I have a 1986 trans am with a 1987 350 TPI from a GTA. Whoever put the engine in did several things wrong, but I am coming up with a code 34 with a new maf, burnoff relay, and power relay. I found that there was a round plug with a tan/white and orange wires. I looked at a wire diagram and the tan/white goes from the power relay to a junction, to this mystery plug. The wire diagram called this plug a fuel pump switch. My car acts like it is starving for fuel as it stalls immediately after firing. When maf power relay is unplugged, the car will start and run great. jumping this plug caused the fuel pump to run. Any ideas? I will attach a picture of the plug. Thanks!

 

Looks like the plug for the oil pressure unit that should be located right above the oil filter. Called a fuel pump swithc in alot of places, since it senses oil pressure and thus runs the fuel pump if oil pressure is high enough.

BUT - this should ONLY be a backup circuit to the fuel pump relay setup that is controlled by the ECM. Maybe the fuel pump relay is bad? Does the pump prime when key turned on but not started?

 

The oil pressure unit was my first thought and looked it up and found two different locations. One above the oil filter and one next to the distributrr. There is some sort of sensor next to the distributor that does run a single tan/white wire but i will check around oil filter. Yes, the pump runs for a couple of seconds when the key is turned. My though was maybe the computer primes the fuel pump but then the fuel system takes control once car is started. That would explain when the maf power relay is removed, then the computer bypasses the entire system and controls fuel? I'm not sure, just a thought, but i will try fuel pump relay. Thanks for the help and let me know if you know of anything else this plug might be.

 

Fuel pump switch is only there as a backup should pump relay fail in which case the pump is run direct from batt once oil pressure over 4 psi ; completely bypassing ECM control of pump.
Under normal conditions; both the relay and OP switch supply power to pump

Typical TPI pump circuit

 

Most likely a faulty MAF unit
Any fault codes showing?
Look for DTC 33 , 34 , 36

 

I used to get code 33 for awhile, then after replacing burnoff and power relays, I am now getting code 34 when the car stalls and dies. Maf is new and the Problem occurred over a period of time. The car has always cOded a 33 or 34 or both the entire time I have had it but only now will it not start. Thanks fir all replys. Any input appreciated.

 

both 33 and 34 can indicate circuit wiring / ground problems
http://www.chevythunder.com/maf_code_33.htm

http://www.chevythunder.com/maf_code_34.htm

Code 33
This code is set when the ecm sees a indicated airflow of greater than 45 grams per sec (gps) and the tps is less than idle, and engine rpm's is around 2000.
This can be set by intermittent problems, usually a bad connection. These can be extremely difficult to find. Check the harness and connections very thoroughly.
Also check for routing of wiring near the spark plug wires, this can induce a voltage high enough to cause problems.
If this code is being set along with other maf related codes (34 and 36) suspect strongly a bad maf connector. If all else checks out, the maf is bad.
But since this sensor is very expensive, exhaust all your efforts to find and correct a wiring problem first.

Code 34-
This code is set when the ecm sees the following conditions: airflow less than 2.5 gps, engine speed of 600 rpm or greater and the tps is above 6% angle.
The typical problems are usually false air, vacuum leaks, or residue build up on the maf element or behind the throttle plates
. Check the wiring and connectors very carefully, especially if this code is also present with a code 33 and 36.

 

well i was looking to extend that plug down to above the oil filter, but the plug does not look like it will fit. The oil pressure switch looks like it has a **** for the plug to lock down into. This leads me to believe that this wiring harness does not belong to this car because of the engine swap. I am so overwhelmed I feel like ripping out all wiring and putting in a new wiring harness and wiring it up with a map system. Would a wiring harness from a '87 350 be that much different from the '86 305 wiring harness? Also, I found a burnt spot on a spark plug wire because the guy who owned this car before me is a turd and didn't route plug wires correctly. Could that throw a code enough to make the car stall and die? again, maf is new, relays are new, and car will start/run great when power relay or maf is unplugged. Thanks!

 

do you know if the car has the right knock censor in it? they are different for the 305 to 350.