98 Jimmy, quit while driving, won't start

[pitbullvassar]

Ok, here is my problem. While driving down the highway yesterday about 70 mph, my jimmy quit running. I towed it back to my work and all it does is crank over. If you put fuel into the carburater it runs till that is gone. I changed the fuel filter. the fuel pressure is only about 13psi. We hooked a OBD thing on and got codes 0122 and 1351. 0122 is throttle position sensor/switch low input and 1351 is IDM malfunction. we also replaced ignition modulator. I am trying to not replace the fuel pump but i think it might be inevitable. I only have 81,000 on it and up to this it has been very dependable. Could it be the throttle position sensor. I already have about 200 dollars sunk in and am now trying to figure the right fix for the proble. any advice is appreciated
Thank you

[DelCoch]

Sounds like your fuel pump is toast, as 13 psi on fuel pressure is a no-start/no-run.

Try the following to check out the fuel pump.

1) Check that you have at least 1/4 tank of gas.

2 ) Check the fuel pump maximum pressure at the schrader valve with a fuel pressure gauge. Be aware the fuel pump only runs for 2 seconds when you turn the key on (engine off). Then the key has to be off for 10 sec before the pump will run again. (Fuel pressure gauge is about 35 bucks if you need to buy one)

With a properly working pump, the fuel pump reaches its max pressure during that 2-seconds, which should be something over 61 psi. When the pump shuts off the fuel pressure will immediately fall 5 or 8 psi. (This is normal) It should not fall below 50 PSI.

To see the max pressure put the gauge where you can see it when you turn the key on (engine off) or else get someone else to turn the key or watch the gauge. You need at least 61 PSI to start the engine.

If maximum fuel pressure is low: Check the battery with a load type tester. AutoZone will do it for you. A weak battery will cause a no start, as the fuel pump needs max voltage to get the fuel pressure up to and above 61 psi, which is needed for the engine to start.

However, before giving the fuel pump its last rights try this:

Under the hood, on the driver's side fender towards the firewall, there should be a red fuel pump test wire, it should be hanging down by the electrical junction box. It won't be connected to anything, just hanging there with a gray or black plastic insulator on the end of it.

After you find the test wire, apply a 12v supply to the red fuel pump test wire and leave it there while checking the fuel pressure again. (By applying 12v to the fuel pump test wire you bypass all other electrical components in the fuel pump circuit)

If you still don't have 61+ psi, disconnect the fuel pump wire connector at the gas tank, apply a 12v supply to the red fuel pump test wire and leave it there while checking for current on the 12v feed wire in the wire connector at the gas tank. (On my 95 the 12v feed wire going to the tank is gray) Test the current with a voltmeter, while using the ground wire in the connector for a ground. It should read between 12 & 13v or something more than 12v.

If you don’t have at least 12v on the Gray wire try using a different ground. If you have 12v, then make sure the wire connector at the gas tank is making a good connection to the fuel pump wire connector.

If you have 12v+ and the pump still doesn't put out 61+ PSI, the pump is toast and needs replaced. (Make sure the battery has 12V+ when doing this test)

If you need to replace the pump, get a Bosch, Delco or Delphi – in that order. The rest are junk. Here’s a link for a good price on a Delphi fuel pump, but also check out the on-line prices at AutoZone and O’Reilly’s.

http://store.getgmparts.com/index.html

Good luck and let us know what you find, as it will help others.

[Scrapper]

i don't think it will ever run until you change fuel pump sorry...psi way to low...


GOOD LUCK....

[pitbullvassar]

Replaced the fuel pump, go the 60 psi, so problem solved for now, thank you for the quick help very much. I never even tried to test the wire like you suggested. I just figured you knew what you were talking about and you did. Thanks again.

[twistedtech]

One more piece of advice is never trust the fuel gauge on that truck,they are known for not working to well.The perfect world would have been to change the sending unit while you was at it.