1999 GMC Sonoma engine

FCJH007

MEMBER
1999 GMC SONOMA
6 CYL
2WD
AUTOMATIC
112,100 MILES

My truck after it sits for a few hours or overnight, I get in to it and I use to be able to take right off now it dies down and the rpms drop alittle then I take my foot off the pedal and it goes fine till it sits for a few hours. What could it be. Its a new used engine, I put on new plugs and a new cap and rotor. I got the fuel system cleaned at jiffy lube and that di not stop it. Can you help me please.

3 Replies

RACEFAN966

MECHANIC
5,029 POSTS

So if I understand you correctly when it sits for a while and you go start it it has to crank over longer to start? Have you checked the fuel pressure after it has sat? If not I would check it by hooking up a fuel pressure tester and then seeing what it is and then turn the key on and see what it goes to and then crank it and see what it goes to. This will tell us weather or not it is the fuel pump. Now I also have ask how old is the fuel filter?

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Thursday, September 3rd, 2009 AT 10:56 AM

FCJH007

MEMBER
3 POSTS

No its not when I start it its after I start it and put in drive to take it hesitates then takes off fine. My fuel filter is like a month or two old. It cranks over fine and starts right away.

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Thursday, September 3rd, 2009 AT 11:15 AM

RACEFAN966

MECHANIC
5,029 POSTS

OK so it hesitates on take off. That can be caused by a few things. First I would like to know how does it idle? Does it idle rough at all? I would like you to unplug the mass air flow meter and see how it runs. I also need to know if you have a digital multi meter? If so then I would like to test the TPS first and go from there. Let me know and we will go from there.

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Friday, September 4th, 2009 AT 9:54 AM