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5.2 Magnum startup...

1461 Views 12 Replies 3 Participants Last post by  cheve5
Good morn lads...
I recently built a 5.2 MPFI Magnum, 1997 Jeep Grand Cherokee donor car recently, it was mounted on a B body, original Wiring Harness and sensors... It Starts, runs good idle for 6 seconds and stops inmediately, without any hassle. The ASD relay was jumped in order for it to start.. I know you lads know much more than me as far as this concerns, id take it to another forum but i can see you know magnums better than in any old B body forum...
Thanks in advance...

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What are you using for a fuel pump and pressure?
Im using an internal holley 120 psi high pressure pump... its regulated to 45 psi... but it isnt fuel, it would hassle when it stops if it was fuel what it lacks. Im thinking of something electrical.

its hard to beleive no one has had this kinda problem before.
just wondering, have you checked the igntion switch? a few months back my mothers car would off and on do something like that, ended up the switch would nt slide back into the run position enough to stay running.just an idea. tom
I have, and its unfortunately not that...
theres a chance it could be the fuel pressure regulator, y checked pressure and it was delivering 80 psi. How could I further regulate pressure? does anyone know of a particular product?
what b-body do you have?you are using a holley 120 psi internal pump,what #, and how are you reg it to 45 psi? are you using the computer for the 5.2? what mods have you done to the motor. any more info would help us out.
no mods on the 5.2, just rebuilt... i do not have the number of the pump... I tried to regulate it with a std. regulator, but as you can see,it aint workin.
the bbody is a 72 charger.
injectors were cleaned, engine will run if fed with external fuel injector cleaner supply. idles smooth...
this might sound stupid, do you have a fuel line return to your tank?
Not stupido at all, in fact I managed to lower de pressure up to 55 psi justo by relocating the same pressure regulator into the return line. However, I found out that wasnt the problem.
Even with regular pressure the car would start, run for 6 secs and stop, just like before.
I made it run with an injector pulsing device and the car ran stable and for as long as i wanted. Obviously meaning there is no signal in the injector cables, in all of them...
My newer question, is this necesarily the Powertrain Control Module or could it be something else still?
Help appreciated, thanks.
If there's a failure in the distributor (cam position sensor) or the crank position sensor, the PCM cannot determine injector sequence, nor can it distinguish between fuel injection and spark events. Gotta start somewhere.
The crank position sensor is new, the cam position isn't. However, everything was supposed to be from a moving truck. Its strange that the engine starts however, there is also a sign that there is spark going thru in the fact that the engine keeps running only with the injector pulsing device.
I was told by some people that the PCM could need coding in order for the engine to keep running, however I was under the impression that pre 1999 dodge/jeep/chrysler cars did not need other coding than that provided by the transponder in the key to the key module... Do any of you guys know something?
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