BellTech

Alrighty, so I got my 1997 Trans-Am now, picked it up Sunday, unfortunately it's not running. So here's what I've found in my diagnosis last night:

Engine will crank and will fire, the T/A starts and actually runs without holding the key in the crank position, when it fires it does one of two things:

1st being it will fire and lobe heavily between >100 and 500RPM's, stuttering and shaking violently during the whole time (anywhere between 10 seconds and 2 minutes) it's running.

2nd being much shorter lived, usually only lasting for 15 seconds, but firing and revving to 1,100RPM's, followed by the RPM's dropping to >500 and holding for about 5 seconds, after that it will make a very loud backfire / bang like it's firing on the exhaust stroke, then will die.


I have not pulled any codes yet although the light is active.
Haven't checked compression yet either, both of these I'm planning on doing tonight.



This is a quote giving advice to a user with a similar but not exact same issue like I'm having:

"The crank sensor (CKP) will not prevent the engine from starting. The CKP was only added in 96/97 to meet the OBD-II requirement for misfire detection. That's all it does... measures the crank velocity, so the PCM can look for the tiny variations in the velocity caused by misfires.

What I have found is that when the Opti optical sensor takes a dump, it may cause the CKP sensor codes. But if that is the case, you should be getting the codes for the high resolution (P0372) and low resolution pulse (P1371) signals from the Opti. If you lose the low resolution pulse, the engine will not start because the PCM kills the fuel system. It needs the low res signal to time the ignition and the injectors. Check the codes again."




This is what I'm going to do:

Pull the codes, find out exactly what they are and where they're coming from (what's causing them to become active) and then based off the codes (if any shooting a misfire code) i'll pull the plugs and check compression, if I don't have compression will this indicate bad rings or valves - OR could this be caused by the Opti-Spark alone? I've been hearing and reading nothing but negative comments towards opti and all the issues is can cause. Also my digging through forums has been showing me nothing but complaints regarding the optispark system for it's sensitivity.

ANYWAYS - Hopefully if it's got good compression, I'll go ahead and replace the opti-spark with (any recommendations are welcomed) MSD or Delphi (saw this posted by firehawk and another user stating they've used these) and replace the plugs and wires.



Right now I'm only posting this to keep track of what's actually going on with the car from day one, if anyone has recommendations as to what distributor, plugs, wires should be used or what else I should look at while I'm diagnosing it tonight, PLEASE don't hold back. This is my first trans-am, I know absolutely nothing about them although I really want to..



Also have been reading a lot about other issues causing similar problems (though I doubt they're the culprit) like the MAF, IAC, CKP (Check the CKP last night, was extremely wet and covered in road grime and mud - cleaned it out and connections are tight).

Pictures and a link to a video recording of me starting the car will hopefully help give everyone willing to help a good idea of what the car is actually doing - but I can go ahead and warn you from me using YouTube as a site for video uploads for diagnosing, the sound quality will more than likely be horrible, so sorry in advance..

azmarkus

You're on the right track, but in order for some proper advice and guidance it helps to know the general condition, mileage, transmission type, and any modifications (pro or hack job) that have been done to the vehicle.

BellTech

overall sounds healthy, clean oil.. good coolant, only issue i've seen is every fuse is a 30A.

182000 miles, manual 6spd, no mods (that i've seen)


here's a link to the video

BellTech

update -


Hooked up a scanner to the car last night, pulled 4 total codes.

1st two were:
P0122 - Generic - Throttle/Pedal position sensor a circuit low input

2nd two were:
P0100 - Generic - Mass or Volume air flow circuit



No codes were found regarding loss of compression or misfires. Thinking maybe he cleared the codes before I got the car, if there were any misfire codes would they show up with as little as this car runs on it's own? Or are they only triggered after the misfire has been happening for a certain length of time?

LandcruiserNZ

those 2 codes are telling you there's a problem with the TPS and MAF sensors, you'll need to check them out and rectify those problems before you go looking at diagnosing anything else

BellTech

checked out TPS and there were exposed wires, buying the new pigtail tonight and going to put it on to make sure i'm making good connection, MAF i didn't see any issues with the wiring but i have a new one in my toolbox at work i'm gonna bring home with me tonight to put it on and see if it clears the code.

regardless of these 2 issues the car is still running like crap and i need to make sure that it running like it is now isn't causing inaccurate readings from those two sensors.



also, are these lt / ls engines anything like the old tbi 350's? Last 350 i worked on had same codes and replacing the CKP (crank position sensor) cured both issues..?