99 silverado LTFT, U7198

[jackd]

I am tuning my son's 99 Silverado Z71 5.3L, Flowmaster exhaust and K&N CAI. Does it sound normal to adjust LTFT's -17? Seems like a large adjustment to me.

I had this programmer on my 2001 and only adjusted -4.

[06MonteSS]

yes, that is a LOT...

check everything for air leaks anywhere.. from the air filter back through to the throttle body, make sure all clamps/bolts are TIGHT...

make sure the intake manifold isn't leaking anywhere...

check the exhaust from the engine manifold back through to the mufflers, make sure all clamps/bolts are TIGHT and that there are no holes in the pipe anywhere so that there are no air leaks...

[jackd]

I just went back over everything. All clamps and bolts are tight on the CAI. The throttle body doesn't indicate any leaks with carb cleaner. Engine pulls a steady 19.5 in. of vacuum which I think is extremely good for 199,000 miles. The exhaust doesn't have any leaks. Anything else to check or could this just be what it needs? I can say the tune made a lot more difference on the 99 than it did on my 01. I am wondering if there is something different between the year models. Maybe something was upgraded on the 01?

[06MonteSS]

nah... something's up somewhere man... with those minimal mods you have done for air intake/exhaust, your fuel trims shouldn't be that high...

you still have the stock MAF sensor on there with the screen still in it?? if not, you should....

[jackd]

The truck runs very well. I bought this truck pretty cheap with 190,000 miles on it and we have done a lot of work. Plugs, wires, fuel pump(from GM), fuel pressure regulator, clean the throttle body, clean the stock with screen MAF(with MAF cleaner), new exhaust, motor mounts, water pump, you get the idea. The truck was running great already, but with the new tune it seemed to just smooth out and find a unusual amount of extra power.
With that kind of vacuum, would you suspect a vacuum leak anywhere?
I am not sure about the catalytic converters. If they have been gutted, could that cause the high fuel trims?
I appreciate your help. Any other suggestions will also be appreciated.

[jackd]

Just wondering if anyone else has run into this and what was found or if anyone has any other ideas. Thanks

[jackd]

Anyone have any suggestions or a similar problem? I noticed another topic where an adjustment to the MAF table was suggested. Would this need to be done for this truck as well?

[Wireman134]

My 00' has a MAFT to do most of the offsetting after a K&N FIPK & 3" K&N/JBA catback. Trims were off about +8% before MAFT and LIFT adjustments. The MAFT is a old school MAF tuner to adjust for different air densities across the table. Mine was set at +5% last year and Predator set trims at -3% during the summer. I'm doing some experimenting now to keep the LTFT's negative during cruse rpm loads, setting the MAFT to +10% and Predator at -1%. For a total of -11% at idle. LTFT's are in this cool spring weather 0 to -1.56% @1900rpm. I expect them to go a few % neg. as the weather gets warmer. My truck new had the LTFT's around +7 to +8% no leaks brandy new...

[Wireman134]

You've got smaller injectors in your 5.3L? I herd they made them bigger after 99' See here

http://www.lt1swap.com/inj_maf.htm

[jackd]

Good information

[Wireman134]

Sorry they were smaller in 99' and yes that would mean leaner or needing to add more fuel (more positive LTFT's) in closed loop.

http://www.lt1swap.com/inj_maf.htm

[jackd]

That should explain why I had to make a much larger adjustment. Should change anything or just let it run with the settings like they are in the program? I am sure the WOT AFR is not correct either, but the 99 doesn't offer a parameter to check it. Thanks for the information.

[jackd]

Can the MAF tables be adjusted with a custom tune or will I need to add a MAFT?

[Wireman134]

Those gutted cats made it leaner too. These guys might say if you don't have any leaks get a custom tune but I'd try to get a old MAF Translator and splice it in your MAF harness. Set it at +15%. If your LTFT's are negative when you go full throttle you can adjust with the Predator WOT fueling % to get your AFR around 13.2% (900mv) O2 reading while viewing Predator or maybe the v9r15 logs this O2 readings. There are tables on the net to convert the O2 mv to AFR. I hear the short band O2 senors on these trucks are pretty accurate. Custom tune would be easier though...

[jackd]

I am not sure the cats are gutted, but I am suspicious. Where would I find a MAF Translator? I will do some searching for the charts. If you know where to find them, I would appreciate the site. I really appreciate this information.