rich ONLY at idle...
Thread Starter
Race Director
Joined: Nov 2000
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From: stop the fun suckers
rich ONLY at idle...
it smeels rich at idle.. and my idle Lterm blms are 108!!! at least the split blms are gone.. what causes the engine to run rich at idle? would this be because of the cam (similar to hotcam spec)? it appears to be good at other rpms.. jsut at idle its WAY rich! please help! Sterm blms level out about 110-112 for both sides..
Thread Starter
Race Director
Joined: Nov 2000
Posts: 17,103
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From: stop the fun suckers
Re: rich ONLY at idle... (southern_son)
I checked the FPR vaccum line as outlined in the factory serivce manual.. there is no fuel in the line.. also fuel pressure is 44psi at key on and falls to 38psi when the engine is turned on and the car at idle.. the pressure fluctuates a bit.. maybe 1-2 psi or so..
Burning Brakes
Joined: Jun 2003
Posts: 949
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From: smithtown ny
Re: rich ONLY at idle... (southern_son)
do you have a fuel pressure gauge if so turn the key on then shut it off see how long it takes for it to bleed down mine takes about 2 hours to go to 0 how old are your injectors??????
Thread Starter
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Joined: Nov 2000
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From: stop the fun suckers
Re: rich ONLY at idle... (Br1dgeman)
yes.. The car is a 1993/Auto/LT1
Mods: I stroked it to 383, Comp Cam (similar to hotcam specs)COMP extreme CCA-218-224-12 218 224 .495 .503 112 , eliminated the cat converters and welded a pipe in their place, raised compression ratio to 10.8:1..
Also, I had pcmforless make me a new chip.. however, I had a nice exhaust leak in front of the 02 sensors when i logged the data for him to program the chip.. could that be why its running rich at idle now (fixed the exhaust leak)?
the blms look good about 800rpm or so and under any load..
Mods: I stroked it to 383, Comp Cam (similar to hotcam specs)COMP extreme CCA-218-224-12 218 224 .495 .503 112 , eliminated the cat converters and welded a pipe in their place, raised compression ratio to 10.8:1..
Also, I had pcmforless make me a new chip.. however, I had a nice exhaust leak in front of the 02 sensors when i logged the data for him to program the chip.. could that be why its running rich at idle now (fixed the exhaust leak)?
the blms look good about 800rpm or so and under any load..
Instructor
Joined: Sep 2003
Posts: 109
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From: Ft. Lauderdale FL
Re: rich ONLY at idle... (BluByU)
That exhaust leak may very well have done you in- he calibrated with the leak and now things have changed. Chances are you will need to have some tweaking done to the chip to correct the idle. Your ECM actually has a prom chip? Later LT-1 PCM's have a flash memory - no chips.
I am not too familiar with the LT-1 set-ups, but they have both a speed density map and a maf sensor table and I am not exactly sure as I write this what would need to be changed unless some trial and error was done. I burn my own chips, but I do not think this is something I could do for you in one shot and feel 100% certain that I solved your problem.
Contact the company who originally made your chip and see if they would tweak the idle for you if you provided new scan data. I would think if the chip was burned fairly recently, they should make that adjustment for you.
Good luck.
I am not too familiar with the LT-1 set-ups, but they have both a speed density map and a maf sensor table and I am not exactly sure as I write this what would need to be changed unless some trial and error was done. I burn my own chips, but I do not think this is something I could do for you in one shot and feel 100% certain that I solved your problem.
Contact the company who originally made your chip and see if they would tweak the idle for you if you provided new scan data. I would think if the chip was burned fairly recently, they should make that adjustment for you.
Good luck.
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Thread Starter
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Joined: Nov 2000
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From: stop the fun suckers
Re: rich ONLY at idle... (Br1dgeman)
I have a speed density car.. no maf sensor.. which makes things harder to tune.. i already sent the file to the programmer.. lets see what he'll do.. :leaving:
Instructor
Joined: Sep 2003
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From: Ft. Lauderdale FL
Re: rich ONLY at idle... (BluByU)
Actually, it may be pretty easy to fix now that you say it is only speed density...that should be some changes to the MAP tables in the idle regions...
Anyway, hopefully your programmer will take care of it for you. Keep us posted..
:thumbs:
Anyway, hopefully your programmer will take care of it for you. Keep us posted..
:thumbs:
Instructor
Joined: Oct 2003
Posts: 147
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From: Holbrook NY
Re: rich ONLY at idle... (BluByU)
BluByU,
I have been trying to get your name on my plates, for my blue on blue 12.9 sec '85 'Vette!
Either your vacuum at idle is poor - possibly from a cam with more overlap - or you FPR is defective (unlikely). You sad that:
"......... fuel pressure is 44psi at key on and falls to 38psi when the engine is turned on ......."
That is not enough of a change.
Your fuel pressure - 44psig(gauge pressure), is fine for 15psia (absolute pressure - atmospheric). But your idle fuel pressure should be about 34 or 35psig. Apparently your idle vacuum is poor (caused by large valve overlap?). Some of the air entering the motor at idle is wasted - just like a normal cam in an engine with a vacuum leak! Unlike a vacuum leak, all of the air is metered - suggesting a rich condition - and the fuel pressure is too high for an idle engine. Those 2 factors both tend too force richness. Perhaps the condition is so far off from closed loop driving, that the CPU is having trouble making the corrections.
A good tuner would have no trouble burning you a new chip. Good Luck!
George
I have been trying to get your name on my plates, for my blue on blue 12.9 sec '85 'Vette!
Either your vacuum at idle is poor - possibly from a cam with more overlap - or you FPR is defective (unlikely). You sad that:
"......... fuel pressure is 44psi at key on and falls to 38psi when the engine is turned on ......."
That is not enough of a change.
Your fuel pressure - 44psig(gauge pressure), is fine for 15psia (absolute pressure - atmospheric). But your idle fuel pressure should be about 34 or 35psig. Apparently your idle vacuum is poor (caused by large valve overlap?). Some of the air entering the motor at idle is wasted - just like a normal cam in an engine with a vacuum leak! Unlike a vacuum leak, all of the air is metered - suggesting a rich condition - and the fuel pressure is too high for an idle engine. Those 2 factors both tend too force richness. Perhaps the condition is so far off from closed loop driving, that the CPU is having trouble making the corrections.
A good tuner would have no trouble burning you a new chip. Good Luck!
George
Thread Starter
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From: stop the fun suckers
Re: rich ONLY at idle... (Br1dgeman)
I sent the chip to the tuner for re-programming.. however, it seems to have gotten lost in the mail..I think hes just gonna burn me a new one and send it.. I'll give you another update when the chip FINALLY arrives and is installed..thanks!