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4.0 engine stall will run for 5 seconds then cuts out


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I am trying to fix my brothers 90 Comanche 4.0 2wd manual truck it will start for 5 seconds and cuts out. Not sure where to start , seams like it has fuel. It will crank right back up and run for 5 seconds. Its been20 years since I owned my 89 AMC 2.5L and I don't to just throw parts at it. Where should I begin?

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Corroded connections on the ballast resistor, a faulty ballast resistor, or a faulty fuel pump ground.  Possibly a failing fuel pump, but less likely.  When cranking, the ballast resistor is bypassed and the fuel pump gets a higher voltage.  If there is an issue and the pump is operating below its normal levels, this is enough to raise the fuel rail to an acceptable pressure before dropping shortly afterwards and stalling the engine.

The ballast resistor is on your driver's side fender:

20210511_192822-min.jpg.07f586f1ef7b3498ef357e4cbc711b36.jpg

(The white thing with two orange wires)

Clean up the connectors with a wire brush and check resistance across the two pins.  Should be about 1.2Ω.  Refresh the fuel pump ground.  Details can be found here:

http://cruiser54.com/?p=19
tshould work fine afterwards.

 

Refresh the other grounds on that same page for a general performance boost.  Tips 1 - 5 are all recommended for new owners, as well.

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49 minutes ago, Lil jonesy said:

Thanks everyone it was the ballast resistor I jumped it with a blade fuse to get it home and replaced it. 

 

 

if you ever want to install an anti-theft switch, this wire is awesome.  the thief will likely think the truck is just an old pile of crap because it starts and stalls, rather than a purely dead jeep that might indicate a kill-switch he might then look for.  :L: 

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15 minutes ago, Pete M said:

 

 

if you ever want to install an anti-theft switch, this wire is awesome.  the thief will likely think the truck is just an old pile of crap because it starts and stalls, rather than a purely dead jeep that might indicate a kill-switch he might then look for.  :L: 

Ha!  That's a really smart idea, Pete.  I think I might throw that on my truck!

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the quick-n-dirty is to just unplug the resistor, but that's more for long-term parking rather than a trip to the store.

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