1985 Trans Am (VIN F) Code 42 Running Strange! Please Help! - Third Generation F-Body Message Boards


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1985 Trans Am (VIN F) Code 42 Running Strange! Please Help!

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Old 08-14-2015, 01:23 PM   #1
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Join Date: Aug 2015
Location: Houghton, MI 49931
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Car: 1985 Pontiac Trans Am
Engine: 5.7 TPI

1985 Trans Am (VIN F) Code 42 Running Strange! Please Help!

Hello Everyone,

This is my first post to the forum, Though I have used it for the last few months for some extremely valuable information about my Trans Am. Thank you all for that. I'm hoping to get some help with something.

I'm having a very difficult time diagnosing what is going on with this car. I am also quite a novice when it comes to computer controlled engine management.

Here is what it's doing:

Occasionally it will fire and immediately die.
Occasionally it will idle at 400rpm
Occasionally it will have an oscillating idle from 500rpm to 1000rpm.
Occasionally it will die when put into gear and when stopped at lights.
Occasionally it will miss while going 60mph down the highway
Occasionally it will run perfectly and try to burn the rear tires off.
It always has an exhaust smell that I can't compare to anything else.
The radiator fan runs when the key is on
The tach is at 1000rpm with the key off

I know the timing is off, I just don't know where to start investigating. From the things I've been reading online, it involves probing for Ohms and Voltage at the ECU connector. and talks about ohms on CKT 432, I was unable to find what CKT 432 is. From what I can tell there is A1 to A12, B1 to B12, C1 to C16, and D1 to D16 pin outs on the ECU connector.

I had found a chart with what the voltages of those pins are supposed to be when connected to the ground pin. and when testing something labeled the SES Controller was supposed to have 0 volts with the key on, but had 11.82 volts with the key on. Does anyone know what the SES Controller is? There were other voltages that weren't consistent with the chart I had found for my ECU.

Here is what I've done to the car:
New air filter
New spark plugs
New spark plug wires
New distributor cap and rotor
Oil Change
Coolant Flush
New radiator fan motor and relay
New Belt for the Water Pump and Alternator

When I got the car, There was some backyard wiring done to it. It has the ground wire from the battery relocated, the radiator fan was hotwired with a switch, and the mass air flow sensor was left unplugged. (The car runs better with it unplugged for some reason) and the cruise control connector was unplugged. I'm not sure of anything else the previous owners did to its wiring.

I know this is a long post, Thanks for reading, Any insight would be greatly appreciated!

Best Regards,
Eightsixseven.
First time 3rd gen F Body owner.
eightsixseven is offline   Reply With Quote
Old 08-14-2015, 04:09 PM   #2
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Re: 1985 Trans Am (VIN F) Code 42 Running Strange! Please Help!

SES = Service Engine Soon (warning light)... the "controller" is just the driver that drives the light

The tach might read almost anything with no power. 1000 RPM is pretty normal. As long as it goes to 0 when you turn it on, life is good.

Get rid of EVERY wiring hack job you can find, and put it back like it belongs. Especially the radiator fan; virtually EVERY hack job I've ever seen where somebody hallucinated they were "improving" it, made it FAR LESS reliable than it was. There's no way in hell any of us out here can tell you what to look at, since we can't possibly have a clue what's been hacked up. You gotta track all that down yourself, since you're the only way who can place a physical eyeball on it.

I would suspect that at least part of the idle and other driveability problems stem from the same numbnutz that hacked the fan wiring, hacking the PCV system, although of course I can't see that like you can. Restore that whole system to its factory state, with one valve cover grommet having a hose that goes to the throttle body fitting in front of the throttle blades (has no vacuum on it), and the other with the PCV valve in it going to the port that does have vacuum. That by itself might make it run right with the MAF hooked up.
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