Help, After-mods idle problem
Thread Starter
Melting Slicks
Joined: Dec 2001
Posts: 2,321
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From: Reno NV
St. Jude Donor '08
Help, After-mods idle problem
OK so i needed to change my injectors out. I went with the FMS 24# and then ported my plenum, cleaned up my TB, did a coolent bypass, put on an AFPR and put her back together.
On assembly, the vaccum tube that goes up on the bottom of the plenum, near the intake, broke. I replace that and checked for leaks but didnt find any.
My idle fuel pressure is 45 pounds and ~58 at WOT
This is an 88' with stock motor- auto if that matters at all
The idle is way too fast but is steady. No other problems.
Any thoughts? i have a few of my own but i want them confirmed before i get started again. Thanks alot guys :)
:cheers:
[Modified by 88'Cubka, 11:03 AM 9/3/2002]
On assembly, the vaccum tube that goes up on the bottom of the plenum, near the intake, broke. I replace that and checked for leaks but didnt find any.
My idle fuel pressure is 45 pounds and ~58 at WOT
This is an 88' with stock motor- auto if that matters at all
The idle is way too fast but is steady. No other problems.
Any thoughts? i have a few of my own but i want them confirmed before i get started again. Thanks alot guys :)
:cheers:
[Modified by 88'Cubka, 11:03 AM 9/3/2002]
Team Owner
Joined: Aug 2000
Posts: 42,930
Likes: 18
From: Sydney, Australia
CI 6-7-8-9-10 Veteran
St. Jude Donor '07-'08-'09-'10-'11-'12-'13-'14-'15-'16-‘17, '22
Re: Help, After-mods idle problem (88'Cubka)
What is the idle problem?
If it just the idle speed the areas I would check are:
IAC valve adjustment/operation
Throttle body stop adjustment
Vacuum leaks
Maybe even fuel pressure
I'm not sure if the FMS #24's are equivslent to the OEM 88 injectors, that might be related but I would worry about the easy stuff like the IAC/throttle body adjustment first.
If it just the idle speed the areas I would check are:
IAC valve adjustment/operation
Throttle body stop adjustment
Vacuum leaks
Maybe even fuel pressure
I'm not sure if the FMS #24's are equivslent to the OEM 88 injectors, that might be related but I would worry about the easy stuff like the IAC/throttle body adjustment first.
Race Director
Joined: May 2001
Posts: 14,165
Likes: 9
Re: Help, After-mods idle problem (88'Cubka)
Sounds to me like your fuel pressure is WAY too high.
I'm not 100% sure what idle pressure should be on an L98, but I know 42 is the idle norm on an LT1, 48 at WOT. Also FMS injectors are rated for flow on a lower fuel pressure than GM injectors. That's the reason everybody likes them, they run richer for any given rating.
If your fuel pressure is that high and the injectors are rated at 24# on something like 37 PSI then you are probably looking at something like a 32# injector effectively. All of this on a stock motor is probably way too much for the computer to compensate for.
Maybe if you had a cam and some intake mods it wouldn't be as bad, but stock my guess is that you're basically flooding it.
I'm not 100% sure what idle pressure should be on an L98, but I know 42 is the idle norm on an LT1, 48 at WOT. Also FMS injectors are rated for flow on a lower fuel pressure than GM injectors. That's the reason everybody likes them, they run richer for any given rating.
If your fuel pressure is that high and the injectors are rated at 24# on something like 37 PSI then you are probably looking at something like a 32# injector effectively. All of this on a stock motor is probably way too much for the computer to compensate for.
Maybe if you had a cam and some intake mods it wouldn't be as bad, but stock my guess is that you're basically flooding it.
Race Director
Joined: Aug 2000
Posts: 11,506
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From: Vancouver,Wa.
Re: Help, After-mods idle problem (Nathan Plemons)
I have the same injectors on a built motor at 40psi. I will bet that your car is hunting for the idle. Loading up and the motor revs and burns the fuel and drops back down and then back up. all this happening in like a second of so?
Thread Starter
Melting Slicks
Joined: Dec 2001
Posts: 2,321
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From: Reno NV
St. Jude Donor '08
Re: Help, After-mods idle problem (corvette0096)
:lol: My idle problem is its idleing WAY too fast. Like 1100-1300 Sorry about that
Like i said, i had a feeling i knew what the problem was, but i wanted confirmation. Im gonna go drop that pressure down to around 38 idle and see what happens. That should bring be down to a slightly rich for stock.
But yeah, when i get into the gas off idle, it sputters, then goes like a bat outta hell. Sure makes those WOT shifts something a whole lot more interesting though :jester
Thanks guys, ill let you know what happens
EDIT: I dropped the pressure to 38, which is as low as i can get it, and my idle is still fast. Like 1000-1200 now. IAC and vac leaks then i suppose.
:cheers:
[Modified by 88'Cubka, 10:37 AM 9/3/2002]
Like i said, i had a feeling i knew what the problem was, but i wanted confirmation. Im gonna go drop that pressure down to around 38 idle and see what happens. That should bring be down to a slightly rich for stock.
But yeah, when i get into the gas off idle, it sputters, then goes like a bat outta hell. Sure makes those WOT shifts something a whole lot more interesting though :jester
Thanks guys, ill let you know what happens
EDIT: I dropped the pressure to 38, which is as low as i can get it, and my idle is still fast. Like 1000-1200 now. IAC and vac leaks then i suppose.
:cheers:
[Modified by 88'Cubka, 10:37 AM 9/3/2002]
