Should the fuel pump be on during crank?

cjmatt

cjmatt

Club Member
Ive been trying to diagnose my hard start, could never figure it out until just recently. I had it on the dyno and noticed that the fuel pressure dropped off as soon as you cranked it. well Ive been tinkering with it today and just realized that the fuel pump and fan turn off when you turn it from on to crank, in which it doesnt get power. Should i rewire it to be on during crank as well, or is there supposed to be some sort of pressure valve that will keep the fuel from flowing backwards when it turns off.

this is on an A1000 pump btw
 
well, however you set it up to keep pressure during crank, factory there is a check valve in the pumps to keep pressure in the line, for you, cheapest way is to have the pump run in crank as well as run



hell, we maxed out the prime time length in my Z71, it now primes for something like 60 seconds, lol
 
Fuel pump should be on while cranking, how else would it get fuel if its not running??? Fan doesn't need to be on while cranking.
 
It's running a stock regulator. You can tie the relay activation to a relay switching to ground on the S terminal on the starter if it has one. That will give you primming during cranking. Also you can change the pump priming time in some aftermarket and some factory pcms. So if you engage the key to crank at a resonable rate it should stay on during crank.

CableGuy said:
return or returnless? What kinda regulator?
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Sean said:
It's running a stock regulator. You can tie the relay activation to a relay switching to ground on the S terminal on the starter if it has one. That will give you primming during cranking. Also you can change the pump priming time in some aftermarket and some factory pcms. So if you engage the key to crank at a resonable rate it should stay on during crank.
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whatchu talkin bout willis? ive got all stainless lines to an aeromotive regulator, then it returns back to the tank. This is an ls1 in a 89 notchback. The fan and pump are wired to come on with the ignition on, they will stay on the whole time the car is in the run position, no priming
 
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why would a stock regulator shut the pump off while cranking?

My buddy and i noticed his 255 in his LT1 trans am seems to do this too, but my stock pump primes like it should (except its dying haha).
 
Sounds like the pump is wired to the run mode portion of the ignition switch and not a hot in start and run mode portion of the switch. .

cjmatt said:
whatchu talkin bout willis? ive got all stainless lines to an aeromotive regulator, then it returns back to the tank. This is an ls1 in a 89 notchback. The fan and pump are wired to come on with the ignition on, they will stay on the whole time the car is in the run position, no priming
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Sean said:
Sounds like the pump is wired to the run mode portion of the ignition switch and not a hot in start and run mode portion of the switch. .
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So I guess the cool thing to do would be to wire myself in a push button starter for the dash. that way I can keep the ignition switch in the run position, then use the starter.

Anyone wired one up on a fox before?
 
cjmatt said:
So I guess the cool thing to do would be to wire myself in a push button starter for the dash. that way I can keep the ignition switch in the run position, then use the starter.

Anyone wired one up on a fox before?
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you could do that or you find the hot that used to go to the factory EFI relay and change the relay from ground activate to hot activated and solve your problem easily. Should be red/green stripe Most likely thats now the ignition feed for the LS! pcm in the car if its running a stock pcm.
 
If the A1000 is like the Tsunami or 700HP EFI Aeromotive pumps, you need to have a check valve on the outlet side of the pump. That would allow for some fuel pressure to remain while cranking (thats how the oems do it).

If you run the pump during cranking, it will drop the voltage to the starter (and may crank slower / not start).

Aeromotive makes a check valve. PN 15107 I can get them locally if needed.

Kendall
 
I agree with Kendall, a check valve for the supply line at the pump or a different pump (I chose a different pump).

I was running a weldon 2025 pump on the street and I was constantly losing pressure at crank, when I shut the car off (immediately losing pressure). It was creating hard start/ bucking when started issues due to irratic pressure. I even wired the pump to be constant on and that turned out to be a PITA since anytime I had my ignition on for tuning, diagnosing other stuff, etc. it was running and draining the battery quickly.

After installing a check valve it was much better, not completely fixed. So I got dual inline Pierburg pumps which put out hellofa amount of fuel and have built in check valve on the outlet side of the pumps already. They are quiet, made for daily driving, and work just like stock now. although the areomotive regulator still doesnt hold pressure that long, its leaking pressurized fuel back to the tank. a lot of areomotive reg's do that, im thinking of switching.

So, id start with the cheap check valve and wire your pump like stock (prime/run/not while cranking) and see if that clears your issue up.
 
I would pass on the check valve. I have seen them slam shut and block off the fuel system. Just arm the pump during cranking and run a large battery. Problem solved.
 
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