[Silveraydo00]

I've had my '00 Silverado 1500 4.8 RCLB 2wd for a little over a year now. It's been a great truck with no major issues until now. Among other unrelated problems (typical GM abs light, brake light, fuel sending unit showing low fuel, oil pressure sensor) I now have an intermittent hard start/start & stall issue with the weather getting colder. I didn't have any of these issues last winter, the truck always started up and ran like a champ. No issues in the summer either.

When I start it up cold in the morning it will sit there and crank for 2-3 key cycles without even trying to start. Eventually after about 3 primes of the fuel pump it will run no problem. After driving it and warming it up I shut it off and leave it for a few minutes, then come back and it will start up and run for a second, then stall. It does this 5-10 times before it will finally run. When it does run it idles smooth as glass and has plenty of power. We can rule out the security chip key as my truck is a base model that doesn't have that "feature".

The fuel pump was new a couple of years ago but the fuel pressure regulator has never been touched. No fuel comes squirting out of the vacuum line when I take it off the FPR so the seals inside are good, I'm stumped. any ideas?

 

[wildchevy]

some pumps only last a year, have you put a pressure gauge on it yet?

 

[Silveraydo00]

I haven't, but if fuel pressure was consistently low wouldn't you think that it would cause some drivability concerns like a misfire under load? My thoughts are that the fuel pressure regular is bleeding off fuel pressure when the truck sits. That'd explain the hard start, but I'm still stumped on the start and stall issue.

 

[apcnc]

I haven't, but if fuel pressure was consistently low wouldn't you think that it would cause some drivability concerns like a misfire under load? My thoughts are that the fuel pressure regular is bleeding off fuel pressure when the truck sits. That'd explain the hard start, but I'm still stumped on the start and stall issue.

If that's the case kick the switch on and off a few times to build pressure... If it starts up ok then you have it. The gauge would tell you whats there though.

 

[GR2017]

Have you tried using a known good battery or jumped to another vehicle for the first cold start of the day?

 

[Silveraydo00]

Thanks for the suggestions guys. I bought a fuel pressure gauge and hooked it up. After sitting overnight, there is almost zero fuel pressure and is slower to build up than I expected. As it cranks it builds, but it takes some cranking and some key cycles to get it to build enough pressure to turn over. So it sounds like the issue is definitively something to do with fuel. Now I suppose my task is to start figuring out whether it's a fuel pump or FPR, or perhaps an EVAP issue? Something somewhere is bleeding off fuel pressure as I wouldn't think it would bleed off all fuel pressure overnight? I'm not hugely educated on fuel systems so this is a learning curve for me but I don't want to be firing the parts cannon and dumping money into an old truck with a questionable transmission.

The battery was new in July, as was the fuel filter.

This morning the truck was hands-down the most stubborn it has been and it is not the coldest morning it has been either. It finally fired after what seemed like minutes of cranking, key cycles, swearing, contemplating adding bailey's to my coffee etc. But Sunday morning, Monday morning and yesterday morning the truck fired up without a hiccup and ran great throughout the day.

 

[apcnc]

Do you hear the pump when you turn the switch on? Could even be leak in the tank. What is the pressure when it runs? Have someone turn the switch on and listen to the tank. See if you hear a lot of fuel draining back or just the pump running. Is it irregular or consistent sound? You should have another relay you can swap it out with also to check the relay.

 

[Silveraydo00]

Do you hear the pump when you turn the switch on? Could even be leak in the tank. What is the pressure when it runs? Have someone turn the switch on and listen to the tank. See if you hear a lot of fuel draining back or just the pump running. Is it irregular or consistent sound? You should have another relay you can swap it out with also to check the relay.

It is around 52psi when running. I can hear the pump prime when I turn the key on, and when the truck is running I can hear the pump running as well. Makes a faint whining sound that's consistent.

 

[apcnc]

What PSI do you see just turning on the switch? How fast does it loose pressure after the pump turns off? It should come up pretty quick when you turn the switch on. Sounds like the regulator. Unless pressure is coming up when you turn the switch on. How long just switching off and one to build 50 PSI?

 

[puppeteer]

Could be getting air into the system somewhere. My diesel does this too only when cold. Fuel pressure bleeds off and air gets in the lines, Have to manually prime it to start.

 

[MUDCVRD]

Could a defective gas cap cause the bleed off?

 

[ASTE25]

Sounds like a typical bad fuel pump.

 

[MUDCVRD]

Definitely could be. Hard starts and pressure instability are telltale signs of a bad fuel pump. That's where I'd look.

 

[Silveraydo00]

Thanks gents, I'll do some more investigating when I have some time this weekend. I'll also look up my records and see if there's a warranty on the brand new fuel pump that was installed just a couple years ago.

While the truck seems to start ok lately the problems continue to pile up. Now the truck starts fine (most of the time) however after awhile of driving it seems to have delayed/hesitating shifts, and idles at about 900rpm in park and 700rpm in gear. Shutting the truck off and starting it back up fixes it temporarily, it goes back down to normal idle and shifts fine. This seems all too coincidental.. I replaced the air filter, cleaned the throttle body, MAF and IACV last night to no avail, I'm thinking I should be looking into the TPs?

 

[MUDCVRD]

Fuel pump could be your hesitation too. Those RPM values seem to be within spec. My 5.3 will idle 550-650 in gear (give or take depending on what accessories are running) and very slightly higher when in park... after initial warm up and in closed-loop of course.