3.9 hesitation, random backfire
#1
3.9 hesitation, random backfire
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.
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Have you resolved your problem yet?
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 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.
#7
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
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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)
Last edited by aidankyle; 10-09-2008 at 06:14 PM.
#10
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.