have some electrical or ECM related issues.

I will attach below an example of a datalog from a recent drive and the error codes that I got during that drive.

DTC CODES from this particular drive:
24, 24/87, 14, 80, 47, 87/94, 19, 62.

Thank you so much in advance.
Look forward to hearing back from you all.

 

Not sure who's going to invest time looking at the data logs. I'm no longer doing it.

https://www.camaroz28.com/forums/com...-guide-886891/

Read post #2.

Codes seem bogus…. several of them don't exist for a 94. They could be due to interference on the data line from the PCM to the DLC connector. Usually if there is a code that shows up on a single line of the log and doesn’t increment the DTC count, the entire line of data or a significant part of the data line may be corrupted due to the interference.

Do the coolant temp readings in the log match the gauge (1/4 max)? If the log data shows normal, higher temperatures, the gauge sensor or wiring is faulty. Should be easy enough for you to check.

What brand is the Opti cap? About 5+ years ago I found an error with an MSD Opti causing erratic idle and surges, with excursions as high as 2,700 RPM. When I sent the data to MSD they apparently found a defect in a batch of caps was causing the problem. Never gave me any details. Didn’t even say “thank you” for giving them the data.

 

Thanks for the quick response! Appreciate it.

I really can't blame you for not wanting to spend your time looking at other peoples datalogs. It was a long shot.. but thanks anyway!

That's what I thought.. Those codes are not making much sense and some of them don't even appear on the DTC Error code list.

I had a look and compared a couple of datalogs. One from a drive where the temps never went above 1/4 and another where it did go all the way to 1/2 and above.
The data confirmed that when the gauge was at 1/4 the temps didn't go above 190. On the other log they were going above 200.
I suppose this confirms that my thermostat needs to be replaced - which I was going to do anyway.

The distributor cap was replaced by some mechanic a few months ago. Unforuntatly I can't confirm the brand but I would assume it's an AC Delco. They definitely wouldn't have put an MSD one.

I had a look at the link you sent me.. Thank you!! Much appreciated.

I guess I will try and carry on troubleshooting. I was going to start inspecting the wiring next and all the grounding points.

 

Ooops..Fred I am sorry. I referred this guy here and to rely upon you for advice. My mistake. Sorry to the OP also.

OP, I do not see any trouble codes in your log file. Where do you see those?
Were you continuously pumping the throttle in the log file period. I see a lot of throttle activity. Or maybe this was just a very long log?

 

Hi,

Thanks for getting back to me. And no worries.

That is a very long log file. So that's why it looks like there is a lot of throttle activity. I am brand new to this kind of stuff so I do apologize.

I do not get any DTC codes that get saved or that are visible by the scan software.. But I've noticed the DTC box in the software flash red while the engine is running but nothing gets saved.
If I open the logs up as a spreadsheet and scroll down there are codes flashing in the far right DTC column (where it usually just says ---).

 

I would ignore any codes that are brief. Those are not real, just an anomaly of the GM PCM.

 

Okay.. I guess I will have to ignore those and look elsehwere for my problem.
I do find it very strange how there are no codes or SES light and the car is running so poorly. I will keep trying and maybe I will catch something.

Thanks for your explanation and help so far. Appreciate it!

 

OK... now I feel guilty.

I will take a very quick look at the engine log. I really don't know much about the auto transmission.

 

And could you explain how you reached this conclusion:



1/4 mark of the gauge is 185-degF. In the log the coolant temp reaches 198-degF. The stock thermostat is rated 180-degF. That's when it starts to open. It won't be fully open until the coolant reaches about 200-degF. I don't see anything unusual in the data log you posted. What is the history of the car? Did you buy it used? If so, the t'stat could have been changed to a 160-degF, and the fan on/off temperatures reprogrammed to operate at lower temperatures. That's a popular modification.

If we reach the point where I can look at a log in detail, it has to conform to the steps contained in my post linked above. That requires a cold start.

Before spending money on the correct LT1 style thermostat (not the same as the normal SBC 'stat), test the one you have now in hot water to see at what temperature it opens.

 

Hi Injuneer,

Thanks for your responses and pointers so far.

When I first got the car the temperatures were always around 1/2 or above on the temp gauge once the car reached operating temperature. Recently the temps started to just get stuck at 1/4 mark and very rarely going above (whether I'm sitting in traffic or moving or driving long distance).
Occasionally the temps will rise above to the usual levels and then go back down and get stuck at the 1/4 mark again.
Also when I start the car I immediately hear the fans come on. I don't remember this ever being the case?

I have a datalog from a drive where the temps did reach higher on the gauge and it logged it in the data too. Recording temps up to 230.
The log that I attached above it stays around 195. Peaks at 198 but that's it. (and that was a long drive with traffic and highway speeds).

History about the car:
I got her less than a year ago.. She has been mostly sitting for a few years but started and driven occasionally.
Unfortunatley I don't know much about the history of the car. I got the car from a friend of a friend, I recently contacted her to find out more about the history of the vehicle but she was very ill and sadly passed away a few weeks ago.

When I get a chance I will do a datalog exactly as instructed in your post that you linked and hopefully that will be more useful.

Thanks
M