car starts, runs for 10 secs, then dies

[cheap]

I have an issue with my 347. The motor will start (after some coaxing), run for about 6-10 seconds at 2k rpm, then suddenly dies completely - no stuttering, no hesitation, but like I killed it intentionally. Additionally, if I TOUCH the throttle it will immediately die as well.

My searches on here came up with a million references to the surging idle thread, and a lot of people were pointing to the IAB/IAC in other threads. Thing is, the IAC is brand new. The whole motor is pretty much brand new, it hasn't even run long enough to burn in the gaskets and such. There is no EGR, instead there is an EGR eliminator, and no ATC either but I borrowed one from a friend's car and it made no difference. Fuel pressure stays strong at 40+ the entire time.

Is there a cycle inside the computer programming that changes something from a "start" mode to a "run" mode? Why would me touching the throttle cause it to die instantly?

 

[PUNISHER RACING]

I had a similar problem with a Lincoln LSC it was the fuel pump relay

 

[bdollarbill]

Give us some background on setup. What have you changed besides the motor? Injectors, mass air meter, etc.. could be a number of things based on description anything would be a guess.

 

[cheap]

Its a kit car with 0 miles, so it's an unproven setup. The motor was purchased used, shortblock complete, with about 10k on it but disassembled except for the shortblock of course. The intake is a Edelbrock RPM airgap w/ a mass-floefi.com intake setup (4-bbl throttle body and GM mass air meter w/ converter for Ford fuel injection).

We found and fixed two large vacuum leaks today, no change. Also discovered our ground reference voltage for the TPS, baro press sensor, etc was energized w/ 5v so I cut the grey/red wire before the PCM and wired it directly to ground. The TPS now is showing 1.04v at idle and increases as the throttle is pressed, aka within limits. We disconnected every sensor in the grey/red (1993 harness) circuit (pin 46) and the brown/white circuit (pin 26) but with no luck. Disconnecting the MAF had no effect.

As I said, fuel pressure was good, and the timing was set at 10*btdc as well. It starts, which means I have fuel, spark, compression, etc, it just won't stay running past that 10 second point or so. I think the fact that it will start at all eliminates a LOT of possible suspects and at this point I am fairly confident that something either in the computer something the computer is looking for is not right. This is the second PCM I've used as well, current model is an A3M aka 5-speed PCM from a '93 GT (approx).

I'm using the factory wiring harness, but aftermarket gauges (all of em), everything is grounded that I can find (including the wire behind the intake, the wire at the PCM, a couple more behind the dash, one each for the headlights, etc) although I think there might still be one missing since that pin 46 wasn't grounding properly on it's own. I doubt it's a vacuum problem sine the intake A)doesn't have a PCV, B) has no vacuum lines running off it, and C) has the air filter directly on top of the throttle body/intake.

Fuel pump is a Mallory Georotor so by design it doesn't hold fuel pressure after it stops running, but I had an independent observer today watch the fuel pressure gauge on the Aeromotive FPR verify that pressure stayed above 40 until a few seconds after the engine quit, so that eliminates the pump, filter, regulator, and relay.

 

[Black1987Stang]

TFI module maybe?
Have you tried pulling your codes?
I don't know much about the proflowefi system so can't help ya with anything with that.

 

[cheap]

It's a mass-flo system, not the proflow. It's a mass-air setup. The TFI shouldn't be the cause since the distributor has been replaced (had an MSD one sieze on me) and the PC wont have any codes stored since the battery is disconnected when I'm not working on it.

I wonder if 42psi fuel pressure w/ 1/2" supply lines and #42 injectors may be flooding the motor out.

 

[PUNISHER RACING]

wow thats a lot of injector whats in that unit, trim your fuel down to 35 and try it

 

[cheap]

tomorrow I am going to turn down the FP and also pull the fuel cap off to make sure there are no negative pressure issues.

 

[TrickFlowd]

Take the two bolts out of your TFI module and take it to your local parts store(autozone, advance auto), and have them check it.

I had this same exact problem a few weeks ago. The TFI module gets weak, and can't trip the coil consistantly while being weak. Hense when you hit the gas, the motor dies. Its possibly because of the TFI being weak and not being able to trip the coil fast enough for the amount of rpm/fuel the motor is getting.

Does the car have spark after it dies? Could also be the pickup coil in the dist. That is, if your loosing spark after it dies. Just my experience.

 

[Bottomlesspit]

I might have missed it when I read through your description, so please forgive me, but have you tried replacing your ignition switch on the steering column? I have had, and seen many other folks have plenty of problems due to that darn switch. They are known to be a weak link, tend to pull apart and cause all kinds of funky electrical woes. We had one car doing exactly the same as yours...replaced the ignition switch and it solved the problem.
Good luck,
Ken

 

[cheap]

Well, this car doesn't exactly have an ignition switch - I made it a "keyless start" and instead wired in a momentary pushbutton for the starter and a toggle switch for the ignition "run/start" circuit.