1999 cuts out after 3 seconds

[Dre]

What went wrong? Truck starts but then engine cuts out after 3 seconds. PATS is the culprit, I know but I do have replacement modules, programmed and ready to go in and after replacing all of them it still does the same thing.

anyone?

 

[Macgiobuin]

It sounds like your fuel pump is priming (when you turn on the key it charges the fuel system by running for a few seconds.) Then when the PCU senses that the engine has started, it feeds constant current to the pump to keep the engine running. This part of the system is not working. Jump 12 volts to the fuel pump or the fuel pump relay. If the PATS system were the problem, the starter wouldn't even engage. If your theft light goes out after a few seconds, (not even blinking), then PATS is not the problem.

 

[koda2000]

It sounds like your fuel pump is priming (when you turn on the key it charges the fuel system by running for a few seconds.) Then when the PCU senses that the engine has started, it feeds constant current to the pump to keep the engine running. This part of the system is not working. Jump 12 volts to the fuel pump or the fuel pump relay. If the PATS system were the problem, the starter wouldn't even engage. If your theft light goes out after a few seconds, (not even blinking), then PATS is not the problem.

PATS does not prevent the starter from turning. It only turns off the fuel injectors.

 

[Dre]

I'll check the pump. That would be ECM issue then - I can't explain it any other way.

 

[Dre]

Update - checked the fuel pump - fuel pump has constant current - checked injectors - after three second injectors go dead - ECM stops sending signals to injectors - and that's usually done by PATS - what gives?

 

[koda2000]

Dumb question, but what year is this truck? If it's the '94 in you photo, '94 didn't have PATS. First year for PATS was '98.

Never mind, I see it's a '99.

 

[Dre]

KODA - it's a 99 - all possible modules have been replaced, checked and checked again - I do have spares back from the long trips I've been taking a while back. All seems normal, there is something critical though that happens withing the first three or so second after it starts that causes the PCM to shot down - not sure yet what it is - check crank position sensor, it's good. I get no codes at all. fuel pressure is good, pump has current... PCM shots down injectors though and that's what's causing engine to stall.

 

[koda2000]

KODA - it's a 99 - all possible modules have been replaced, checked and checked again - I do have spares back from the long trips I've been taking a while back. All seems normal, there is something critical though that happens withing the first three or so second after it starts that causes the PCM to shot down - not sure yet what it is - check crank position sensor, it's good. I get no codes at all. fuel pressure is good, pump has current... PCM shots down injectors though and that's what's causing engine to stall.

Crank position sensor is for spark only. Cam position sensor is for injector timing, but it should run, although very poorly, with a bad cam position sensor. I'm leaning toward something with PATS or the ECU, but I don't know how to test and if something special happens in the first 3 seconds I've never heard anyone talk about it. Is there anything unusual about the ignition key your using? Do you have another key you can try? Hows the anti-theft light and behaving? Normally?

 

[Macgiobuin]

All your injectors are fed +12v from the same source, through a relay. The PCM grounds the circuits one at a time to let each injector open. So, if your injectors are not activating, it is because: 1. you lose your +12v to the injectors, probably through the fuel injector relay, where the relay is bad or the bus it feeds from has corrosion on it that causes the current to be stolen away to other more amp drawing loads; or 2. when your PCM grounds the injector circuits, the other loads that ground-activate through the PCM are drawing too much amperage at a bad ground, shutting down the injectors. I would check the grounds of the PCM and the ground connections to the frame where the PCM board is attached, but I think the +12v fuel injector relay circuit is the more likely culprit. Look for burned out terminals where the fuel injector relay plugs into the harness.

 

[Dre]

Case solved but - before we found out what the problem was we have moved pretty much everything electronic into another Explorer and it all worked - ECM, PATS, etc... checked crank position sensor, inertia switch, fuel pump, relays, connectors - nearly all electronic components and in the end, just before giving up and before swapping another complete engine in we removed and replaced MAF - and voila! It started and ran fine - this time for more then just 3 seconds. Have no idea why bad MAF would cause engine to stall right away after starting but somehow it did manage to send some crazy signal to the ECM. Just because of the PATS system we thought of the worse possible scenario but it might sometimes be something as simple as this was.

Thanks for all your ideas - brain storms like this are good you know - some other guys could learn from this.

 

[SupaSwope]

Glad to see you got it figured out.

 

[Runnin'OnEmpty]

Thanks for posting the fix. What bothers me is that there were no codes triggered. MAF issues are supposed to store a code.

So much for OBD II...

 

[Dre]

Beats me. You'd think that MAF should trigger something, I mean anything to give me an idea where to start when something like this happens - oh well. "All's well that ends well".

 

[koda2000]

Case solved but - before we found out what the problem was we have moved pretty much everything electronic into another Explorer and it all worked - ECM, PATS, etc... checked crank position sensor, inertia switch, fuel pump, relays, connectors - nearly all electronic components and in the end, just before giving up and before swapping another complete engine in we removed and replaced MAF - and voila! It started and ran fine - this time for more then just 3 seconds. Have no idea why bad MAF would cause engine to stall right away after starting but somehow it did manage to send some crazy signal to the ECM. Just because of the PATS system we thought of the worse possible scenario but it might sometimes be something as simple as this was.

Thanks for all your ideas - brain storms like this are good you know - some other guys could learn from this.

Humph, I wouldn't think the MAF could cause the fuel injectors to turn off, but glad you finally got it figured out.