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1998 gmc sonoma problems

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Old 01-17-2010, 05:51 AM   #1
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1998 gmc sonoma problems

i have a 98 sonoma thats will only crank with gas or carb cleaner sprayed into the tb but once it cranks it will run and crank good till it sits overnight then won't crank again.haven't changed anything yet looking for ideas before i start.thanks for any suggestions you may have.
Old 01-17-2010, 06:23 AM   #2
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Re: 1998 gmc sonoma problems

check the fuel pressure. if you don't have a gauge just turn the key on you should hear the pump. then on the silver lines going into the throtal body unscrew the cap use your finger nail to push the valve fuel should spray out this will tell if you have pressure at all on startup.
Old 01-17-2010, 07:57 AM   #3
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Re: 1998 gmc sonoma problems

Quote: Originally Posted by flynlo
check the fuel pressure. if you don't have a gauge just turn the key on you should hear the pump. then on the silver lines going into the throtal body unscrew the cap use your finger nail to push the valve fuel should spray out this will tell if you have pressure at all on startup.
there was a small spray out,so i turned the key back on and about the same sprayed out.so i guess next step is to go get a pressure tester to check it,what would be a good start up pressure?
Old 01-17-2010, 09:46 AM   #4
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Re: 1998 gmc sonoma problems

So your 99 4.3 won't start without the help of starter fluid....

Your symptoms are common to fuel pressure issues. The key is to troubleshoot with the use of a fuel pressure gauge. The injection system needs between ~56 to 60 lbs at the fuel rail to start the engine. Then you need a little less to keep it running.
When you first turn the key to RUN (not start), the fuel pump relay turns on for ~4 seconds. The system is expected to have held at least ~35 lbs from the last time it ran. If you have a leak (fuel pressure regulator, fuel pump check valve, spider, injectors) the system may not be able to pump enough gas that quick to reach ~58 lbs. To test for this, you would watch the gauge after turning the engine off. Ideally it should hold pressure for at least a day.
A rapid drop would point away from the pump, but not the pumps check valve, FPR, Spider or injectors.

If it holds good pressure but fails to come up to a high enough pressure to start; expect Suspect plugged fuel filter or weak pump. Continue by supplying fused +12volts to the fuel pump test lead found on the pass. side fire wall (Tan, Brown or gray some times found by the brake boster on 4wd's) for 5+ seconds. If the pressure comes up to par: then replace the fuel pump primer relay. Often when they wear out it takes them longer then needed to energise the contacts.

If the pressure bleeds off too fast; open the veiw cover on the upper intake (covers the fuel injectors) and look for signs of washing. Where gas leaks wash the build up away. You can post a pic here and the experts will point out the leak.
If you don't have a leak but it drops fast, then suspect the check valve at the pump. 3 options; replace the pump. Install an inline check valve. Supply fused+12v to the test lead until the engine starts.

Post you pressure results. Key on run, after start, and leak down after turnned off.

Good luck
Old 02-03-2010, 04:26 PM   #5
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Re: 1998 gmc sonoma problems

yep it was the fuel pump thanks all
Old 02-03-2010, 05:00 PM   #6
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Re: 1998 gmc sonoma problems

Quote: Originally Posted by Bill Wheats
If it holds good pressure but fails to come up to a high enough pressure to start; expect Suspect plugged fuel filter or weak pump. Continue by supplying fused +12volts to the fuel pump test lead found on the pass. side fire wall (Tan, Brown or gray some times found by the brake boster on 4wd's) for 5+ seconds. If the pressure comes up to par: then replace the fuel pump primer relay. Often when they wear out it takes them longer then needed to energise the contacts.
is this test lead a loose connector by chance? i have this same problem in my 99, but i havent tried starting fluid. i only get about 12lbs of pressure on the rail while priming. installed a new fuel filter, same results....id like to try bypassing the relay to test that, though i do hear it clicking when turning the key to run.
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