TCCoA Forums banner

1 - 20 of 60 Posts

·
Registered
Joined
·
325 Posts
Discussion Starter #1
I have a 97 T Bird with the 4.6L V8. It has a bad intermittent stalling problem. I can drive it for days and everything is fine. Then when pulling up to a stop sign or driving at very low speeds, it will stall and not restart. If you let the car sit for hours and then come back to it, it may start and run fine again. Replaced fuel filter, fuel pump and sock in tank with zero change. Still intermittently dies with no restart. Fuel pressure is up to 40 lbs. with no start. I thought about changing the IAC next but if that is bad, I would think it would still restart but not idle???? No restart until much later. The car has about 130K on it but has always run fine. What to do next??? The only OBD II code I have is for the canister relay. Where would you go next??
 

·
Super Moderator
Joined
·
11,961 Posts
sounds like it could be a failing iac valve...only way to really know is to try another known working one

otherwise, if the pcm loses the crank signal, there will be no spark....check the wires and repair/replace the sensor as necessary

inspect all chassis and engine block grounds
 

·
Super Moderator
Joined
·
11,961 Posts
it depends if the throttle stop screw has been messed with.....the iac is responsible for allowing air in during both cranking and idling, but the angle of the TB blade affects this.....with a non-functioning iac, the engine should fire once (due to the minute amount of air in the cylinders), but should die pretty much immediately
 

·
Registered
Joined
·
325 Posts
Discussion Starter #6
When the car stalls, It will not restart no matter how you hold the throttle. It is totally dead in the water when acting up. Starter spins like crazy but no start.
 

·
Registered
Joined
·
325 Posts
Discussion Starter #9
The crank position sensor harness was replaced not too long ago and the car has had 3 new crank position sensors installed. Two FOMOCo ones and one aftermarket one. This was all to correct an intermittent no start condition but it never stalled. This time , it stalls too. I will check spark and replace the IAC. This car has a long history (10 + years of hard starting issues). AAA towing knows the car on sight. They love the business. This time it is stalling too whereas before it was only hard starting.

Thanks!!
 

·
Registered
Joined
·
3,902 Posts
You just need to find out what you are losing when it is not able to run. Its losing either spark or fuel. Get a fuel pressure gauge and keep it with you. The next time it dies and wont restart, do a fuel pressure test. You should also check for spark at the same time if fuel is ok. This will really help you narrow things down. It could be a bad fuel pump relay in the CCRM. Good luck buddy!
 

·
Registered
Joined
·
325 Posts
Discussion Starter #11
I think the problem is threefold. The PCM is putting out a low voltage signal to the CPS. So we are changing the PCM, the CPS harness (again) and the CPS (again). Apparently this CPS harness is shielded and any break in the shield can cause any other 12V signals interfere with the CPS signal. This has been a long standing issue with this car. We are going to a later harness and CPS sensor out of a 2005 4.6L which is supposed to be a much improved CPS set up. The old 97 configuration has been an issue from day one. Will let you know how all this works out.

Thanks for all the help, Phil Swanson
 

·
Registered
Joined
·
325 Posts
Discussion Starter #12
Crank Senson Loses Signal On Restart Only

One of my two 97 TBirds is at the tuners shop and has been there for two weeks now for low speed stalling and intermittent very hard starting. He checked out the fuel system and it was ok but replaced the pump and filter anyway. No change. He replaced the Crank Position Sensor twice and still no change. He replaced the shielded CPS harness wires without splicing, no change. I went to the junkyard and stripped out another unspliced shielded CPS wire for him since mine had been spliced near the connector. He tried another computer from another 97 T Bird w/ 4.6L. Still no change. When he puts a scope on it, it shows that on restart, it loses all spark and fuel injector signal indicating that the CPS circuit is failing, we think. The car has intermittently done this for at least 10 years but now but it is much worse. After the car finally does start, it runs perfectly. No misses or hesitation. Shut it off and no restart. When cranking, no spark or fuel. Shut off the key and then try it over and over, sometimes you can get it to re-start. When it starts, it always runs fine. What the heck is going on? My tuner has never come accross this before and he specializes in Ford modular engines. He is convinced that it is failure of the CPS circuit but where?

Thanks, Phil Swanson
 

·
Registered
Joined
·
2,435 Posts
Replace the cam sensor it uses that to find number 1, just try it and see it's easy to change

Robert
 

·
Registered
Joined
·
325 Posts
Discussion Starter #15
Replace the cam sensor it uses that to find number 1, just try it and see it's easy to change

Robert
Robert,

Why would the cam sensor knock out the fuel as well? My tuner is thinking the crank trigger wheel is cracked or broken. The problem appears to be the crank position sensor circuit because both fuel and ignition shut down during non start conditions. What would #1 TDC have to do with fuel shutting down too?

Phil
 

·
Registered
Joined
·
3,902 Posts
If you really think the wires to the CKP circuit are bad, the ultimate test would be to power a headlight bulb through the wiring with the PCM and CKP unhooked. This allows you to see what happens when there is a load on the circuit. If the wiring was good, the light should illuminate brightly. If there was excess resistance in the wiring, the light might only come on dimly. You could even have some "hogged out" pins in your connector. This can happen when the connectors are probed improperly.
 

·
Registered
Joined
·
325 Posts
Discussion Starter #18
If you really think the wires to the CKP circuit are bad, the ultimate test would be to power a headlight bulb through the wiring with the PCM and CKP unhooked. This allows you to see what happens when there is a load on the circuit. If the wiring was good, the light should illuminate brightly. If there was excess resistance in the wiring, the light might only come on dimly. You could even have some "hogged out" pins in your connector. This can happen when the connectors are probed improperly.
We really have eliminated the CPS sensor wiring because we replaced it and no change. An ohm meter would work better than a light bulb but we know the wire is ok now because we replaced it already.

Thanks, Phil
 
1 - 20 of 60 Posts
Top