2000 GMC sierra 4.8, in the last two weeks if i jump in, in the morning i can try to crank the truck and it will turn over for about 4-5 seconds before cranking. This does not tend to be the case during the day. I'm assuming the system loses pressure over night and that this is a fuel pump issue.

If i get in, turn on the key for that same duration of time, it will crank right up, which confirms to me or leads me to believe that the pump just needs to pressurize the system. I did not have this issue before about 3 weeks ago, also, i noticed a slight stutter at a higher rpm when playing around, this also could re-enforce the idea that the pump is not maintaining pressure. Would anyone else agree? Have other suggestions on what it could be? I believe my fuel system is a return system with a regulator, but I am not sure. As of today i have not checked the pressure. Thoughts?

If you do think it is a pump, any suggestions on a nice aftermarket? I"m familiar with walbro 255's but thats from my import days, not sure what is all available in the domestic market. I find mixed results on different sites but i would like to go ahead and get a pump that can support a FBO 6.0 with a bottle - that will all be coming soon.


So, does it look like i'm on the right track as far as troubleshooting this particular issue?
Suggestions on a decent truthworthy aftermarket pump if so.

 

Put a fuel pressure gauge on it, but it sure sounds like a pump. A walbro 340, 400 or aeromotive 340 should do you fine.

 

Does the obd2 systems on these truck have a parameter for measuring fuel pressure? The reason i asked is because i ordered an ELM327 to play with and just curious if it can read the fuel pressure, if the system has the ability i'm sure it can, if not i will have to get a gauge and measure manually.

 

No, it does not(unfortunately).

It does sound like a fuel pump. Get a pressure gauge on there before you find yourself stranded. Your local auto parts store probably has a loaner tool program, check it out. You're looking for 58 psi with the key on, engine off. You want to see it pop up quickly, not build up slowly.

 

Is ~58 psi an exact figure? I'm assuming I will not see that instantaneously but build slowly (up to 4-5s). I will try to check it out this weekend, yes that is not something I can afford to deal with right now, might as well get it knocked out if it is the problem.
I would probably change my filter again since it is relatively cheap/easy just in case the filter has gone bad in the last 2 years (25k miles). Any suggestions on a good aftermarket pump? My sending unit has acted crazy below 1/4 tank since i got the truck so i will probably change the entire assembly with something that can give me more headroom for future upgrades and a bottle.

 

KEy on engine off should be in the 50-55 range.

 

Not a pump, put a fpr on it and your problem will be solved!

 

It's right on the driver side fuel rail and very easy to get to. 5 minute fix and I think they run around 45 bucks if I remember correct.

 

What makes you think its the regulator? I haven't went outside and looked yet but is the regulator vacuum driven?

 

Have replaced several of them here at the shop, yes it has a vacuum line on it, it will sometimes have fuel in it when you pull it off also showing its bad.