I have been having this problem with my truck i think it is the tps, when I let off the gas sometimes it would die, i would have to hold the throtle down until the truck will hold its own idle. I can hear the fuel pump prime. but i do not think that is what is causing my current problem. It ran fine all day. i parked it for the night and in the morning it wouldn't start. I have replaced the battery and still nothing it turns over fine but it won't start. i pulled a plug wire off to see if i had a spark and I don't see any blue spark coming out of the boot when it is close to the block. i also tried testing for spark by putting a screwdriver into the boot and laying the screw driver on the block and still nothing, no spark. AM I DOING SOMETHING WRONG? AND IF I AM NOT WHAT COULD BY MY PROBLEM? PLEASE HELP!!!!!!

 

You said you can hear the fuel pump prime. Try swapping the Automatic Shutdown Relay and Fuel Pump Relay. (They are located behind the battery, in a black box). If, after you swap them, you don't hear the fuel pump prime, but you do get spark, the relay is bad.
However, I doubt that is the problem, because relays are typically pretty reliable.

Try testing for spark at the secondary ignition wire (the one going from the coil to the distributor cap). If there is spark coming off of that, but not off the ones going to the plugs, remove the distributor cap and inspect for any problems (carbon/dirt buildup, bad contact from the rotor, etc)

If still a no go, I would test for voltage at the connector for the ignition coil. You just need to unplug the electrical connector, hookup a multimeter (or voltmeter), and while cranking it (briefly) see if there is a 12V voltage reading. If there is a 12V reading, the coil is bad. If there is not 12V, there is a fault in the wiring somewhere. *Note* Be careful to not get anything caught in the belt.

As for letting off the gas and it sometimes dying, it may be the idle air control valve (IAC). This is mounted on the rear of the throttle body.

Let us know what you find. If you need more help, just ask.

 

Ok. I changed the cap and rotor and the plugs I HAVE SPARK!!! The truck still wont start. it cranks and after a few cranks it almost sounds like a backfire and then back to cranking and it just doesn't start. Now what could be the problem?

 

Sounds like when changing the cap you got a wire or two mixed up?

 

how are the wires? i have seen this on two dodge engines, one of them being mine... the contacts for the coil wire were not touching or something, pull the wire off the coil and squeeze the conacts together and put it back on a see if that fixes it!!!

 

1995 3.9L.

I Just replaced the wires on the truck like 3 months ago.
How would I know if the wires are hooked up wrong?

 

I agree withkahanabob. (I've done this twice... [&:], both times being "sure I've checked them and put them on right!," but check again, and sure enough, the wires were switched up a little.)
I posted a picture ina post that shows which point on the ditributor cap goes to which cylinder (and which cylinder is which).
However, the internetI amon is really slow today, so... just do a search and use my name (dodgerules86) for author, and something like "spark plug wires" or something like that for the search term.