2000 4x4 Z71 surging at cruising speeds

The truck seems to run fine, idle fine, etc. but when I'm cruising down the highway, with my foot in a steady position and the speed constant, I can feel the truck surging (best I can describe it) every so often. I don't hear the motor change, and it's very quick. It just feels like it stumbles for a sec then is fine. I never notice it anywhere but cruising at 55 plus down the highway. Any ideas what could cause this? I'm afraid it's an early warning sign of something worse...and it's annoying as hell!:mad:

*edit* Truck has 80k miles and has been very well maintained with all scheduled services done by GM techs. Motor is 4.8

The truck seems to run fine, idle fine, etc. but when I'm cruising down the highway, with my foot in a steady position and the speed constant, I can feel the truck surging (best I can describe it) every so often. I don't hear the motor change, and it's very quick. It just feels like it stumbles for a sec then is fine. I never notice it anywhere but cruising at 55 plus down the highway. Any ideas what could cause this? I'm afraid it's an early warning sign of something worse...and it's annoying as hell!:mad:

*edit* Truck has 80k miles and has been very well maintained with all scheduled services done by GM techs. Motor is 4.8

this could be the fuel pump....with a gauge attached to the fuel rail with a long hose monitor pressure as you drive to see it its a fuel supply problem....

*Hmm, I posted this before but it disappeared*

I did some research last night though old posts here and found another clue about what might be going on. Every once in a while my truck has a hard time starting. It'll just crank and crank, sputter a bit, then finally start. When it does start it revs way up, then almost dies, then back up again, then almost dies...then it will finally idle right. Sometimes it will do this a couple days in a row, sometimes not for a week straight.

Some of the posts suggested this may be the pressure regulator failing. Would this cause the surging I'm experiencing as well? If so how would I test for this?

*edit* I pulled the hose off the regulator as some posts suggested doing this to see if there was any gas in it. It was dry but it smelled pretty strong like gas. Not sure if the smell is normal or not, but maybe that's something? How would I test this part to be sure it's the one failing (if in fact it could cause the problems listed above)?

Thanks a bunch
Chris

I think, you have stumbling, not surging problem.
sounds like jcat is right - you might have occasional fuel cutoffs.
fuel line should be full of gas even with engine shut off.
http://autorepair.about.com/cs/troubleshooting/l/aa042603a_03.htm
http://autorepair.about.com/cs/faqs/l/aa042603a_1.htm

definitely read error codes.

try to get to fuel pump ground contact and clean it, some say, it rusts very fast and causes all kinds of havocks.

Did you pull the vacuum hose off the regulator while the fuel pump was on? It may be leaking if you smell gas in the vacuum hose.

What does the fuel pressure do when you turn off the ignition? It should hold pressure after dropping a little bit.

//2000CAYukon

Did you pull the vacuum hose off the regulator while the fuel pump was on? It may be leaking if you smell gas in the vacuum hose.

What does the fuel pressure do when you turn off the ignition? It should hold pressure after dropping a little bit.

//2000CAYukon

ya! I agree the reg. vac line should not smell of fuel....
I'd replace the regulator ...must have a small pin hole...

Ok, I pulled the vac line off and started the truck. I saw no fuel. The weird thing is the truck didn't run funny at all, even with the vac line hissing away :eek7:. I reved it up quite a bit and it ran fine at high rpm's as well as idle. It was a cold start though and I didn't let it warm up all the way, but I did run it for several minutes. Maybe that makes a difference but in my limited knowledge any vac leak should casue it to run like ass. Shouldn't it?

I'm no expert but isn't this a bit odd?

Any input on this ^^ Still having this issue and looking for a way to be fairly certain what the problem is before I just start throwing money at it.

You really need to do a fuel pressure test to determine if the regulator is getting weak or whatever

ok, i understand lack of desire or funds to check on fuel supply.

try this: get a can of choke cleaner, and with engine running, give short bursts of it on vacuum lines and gaskets, where it's safe to do, as it's very flammable. if engine stumbles or chokes after such shot - you found leak.

otherwise, you do need to check on your fuel supply.