Mechanics

'S FREAK OF NATURE?

Dodge Dakota

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.
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Redfury
February 11, 2007.



With the check engine being on so long, multiple problems are possible. Odd that it went out.

The cat has been replaced then? If not, I would get that in and recheck for codes. The Os is depending on the cat to tell the computer how to make adjustments.

The cat has not been replaced yet, it's currently in the state of being just a straight pipe at the moment.

I drove the truck home this morning ( 5am ) and it started right up and idled. Drove down the road a bit and as soon as it hit second gear, or was about to, it started slugging again. The rest of the way home, no problems.

The check engine light was on for a long time, but I had it checked when I first got the truck and had those 2 codes come up ( O2 and IAC ) originally, and after I had replaced the O2 sensor. When they cleared the codes the last time, the light came right back on and they pulled the codes for me, which were the same as they've always been. But, the truck started acting up like it is now, and then suddenly the Check engine light goes off ( after replacing the IAC ). It's just weird to me that the light would be on all this time, and run like garbage, then the light mysteriously goes off, and it still runs like garbage.

Tiny
Redfury
Feb 12, 2007.
Well, since I couldn't get the truck to a shop, I decided to do some investigating for myself. Since I only have a digital multimeter, I don't trust exactly what it said in regards to testing the map sensor voltages as I ran the throttle, but here goes anyway.

4.5 volts key on, 1.38 volts at idle. Then I would get fluctuating voltage if I held it at a position off idle, but that could be partially due to me trying to run the throttle and trying to hold the lead on the probe I had in the MAP sensor. I read that idle the voltage should read between 1.5 v and 2.0 v which makes me wonder about the sensor.

The check engine light came back on while I was warming the truck up ( hadn't touched anything ) and I got under the truck to notice that I had not reconnected the O2 sensor. So, that means the light went out with the O2 sensor disconnected. I still can't seem to find evidence of a second O2 sensor on the truck either. I can only assume that the upstream sensor would be on the Y pipe near or at where the Y meets at the collector. No dice.

If I get lucky and get done with work early enough tomorrow, I think I'm going to run over to the Dodge dealer by my shop and see what they have to say.

Tiny
Redfury
Feb 12, 2007.
Okay, upon getting ahold of a good picture schematic, and looking under the truck with a flashlight tonight.I did indeed find the Upstream O2 sensor. I can't believe I missed the darn thing all this time. I guess I wasn't expecting the Wiring to be coming off from the Transmission area and for it to be on top of the pipe. Wow, do I have egg on my face.

Tiny
Redfury
Feb 13, 2007.
Egg? You had more foritude to find it than most people would ever attempt.
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Well, I appreciate that comment. But, I was pretty adamant that my truck didn't have the upstream sensor with other people.

I guess in the end, if the truck ends up running better and I don't throw a truck load of money at it trying to fix it because I'm the one being stubborn. It's all good in the end.

I tried to learn this after spending 5 months tracking down a problem with the wifes Grand Am. After essentially taking the engine down to the short block and putting it back together swearing up and down that I had discovered the problems with it.I find in the end that the camshaft had frozen a bearing and broke in 2 pieces. I figure I had about 40 shop hours into the thing before I figured it out and ended up replacing the motor. Could have saved myself a lot of trouble if I had just been a little more thorough with my diagnosis ( and had listened to the voice in my head telling me that the part about the oil light coming on had something to do with the problem )

The cam had broken halfway back, which rendered the oil pump inoperative, but the front 2.5 cylinders ran, which made the car sound like it was out of tune. It was a nightmare, especially since I have to do all my automotive work under the stars.

Tiny
Redfury
Feb 14, 2007.
I'll be if you hang around this forum a little bit, you could probably help out some folks here.

Tiny
Cleavage4U
Feb 15, 2007.

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