So I've got an air leak somewhere
04-25-2009, 11:42 AM
#21
I have a very similar problem after installing my new intake and TB. I am scared to even drive it because at idle and when I am tring to rev it up it back fires left and right. Throttle response is crap, and everything up top is new, rails, injectors, fuel lines, regulator, everything needed to do the swap. I do not know enough about efi live to go in and change the fueling properly but I did adjust for the injectors. I sure I may have a leak but I also think my fueling is off. The fuel pressure stays at 58psi. Im going to try the carb cleaner thing, does it have to be carb cleaner? Also what should a LTFT be at idle cause mine are between 17-21 at idle.
04-25-2009, 04:54 PM
#24
LTFT's around 20 does not sound good at all. I imagine that means you're running about 20% leaner than what you should.
My issue doesn't appear to be an air leak since I've sprayed about 1/4 can of brake cleaner and can find anything.
Gonna try fuel pressure next.
My issue doesn't appear to be an air leak since I've sprayed about 1/4 can of brake cleaner and can find anything.
Gonna try fuel pressure next.
04-25-2009, 07:34 PM
#26
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here is something you can do to find a vacuum leak! find something to plug in your intake tube after the maf, make sure it stays in place, crank the engine and it will run for about two seconds then it will shut off creating vacuum inside your engine, listen for any air leaks around the gaskets, if the engine still runs then you have a BIG leak.
something to try!
something to try!
04-25-2009, 09:59 PM
#27
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.
It IS very common for fuel to be an issue, however in this case, a leak or faulty MAF is to blame. Take a look at peak MAF flow as well as peak cylinder air mass. This log is showing mass air flow that is lower than what you'd see on a stock 5.3L (at sea level).
From frame 9050 to 9100, RPM increases from 4360 to 5400 while MAF flow stays almost flat. Maf flow increases from 28# to 30#.
Either this engine is exhaling through a straw (which wouldn't explain the lean fluctuation) or the MAF is crap/there is a leak.
GMCtrk, try failing the MAF temporarily (set C2901 - C2903 = 1) and see how it runs.
04-26-2009, 06:37 PM
#30
It IS very common for fuel to be an issue, however in this case, a leak or faulty MAF is to blame. Take a look at peak MAF flow as well as peak cylinder air mass. This log is showing mass air flow that is lower than what you'd see on a stock 5.3L (at sea level).
From frame 9050 to 9100, RPM increases from 4360 to 5400 while MAF flow stays almost flat. Maf flow increases from 28# to 30#.
Either this engine is exhaling through a straw (which wouldn't explain the lean fluctuation) or the MAF is crap/there is a leak.
GMCtrk, try failing the MAF temporarily (set C2901 - C2903 = 1) and see how it runs.
From frame 9050 to 9100, RPM increases from 4360 to 5400 while MAF flow stays almost flat. Maf flow increases from 28# to 30#.
Either this engine is exhaling through a straw (which wouldn't explain the lean fluctuation) or the MAF is crap/there is a leak.
GMCtrk, try failing the MAF temporarily (set C2901 - C2903 = 1) and see how it runs.
As per your instructions, I disabled the MAF and I did not notice a difference in how it drove. It was however commanding max line pressure, so I didn't go WOT. I don't want to break anything. The only real difference I noticed is the fact that with the MAF disabled my LTFT's on the highway under load (~30% TPS) went to about zero. In the same situation with the MAF on, 1 bank is at 9% and the other is at 11%.