I have a 99 T/A which has the following mods: FTRA, MTI Lid, Airflow Research bellows, Ported Maf w/1K ohm 1/2 watt resistor mod, Predator Tune and Magnaflow Catback, 180 T-stat w/reprogrammed fans

I have been monitoring my LTRIMs and have noticed that at idle I am between -8 and -12 since doing the MAF resistor. (Used to be +6 to +8 before resistor at idle) My cruise LTRIMs seem to hover around +4 to +7 now. I have not had enough time to test for O2s with the weather around here.

My question is should I get a MAFT for additional tuning for the LTRIMs or should I just get a stock MAF to replace the ported MAF I currently have?

Could the FTRA be causing my LTRIMs to be off at 60 Mph +?

mike

 

Whose ported MAF?

I know about tuning the 85mms but only in the lean
direction. If this is a stocker, where did you put the
resistor and how much did it pull the tune?

BTW, I only need a 3K resistor on my ported SLP/
Delphi, up from the standard 2.7K that SLP uses. A
1K on that MAF would truly whack the mixture lean.

On my MAF, hacked as it it, I have idle LTFTs about
-10 and -1 to -1.5 right before rolling into WOT.

FTRA might present more air but it's the MAF's job
to tell the truth and it isn't.

 

It is a stocker that I home ported. then I added a 1K Ohm 1/2 Watt resistor to the side spaning 2 arms. BTW my timing at idle is also around 20-22 degrees.

should I remove the resistor and swap it? or should I just replace the MAF? or even get a used MAFT?

thanks

mike

 

Stocker would be the straightest, no worries.

 

Thanks I just ordered one from gmpartsdirect. Hopefully this will correct my LTRIMs

mike

 

Where can you put a resistor in the maf to"fool" the pcm?? and what tables would it change

 

I used instructions like this http://www.ls1.com/forums/showthread...t=MAF+Resistor

do a search there is one there with a picture

 

The picture link is busted now that Boggs left LS1.com, but
it's still interesting. I think the guy could have gone further
with resistor value (lower) and gotten to all LTFTs < 0.
The value you'd need will vary with how you port.

This seems to be the flip side of what SLP does, and I've done
to my 85mm (pull lean, on the 3-leg side)

 

For what its worth, the resistor goes between the two longer bars that span both sides of the MAF. If the 1K ohm is not enough, find a slightly lower value resistor, or calculate two resistors in parallel (ohms law) that will give you a value slightly lower than 1k. I used alagator clip leads while I was experimenting so that I could easily and quickly change resistor values.

I was running around 880 ohms over the winter (parallel resistor setup) and my LTFTs were all between -1 and -5. I did have to dial in some more at WOT using my MAFT however.

-Tony

 

In a sense - yes. Try to look at the wires of your MAF. I had mine dirty and that apparently killed the calibration. I cleaned with lots of alcohol and it runs like a charm. If you do a search under my name, I described the whole affair few days earlier.

 

If you have a Predator, you don't need MAFT.

 

I have a predator and I have replaced the MAF with the stocker and I am still reading like 4.6 - 6.5 + LTrims at crusing speed. I am thinking that I must have a vacuum leak that I need to resolve since at idle it is - and my timing is like 20 - 22 degrees @ idle as well. Once I nail that down I will do some more experimenting with the Ported vs Stocker MAF. I did read somewhere that someone had setup a Ghetto flow test with a shop vac to test the two calibrations for the MAF signal.

mike

 

Found the problem... EGR Gasket was starting to suck in and was a vacuum leak. Diagnosed that using a bike tube cut and attached to the air bellows using duct tape Pumped up with pressure and the EGR started whistling... Now LTrims are mostly 0 or -

mike