Job Title

[ChevyGuy]

I was just wondering who in here is a mechanic. The reason Im asking is because I have a project Ive been working on for a friend and Im stumped on the problem Im having with his car.

[123 pugsy]

So,what's the problem?

[roundedline]

Ditto, Post it.

Chris Lucas
www.73-87chevytrucks.com
www.captkaoscustoms.com
Project Su
Jimmy 2WD Project

[ChevyGuy]

I helped out a friend put a used motor and tranny into his 92 Grand Prix it has a 3.1 with auto. It will not start up on its own. You have to used starter fluid or gas. But when its running it runs fine except for idle but it comes down once you put it in gear. We have changed the fuel pump, filter, and tried a fuel pressure regulator that worked on another car and still no go. We also tried a different computer. It was giving me a code of 43 for awhile without running it very much and then if you run it for awhile it gives you 15 and a 21. I havent got a straight answer on what to look for to get it to start on its own. I thought it was fuel pressure but the second time we tried to run the pump in test mode as we fired didnt get it started. I was just wondering if any of yall maybe stumbled across this before?

[DnStClr]

The idle air control (motor) valve might be dirty. It's located on the throttle body- should be about 4 wires coming from it. remove it carefully and clean with a small stiff brush and throttle body spray cleaner. I think there's a pic somewhere on this site .

Don St.Clair
Culleoka Tn

[ChevyGuy]

I changed it with the one off his old motor and it didnt make a difference but I can see about getting another.

[VileZambonie]

Ok start with the basics here. In order to start the car you have to add fuel. Check the Coolant temp sensor near the thermostat housing on the intake. It's a 2 wire device. This is what tells the PCM how much fuel to add during start up. Also it sounds like the TPS (throttle position sensor) might be tricking you. If it reads over 3.5 volts at idle the pcm will put the car into clear flood mode and not energize the injector drivers therefore no fuel to the engine while cranking.

Do you have access to a digital volt meter? At the throttle position sensor back probe the wires with a paper clip and hook your meter up in parallel with one leg to a good ground and the other leg on each paper clip. With the Key on engine off you should see:
Cavity A) approximately 5 volts
Cavity B) zero volts and do a continuity test to ground to verify your ground but only do it on this terminal! Do not try to measure resistance of a live circuit.
Cavity c) with the throttle closed approx .55V thats 550 millivolts. With the key on engine off remember, slowly open the throttle and the voltage should steadily increase to approximately 4.5 volts at wide open throttle. Let us know your results.

Also make sure all of your ground wires are clean and tight! This is critical.

[ChevyGuy]

The wiring is what we coming to conclusion to. The wiring was all screwed up and smashed and melted together. My friend bought a lemon. I didnt the best I could without spending hours replacing and soldering new wires. The ones that were smashed are on the bank thats feeds the back injectors and didnt include the wires that feed the front that included the iac, tps and the cts. The cts is brand new. Ill be getting the car back tomorrow or Monday and Ill do the test with the dvm. The book doesnt really help with major problems just light ones. I worked on alot of these type motors but never had this problem.

[ChevyGuy]

I did the test with the digital multimeter and check the ground and it was fine. I check the power to the senson and it was 5V and the other that was suppose to be 55 millivolts was topped out at 5V. Im guessing I have two bad TPS or that the wires are shorted together maybe.

[DnStClr]

I think you can adjust the TPS to get that millivolt setting can't you, Vile?

Don St.Clair
Culleoka Tn

[ChevyGuy]

Thanks for the info Vile. I took the wiring harness and found the wires shorted together. We got everything squared away and it started with no more check engine light.

[VileZambonie]

Glad to hear! 5V back to the PCM puts it in clear flood mode and the pcm will not ground the injectors.  

[ChevyGuy]

It was the best info anyone has given me when I was working on something that I couldnt figure out.  

[WickedC20]

If the used engine came with injectors, never install them or the fuel rail, they tend to clog, use the fuel rail and injectors from the OE engine.
Edit #3 LOL cause I didn't read all the way earlier.

Edited by: WickedC20 at: 9/12/06 11:09 am