AndyM

Posted this on the conversions board, but didn't get a response. I have 5.3l Vortec from an '07 Siverado swapped into my Jeep. It'll start and idle, but as soon as you press the gas, it revs, then cuts the gas. It recovers when the rpms drop, then continues the same cycle. Fuel pressure and MAP seem fine, but I think I have a bad MAF. Its at 1 lb/min at idle and never goes above 2 lb/min. This seems low to me, but I don't know what the upper values should be. If I open the throttle slowly I can get it to keep the motor running up to about 2k rpm, then it drops off. The MAF values don't seem to correspond with the throttle opening after the initial jump to 2 lb/min right off of idle. I checked the wiring and it is all fine. I'm starting to think the MAF is bad -- I know it took a trip from the fender to the garage floor a while back, but I didn't think twice about it. Anyone have any thoughts on this before I drop $$$ on a new MAF. And, if I need to do that, is stock the way to go, or Granatelli or ???

YellowToy/A

iTrader: (1)

Unpulg the MAF. It should run SD. How does it run? What is you air/fuel ratio? If you dont know find out. Same with timing.

AndyM

It runs the same with the MAF unplugged. I've tuned TBI and early TPI in the past, but this is my first time screwing around with something with a MAF. I didn't think it would run without it -- sounds like it should, though, based on some of the searching I've now done.

I have a timing light on it and the spark is consistent and appears to be advancing fine. I haven't put the WB on it yet since its installed in my other car. Seems like something is cutting off the fuel when it reaches about 2k rpm then it resumes after it drops back down to about 1k. If I mash the throttle is quickly revs to 2k, then drops down to 1k, catches again and runs up to 2k, then drops back down again. The cycle continues until you let off the throttle, then it goes back down to a rock-solid idle. If I slowly increase the throttle it will run smoothly up to 2k again, then drop.

The motor is a stock '07 5.3 from a Silverado "classic" vin Z (Flex-Fuel). I reflashed it to remove VATS, convert to manual trans and remove the rear O2 sensors. I understand this PCM doesn't need a separate fuel composition sensor, but I wonder if this may be somehow related if the MAF isn't the culprit. Curious if anyone has screwed around with a similar swap for a Flex-Fuel motor.

wait4me

iTrader: (10)

If you have efilive send me the tune, ill figure it out..

AndyM

Unfortunately, I don't have EFIlive -- yet -- since I ended up with the JET DST. Thanks, though.

jimmyblue

iTrader: (11)

Look at the dynamic airflow and the MAF airflow numbers (prefer
g/sec, but whatever). They should be roughly similar at the lower
RPM steady throttle and identical above 4000RPM steady (if you
ever get there). You should see a MAF frequency of about 2500
Hz, more or less, at idle. Can you see these parameters?

AndyM

All fixed! I had a couple of random auto trans diagnostic faults that I missed when I converted over to the manual trans. I turned them off and it runs like a champ. Thanks for all the help!