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1998 GMC Jimmy Hard starting.


robbins1
12-10-2008, 11:21 AM
I have a 1998 GMC Jimmy 4.3 V6 it has a hard time starting when it has been setting for a little while, especially when it is cold. I hace replaced some parts on it including the engine coolant temerature sensor,spark plugs, crank sensor,fuel filter. I can hear the fuel pump kicking on and off.

MT-2500
12-10-2008, 12:01 PM
The only true test on a fuel pump is to check the direct fuel pressure from fuel pump.
A quick test is to block off the return line and see if fuel pressure comes up to 75-85 lbs.
But do not run the pump at full pressure very long.
Also when testing fuel pump and pressure you need to tape a gauge to outside windshield or outside mirror and drive it on the road for 20 -30 minutes
until the pump gets has run a while to check for a pump fading out after hot.

Hard to start cold and fuel pressure testing guide line.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
If pump has full pressure with return line blocked and low pressure without it blocked most usually the fuel pressure regulator is leaking or not holding pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 64-65 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak in system.
Post back fuel pressure readings.

icenguppy
12-10-2008, 04:24 PM
im not a mechanic by any means, but this might help. i also have a 1998 jimmy and was having similar problems starting. i would have to turn on the ignition a couple of times just enough to turn on the fuel pump to get gas to the engine. all of my pressures were fine. talked to a gm mechanic and he said it was probably the fuel pressure regulator. so we installed a new one and its started fine ever since. we replaced it in about 1 hour. take the time to clean the upper intake and replace the upper planum gasket and the 2 other gaskets that come with it ( they are cheap). fuel pressure regulator was about 56 bucks, and i changed the thermostat since it was right there. hope this helps. let us know.

MT-2500
12-10-2008, 04:54 PM
im not a mechanic by any means, but this might help. i also have a 1998 jimmy and was having similar problems starting. i would have to turn on the ignition a couple of times just enough to turn on the fuel pump to get gas to the engine. all of my pressures were fine. talked to a gm mechanic and he said it was probably the fuel pressure regulator. so we installed a new one and its started fine ever since. we replaced it in about 1 hour. take the time to clean the upper intake and replace the upper planum gasket and the 2 other gaskets that come with it ( they are cheap). fuel pressure regulator was about 56 bucks, and i changed the thermostat since it was right there. hope this helps. let us know.

How could the pressure be good and the pressure regulator bad.

To test for a bad fuel pump or regulator do the fuel pressure test as posted.
or you will just be throwing parts at it.
Good Luck

icenguppy
12-13-2008, 11:45 AM
How could the pressure be good and the pressure regulator bad.

To test for a bad fuel pump or regulator do the fuel pressure test as posted.
or you will just be throwing parts at it.
Good Luckpressure was good while running.

old_master
12-13-2008, 12:40 PM
pressure was good while running.

Your GM mechanic is misinformed. GM does not publish ANY engine running fuel pressure specifications for the CSFI system. Straight out of the GM dealer issue shop manual: All fuel delivery diagnostics are done while the engine is off. As MT mentioned, you're throwing parts at it and throwing money away needlessly. It's always best to have things diagnosed by someone that understands the system.

icenguppy
12-13-2008, 10:29 PM
Your GM mechanic is misinformed. GM does not publish ANY engine running fuel pressure specifications for the CSFI system. Straight out of the GM dealer issue shop manual: All fuel delivery diagnostics are done while the engine is off. As MT mentioned, you're throwing parts at it and throwing money away needlessly. It's always best to have things diagnosed by someone that understands the system.look, i thought it was something worth diagnosing. i know of 2 jimmys and a tahoe that had the same symptoms and all were fuel pressure regulators. i didnt say to replace it but to check into it. i do recall saying that i wasnt a mechanic.sorry to try helping, ill leave it to you pros.

98_Jimmy_Owner
09-13-2010, 03:04 PM
I know this is an old post, but...
old_master I wish you had not shut down icenpuppy so quick. I am having the same problem with my Jimmy and I would have liked to have heard more from him then you. From reading this post it appears he actually owned the same vehicle and had the same problem whereas you were just :jerking: off.

icenguppy
09-13-2010, 03:38 PM
we thought we had the problem fixed with the replacement of the fuel regulator but the problem came back after a while. we figured out that we needed to replace the fuel injection system. problem solved.

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