Hello,
I want to start off by saying I'm soooooo glad there are dedicated forums still active for these cars. I was dealt a bad hand, and have a 1987 trans am 305(i think), which has apparently been swapped from a manual to an automatic by the previous owner. The car hasn't run right since I've been working on it the past few weeks. I'm not sure it every was running correctly. The wiring is a rotten spaghetti mess, and the motor looks like it is 100% untouched. I am fixing this for a friend as they have no money and need help getting it to idle and not die. I have plenty of experience with OBD2, have made my own OBD1/RS232 adapter and re-flashed my 94 Trans Am PCM. I have SOME experience with aftermarket EFI retrofits. But i have NOT dealt with the 80's era OBD1/PROM. Almost all of the links listed on this site have been dead for many years, so finding adapters and software has been a dead end for me.

The car will not idle stable, unless i jump the diagnostic pin on the OBD1 connector. The ECM is obviously idle hunting all over the place. I can tell that the IAC IS moving, but it could be slow. This sounds more like the ECU is rapidly changing timing to lower the idle, but the car will NOT stay running under 700 rpm according to my timing light. At highway speeds, coasting causes the idle to jump from 800-2000 constantly with a check engine light. As i understand, the PROM for the manual and the automatic are different.... Can anyone help me verify what the PROM in the vehicle is? It looks like it has an original GM(delco) MAF. Do i need to test values on this? The tachometer is WAYYY off, and most of the gauges are dead. I need serious help with this vehicle.

So far I have .....

• replaced the distributor and set base timing to 6 degrees advanced,
• replaced Spark plugs w/ NGK copper
• replaced O2 sensor (Denso),
• cleaned the TB/IAC
• verified TPS readings both throttle closed and WOT
• Verified 43lbs of fuel pressure at the rail at idle AND 4000+rpm

 

Post the letters on the chip, 700r4 ? Do you have a Vss signal to the ecm ?

 

Correct, the PROMS for both are very different. back in the day i found an abandoned camaro and took the ECM and threw it in mine... mines an auto, the camaro was a manual lol


You def need the correct PROM.... you cna probably tell if its been touched / changed / removed though.

 

I was finally able to work on it again today and pulled the computer out.

 

Yes, it has a cable driven detent at the TB, so i am going to assume it is a 700r4.

 

How does the PROM (blue part) fit in the port with the JET chip in the way?

The Jet chip could be messing things up.

 

try just the memcal acxs and see how it performs

 

I wanted to post a quick update on this. I plugged the GM PROM chip directly into the computer, and it ran the exact same, so i plugged the JET riser/chip back in. I went ahead and replaced the IAC with a Standard T-series, and it seems to be able to catch itself from dying now, so it seems the old IAC valve was too slow. However, still a rough start when cold, and idle hunting all over the place until it warms up. Once it's warm, it now is able to find a low idle.

I was also able to figure out how to grab the codes from this dinosaur. It is reporting BOTH code 33, and 34. Which indicated MAF low voltage, and MAF high voltage. Looking at the wiring around the MAF relays, i'm going to go ahead and rewire those. Thankfully we have forum posts like this to pull from https://www.thirdgen.org/forums/tpi/...ble-codes.html

Does anyone have a more official wiring diagram for how the MAF is wired, powered, pinned out, ect?

 

http://austinthirdgen.org/mkportal/m...ine_wiring.gif

 

I have re-wired the MAF power relay, and checked connections to the burn-in relay. I have also reset the PCM again, and tried a cold start. The same issue is occuring. The IAC opens up for the cold start, it starts up, hits high idle, then within 2 seconds dies. I have uploaded a few videos to youtube, so you can see it in action. Mind you, the tachometer is about 450RPM high, according to my timing light. I am still getting the code 34 according to the CEL. Hopefully I'm reading the codes correctly. I get a 1, 2, pause 1, 2, pause 1, 2, pause 3, 4, pause 3, 4, pause 3, 4.


Here is the relay harness before and after...




I also found a few pigtails unplugged in the engine bay. The first picture is on the passenger side of the motor towards the head, and the second is on the drivers side by the manifold. Does anyone know what these pigtails are for? I'm assuming the ones on the passenger side are for A/C? One is for the A/C compressor, and the other is for the A/C pressure switch?

 

Because you're using a V6 tachometer on a V8 engine.

The first pic sensors are: plug on left = AC hard-line; plugs on the right SMOG

The second pic plugs are for the AC compressor

** there should be a small spacer on the 10mm bolt that secures the Tranny VSS into the tailshaft.

** Nice work fixing up the wiring to that relay !


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man that relay wiring looks pretty bad...Hawks sells a new one if you just want to repalce it.......there are some on ebay as well!

 

That kinda looks liek a bad MAF the way it's running / idling....have you tried disconnecting the MAF and starting it?


If it runs better with the MAF disconnected then the MAF is bad