A little frustrated with this. I have no codes. 98 Dakota heats up, I believe it's going into closed loop and it just stops. After this happens, the truck runs fine the rest of the day. I used autotap software and monitored functionality of the sensors. The only thing I noticed was on a graph the downstream O2 sensor is flat lined in the high position. I unplugged for now, waiting for a new one. I will be testing over the next couple of mornings to see what happens. Oh yeah, when it stalls, it won't start immeadiately, have to wait a few seconds and try again, then it starts and it may stall again and stat right up. After this happens, it runs good all day long? Any input would be appreciated just in case the O2 is not causing the problem. Thanks!

 

I'll move this to the regular forum.

No codes with a disconnected O2 sensor? Seems odd. The downstream sensor should give you a catalyst efficiency code.

What engine/transmission?

Does it just die, like the ignition was switched off, or sputter like it's running out of fuel? Coils can fail hot/cold. It probably wouldn't immediately start up though.

 

Thanks, I realized I posted in the wrong place too late. Thought is was strange also with a flatlined O2 sensor that I didn't get a code. I just unplugged the sensor so I don't know yet what's gonna happen, just trying different things at this point. Yes, it just dies like somebody switched off the ignition yet as the truck rolls sometimes it starts running again. Auto trans 3.9L magnum. It has over 200K but is kept up. Rotor, dist cap wires and a new IAC because of age just added. Bench tested the O2 and although I get readings of 3.6 Ohms on the heater the voltage is a little erratic so, I'm going to replace that cause it's in question especially on a running graph it's flatlined near the .9 volts and drops like a rock when the engine stalls. I changed out Ignition coil as well cause I did catch a code for it once.

 

Intermittent problems are tough, especially without a code.

Cam position sensor, the pickup in the distributor - maybe?

 

Thanks! Got a code with the downstream sensor unplugged. I guess the PCM is okay. I found a paragraph that makes sense to me doing searches. It states that; "Engine starts okay. O2 is open loop running on mapped data in the controller. Engine warms and switches to closed loop (tis when my problem arises) O2 sensor hasn't started putting out valid voltage levels yet so, engine stalls. After a few more minutes O2 sensor is hot enough and is able to supply valid closed loop info to the controller. called a lazy sensor."

This sounds exactly like what I'm experiencing. I have one ordered and gonna order another for upstream. At least I will have them out of the equation.

 

The upstream 02's do the fuel trim. The downstream is just a catalyst monitor.

Whatever you do, do NOT use a Bosch O2 sensor. Dakota's hate them with a passion.

 

Ya know I think that's what I have in there, there not that old. I thought Bosch would be the better of what was offered....learn something new everyday. When I replaced the cat a few years ago I replaced the O2 as well and had one fail, had to replace it again. All has been well for approx. 5oK now but you might have a point about the Dakota's hate issue. Thanks for the post!

 

Wanted to give an update with this stalling problem. Over 200K on the odometer so I decided to replace a few sensors....O2's, stator, IAC, Ign coil. Well, none of these were the issue however, time to be replaced in fear of them going bad. Again the truck stalled almost at a specific time as it went into closed loop and the truck is good all day long after this so I have only a small window even though it's almost a sure thing every morning. Wait about 30 to 45 seconds and it would fire right up...

With the truck running I started checking all wiring harnesses and sure enough as I started to put a little movement on the plugs in the PCM, it stalled. Did this three times and it stalled three times. Unplugged and all looks well under a glass, no corrosion, clean connections, just not making good contact I guess. Anyway for now, unplugged several times and plugged back in again and I can't get it to stall so I figured I'll run a wire tie around the plugs and PCM just to hold them in a little tighter. Gonna test over the next several days and see what happens. I'm ready to take the PCM apart if I still have any trouble cause this is my suspect area....maybe bad solder connections inside??? Anyone ever take one apart? I know it works, it's just a connection problem. Thanks!

 

It could be a poor connection at the PCM. Good find.

Keep us posted and good luck.

 

I could get my 98 dakota with the 3.9 to stall too if i wiggled the pcm connectors or closed the hood or door hard. i just wire tied them tight and it was fine.
My downstream o2 was shot, the end was all messed up and im surprised i didnt get a code(wish i had a picture from when i pulled it out). Now i put the Bosch o2 sensors in my dakota and never had a problem with them, but if i would have known before hand i wouldnt have went with them.