Crandall

So I just bought a 1995 z28 and the guy I bought it from said optispark, coil, and ICM are all new, but after like 45 mins to an hour the car runs badly, idles rough, loss of power, unless I stomp the gas then it appears to smooth out, if I let it cool down and unplug the battery to let computer reset, it runs fine. I have ruled out most things except bad o2 sensors or the optispark. And it has to be like an hour before it acts up and the ses light will come on for a few mins and turn off, but so far it has ran perfectly when ses light is on, it just started running bad toward end of my about 75 mile drive, no ses light, so basically what do you think and i have heard the waterpump can leak onto opti , is there a way to tell that without pulling a bunch of parts any help would be very welcomed

Injuneer

Have you scanned it to see what's turning on the SES light? 95 can be a problem to scan. People see the 16-pin ALDL connector and assume it’s for an OBD-2 PCM. But the 95 PCM is OBD-1. If you have an OBD-1 scanner, you need a plug adapter, or need to use jumper wires, per Shoebox:

http://shbox.com/1/xraycable.jpg

For a more complete scan, including data logging, take a look at Scan9495 free download:

https://www.camaroz28.com/forums/com...95-lt1-874306/

Crandall

Thanks for quick reply yeah just reading up on scanning now I have like an adapter that plugs into the 16 pin and is usb on my side so I figure I am gonna download scan9495 and post the data, so I will likely take pics and post them, I am new to this but I am a quick study lol, also I read up on temp control sensor can cause these issues, and when I checked it the wires are in awful shape so I am soooo hoping thats the issue

Injuneer

SES light off - engine runs fine. SES light on - engine runs poorly. Code should tell you most of what you need to know. Photos of the data screen are usually of limited value. A running log, exported as a .csv file is extremely useful, particularly if you can catch the transition from "runs fine" to "runs poorly", and see the code setting. I can review the data log for you. But the code may be enough to solve the problem.

Crandall

The only trouble code I get is for 66 a/c refrigerant pressure sensor which makes sense because a.c. is gone but I did the scan and have the results so if anything looks off

Crandall

Also lol do I need it to throw the ses

Injuneer

The code that turned on the SES light should be stored. Unless you pulled the power to the PCM, clearing the code.

Crandall

yeah I did a few days ago and has not acted up again is there anyway the scan results can be helpful as like my o2 sensors have very low volts and like other values that seem off I can't find anything on what good values should be on the forums

Crandall

My bad how do i attach a file to a post

Crandall

LOL i gots it, the file is attached,

Injuneer

Opened OK on my iPad. Looks like just a couple minutes of idling. Engine didn’t get very warm. This will tell us a little bit about the condition of the engine control system. But it needs to be driven a while to see all the possible operating conditions. Somehow you have to anticipate the onset of the transition to "running badly", and start logging. You can run the log for about 20 minutes before it becomes unwieldy.

When I can get back to my PC and load it in Excel, I'll review what it looks like at idle.

Have you disconnected the battery or pulled the "PCM BAT" fuse since last time the SES light was on?

Crandall

Okay yeah i will drive it around town until i can get it to act up and then run a longer scan, yeah i did unhook the battery to reset the PCM and it has not acted up since then but i will make sure not to do that, i am quite the newbie lol but you said to test for about 20 mins when the car is running badly, i will be able to drive it around in about an hour or 2 then upload the results, and btw i am super super thankful for the help, but with what you seen so far i take it nothing was super drastic i am hoping

Injuneer

Pulling power to the PCM clears the codes, and also clears the long term fuel corrections (LTFT). The LTFT's are critical to learning under what conditions the engine operation departs from the way it is supposed to run, particularly with regard to A/F ratio. Once you clear the PCM, the LTFT's revert to 0% correction, and the engine needs to be driven under a very wide range of RPM and engine load (as indicated by MAP) in order to relearn the required fuel corrections. There are 16 different combinations (cells) arranged in a grid of RPM on one axis and MAP on the other. And there are separate LTFT's for each of the two banks of cylinders. Plus additional cells for idle, open loop accel, and decel.

Sometimes you can find the cause of the problem. Other times, not.

Crandall

Okay here is data from driving around town varied speed and loads, however was not super heavy on throttle as i didn't want my laptop to go flying, but tomorrow i am gonna take it down the highway until i can get it to throw a code, it has happened both times at 60 to 70 miles an hour, for about 50 miles cruse controlled, the car ran perfectly of course because i was trying to get it to throw a code but i will be trying again tomorrow with the highway. If anyone wants to take a look it would be helpful the only thing i noticed and i drove for over an hour the closed loop value stayed at 1 the entire time, and car was nice and warm, the heat could have cooked a turkey in the car lol

Injuneer

Just looking at the first log with only idle, not a lot of problems. Appears to be a stock tune - any mods to the engine?

Things that look normal:

- idle air control counts
- inlet air temp
- coolant warming up maybe a bit slowly
- system voltage
- barometer
- throttle position sensor volts
- mass air sensor air flow
- manifold absolute pressure
- spark advance
- no knock retard
- long term fuel trims in Cell 16 (idle) 130 left / 128 right
- left O2

Possible problem:

- right O2 very slow... should be switching rapidly between rich and lean, but it hangs rich for several seconds, then hangs lean for several seconds

In general, looks like a healthy engine.

I'll take a look at the other two later today if I can.