GMCtrk

iTrader: (27)

So I sent Justin (Blackbear) a log with EFI Live and eventhough I'm commanding 12.5 AFR at WOT, he is saying I'm running very very lean. And I am getting a lot of KR. I suppose this is why my truck was sounding like a popcorn machine under load with the headers.

"You may be commanding 12.5, but it's right at 14.7:1. Narrowband O2s are showing it being very lean at WOT.

A leak after the MAF could contribute to the problem or a faulty MAF could be to blame."

"No, it's definitely lean. Your trims at high load are around 10%, once you hit WOT, they drop to 0 and O2 voltages fluctuate. Check frame 9050 in your log file there. You're running at least 10% leaner than commanded at that point, which puts you at 13.9 on the rich side. Also explains your knock situation. Your MAF reading confirms this, as it's reporting a peak of only 32# of air. With a 6 liter, you should be seeing 36-37 at a minimum.

It appears you have unmetered air entering the engine or a modified/faulty MAF."




So, what should I be looking at here? The intake box/tube is all stock. The MAF is also all stock, I recently cleaned it with a lot of electrical contact cleaner. Ever since I put on a ported TB a while ago I would get a whistling sound on the highway when I got on the throttle. I've still got it now eventhough Im using the stock TB. I'm thinking I need a new TB gasket. Maybe air is getting in there.

Another issue is that my nearly new oem fuel pump whines every now and then. Sometimes it will whine when I start it up and then be gone after driving around? I just put in a new NAPA fuel filter maybe 2 months ago.

Also, on my exhaust the post cat o2 bung is open to the atmosphere because I had to use my rear o2 on the front and I have no replacement for the rear at this time. Maybe that is throwing off the o2 sensor reading somehow?

Basically I have a crap ton of things to consider here. I suppose I should start by measuring fuel pressure and put a wideband to measure actual AFR?
Maybe my intake gaskets are bad? Replace the MAF?

The very weird thing is, on the tune Wheatley sent me to practice on, PE was set to command 11.3:1 AFR at WOT. When I went WOT with this setting, my truck smelled like a fuel pump...it smelled every bit that rich, and that was with the wind going 80 mph. So I'm just having a hard time believing I'm running so lean....making me think it's some kind of logging anomaly?

I'm attaching the log and tune, any help/comments is appreciated.

00Silv4.8

iTrader: (10)

I would plug that rear O2 sensor and see if that helps. Air could possibly be entering in and exiting and causing some miss information. Plug those and then go from there. Start small, haha thats usually what causes problems

GMCtrk

iTrader: (27)

Yeah, I'm gonna go see if I can buy a M18 x 1.5 plug. I doubt that's the issue though because Justin's theory explains my KR well. Even if I plug it up, it's really not going to be a good idea to be going WOT anymore until I figure out what's wrong, with it being that lean! Anyone have any ideas on how to test the MAF?

BlackGMC

iTrader: (31)

You have EFI Live right? If so then this is how i would trouble shoot the lead. Start your truck, drag your laptop out infront of your truck with the truck running. Log your STFTs on dashboard (the graph looking one), get some carb cleaner, start spraying everything, while watching the log (having a buddy watch while you spray helps). Once you hit a leak your trims will change then you will found your leak. I would check your fuel pressure vacuum line, injector orings, brake booster line, PVC vent line (passenger side valve cover), PCV line (drives side valve cover), all the intake track, TB to manifold gasket, lastly hose down where the intake gaskets are...

I did this troubleshooting a friends truck when he got his tune from Justin... Justin was dead-on about the leak.

Wheatley

iTrader: (12)

All your fuel tables were put to stock when I sent it to you.That was the stock values

GMCtrk

iTrader: (27)

where did the leak end up being? What are normal STFT's and how much should it change when i hit the leak?

I'm also going to change the fuel filter again.

GMCtrk

iTrader: (27)

I've had this problem long before the stock values, so it really has nothing to do with the tune, so no problems on your part. I guess I'm very fortunate there wasn't a piston meltdown or something from being so lean.

budhayes3

iTrader: (19)

This is excellent advice, I've used this method as long as I could remember, only without logging software. I would spray carb cleaner anywhere that a vacuum leak could occur, and listen for a change in the idle. With scanning software, this method is even more accurate. Don't go out and buy a MAF until you've ruled out a vacuum leak for sure. It wouldn't hurt to check fuel pressure also, even though your pump is new. There could be debris in the bottom of the gas tank that is clogging the sock at the end of the pump. I've also heard of pinholes in the plastic tube coming off of the pump on the module in the tank, although if you had a complete pump/module assembly replaced that would be ruled out.

BlackGMC

iTrader: (31)

He had 2 leaks, one at the fuel pressure vacuum line going to the regulator, and i forgot where the other one was. Sorry it was awhile ago..

dewmanshu

iTrader: (4)

Justin is probably correct if it is affecting you all over the trim maps (idle, PT, and WOT), but don't go buying a MAF if you CAN'T find a leak. Eliminate the fuel as a problem as well. This isn't like the old days where fuel pumps either worked or didn't. They can putter out now. Seen a bunch of times. Test fuel pressure at the rail in all scenarios.