efi starts, but dies immediately

[archemitis]

so i got this mpfi that hasnt ran in a couple years, supposedly due to a fuel pump. so i changed the pump to a junkyard unit. now the car starts, idles for about 1-2 seconds, then dies. if i throttle it, it will rev up fast, and run out of juice even faster. if i pour gas down the throat, it will run, and rev up, untill it runs out of fuel.

i pinched off the return line, after the regulator, and it does the same thing, but... theres so much fuel pressure, that doing this makes the lines leak, at the hose clamps. so it seems like i have adequate fuel pressure.

and since its starting for a second, my injectors must be opening, then the computer is telling them to shut off.

could this be something as stupid as a tps? andybody have anything i can try?

thanks in advance

[iluvdrt]

did the fuel pump come out of a suby with the same unit? the mpfi, has a very high fuel pressure where as the carbed versions and tbi versions do not. the pumps look the same too.

 

 

also something to think about, are you sure its running out of fuel? maybe it is shutting off because of something else. maf sensor maybe, thats the ways a car acts when you unplug the maf. also does it have a new fuel fiter?

[MilesFox]

sounds MAF related. unplug the wire to it and it will do what you describe.

 

is the fuel pump coming on? my mpfi turbo will kick the relays, but no pump, i had to make a toggle switch. the problem is between the wiring between the relay and the pump

[iluvdrt]

i think he said it was getting fuel, it just acted like it was stopping.

 

i also think it was the maf.

[GLCraig]

One thing to be aware of is that the ECU is designed to turn on the pump for a certain period of time while the engine is being started. After this period of time the ECU expects to receive a signal from the distributor. When it dose the ECU will turn the pump back on, if it doesn’t the pump will stay shut off and the engine will run until it uses up what's left of the fuel in the system.

[aba4430]

Is there an idle air control valve (IAC) on these. If it starts up and dies, the IAC could be a culprit.

aba4430

[bigjim5551212]

Im not sure about this, but on cars with a ballast resistor in the ignition, the starter circuit has high voltage, but then the ballast cuts the voltage to the ignition. Then the engine runs faster after that, it gets more voltage. Could the ignition be cutting out after the engine starts?

[rallyruss]

no balast resistors here but good thinking. if the car is starting the disty signal is probably not it.

 

I vote maf as well. if the computer does not see air flow it will shut down the fuel pump. its a safty feature. I know the flaper style mafs actually have a little switch inside for this purpouse.

not sure how the hot wire mafs do it but its the same theory.

 

of course wiring could be the problem as well if the signal never gets to the ecm.

[archemitis]

the mpfi car i wired myself, will run with the maf unplugged, good enough to go around the block(tried it on accident once)

[MilesFox]

ok if you were to hotwire the pump and it still runs, then the following quote below would be the problem. makes sense to me.

 

 

One thing to be aware of is that the ECU is designed to turn on the pump for a certain period of time while the engine is being started. After this period of time the ECU expects to receive a signal from the distributor. When it dose the ECU will turn the pump back on, if it doesn’t the pump will stay shut off and the engine will run until it uses up what's left of the fuel in the system.