Key off fuel pressure issue - Zilvia.net Forums | Nissan 240SX (Silvia) and Z (Fairlady) Car Forum

S14rebuild · 11-10-2020, 03:34 PM

Getn some insight here....

Sr20det key on get solid fuel pressure about 40psi. Soon as you cycle the key off fuel pressure drops to 0 with in 5-10seconds. Theres no hold of pressure.

Running new bosch fuel pumps
Tomei fpr new
-6an line
Top feed injectors and rail

System has no leaks at all.

Is this typical of sr setups? I cant remeber been sooo long messn with these cars. I know stock cars hold pressure for hours.

Any insight guys would be awsome.

SpaceKADET · 11-10-2020, 04:06 PM

If the Tomei fuel pressure regulator is anything like the ball seat Aeromotive ones, they will loose fuel pressure within a few seconds and it's considered normal for that design. I had the same thing happening with my vehicle.

S14rebuild · 11-10-2020, 04:27 PM

Quote:

Originally Posted by SpaceKADET

If the Tomei fuel pressure regulator is anything like the ball seat Aeromotive ones, they will loose fuel pressure within a few seconds and it's considered normal for that design. I had the same thing happening with my vehicle.

Ahhhh gotcha. I beleve it is like that style

SpaceKADET · 11-10-2020, 04:31 PM

Okay then yeah, you should be good. Here's a quote from Aeromotive's website:

Quote:

6.) I?ve installed my new Aeromotive bypass regulator. Fuel pressure seems to adjust fine and holds great when the engine is running, but when I shut the engine off, pressure drops quickly to zero. Shouldn?t the pressure hold like it did with a stock regulator?
No, Aeromotive EFI bypass regulators may not seal perfectly when the pump is off. They are engineered for the highest possible performance when the engine is running. OEM regulators must hold pressure for 30-minutes after shut-down to pass EPA emissions standards. At Aeromotive we know our customers priority is to have the best possible flow and pressure control when the engine is running and we don?t compromise this standard to force the regulator to seal when the engine is off. If extended crank or hard-start becomes a concern, first allow the pump to run and prime as long as possible after turning the key to the run position, then start cranking the engine, just before the pump shuts off. If the priming cycle is too short to allow the engine to start easily with this approach, extend the priming cycle in the ECU if programmable, or ad a timer board or momentary button to the fuel pump run circuit.

S14rebuild · 11-10-2020, 04:31 PM

For some reason i beleve this fuel drop is giving me a hard start issue...

SpaceKADET · 11-10-2020, 04:45 PM

Well, I guess my posts are still being screened by moderators so the post that I had written out earlier probably won't be seen. Do you have a tuned ECU? Are you running dual fuel pumps in the tank? What you can do is use a paperclip to bypass the fuel pump relay and have them continuously running to rule out the pressure drop as the cause. If that works, maybe you could wire in a switch so you could manually bypass the relay whenever needed and you'd essentially have a fuel pump cutoff switch in the even that would want that.

zombiewolf513 · 11-10-2020, 04:39 PM

Are you running the bosch 044 with or without the checkvalve?

S14rebuild · 11-10-2020, 04:48 PM

Quote:

Originally Posted by zombiewolf513

Are you running the bosch 044 with or without the checkvalve?

With check valve

S14rebuild · 11-10-2020, 04:51 PM

Both pumps are ran external. 30amp reays direct feed from battery, using stock relay as a trigger.

When running i hqve 0 fuel pressure issuses....its only first key on/key off start.

Worked on numerous cars and seen them all hold fuel pessure key off.

Im not 100% sure this is my starting issue im seeking to resolve. But the issue seems tobe resolved after priming the fuel system a few cycles quickly

SpaceKADET · 11-10-2020, 05:04 PM

Yes, most cars will maintain that pressure using a stock pressure regulator. The ball seat style aftermarket regulators seem to bleed off that pressure by design so you may just have to prime it multiple times. Also, depending on the tune, I know the newer turbo Nissan builds need the throttle partially opened in order to start on the first try.

zombiewolf513 · 11-10-2020, 05:01 PM

can you tune the ecu for a longer prime?

S14rebuild · 11-10-2020, 05:03 PM

Quote:

Originally Posted by zombiewolf513

can you tune the ecu for a longer prime?

Power fc....that i dont know

S14rebuild · 11-10-2020, 05:05 PM

I think its probly the tomei fpr. As suggested earlier

Does anyone know of a fpr i could run that would still hold pressure after key off or primed?

zombiewolf513 · 11-10-2020, 05:42 PM

i had a tomei fpr and it held pressure just fine. it bled off but over the course of like 45 minutes.

S14rebuild · 11-10-2020, 06:11 PM

Quote:

Originally Posted by zombiewolf513

i had a tomei fpr and it held pressure just fine. it bled off but over the course of like 45 minutes.

Fukkkk...

Ill be doing more tests this weekend. See what more i can find out. Not tryn to buy parts i dont need.

inopsey · 11-10-2020, 06:08 PM

im gonna assume that you have a d jetro PFC if your having starting issues, IME its the ecu causing the starting issue.

is the issue with cold starts only? or is it tough to start if you were run into the store for 20 minutes and come back ?

S14rebuild · 11-10-2020, 06:10 PM

Quote:

Originally Posted by inopsey

im gonna assume that you have a d jetro PFC if your having starting issues, IME its the ecu causing the starting issue.

is the issue with cold starts only? or is it tough to start if you were run into the store for 20 minutes and come back ?

Its a L-jetro model(maf)

As of now just cold start...havent driven it or put long run time... fresh motor

zombiewolf513 · 11-10-2020, 06:16 PM

ive got a brand new p2m fpr (same thing) that ill sell ya pretty cheap. lmk

S14rebuild · 11-10-2020, 06:18 PM

Might take ya up on that.... let me do some more messn around with it on my free time and go from there. Thanks

MR24U · 11-10-2020, 08:07 PM

I had a similar issue of not holding pressure after priming. Turned out to be a partially bursted fuel line inside the tank. Maybe you might have a leaking check valve or injector

Sent from my SM-G955U using Tapatalk

S14rebuild · 11-11-2020, 08:57 AM

Quote:

Originally Posted by MR24U

I had a similar issue of not holding pressure after priming. Turned out to be a partially bursted fuel line inside the tank. Maybe you might have a leaking check valve or injector

Sent from my SM-G955U using Tapatalk

Running all new 6an braided lines and a fuel cell

S14rebuild · 11-11-2020, 09:03 AM

Can anyone confirm 100% on an sr, aftermarket fuel pressure regulator, key on prime, key off fuel pressure holds steady?

This is annoying the fuck out of me and want to resolve it.

Thanks

projectsupra · 11-23-2020, 06:37 PM

Quote:

Originally Posted by S14rebuild

Can anyone confirm 100% on an sr, aftermarket fuel pressure regulator, key on prime, key off fuel pressure holds steady?

This is annoying the fuck out of me and want to resolve it.

Thanks

A little late, but my SR with a Fuelab FPR and Bosch 044 build full pressure then falls back to 0 in maybe 10 seconds with key on initial prime. Car always starts 2-3 seconds though no issues.

S14rebuild · 11-11-2020, 05:20 PM

Small update....

I clamped off the return line AFTER the regulator..pressurized the system, it held no problem at all. So that eliminates the fuel backing feeding thru the pumps.

Lookn more n more like its the fpr.

Question.... i know the fuel pump comes on for a few seconds during priming. But does the pump stay on durning cranking? Or only once the engine fires up?

Idk why this seems so complicated to me..feel like im maken this worse then it needs tobe lol

SpaceKADET · 11-12-2020, 08:54 AM

The relay should turn back on while cranking.

S14rebuild · 11-12-2020, 03:52 PM

Resolved for now.... i went ahead and removed the fuel pump relay ground trigger via ecu and just gave it a chassis ground. Now when the key is on, i have constant fuel pump flow, holding rail pressure at 45psi. Car starts right up. Now i gotta replace this 15plus year old starter. Didnt like all those long cranks tryn to start the car.

S14rebuild · 11-23-2020, 06:58 PM

Thanks! I reached out to aeromotive and was told their efi fpr arent designed to hold pressure after key off as it would hinder its performance if it was made todo so.

The remedy ive done so far has worked for now.

11-10-2020, 03:34 PM	#1
S14rebuild BANNED Join Date: May 2019 Location: Florida-FAIL Posts: 2,497 Trader Rating: (8) Feedback Score: 8 reviews	Key off fuel pressure issue Getn some insight here.... Sr20det key on get solid fuel pressure about 40psi. Soon as you cycle the key off fuel pressure drops to 0 with in 5-10seconds. Theres no hold of pressure. Running new bosch fuel pumps Tomei fpr new -6an line Top feed injectors and rail System has no leaks at all. Is this typical of sr setups? I cant remeber been sooo long messn with these cars. I know stock cars hold pressure for hours. Any insight guys would be awsome.

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11-10-2020, 04:06 PM	#2
SpaceKADET Join Date: Oct 2020 Location: Tampa, FL Age: 30 Posts: 21 Trader Rating: (0) Feedback Score: 0 reviews	If the Tomei fuel pressure regulator is anything like the ball seat Aeromotive ones, they will loose fuel pressure within a few seconds and it's considered normal for that design. I had the same thing happening with my vehicle.

11-10-2020, 04:31 PM	#5
S14rebuild BANNED Join Date: May 2019 Location: Florida-FAIL Posts: 2,497 Trader Rating: (8) Feedback Score: 8 reviews	For some reason i beleve this fuel drop is giving me a hard start issue...

11-10-2020, 04:45 PM	#6
SpaceKADET Join Date: Oct 2020 Location: Tampa, FL Age: 30 Posts: 21 Trader Rating: (0) Feedback Score: 0 reviews	Well, I guess my posts are still being screened by moderators so the post that I had written out earlier probably won't be seen. Do you have a tuned ECU? Are you running dual fuel pumps in the tank? What you can do is use a paperclip to bypass the fuel pump relay and have them continuously running to rule out the pressure drop as the cause. If that works, maybe you could wire in a switch so you could manually bypass the relay whenever needed and you'd essentially have a fuel pump cutoff switch in the even that would want that.

11-10-2020, 04:39 PM	#7
zombiewolf513 BANNED Join Date: Mar 2011 Location: AZ Age: 33 Posts: 1,682 Trader Rating: (6) Rides Gallery: zombiewolf513 Feedback Score: 6 reviews	Are you running the bosch 044 with or without the checkvalve?

11-10-2020, 04:51 PM	#9
S14rebuild BANNED Join Date: May 2019 Location: Florida-FAIL Posts: 2,497 Trader Rating: (8) Feedback Score: 8 reviews	Both pumps are ran external. 30amp reays direct feed from battery, using stock relay as a trigger. When running i hqve 0 fuel pressure issuses....its only first key on/key off start. Worked on numerous cars and seen them all hold fuel pessure key off. Im not 100% sure this is my starting issue im seeking to resolve. But the issue seems tobe resolved after priming the fuel system a few cycles quickly

11-10-2020, 05:04 PM	#10
SpaceKADET Join Date: Oct 2020 Location: Tampa, FL Age: 30 Posts: 21 Trader Rating: (0) Feedback Score: 0 reviews	Yes, most cars will maintain that pressure using a stock pressure regulator. The ball seat style aftermarket regulators seem to bleed off that pressure by design so you may just have to prime it multiple times. Also, depending on the tune, I know the newer turbo Nissan builds need the throttle partially opened in order to start on the first try.

11-10-2020, 05:01 PM	#11
zombiewolf513 BANNED Join Date: Mar 2011 Location: AZ Age: 33 Posts: 1,682 Trader Rating: (6) Rides Gallery: zombiewolf513 Feedback Score: 6 reviews	can you tune the ecu for a longer prime?

11-10-2020, 05:05 PM	#13
S14rebuild BANNED Join Date: May 2019 Location: Florida-FAIL Posts: 2,497 Trader Rating: (8) Feedback Score: 8 reviews	I think its probly the tomei fpr. As suggested earlier Does anyone know of a fpr i could run that would still hold pressure after key off or primed?

11-10-2020, 05:42 PM	#14
zombiewolf513 BANNED Join Date: Mar 2011 Location: AZ Age: 33 Posts: 1,682 Trader Rating: (6) Rides Gallery: zombiewolf513 Feedback Score: 6 reviews	i had a tomei fpr and it held pressure just fine. it bled off but over the course of like 45 minutes.

11-10-2020, 06:08 PM	#16
inopsey Nissanaholic! Join Date: Jul 2008 Location: canada Posts: 1,665 Trader Rating: (21) Feedback Score: 21 reviews	im gonna assume that you have a d jetro PFC if your having starting issues, IME its the ecu causing the starting issue. is the issue with cold starts only? or is it tough to start if you were run into the store for 20 minutes and come back ?

11-10-2020, 06:16 PM	#18
zombiewolf513 BANNED Join Date: Mar 2011 Location: AZ Age: 33 Posts: 1,682 Trader Rating: (6) Rides Gallery: zombiewolf513 Feedback Score: 6 reviews	ive got a brand new p2m fpr (same thing) that ill sell ya pretty cheap. lmk

11-10-2020, 06:18 PM	#19
S14rebuild BANNED Join Date: May 2019 Location: Florida-FAIL Posts: 2,497 Trader Rating: (8) Feedback Score: 8 reviews	Might take ya up on that.... let me do some more messn around with it on my free time and go from there. Thanks

11-10-2020, 08:07 PM	#20
MR24U Join Date: Aug 2017 Location: Lafayette, La Posts: 1 Trader Rating: (0) Feedback Score: 0 reviews	I had a similar issue of not holding pressure after priming. Turned out to be a partially bursted fuel line inside the tank. Maybe you might have a leaking check valve or injector Sent from my SM-G955U using Tapatalk

11-11-2020, 09:03 AM	#22
S14rebuild BANNED Join Date: May 2019 Location: Florida-FAIL Posts: 2,497 Trader Rating: (8) Feedback Score: 8 reviews	Can anyone confirm 100% on an sr, aftermarket fuel pressure regulator, key on prime, key off fuel pressure holds steady? This is annoying the fuck out of me and want to resolve it. Thanks

11-11-2020, 05:20 PM	#24
S14rebuild BANNED Join Date: May 2019 Location: Florida-FAIL Posts: 2,497 Trader Rating: (8) Feedback Score: 8 reviews	Small update.... I clamped off the return line AFTER the regulator..pressurized the system, it held no problem at all. So that eliminates the fuel backing feeding thru the pumps. Lookn more n more like its the fpr. Question.... i know the fuel pump comes on for a few seconds during priming. But does the pump stay on durning cranking? Or only once the engine fires up? Idk why this seems so complicated to me..feel like im maken this worse then it needs tobe lol

11-12-2020, 08:54 AM	#25
SpaceKADET Join Date: Oct 2020 Location: Tampa, FL Age: 30 Posts: 21 Trader Rating: (0) Feedback Score: 0 reviews	The relay should turn back on while cranking.

11-12-2020, 03:52 PM	#26
S14rebuild BANNED Join Date: May 2019 Location: Florida-FAIL Posts: 2,497 Trader Rating: (8) Feedback Score: 8 reviews	Resolved for now.... i went ahead and removed the fuel pump relay ground trigger via ecu and just gave it a chassis ground. Now when the key is on, i have constant fuel pump flow, holding rail pressure at 45psi. Car starts right up. Now i gotta replace this 15plus year old starter. Didnt like all those long cranks tryn to start the car.

11-23-2020, 06:58 PM	#27
S14rebuild BANNED Join Date: May 2019 Location: Florida-FAIL Posts: 2,497 Trader Rating: (8) Feedback Score: 8 reviews	Thanks! I reached out to aeromotive and was told their efi fpr arent designed to hold pressure after key off as it would hinder its performance if it was made todo so. The remedy ive done so far has worked for now.