Hey guys. My wife's 2001 Yukon has been having trouble starting lately. I checked fuel pressure and it seems correct. Primes to around 55, starts at around 60 and idles around 48(if I remember correctly). I just changed the fuel filter, cleaned the MAF, cleaned the air filter, new MSD wires, new NGK plugs gapped to either .040 or .045(can't remember exactly). It used to throw codes for a misfire, but we fixed that problem(someone snagged a plug wire off the truck). A few months ago it threw codes for both banks being lean, but they never came back after clearing them. Recently it was throwing codes P0440-Evaporative Emission Control System and P0300-Random multiple misfire. They were cleared and haven't come back. I don't know what else to check for the starting problem. It cranks for a few seconds and finally stumbles to an idle. What should I look at next?

 

Have the intake gaskets been replaced with the newer design ? This will cause a lean condition .
Also try cleaning the IAC and see if it helps with your starting issue .

I had a random misfire issue that plagued me on my LQ4 van , turned out it was the O2 sensor wire was touching the exhaust , new sensor fixed it once I found out which one it was .
Scan your o2s while it's in closed loop and see if you get any wierd readings or none at all from a possible bad one .

 

Ok, I'll check the O2's. It's DBW so I don't think I can clean the IAC. I bet those intake gaskets haven't been changed either. Thanks.

 

Oh ok I forgot some early tahoes/Yukon were fly by wire .

 

Smart money is on the intake gaskets, as Tim suggested.