LT1-LT4 Modifications 1993-97 Gen II Small Block V8

LT1 fuel split

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Old 01-15-2013, 08:51 PM
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The LT1 has an idle air distribution circuit cast/machined in GM didn't do that extra R&D for nothing.
Old 01-16-2013, 12:50 AM
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Originally Posted by 96capricemgr
The LT1 has an idle air distribution circuit cast/machined in GM didn't do that extra R&D for nothing.
So you also know how many different sizes the holes are and what years they changed?


I do
Old 02-01-2013, 10:10 PM
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Installed new header gasket and still have split fuel trim.
I'm lost.
Old 02-02-2013, 08:56 AM
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Originally Posted by Green3spd
Installed new header gasket and still have split fuel trim.
I'm lost.
Have you re-checked to make sure the new gasket sealed it up? If you open the throttle to something like 1500 RPM, is the fuel trim split the same?
The individual cylinder fuel adjustment table is there '94 thru '97. If your software lists the cylinders as 1,2,3,4,etc, they follow the firing order, I re-numbered mine as 1,8,4,3,6,5,7,2 so I could stop counting on my fingers.
If everything is mechanically sound, the needed adjustments should not have to be very big. I don't remember seeing your fuel trims.

If you have an infrared temp gun (most auto techs have them) you might shoot the headers near the heads to look for a problem cylinder. On the lean/high fuel trim side you want to add more fuel to the hottest cylinders instead same to all four. If you find a cold header tube on the high fuel trim side, suspect incomplete combustion. That puts more oxygen out the exhaust port. The O2 then sees more oxygen and the dumb-assed PCM thinks that always means lean, so trims go up and it throws more fuel at it.

If you pulled plugs and looked for dark plugs on the high trims side I must have missed it.
Good luck.
Old 02-02-2013, 03:07 PM
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Originally Posted by Ed Wright
Have you re-checked to make sure the new gasket sealed it up? If you open the throttle to something like 1500 RPM, is the fuel trim split the same?
The individual cylinder fuel adjustment table is there '94 thru '97. If your software lists the cylinders as 1,2,3,4,etc, they follow the firing order, I re-numbered mine as 1,8,4,3,6,5,7,2 so I could stop counting on my fingers.
If everything is mechanically sound, the needed adjustments should not have to be very big. I don't remember seeing your fuel trims.

If you have an infrared temp gun (most auto techs have them) you might shoot the headers near the heads to look for a problem cylinder. On the lean/high fuel trim side you want to add more fuel to the hottest cylinders instead same to all four. If you find a cold header tube on the high fuel trim side, suspect incomplete combustion. That puts more oxygen out the exhaust port. The O2 then sees more oxygen and the dumb-assed PCM thinks that always means lean, so trims go up and it throws more fuel at it.

If you pulled plugs and looked for dark plugs on the high trims side I must have missed it.
Good luck.
I've pulled plugs and the two rear plugs are black. Not dripping fuel by any means, but no where near white/lean
Old 02-02-2013, 03:33 PM
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The rear on both sides, or the two rear on one side?
This a stock intake? Or a single plane?
Old 02-02-2013, 04:21 PM
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Originally Posted by Ed Wright
The rear on both sides, or the two rear on one side?
This a stock intake? Or a single plane?
Both sides, stock/ported
Old 02-02-2013, 04:28 PM
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What are your trim numbers?
If you rev it up to 1500 RPM, and hold it steady, and the trims don't even out, it won't be the idle air passage.
Old 02-02-2013, 05:03 PM
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Originally Posted by Ed Wright
What are your trim numbers?
If you rev it up to 1500 RPM, and hold it steady, and the trims don't even out, it won't be the idle air passage.
I'll start it tonight and idle it up to 1500 and watch for it.
I've done the IAC passage BS and it didnt change a bit. It does however idle on its own with the TB almost completely close
Old 02-03-2013, 08:48 AM
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Rev to 1500, 2200, still has a split. Found a plug wire with bad resistance, replaced it. No change.
Old 02-03-2013, 08:53 AM
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I would check for cold header tubes, extremely hot header tubes, also swap sides with the injectors.
What kind of headers, and which side appears lean?

And, why won't you post your fuel trims?
Old 02-03-2013, 12:24 PM
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Originally Posted by Ed Wright
I would check for cold header tubes, extremely hot header tubes, also swap sides with the injectors.
What kind of headers, and which side appears lean?

And, why won't you post your fuel trims?
They're Hooker headers.
I don't have fuel trims on a laptop. My tuner explained my problem and so I've been resorting to my Interceptor gauge. It's a simple gauge but clearly explains weather B1 & B2 are close or split.

0.0 is even.
B1 reads +49.9(max)
B2 reads -17.x to -24.x

I've been trying to get ahold of an infrared gun but no luck.
A few mins ago I was monitoring my garage, and took some carb cleaner to each indivual Header primary, and while I was spraying on the primary, B1's +49.9 would start to drop drastically, then back up as soon as I stopped. I moved on the the next primary & and the next, with the same results.
Old 02-03-2013, 12:40 PM
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Try spraying the slip joint on #1 primary tube. Known leak with Hooker long tubes.
Old 02-03-2013, 05:06 PM
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Originally Posted by Ed Wright
Try spraying the slip joint on #1 primary tube. Known leak with Hooker long tubes.
Also inspected that area. No luck.

Update:
I installed my facotory TB on it and the fuel split went from:
B1 +49.9(max on gauage)
B2 -17.x to -24.x

After stock TB:

B1 +49.9
B2 +32.x(cold) +5.x to +15.x(warm)

So I've still got a split, but it isn't a lean/rich split. Just Lean/not as lean lol
Old 02-03-2013, 05:22 PM
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That split could very well lessen when your tuner adds some fuel. The rear cylinders had the black plugs. Those holes are way rich if there are no ignition problems. What kind of spark plugs? What brand injectors?
Old 02-03-2013, 05:50 PM
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Originally Posted by Ed Wright
That split could very well lessen when your tuner adds some fuel. The rear cylinders had the black plugs. Those holes are way rich if there are no ignition problems. What kind of spark plugs? What brand injectors?
Autolite plugs 106(don't judge me) lol
Delhi/MSD 55lbs injectors.
Old 02-03-2013, 06:08 PM
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Autolites are a good choice. Was afraid they were NGKs. LOL

Has anyone messed with your MAF?
Old 02-03-2013, 06:28 PM
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Originally Posted by Ed Wright
That split could very well lessen when your tuner adds some fuel. The rear cylinders had the black plugs. Those holes are way rich if there are no ignition problems. What kind of spark plugs? What brand injectors?
Originally Posted by Ed Wright
Autolites are a good choice. Was afraid they were NGKs. LOL

Has anyone messed with your MAF?
It's a stock MAF with the aftermarket ends. Just makes it open all way through. Had it On my car for years. No problems before with it and it's reading ok from what I can see
Old 02-03-2013, 06:58 PM
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Unless your tuner knows what those MAF ends require, and has addressed that, your lean issue is those MAF ends.
Old 02-03-2013, 07:35 PM
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Originally Posted by Ed Wright
Unless your tuner knows what those MAF ends require, and has addressed that, your lean issue is those MAF ends.
So u think MAF ends are causing a 25-50+ split?

I understand a Ported MAF/ends causing lean issues, but I don't understand the split


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