The truck started acting up while driving. It would shut off (no miss or anything), but would start again. Now it is sitting in the driveway and wont run
more than 3 seconds. The fuel pump has been changed and did not help. The fuel pump relay is new and did not help. I read that the fuel pump goes to another circuit after start up. Could it be running to start and then shutting off?
Inertia switch is not tripped.

Any suggestions appreciated. Dont know where to look next.

 

Theres seperate start & run circuits in the ignition switch. When you turn the key one click do the gauges & idiot lights including the check engine light come on?

 

yes the lights come on but the check engine light does not come on every time.

it starts as thou you could drive it but shortly shuts off like it ran out of gas?
We can hear the fuel pump when key is turned on.

 

Turn the key one click & the CEL should come on for 2 seconds & the fuel pump should run for 2 seconds.

Since thats not happening i would swap the PCM power relay with an AC or horn relay etc..
If you're lucky it's just a flaky relay.

The PCM power relay powers the PCM, fuel pump, injectors, sensors etc. etc..

 

I replaced what I thought was the fuel pump relay but am not sure now. there were 2 relays hanging by the powerdistbox. one of them rattled so the parts guy said that would be it. I am suspecting we may have replaced the wrong relay. how would we know which one is pcm and which one is fuel relay. Also have no idea where horn relay is?

 

turned key on and cel came on but not fuel pump. tomorrow I will get another relay and replace the one I had not replaced before and see if that helps. thanks, will repost result

 

Have someone turn the key one click until the check engine light comes on.
When it does come on you will be able to hear and feel the PCM & fuel pump relays close at the same time. 2 seconds later you will hear & feel the fuel pump relay click again.

 

Good idea to put the ECM & fuel pump power relays on the suspect list, as they're a common problem part.
Be mindful that when we turn the ignition key to KOEO before cranking the engine, the ECM/computer power relay has to work Before the fuel pump will get its power to activate the fuel pump. So, as has been said, look for the CEL to light up at KOEO & that'll indicate that the computer/ECM power relay is working. If no CEL at KOEO, the CEL is either burned out, or if its been lighting up so you know it isn't burned out, suspect the ECM/computer power relay has a problem.

 

We replaced the other (PCM} relay with one from Napa that says it is a universal and it started. However I could only keep it running by pumping the gas. I think we may have made a vacuum leak in all our investigation. In any case ,we are getting closer. Thanks for all the info. Will repost when completely solved.

 

Repaired the intake air tube between the filter and the throttle. Had a small worn area and caused a leak when we had moved it. Changed the mass air flow readings. After the repair it runs great. The relay was our original problem. Thanks to all for the information. Hope this may help someone else.

 

Ok, good trouble shooting find, fix, feedback & to hear all now seems well & your on the road again.