Motor popping on idle and now fuel pump not priming?
12-16-2016, 10:28 AM
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Motor popping on idle and now fuel pump not priming? I'm doing a turbo 5.3 swap into a 1968 c10, and I'm running into an issue with the motor popping while idling, and now the fuel pump is not priming.
Issue #1: Motor popping constantly while idling
The motor hasn't idled correctly, it sounded like a machine gun being fired at first. The mechanicals of the engine sound great, so I figured it was ignition related. I changed out plug wires, and it ran a little better (pop every few seconds now). Went to change out coil packs with a known good set and now I'm running into an issue with the fuel pump not priming:
Issue #2: Fuel pump primes for half a second, then shuts off and the truck won't start.
So the issue all of a sudden seems to be that the fuel pump isn't priming correctly and I have no fuel pressure. Nothing was changed, except for the coil packs. Previously, I would hit the ignition switch and hear the pump prime 3 distinct times. Now, it primes for half a second and shuts off, and there's no fuel pressure. Checked all fuses and replaced it with a known good relay, nothing. I then stuck a meter in the fuel pump relay, and saw 3v maximum leaving. I realize there's a delay on a digital meter, but very little is being outputted from the relay. Is this possibly PCM related? Fairly lost right now and could use some guidance...thanks!
Full setup:
L59
comp 224/228
dual springs
7.4 pushrods
rocker trunions
PSI harness
Bosch 044 w/hotwire
-6 an lines to holley rails/aeromotive regulator
3 bar map (denmah one)
The truck is being tuned by a friend who stopped tuning about a year ago, but he's doing it as a favor to me. I'm not trying to be up his ***, so I'd like to figure out as much as I can on my own. VATS has been deleted, and 3 bar segment swap was done. Some of the issue with the popping may be from running an open crossover pipe (there's a wideband in the crossover pipe from the drivers side bank) and I don't have any 02 sensors. I'll get pictures of what I've got going on when I get home...I know it's unorthodox.
Issue #1: Motor popping constantly while idling
The motor hasn't idled correctly, it sounded like a machine gun being fired at first. The mechanicals of the engine sound great, so I figured it was ignition related. I changed out plug wires, and it ran a little better (pop every few seconds now). Went to change out coil packs with a known good set and now I'm running into an issue with the fuel pump not priming:
Issue #2: Fuel pump primes for half a second, then shuts off and the truck won't start.
So the issue all of a sudden seems to be that the fuel pump isn't priming correctly and I have no fuel pressure. Nothing was changed, except for the coil packs. Previously, I would hit the ignition switch and hear the pump prime 3 distinct times. Now, it primes for half a second and shuts off, and there's no fuel pressure. Checked all fuses and replaced it with a known good relay, nothing. I then stuck a meter in the fuel pump relay, and saw 3v maximum leaving. I realize there's a delay on a digital meter, but very little is being outputted from the relay. Is this possibly PCM related? Fairly lost right now and could use some guidance...thanks!
Full setup:
L59
comp 224/228
dual springs
7.4 pushrods
rocker trunions
PSI harness
Bosch 044 w/hotwire
-6 an lines to holley rails/aeromotive regulator
3 bar map (denmah one)
The truck is being tuned by a friend who stopped tuning about a year ago, but he's doing it as a favor to me. I'm not trying to be up his ***, so I'd like to figure out as much as I can on my own. VATS has been deleted, and 3 bar segment swap was done. Some of the issue with the popping may be from running an open crossover pipe (there's a wideband in the crossover pipe from the drivers side bank) and I don't have any 02 sensors. I'll get pictures of what I've got going on when I get home...I know it's unorthodox.
Last edited by DownByTheRiver; 12-16-2016 at 10:34 AM.
12-16-2016, 12:46 PM
#2
Did the engine run ok before you took it out of the donor vehicle? Or has it been modified since? What computer? Sometime the aftermarket fuel pumps don't have a residual pressure valve and you have to prime longer. That can be adjusted in the tune. I have mine set to 6 seconds --- I turn the key to the on position for 3 seconds and then start. This gives the pump time to build pressure and fill the rails. If you don't have O2 sensors, are you set to run in open loop? And did you put the 3 bar MAP linear and offset info in the tune? Pushrods too long??
02-03-2017, 12:20 PM
#3
[QUOTE=dw456post;19480432]Did the engine run ok before you took it out of the donor vehicle? Or has it been modified since? What computer? Sometime the aftermarket fuel pumps don't have a residual pressure valve and you have to prime longer. That can be adjusted in the tune. I have mine set to 6 seconds --- I turn the key to the on position for 3 seconds and then start. This gives the pump time to build pressure and fill the rails. If you don't have O2 sensors, are you set to run in open loop? And did you put the 3 bar MAP linear and offset info in the tune? Pushrods too long??[/
Are you using a P01/411 ECM? If so, where would this table be that allows you to prime the pump longer?
Are you using a P01/411 ECM? If so, where would this table be that allows you to prime the pump longer?
02-03-2017, 12:47 PM
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I literally JUST went through this in my LS10. Same symptoms, popping at idle, then one day, can't get it to start, but I could hear it priming.
The pump was not getting 12V was the initial problem, and likely contributed to the rest. Undervolt an electric motor, it'll overamp itself and burn up. I hotwired it, and I also found out the the pump was grounded very poorly. I filed a spot to some fresh iron on the frame and got a good ground.
Other problem was internal to the fuel pump. The motor could turn, but the impeller was not. After prime, I had zero pressure at the rails. I checked out the external regulator, and it seemed fine.
So, I swapped the pump, since it isn't internally serviceable. New pump was very weak sounding, even though the old pump sounded fine. Even with the pump sounding very weak, I had pressure at the rails, but not enough juice to start the truck. This basically was telling me that the impeller was loose where it connected to the electric motor inside the pump body. Battery was damn near dead, which was interesting too. But, anyway, 50-amp charger plugged in for ten seconds, truck fired up.
I trickle charged it over night. Has not popped at idle since, and it starts up much better than before. All with no change to the tune.
The pump was not getting 12V was the initial problem, and likely contributed to the rest. Undervolt an electric motor, it'll overamp itself and burn up. I hotwired it, and I also found out the the pump was grounded very poorly. I filed a spot to some fresh iron on the frame and got a good ground.
Other problem was internal to the fuel pump. The motor could turn, but the impeller was not. After prime, I had zero pressure at the rails. I checked out the external regulator, and it seemed fine.
So, I swapped the pump, since it isn't internally serviceable. New pump was very weak sounding, even though the old pump sounded fine. Even with the pump sounding very weak, I had pressure at the rails, but not enough juice to start the truck. This basically was telling me that the impeller was loose where it connected to the electric motor inside the pump body. Battery was damn near dead, which was interesting too. But, anyway, 50-amp charger plugged in for ten seconds, truck fired up.
I trickle charged it over night. Has not popped at idle since, and it starts up much better than before. All with no change to the tune.
