Okay, bear with me this is my first post. I have a 2000 ram 1500 3.9 auto, 117070 miles, i've done a full tune-up when i bought it in january(autolite 3923's, plug wires, 180* thermostat, pcv valve, cleaned the IAC and the throttle body, cap & rotor, injector cleaner, Accel coil). Ever since i've owned the truck it has had a slight random hesitation right off of idle(in drive). About a month ago it started bucking back and forth at WOT in first gear around 3400 RPMs, plus the hesitation from a stand-still has gotten worse(it will hesitate, then around 2k RPMs, almost cut out completly like a bad multiple cyl misfire. Now recently(within a week) from a standstill, at random times and light throttle, it will backfire out of the intake around 1700- 2300 RPMs in first gear, sometimes second. If I hold WOT thru 1st gear, it will not backfire until i get to around 3500- to the shift point, out the intake, constantly (like a pop-pop-pop-pop). I've replaced the crank position sensor thinking it was a timing related problem (I checked spark on all the cylinders and it will slightly misfire on each cyl. I checked the spark on the coil, same thing) There are no codes present. I used a Snap-on Modis scan tool to set the fuel sync, and i have done the TPS mod, plug wire re-route. I've checked the belly pan gasket(looking down the intake and also checking for vacuum in the crankcase, theres no vacuum) Still no improvement. Im on nerves end with this problem.

 

I'm not to technical of a mechanic like it sounds you need, so pardon me if this is a dumb idea, but did you check the fuel pump/filter?

 

yeah, thats the next thing on my list of more things to check.(no, its not a dumb idea, iv'e tried so much with this prob, I will go for anything now lol) Doesnt the 2nd gen have the filter in the tank tho?

 

Yes. The filter and pump are in the tank.

 

the fuel filter and pressure regulator are the same thing and is mounted on top of your fuel pump module on the pressure line also a suggestion is your cat clogged up might wanna check your exhaust

 

I have been fighting the same problem for the past year or so in a 1992 3.9L with 113,000 miles. I replaced the exhaust system including the cat. That did not help. I was thinking fuel sync. I set mine statically with a resistance meter (no one in this area has the DBII equipment). After reading that it didn't help your vehicle I guess I need a fresh idea.

I may have forgotten a few things but the list of things I did include the autolite plugs, throttle position sensor, distributor drive shaft bushing, spark plug wires, rotor, cap, coolant temperature sensor, timing chain and sprockets.

A couple of days ago I removed the intake air temperature sensor and plugged the hole. The sensor is still plugged into the harness but is taped to a nearby wire so that it is reading the ambient temperature. I don't know if that is going to make any difference but it doesn't seem to have hurt.

If you solve your dilemna, please post the cure.

 

i checked the fuel pressure today, 49 psi... so it should to be an ignition or timing related problem? i checked the cat with a laser temp gun, it checked out fine but after i drive it a long distance, it smells like sulfur. could it still be the cat?... or maybe the 02 sensor? bc when i disconnect the ustream 02, it runs the same except it throws a code

 

yeah and no if it is misfiring that bad and is runing rich or lean that will cause the sulfur smell and will cause your cat to be warmer because its not firing right causing an inbalancing of air and fuel ratio . i'll sleep on this one

 

i think im gonna try the upstream O2 sensor, it prolly needs replacing anyways (117000mi). is it true that the dodge rams dont like bosch sensors? Can go with an NGK/NTK? does anybody know if a certain parts house carries them, or just order it from their site? thanks (yes i will post the cure if and when I find it)

 

i said that i had put on a new crank position sensor, and it didnt make any difference initialy. Well, its been about a week and i think the computer has learned the new sensor because the bacfiring stopped, so did the surging, hesitation and the high RPM popping. I drove it HARD today during lunch, didnt miss a beat- ran perfect. i guess it was that darn sensor(I'm still going to replace the o2 sensors, just bc theyre the original ones). BTW thanks for everybodys help, i really appreciate it, this is an awesome site.