I have a 97 dakota with the 3.9 i purchased it with it running rough i replaced injectors,tps,plugs,wires,cap,rotor, timing chain, intake gasket,crank and cam position sensors. After all that it was running pretty good thought maybe i just needed to start driving it to clean it out after running so bad for so long. well drove it a few miles and it started to shift erratically then wouldn't even hardly stay running. no you can start it and it idle very poor popping and backfiring if you try to touch the throttle at all. i seriously thought i had it fixed but now its like i didn't do anything. any thoughts would be great. thanks

 

02 sensors, and maybe your cat is clogged (most likely).. lol what else is left

 

has a newer cat, exhaust seems to be flowing freely, checked readings with scan tool and o2 sensors checked ok. not getting any codes either, i was thinking maybe pcm cause this time the scan tool had troubles connecting to the vehicle

 

the O2 sensors can be bad without throwing codes, and work less effectively as they get older so replacing them would not be a bad idea either way

 

dont throw money at the problem. take it one step at a time, you said the scanner had a hard time connecting, try resetting your PCM first, see if that does anything. your supposed to reset after you modify anything anyway, or in your case, replace. you said you changed the intake gasket, i'm assuming you meant intake manifold gasket, in either case, did you change the pleneum gasket on the intakes belly pan? those are prone to failure on our engines. look down your throttle body and look for it to be dirty and full of oil, thats a sign that the gasket went out. also, try running a can of seafom through the engine, some will say that its a snake oil but i love it. just use a maine vacuum line like the brake booster line to suck it up with. do about 1/3 can in your intake like that, then 1/3 can in your (full) gas tank. let us know where you get with that.

 

when you reset the pcm do you just unhook the negative from the battery for a few minutes then hook it back up?

 

Mine (5.2 though) did the same thing and it was a clogged cat.

 

i swapped out computers the next day and it ran fine. parked it come back later fired it up went to take off same thing popping cracking and wouldn't go shut it off fired it up and it took off drove awhile parked it shut it off. firde it back up and same crap barely able to run.

 

still getting no where runs good then next itme like i pulled 5 plug wires off. any other ideas. i tried the seafoam made really no difference. would o2 sensors make that drastic of a change that quick.

 

Same here, I was checking wiring harness and I found a bad connection on the cam position sensor, fixed and it worked for a while. I had a misfire on 1 3 and 5 now when I drive slow it feels like it shuts off and restarts every 10 to 15 seconds. No codes showing I'm looking at completely removing wiring harness and checking for shorts or breaks but will have to put off until tomorrow because there is a severe thunderstorm warning for today and I have to work on it in driveway.