2002 GMC Sonoma Truck wont start

Tiny
SKNOTTS
  • MEMBER
  • 2002 GMC SONOMA
Engine Performance problem
2002 GMC Sonoma 6 cyl Two Wheel Drive Automatic

Dear Tech:
First off I bought this used drove it home and around town for about 100 miles no problems alittle hard to start but that was it. I went outside about 2 weeks of truck sitting in driveway and it wouldnt start so I changed plugs, wires, cap and rotor. Thinking that was it since it was hard to start when I first got it. They was in really bad shape when I changed them, but when I tried to start it the truck still wouldnt run. So I checked to see if I was getting fuel and I was getting fuel all the way to the injectors, I checked spark and I have fire. So I changed injectors and regulator thinking that may be the problem and still wont start. If I spray crab cleaner in intake it will fire and stay running I can even turn the key off and wait a hour and it will still start now that its warm but after engine cools to outside temp(which is about 60 right now) it wont start unless I use carb cleaner to help it. I pulled regulator off and changed it again thinking I may have gotten a bad one and still didnt change anything. I checked fuel filter and its fine. But I dont have a pressure tester to test fuel pressure to see if pump is not putting out the required spec of 55-61 psi. Before I go and put more money in a tester is there anything else that may cause this problem
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Friday, October 2nd, 2009 AT 8:07 PM

6 Replies

Tiny
PEAR69
  • MEMBER
You must first see what the fuel pressure is. Do not change anything until you know the fuel pressure.
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Saturday, October 3rd, 2009 AT 1:38 AM
Tiny
SKNOTTS
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With key on engine off 10psi key on engine cranking im at 45psi what do you think. Required psi is 55-61 with key on engine off
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Monday, October 5th, 2009 AT 12:21 PM
Tiny
PEAR69
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Change the fuel filter (because they are cheap). Then check the fuel pressure again and see if it changes. It probably won't change but it is worth a shot.
Next - do a voltage drop test on the fuel pump. To do this - turn ignition key on - test voltage at the fuel pump relay (hot wire) to the battery negitive terminal (not ground). Then test the fuel pump (hot wire) at the fuel pump to the same negitive terminal. The drop should be 2% or less of the first test.
If the voltage drop is more than 2% clean up the fuel pumps' ground. If the voltage drop test is less than 2% then you probably have a bad fuel pump.
The voltage drop test is important to do because if you have a bad or corroded ground, and you go ahead and change the fuel pump, the new pump will fail in a very short period of time.
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Monday, October 5th, 2009 AT 11:28 PM
Tiny
PEAR69
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Even if the voltage drop is more than 2%, you may still have a bad fuel pump - but - the most common cause of voltage drops being excessive is a corroded or bad ground.

BTW - 10 or 45 psi will not run your engine.
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Monday, October 5th, 2009 AT 11:32 PM
Tiny
SKNOTTS
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I changed the fuel pump cause I wasnt sure how to check that voltage and nothing changed still the same problem can you dumb that discription down alittle for me plz and ill try that im ut of iideas what to do im so ready to give up and junk this thing. Dont have the money to take it to a shop and about out of nerves to deal with it
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Saturday, October 10th, 2009 AT 6:30 PM
Tiny
PEAR69
  • MEMBER
Did you change the fuel filter? Make sure that it is installed correctly - it should have an arrow on it indicating the direction of fuel flow.
You mentioned that you changed the fuel pressure regulator and injectors. Now you have a new fuel pump. Assuming that you have proper voltage at the fuel pump. And a new fuel filter -- look for pinched fuel lines. Sometimes the flexible fuel lines deteriorate from the inside causing a fuel delivery issue, but this is rare.
When you droped the fuel tank to change the fuel pump, did you notice any dirt inside of the fuel tank?

You can check the voltage at the fuel pump simply by unplugging the connector and testing for voltage. You should have at least battery voltage (or within 2%) at the fuel pump with the key on and engine off.
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Sunday, October 11th, 2009 AT 10:12 PM

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