I have an 89 Dodge Dakota with a 3.9L engine. About two weeks ago it started running rough in cold weather. Today was about 60 degrees and it is running rough, I would say this is about the cutoff point in relation to the temperature. It runs rough from idle all the way through 60mph, if I keep on the gas it seems OK until I let off the throttle. It acts up on me in the morning going to work but when I get off in the afternoon and the temperature is much warmer it runs fine all the way home. I think it is a sensor problem, but not totally sure. I don't want to start replacing many parts trying to find the problem. I have checked the computer codes and there is nothing there. Any ideas?
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Well first a tune up is best, all ignition parts, fluids, filters ect. Next do you have a Check Engine light? If so get the codes and see what they say. I will move this to the 1st Generation Dakota section.
Still have no computer codes. I did a tuneup in spring of this year. Checked with a shop that I take my truck to and they told me they have a truck in the shop exhibiting the same symptoms as mine. They talked to a Dodge guru and he told them to change the ignition pickup in the distributor, supposed to be a known problem. I replaced the part, no help. They also told me that the truck they are working on also has no codes even with an external scanner attached. I have also replaced the coolant temp sensor. I checked the voltage from the tps and it looked good. When I did the tuneup with new plugs and wires, I used a spark plug lubricant. When I took the wires off I noticed that there is a crustiness on the plugs. I used a throttle body cleaner to clean the plugs and wires. Not sure if this would cause this problem. This truck runs great in warm weather. After cleaning the throttle body with the cleaner it idled good for about two minutes and then started running rough and would die. I am looking in my manual and do not see anything labeled as an ACS. Any help is appreciated.
Yesterday was in the low 60's and the truck ran like crap. Today the weather was in the middle to upper 70's, the truck ran great. I bought a can of component cooler from radio shack to see if I lowered the temperature of the sensors if I could duplicate the problem. I sprayed the EGR & transducer, TPS, MAP, Idle speed control actuator, fuel pressure regulator, while the truck was running, also checked the spray pattern from the fuel injectors and they looked good. Did not spray the os2, smec, and the plug wires, ran out of coolant. I will start the truck tomorrow morning at 4:45AM and I'm sure the problem will be back. I am going to pull the plugs tomorrow and check the way they look. I have to use the wife's car and I am hearing some flak over this. I would appreciate any help.
If your talking about the computer module, no I did not. They call the computer module on this truck the smec. I think this is a sensor problem but I am not ruling out the computer being sensitive to cool temperatures. The temperatures we are talking about I think, this is unlikely. We are talking difference between 60 something to 70. If it was 30 degrees or 110 degrees, maybe. If you have any good ideas I am all ears.
The temperature outside this morning was a balmy 59 degrees. The truck ran rough and all the symptoms are back. Drove the truck around town yesterday, the temp was around 75 and the truck ran great. I will get a vaccuum tester but wondering why a vaccuum leak would only cause it to run bad in cooler weather. I have already replaced the temp coolant sensor, no help.
From what i have read in the FSM, the coolant temp sensor is a primary signal for both fuel ratio and spark timing. Since you have already changed this with no good result, next thing is map sensor which monitors intake vacuum to provide basic air/fuel ratio control. But a vacuum leak could affect manifold vacuum resulting in overrich mixture and flooding the engine. is your exhaust outlet pipe really black?
before you swap Map sensor, you may want to verify what vacuum signal the sensor is getting.
it could be that when the engine sits overnite, a leak may be due to manifold fully contracted when engine is cold, and as the engine warms, the leak is pinched off to the point that the rest of the engine controls can compensate and engine runs acceptably. A leak could be from hoses or manifold or gaskets.
Just a theory at this point, but a vacuum gauge is probly cheaper than buying the full set of sensors and swapping these out one at a time.
just my 0.02
I should have clarified the fact that even after the engine warms up in cold weather it still runs rough with all the symptoms explained earlier. It either runs good in warmer weather and runs terrible in cooler weather regardles of the engine temp. I will get a vaccuum tester and see what I get there. Thanks
The one I replaced is for the computer. I pulled all six spark plugs this afternoon and four out of six were black and wet. It appears that the wetness on the plugs was gas. I checked the vaccuum for the map sensor and it was good. I bought some component cooler yesterday and used all troubleshooting the sensors with no luck. I did some research on the map sensor and it has a small electronic pcb that detects the barometric pressure/weather. I am having a weather problem. I sprayed some of the air left in the component cooler can into the vaccuum port of the map sensor. The air was not cold but cool. I sprayed my hand first, the coldness was used troubleshooting yesterday. I started the truck and had the same backfire through the throttle body that I had when driving in cold weather. I have ordered a map sensor and will pick it up tomorrow. Not sure if my troubleshooting technique was right for this but I will know more tomorrow.
I picked up a new map sensor at the auto part store this afternoon. The box looked like crap and the sensor looked used. Installed sensor and immediately started having problems. The temperature was 82 degrees and this sensor acted just like the original sensor did when the weather was in the 60's. Checked the computer codes and found that the new sensor created a code of 13 in the computer. This sensor is definitely bad. Took sensor back, they had to get one from another store. The quality of the new sensor was evident as soon as I laid my eyes and hands on it. Installed the new map sensor and the idle seemed be where it should be. I have had a problem with this truck having a high idle for as long as I could remember. It is 8:00pm, I just took the truck out and the temperature is around 65. The truck ran great. I will take the truck out about 5:00 tomorrow morning for another test. I think my problem is cured. I will know more tomorrow morning. I will post again tomorrow to verify that the problem is fixed. Thanks for all the help. I think it is great to have a forum like this to exchange ideas.
Last edited by olddakota89; 10-08-2010 at 09:41 PM..
The temperature outside is currently 49. My problem is back. A lot of backfiring through the throttle body and running like crap. No computer codes. I am at a loss. I think it still has to be a sensor that is sensitive to cold weather. This is starting to drive me crazy. Why only cold weather and not all the time? Thanks
Last edited by olddakota89; 10-09-2010 at 08:06 AM..