Cold Stalling/Stumbling Only

[AndyL]

I keep having stalling/stumbling only when the Engine is cold. Usually it just hiccops but yesterday it died and wouldn't restart, then started fine this morning. This almost always happens about 30 to 45 seconds after startup. I don't get a SES code and the truck has 55K miles. Do you guys think this is still FSD even though it is cold? Will a FSD cooler woid my GM warranty for the IP and FSD?

[Jim P]

My truck has been doing the same thing. It only does it in the morning. After work the only time it ever did it was on a saturday when I only worked till noon. I think it is sucking air into the fuel system somewhere at night because the fuel tank cools down and causes a vaccum in the tank. I loosened my fuel cap a couple turns and it has not done it since. I think maybe the cap is bad. Try opening your fuel cap when it is cold and see if it has alot of vaccum in the tank. If it does have alot of vaccum, try loosening the cap for a couple days and see if it helps. Don't leave the cap loose if it is going to rain, you don't want any water in the tank.

[twaddle]

AndyL,
Check that the fuel lift pump is operating.
A friend of mine had something the same with his 94 pick up. The engine would stall first thing in the morning (he'd get about 250feet down the road)then it'd be ok for the rest of the day.

It hasn't done it since replacing the oil pressure switch which operates the fuel lift pump. (Should not have said that, you know what'll happen now)

Good luck

Jim Twaddle
Biggar, Scotland

[Barry Nave]

When running, open the water drain vavle and see if eng. dies out. Bad lift pump.
Our tanks always have vaccum in them.
On my 95 I can put it in drive and turn key to start and the lift pump will run.
I use this to blead the filter of air after a fuel filter change.
www.imagestation.com/members/95c3500 (http://www.imagestation.com/members/95c3500)

[ 11-28-2003, 02:16 AM: Message edited by: Bnave95 ]

[Jim P]

I know these trucks should have a little vacuum in the tank but mine has an excessive amout in the morning when it is cold. It sounds like it could suck you right in the tank. If I check it later in the day, after the sun comes out, it is not near as bad. I truly believe that the excessive vaccum is causing the fuel system to suck air somewhere at night. When I start it, it runs fine till that air bubble reaches the ip and then it either stumbles or quits depending on the size of the air bubble. The fuel system does not suck air when it is running because the lines and filter are under pressure from the lift pump. I have checked my lift pump and it runs just fine. The fuel comes out the water drain very well when I test it.