Cadillac Repair: Sputter/stalling problem, fuel pressure gage, vortec engine

Question
I have no idea if this is the correct board to go to but I know that the GM dealer also sales Caddy's so here I go...I have a 2001 GMC Jimmy with a 6 cyl.vortec in it that frequently sputters and stalls out while  ideling or driving.  There are no codes that are thrown out and no one seems to know what the problem could be..we have replaced fuel pump/fuel filter/secondary air pump,relays and check valves all becuase we were told that was the problem..it does it in hot,cold,rain,snow...anytime when air conditioning is on or off. itermittently or regularly.I hope that maybe you can help I am almost positive this is the last resort
Tammy


Answer
Hi Tammy, My experriance with the vortec engine is rather limited but they seem to be rather touchy about fuel pressure. Someone will need to hook up a fuel pressure gage and monitor the pressure running and after it stalls if you can catch it. The pressure is quite high...around 55-62 psi...and can varry from year to year so looking up the spec for that year is important. If the pressure is down even 2 psi from the maximum spec then it can cause running problems. Then after the engine has been turned off the pressure should hold and not drop right away. If it does then the injector assembly is suspect and also the nylon fuel lines under the intake manifold could be leaking. If you smell fuel at the engine with the engine off or the oil level is over full then that is a tip off of a bad injector assembly or lines. Running the engine with a scan tool hooked up to watch sensor readings is another thing that must be done. I realize that haveing changed all those parts might eliminate some of the tests but sounds like you need to find a dealer tech that is pretty sharp to help nail this problem down. A call to the GMC zone office might help locate the shop to take this Jimmy to. The tech can then call technical assistance as well as have access to service bulletins so hopefully the problem can be resolved after this next service visit...That is my 2 cents worth. What I would do is repost this question in the Chevy section and with a driveability expert as the Chevy and GMC use the same engine system. Hope that helps. Bill