Lowered fuel pressure
Thread Starter
Melting Slicks
Joined: Nov 2000
Posts: 2,469
Likes: 6
From: Winchester Ontario
Lowered fuel pressure
383
30# FMS injectors
Walbro 340 fuel pump
AFPR
Last weekend I took my car to the track and the fuel pressure was at 50 psi. I knew it was too high, but whenever my buddy told me I was smoking black down the track I knew I had to change it for real.
I lowered it to 45 psi and it did run better. I still had a feeling that even that could be too high. So, I did some reading and found out that FMS rates their injectors at 39 psi. So, at 39 psi, a 30# injector is a 30# injector, not higher.
So, I then lowered it from the 45 psi down to 41 (damn AFPR wouldn't go any lower, lol) and unhooked the battery for 10 minutes. Hooked battery back up and started it and let it run for 15 minutes without touching the gas to set the idle.
Now, I can say it seems to run much better. I must have been drowning my motor before. I will have to take it to the strip and find out if it's running any better with the lower psi.
I still need a tune, and a nitrous refill, so I won't be running nitrous on it again until I get a tune and to see if the psi is correct cuz I don't wanna go lean on the spray.
So... does this sound normal to be running fuel pressure at?
30# FMS injectors
Walbro 340 fuel pump
AFPR
Last weekend I took my car to the track and the fuel pressure was at 50 psi. I knew it was too high, but whenever my buddy told me I was smoking black down the track I knew I had to change it for real.
I lowered it to 45 psi and it did run better. I still had a feeling that even that could be too high. So, I did some reading and found out that FMS rates their injectors at 39 psi. So, at 39 psi, a 30# injector is a 30# injector, not higher.
So, I then lowered it from the 45 psi down to 41 (damn AFPR wouldn't go any lower, lol) and unhooked the battery for 10 minutes. Hooked battery back up and started it and let it run for 15 minutes without touching the gas to set the idle.
Now, I can say it seems to run much better. I must have been drowning my motor before. I will have to take it to the strip and find out if it's running any better with the lower psi.
I still need a tune, and a nitrous refill, so I won't be running nitrous on it again until I get a tune and to see if the psi is correct cuz I don't wanna go lean on the spray.
So... does this sound normal to be running fuel pressure at?
Race Director
Joined: Feb 1999
Posts: 12,772
Likes: 17
From: Indianapolis IN
Re: Lowered fuel pressure (black_89_vette)
It makes sense, I just bought 30 # FMS and the same issue, AFPR will only go down to 40PSI, so I wonder if it MAY need to go down to @ 35 PSI.
We both need to connect the Diacom to see what the readings are.
We both need to connect the Diacom to see what the readings are.
Racer
Joined: Jun 2001
Posts: 422
Likes: 0
From: Berrien Springs MI
Re: Lowered fuel pressure (black_89_vette)
Be careful lowering your fuel pressure lower than stock if your using nitrous. Depending on the kit it may be tuned for stock fuel pressure. I lowered my fuel pressure from 43(Stock) to 37 and it was faster on the motor. On the spray (150hp) I burned an electrode off on #8. My kit is calibrated for the stock fuel pressure setting. Fat (a little black smoke) is safe.
Le Mans Master
Joined: Jan 2002
Posts: 5,320
Likes: 4
From: Kyle TX (Because Mojo Made me fill it in)
Re: Lowered fuel pressure (black_89_vette)
Questions...about an AFPR...
1. The pressure is adjusted by the screw....which way do you need to turn the screw to reduce the FP?
2. Can the screw length be modified to extend the range of the FP?
3. Can the spring tension be modified to extend the range of the FP?
Havent looked at one yet, but just a thought :)
[Modified by VetteNoob, 3:22 PM 9/9/2003]
1. The pressure is adjusted by the screw....which way do you need to turn the screw to reduce the FP?
2. Can the screw length be modified to extend the range of the FP?
3. Can the spring tension be modified to extend the range of the FP?
Havent looked at one yet, but just a thought :)
[Modified by VetteNoob, 3:22 PM 9/9/2003]
Thread Starter
Melting Slicks
Joined: Nov 2000
Posts: 2,469
Likes: 6
From: Winchester Ontario
Re: Lowered fuel pressure (VetteNoob)
Whenever I get my nitrous bottle refilled, I will see to have the car tuned before I use it.
I realize it may be better on motor ( a tad lean maybe) which will hurt motor on spray. I will find out if it's fine for the spray before I use it again.
To reduce the FP, you loosen the screw ( turn it out)
The screw is all the way out and will not reduce any more. I could keep turning, but would probably just end up with screw in my hands.
I realize it may be better on motor ( a tad lean maybe) which will hurt motor on spray. I will find out if it's fine for the spray before I use it again.
To reduce the FP, you loosen the screw ( turn it out)
The screw is all the way out and will not reduce any more. I could keep turning, but would probably just end up with screw in my hands.
Melting Slicks
Joined: Jul 2003
Posts: 3,493
Likes: 876
From: Saratoga Springs NY
2024 C4 of the Year Finalist - Modified
2022 C4 of the Year Finalist - Modified
Re: Lowered fuel pressure (VetteNoob)
Another case of injectors too big for the engine.....
Put smaller injectors in it and run higher psi-much better...
Put smaller injectors in it and run higher psi-much better...
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Thread Starter
Melting Slicks
Joined: Nov 2000
Posts: 2,469
Likes: 6
From: Winchester Ontario
Re: Lowered fuel pressure (CORKVETTE1)
Well, come to think of it, over the past 2 or 3 weeks, my gas mileage is getting pretty poor. I bet a computer tune could fix the 02 readings huh?
The reasoning behind the 30 # injectors a while back was due to my mechanic and machinist figured that I'd need about a 28-29 # injector due to a few calculations they had done, so I figured I'd get the 30 # FMS ones cuz I heard they were better than the Accel's.
Plus, I wanted to err on the side of caution due to nitrous being in my motor. I'm probably sure it was all in my head thinking the larger injectors were safer, but oh well, it's done and they're in.
The reasoning behind the 30 # injectors a while back was due to my mechanic and machinist figured that I'd need about a 28-29 # injector due to a few calculations they had done, so I figured I'd get the 30 # FMS ones cuz I heard they were better than the Accel's.
Plus, I wanted to err on the side of caution due to nitrous being in my motor. I'm probably sure it was all in my head thinking the larger injectors were safer, but oh well, it's done and they're in.