Hi all,

My 1994 3.9L V6 is acting weird. It starts up fine and idles fine, but after driving for about 7 minutes it begins to misfire (at least that's what I think it is). It hesitates when the tach gets above 2000rpms. It will only do this after it has warmed up for a little while, usually after a few minutes of driving. It will continue to dothis for about3-5 minutes and then the problem will go away.It won't hesitate again until theengine cools off. It will not miss or hesitate if the truck is in neutral or park, only if the engine is under load.

I've replaced the spark plugs (Autolite 3923), wires (Belden), and distributor cap and rotor (Mopar). I've also run some Seafoamthrough the fuel system. Thefuel sending unit hasalso been replaced recently. The timing chain and tensioner have been replaced. None of these things havesolved the problem. The truck has a marine battery in it.

So, what doyou think the problem is? The truck had been sitting in a hay field for two years before I bought it, if that matters at all. Thanks in advance for any help.

Jordan

 

Sounds a lot like what mine was doing when I had a dirty injector

 

seafoam would've cleaned the injectors, I don't like the 3.9s.I had problems with mine. mine has 240k's on it and its puked, i replaced everything you could think of, even though mine is carborated. I replaced spark box rotor cap plugs, wires cat muffler rebuilt carb. Its justbeen a waste of money. but um, maybe still gum in the fuel system or lines, since it was sitting for so long.or water in the gas tank?, all i can think of ..

 

Its your distributor. I changed my timing chain just as you did and I had the same issue. It would drive normal and after warming up a little it wouldbackfire/misfire and just about quit. After going through all the same motions of new plugs, cap, rotor, etc, we figured the it was the distributor. All we could think was the new timing chain put enough stress on the cam by bringing it back to a tightertolerance that it messed with the distributor shaft alignments causing it to "skip". It sounds alittle out there but I bought a whole new distributor, installed it and the problem was cleared up. Hope this helps!

 

Thanks guys,
I'm going to the dealer for some other stuff tomorrow so I'll have them check it out. If it was a dirty injector wouldn't it be hesitating all the time?

lghtngblt02, I don't think it's the timing chain that caused the problem because it was doing the same thing before I replaced the chain. I'll take a look at it though. I don't know a whole lot about this kind of stuff, so can anyone tell me how hard it is to remove and replace the distributor? How much does a new distributor cost? Thanks again.

Jordan

 

I don't know if this has anything to do with my problem, but when I pulled the original plugs they were a deep golden brown color. What does this mean?

 

I changed the PCV valve and the crankcase breather filter. I also cleaned out the throttle body and the IAC solenoid. The distributor was also re-indexed. Still having the same problem. Any more ideas? I don't really want to pay the dealership any more, I haven't brought home a paycheck since I bought the truck. I think I'm single-handedly supporting the local dealership and the auto parts stores.

Some other people have mentioned that it might be bad O2 sensors or maybe a clogged catalytic converter or a bad coil. Could any of this be causing my problem? Thanks in advance.

 

i have an 89 thats doing the same thing... i checked the engine codes and it said that it was my O2 sensor and its stuck in rich "mode". If you put a new O2 sensor on it it should clear it right up..

 

Well, I replaced that cat (it was clogged but it didn't solve my problem) and the O2 sensor. Truck is still hesitating/bucking/backfiring when the temp gauge is between cold and normal operating temp. I'm going to try disconnecting the coolant temp sensor to see if my problem goes away.

 

I'm no dodge specialist, but know my way decently around most all cars. I pulled my buddies 88 into the shop tonight with the same problem everyone seems to be having. I dont know emissions like the back of my hand at all. But we are getting a hard bog, occasional backfire and intermittent highy idling I believe. The air pump on this particular truck is siezed, however, i dont think its a big deal. I haven't checked the cat, or thrown a meter on one sensor. But from looking at all the things you and others have tried, helping it bits at a time (just as any tune up would do). I'd say the little devil in our problem here is the EGR valve! If you understand how the emission and ignition systems work together it makes sense to me. The EGR being stuck open would toss the same amount of dead air into the intake at all rps, hence the bog on low end. The o2 sensor gets cold from being far too rich, signaling the pcm to crank up that timing up a pile of degrees. It does so, giving the intermittent high idle, and loss of torque. The loading up of the engine, and rich gasses in the exhaust cause the random backfires. Mine idles high for a while then then drops low (Often dying). This indicates what most, would think is a TPS, MAP, IAC, or vacuum leak.. But what I'm thinking is the PCM advances itself so much, while trying to counter with the IAC, that it maxes out on advanced and resets...? killing the engine from the sudden slap in the face retardation. I don't know about you gut but I'm cutting out a piece of tin, tossin down some black RTV and pluggin a couple vacuum lines after I get out of class tomorrow.... CSXfan a clogged Cat was a good try abd most likely the cause of your stuck EGR. I know on some vehicles there is a solenoid that controls it? Maybe one of the three on your pass valve cover? I haven't looked into what they control.... Anyways I'll let you guys know how it works out tomorrow! Oh and until the PCM gets out of closed loop it doesn't touch the timing I believe, giving you a false sense of hope everytime it runs decent for a little while cold.