1997 Dakota 2wd 3.9 liter 156,000 miles.
I bought this truck with the check engine light on and no power. Thought I had a clogged Cat, so I figured I'd buy the truck anyway and get a good deal.
Long story short, I replaced the 10 amp fuse that controls the dome light, radio and ECM memory. Truck became much more responsive, with one glitch. At 3000 rpm, the engine would produce a noticable amount more of power until it shifted to the next gear. Always a burst of power at 3000rpm under a load ( it shifts before 3000 rpm normally ). I should have left it at that, but the check engine light was bothering me. I had the codes checked, got one for the O2 sensor and one for the Idle Air Control Solonoid. Strange, it idles fine and runs fine. I'm getting 18mpg with the thing.
So, I pulled a vacuum test. Snapping the throttle showed a slow response back to normal vacuum, so I made the assumption that that rattling can under my truck they call a catalytic converter was failing. So, I did what any red blooded american with power tools handy would do.I cut it out.
Well, it made it louder, and the gas mileage got worse, but the check engine light didn't go off, nor did I get any difference in performance.
Okay, hey.I needed to replace that thing anyway, I'll do it after I figure out what is wrong with the beast. So, I go after the O2 sensor. Yes, as in SINGULAR. My truck, OBD2 that it is, only has ONE O2 sensor, and that is after the Catalytic converter, NO UPSTREAM O2 sensor. There is no indication in the harness that there should be one, nor is there an empty or welded shut bung on the Y pipe for one. I have One and only One O2 sensor, which is located a few inches away from where the Catalytic converter used to rattle around annoyingly.
Okay, well. Replacing that with a new NGK sensor didn't do me any good either. AFter some reading and asking around, I find out that I Really need to have the PCM reset. So, I set the wife off to Autozone while I'm at work to have them check the codes, and reset the computer. Same codes before, but now the truck runs horribly. It won't start for her ( I was starting to have starting issues once the temperatures started to fall, or more like it wouldn't stay idling once the temps dropped to around freezing. This was intermittent and a new problem that I expected to diagnose later )
So, I get the truck on the road. I start it up, get it to idle and pull away. Driving at 5mph, I'm doing good, thinking nothing out of the ordinary from what it had been doing. Nope, not any more. Now when I get the truck rolling to about 30mph, it shuts down like the injectors are suddenly turned off and I'm getting some backfiring through the throttlebody. I mash the gas pedal and manage to get power back and drive it to work, but now I have to fight the truck to get it up to speed. Once I've obtained the speed I want, I can maintain it, but it almost feels like there is a bound up brake or something as it seems to be dragging along against its will.
Upon further reading, my next conclusion was that I'm having a MAF sensor malfunction, but I've already thrown in a $60 idle air control solonoid and a new O2 sensor. This is going to get expensive if I keep throwing parts at it. I don't know what else to check or consider. Literally, resetting the computer made my truck run worse than before.
Oh, and on the way to work. That check engine light went out. I thought the bulb burnt out since it's been on for 4 months straight. Nope, I double checked that when I got to work by shutting the truck off and then turning the key back on for the bulb test.
This has got me scratching my head pretty hard, and I've got little hair left to pull out.
Sunday, February 11th, 2007 AT 9:44 PM