No Fuel Pressure
Thread Starter
Staging Lane
Joined: Nov 2023
Posts: 90
Likes: 5
No Fuel Pressure HELP. Let me start by saying everything was working fine until I installed an LSA supercharger with ls9 fuel rails on my 1998 LS1. Now I have zero fuel pressure. The only thing fuel related I unhooked was the fuel rail hose. Whats weird is if I jump the relay my pressure spikes up to 100. Put the relay back in and its zero again. I have swapped out fuel pumps, fuel pressure regulators, relays, injectors and my fuel filter. Nothing...There are no kinks or anything in my return line and like I said all was well before. Any thoughts I would greatly appreciate it as im stuck.
Thread Starter
Staging Lane
Joined: Nov 2023
Posts: 90
Likes: 5
I threw another FPR on it and fuel pressure went to 10. Turned the key off and on again and it went to 35, then a third key off/on and went to 60. Could it be the fuel pump?? Ive got a racetronix 255 in there with like 3k on it. Pulled the fuel rail and injectors arent leaking.. HELP
IMO if you jump the relay and it hits 100 it's not the pump. Make sure that's repeatable.
Did the rise from 10 to 36 to 60 happen just on that first attempt after changing the FPR, meaning the rails just needed primed up?
Hmm... You jumping the relay is just like the car closing the relay. I think next thing I'd do is make sure that the car is indeed closing that relay solidly, meaning your PCM is grounding it or whatever it needs on the control side of that relay. Key cycle I think closes it for 2 seconds to prime and it won't close it again until it sees the engine crank or spinning (computer looks at crank signal if I recall).
I don't know if the tune can be misconfigured to not prime on keycycle but something to google maybe.
You closing that relay is what the computer is doing, doesn't make sense that they don't match.
Did the rise from 10 to 36 to 60 happen just on that first attempt after changing the FPR, meaning the rails just needed primed up?
Hmm... You jumping the relay is just like the car closing the relay. I think next thing I'd do is make sure that the car is indeed closing that relay solidly, meaning your PCM is grounding it or whatever it needs on the control side of that relay. Key cycle I think closes it for 2 seconds to prime and it won't close it again until it sees the engine crank or spinning (computer looks at crank signal if I recall).
I don't know if the tune can be misconfigured to not prime on keycycle but something to google maybe.
You closing that relay is what the computer is doing, doesn't make sense that they don't match.
Thread Starter
Staging Lane
Joined: Nov 2023
Posts: 90
Likes: 5
It’s every time I let the pressure out of the rails through my FPG I have to cycle the key for the pressure to climb. Everything was fine on the ls1 rails. You’re right about it not being the pump. I had another pump (stock one) and tried it after I posted and the gauge didn’t budge. I also found that the pressure won’t hold that it eventually bleeds back down. I pulled the rails and the new injectors aren’t leaking. So frustrating
Some pumps bleed down and that's normal from what I understand. Some don't.
I think you can pull the plastic cap off of the relay and physically watch it to see that it closes long and solid during keycycle prime. You can even close it with your finger as a test to see that it behaves like the jumper did. I can't imagine a relay being different than a jumper unless the relay's control side is weak/intermittent. Your jumper just tests the power side not the control side.
And of course you should hear the pump whine for 2 seconds on each key cycle.
I think you can pull the plastic cap off of the relay and physically watch it to see that it closes long and solid during keycycle prime. You can even close it with your finger as a test to see that it behaves like the jumper did. I can't imagine a relay being different than a jumper unless the relay's control side is weak/intermittent. Your jumper just tests the power side not the control side.
And of course you should hear the pump whine for 2 seconds on each key cycle.
Thread Starter
Staging Lane
Joined: Nov 2023
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I’ll pop the cover off the relay. I even bought a brand new relay but it’s worth a shot. I appreciate the help. Like I said i don’t even know what other hose or fuel related wire I would have touched to pop the old manifold off and toss the SC on. What else is funky is while I have 12v at the injector I only have 6 at the coil .. You mentioned a tune. I actually went the smart route and had a baseline tune done before I even turned it over so I should be good there
Thread Starter
Staging Lane
Joined: Nov 2023
Posts: 90
Likes: 5
Finally got fuel pressure and the car started then died after 2 seconds. Tried restarting and nothing. I figured my plugs were soaked but they were BONE DRY. Injector coils have 12v, fuses and relays replaced. What else could cause the injectors not to spray? VATS are disabled .
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Finally got fuel pressure and the car started then died after 2 seconds. Tried restarting and nothing. I figured my plugs were soaked but they were BONE DRY. Injector coils have 12v, fuses and relays replaced. What else could cause the injectors not to spray? VATS are disabled .
So to summarize, you now do have fuel pressure throughout the starting and dying, including when it died and subsequent retries, right?
Does your tach rise as you're cranking? If the computer doesn't see crank signal it won't keep that fuel relay closed. If you see no tach, check your crank sensor.
This really does sound like VATS, I'd double check that too.
Do you have HPTUNERS or some other method to do some diagnosis? Do you have any CEL codes?
I'd also throw a noid light on an injector even though you said your plugs were dry.
Last edited by mk3cn4; Feb 7, 2024 at 07:56 AM.
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Staging Lane
Joined: Nov 2023
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I didn’t look at the tach I but I will when I go home. I do have HPtuners do diagnose and in fact my tuner sent me a new file yesterday titled vats disabled which I uploaded and led to subsequent start then died. Yes my FP is good and I’ve got spark. I’ll throw the noid light on tonight to check for a pulse. You don’t think it could be my ECM do you? The new motor only has 5k on it but the car itself has 120000(98). I just find it weird it was running fine now all of a sudden I swap 1 intake for another and it’s dogcrap
Make sure you didn't mess up the ground on the back of the driver's head. I can't think what else in that area could cause your symptoms.
I do recall one guy doing a swap in some muscle car or something and since the fueling while cranking used a different ground, he had the symptom of firing and dying like that. Had spark only when cranking I think it was. Or maybe it was fuel only when cranking. But it was a bad ground in his case just on the "run" circuit somehow. So make sure you have noid light AND spark not just while cranking but also when it's trying to run...
Last edited by mk3cn4; Feb 7, 2024 at 06:16 PM.
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Thread Starter
Staging Lane
Joined: Nov 2023
Posts: 90
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good call but yah I checked that. I can see it and it looks ok. Id hate to hacve to rip the SC off to change it if its not bad. Bad grounds have been mentioned a couple of times and really the only wiring I did was adding a coolant pump for the SC itself. I moved the fuse box in the front of the car a bit to get the pump to fit and it shares a ground with another ground for something, The pump works so I am assuming its a good ground but at this point I think im going to ground every wire I can find to the negative on the battery just to be sure. IDK man I grasping here. I added a FPR and when I jump the fuse relay I get a solid 60psi but when I throw a relay in and turn the key on I only get 20 so idk. Frustrating but I appreciate the response and help