LS6 4L60e 1948 Ford Pickup LTFTs 25+ @ Idle

Stock LS6 bolted to 4L60e. 90 mm Edelbrock throttle body (came with the wiring harness/PCM setup). New MAP and MAF. New Vette front O2s. Thoroughly checked for vacuum leaks - all corrected. :) At and near idle LTFTs are +25. I watched stfts and they scale up the LTFTs. Both sides are +25 @ idle. Off idle cleans up. Pull the MAF plug and RPM jumps to around 1700-1800 RPM. Both sides settle down to +8 LTFT with MAF unplugged.

Attached are scans of first drive and pulling the MAF plug (also pulled brake booster vacuum line, and then reattached, early in MAF plug scan) and current tune.

The O2s are 1 1/ 2- 2 feet downstream from the exhaust ports. Are the O2s lazy due to inadequate heat??

***There are idle air problems with the 90mm Edelbrock - I'll replace it with a stock Camaro TB.

Any other ideas??

TIA.

:cheers:

joel

Attachment 17490 Attachment 17492 Attachment 17489

Hey Joel, using GM.MAFFREQ see if you can locate the portion of the MAF table used during idle, and increase it a little, see if this lowers the LTFT's at idle.

Is the TB leaking air...? If so then the extra air is not accounted for by the MAF... but usually a TB leak is fairly small.

Quote:

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Originally Posted by joecar

Hey Joel, using GM.MAFFREQ see if you can locate the portion of the MAF table used during idle, and increase it a little, see if this lowers the LTFT's at idle.

Is the TB leaking air...? If so then the extra air is not accounted for by the MAF... but usually a TB leak is fairly small.

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Hey joecar - I added 25% fuel at the VE table, idle cells and it didn't change it a bit. I'll try the MAF.


Tb - no leaks. I even double checked it with an ultrasonic leak detector.

Thanks!!

Quote:

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Originally Posted by bink

Hey joecar - I added 25% fuel at the VE table, idle cells and it didn't change it a bit. I'll try the MAF.

...

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Then this shows the problem is not due to the MAF... so it might be the O2S like you suggested (insufficient heat).

Quote:

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Originally Posted by bink

Hey joecar - I added 25% fuel at the VE table, idle cells and it didn't change it a bit. I'll try the MAF.


Tb - no leaks. I even double checked it with an ultrasonic leak detector.

Thanks!!

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Did you check other vacuum areas on the intake manifold? We had a leak in the brake booster on a chevelle we did an ls3 in and the thing ran great but the fuel trims at idle were telling is something was wrong, maxed out as well. Pulled the line to the booster, plugged it, and all the sudden fuel trims went close to 0. Sounds like a vacuum leak or bad maf to me.

Quote:

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Originally Posted by picnic_george

Did you check other vacuum areas on the intake manifold? We had a leak in the brake booster on a chevelle we did an ls3 in and the thing ran great but the fuel trims at idle were telling is something was wrong, maxed out as well. Pulled the line to the booster, plugged it, and all the sudden fuel trims went close to 0. Sounds like a vacuum leak or bad maf to me.

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Yes, I checked this. Actually, it's on the early part of the unplugged MAF scan. I think I'll recheck it and scan stfts and ltfts at the same time maybe I didnt wait long enough...can't hurt!! :) We bought a new MAF and a new MAP - no help. I'd read that if exhaust flow is slow the O2s don't heat well and get lazy......read lean???
Thanks for the help, picnic_george! :)

joel

I looked at the attached scan https://forum.efilive.com/attachment...0&d=1410785456 and the mVs stay in 30-50 range - when I pulled the booster and plugged it at the intake. So, it's not the booster. :(

Quote:

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Originally Posted by joecar

Then this shows the problem is not due to the MAF... so it might be the O2S like you suggested (insufficient heat).

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Thanks, joecar! I'll try the corvette rear sensors as they are supposedly less senstive due to greater heating.

:cheers:
joel

Follow up. :)

Hooked up the Corvette rear O2s - no help!! Trims were still +25 at idle. Trashed the Edelbrock 90mm TB and replaced with a new, stock 2000 Camaro TB. The new TB did it!!!! Trims slighly positive. The MAF is incorporated in the "Street and Performance" custom intake - they have modified the housing so I will adjust the MAF table. Thanks guys for the help and input!!

:cheers:

joel

Thanks for the follow up... so the Edelbrock TB was letting too much air thru during idle.