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Discussion Starter · #1 ·
I have seen plenty of threads on this same issue. And never a definite answer. It appears to be a rather common issue in Chrysler including mini vans and dakotas. This is my never ending or answered issue. I have a 95 Vision (intrepid/concorde) a year or more ago it would run rough and backfire on acceleration for the first few minutes of driving until the CEL came on and then it would run like a dream. Did the 3 key twist for codes, yet nothing. Then one day the CEL did not come on and it continued to run rough and backfire. Checked codes and there was plenty. MAP, TPS, too cold etc etc, and one that doesnt seem to be on any research I have found for these visions #12. So now I change the TPS, rough idle backfire goes away for a few days. Then returns. I do the MAP and air flow sensor, NG MAP sensor code still there. Pull the connector and open it to find 2 loose female connectors. Tightened them and refit. Still NG. Did plugs (champion) and wires (kem). Still NG. Took it to a shop and they replaced the TPS connector and all seemed fine again. For a few days and then I am back to the rough idle and backfire. I thought maybe there was a break inside the harness as all those sensors are fed from the same line. Unplugged ECM and checked continuity of the wires and all checked. Recently did find a crack in some quarter inch vacuum line that ran from the drivers fender to the plenum. Patched that and still no change. I even ran Lucas in the fuel and marvel through the oil in the hopes I had a hanging valve from carbon or grud. Still no change. And all of this with only one code still appearing #12. I know others have had this issue. Can anyone give me a path to look towards with an explanation. This has been a long going thing, I'd like to get over. Thanks
 

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Crank position sensor should be looked at, it controls spark and timing. Code 12 usually means nothing.
 

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Discussion Starter · #3 ·
Thanks. I did not think about the CPS. I believe that also runs on the same wire line to the ECM as well. I will first check the connector. maybe a bullet got loose. If they are tight I'll try changing the sensor. There is no #12 on any list that I have seen. Although I always get one long two short, then 55
 

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Intake leak or a secondary ignition cross firing or shorting to ground.

Is it backfiring out the tail pipe or the throttle body?
 

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Code 12 actually means loss of power to the computer, such as the battery was disconnected.
However, code 12 is often set any time another code it set. Sometimes it is always there for no reason.
Unless there seem to be legitimate electrical issues, I just look at code 12 as the start of codes.
 
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The code 12 may or may not be related to the backfiring or running rough issue. It might even be a 'pre-amble' to any other fault codes if you use the 'ck eng' light method of reading codes.
http://www.allpar.com/fix/codes/faults/code12.html
How do the spark plug tips look? Are they black (rich) or white/tan (lean/normal)?
Fouled spark plugs will misfire, may pop-back and might indicate a rich mixture.
It may need more of a diagnostic tool than simply reading fault codes from the 'ck eng' light. A scan tool will give you more of an in-depth diagnosis by reading the freeze-frame (what the engine was doing at the time of the fault code setting) and sensor values (can they be real?).
It could be spark timing, fuel mixture or mechanical (valves?) causing pop-back in the throttle body.
Does this happen warm or cold? Any other symptoms?
 

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Discussion Starter · #9 ·
cold and warm. More increase as the engine heats. When all those codes first came up I had a feeling it may have been a fault in the harness some where. Especially after I read a schematic show all those sensors running off the same line to pin 28 If I remember correctly to the ECM. But all tested good unless while moving them around I completed a faulty connection at that moment. I did not remove the harness and inspect the wires by eye. The old plugs looked fine when I took them out and they were in there a while. A bit black as expected. No white. If 12 is a lack of power to the ECM then maybe the harness is the problem. I am going to check the female connections on the Crank Position Sensor. Maybe as the engine heats they expand enough to leeson contact as I found with the MAP senor connector. All I needed to do was touch that connector and the engine stalled. After tightening them, no more issues with the MAP. I have an Innova reader that claimed to be for obd1 as well. But their OBD1 adapters do not fit the blue plug under my vision's dash.
 

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Discussion Starter · #10 ·
I just read the code 12 link. And now I may be leaning towards a power issue. Years back I drove a commercial truck who's alternator went bad while on the road. It was a gas engine and was told to continue driving and try to make it back. As the engine continued to fire off of the battery only, that engine seems oddly enough to be how my vision's engine is running. I checked the battery at 12.9V standing. And it was getting a charge of 15.2V the first few minutes leveling to 14.7 continuous. Maybe the fusible link is suspect? What a pain in the butt.
 

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When the alternator died in my 92 Grand Voyager with the 3.3 liter I had to shut off the headlamps when I got close to my house and I think the voltage was around 10 volts. The engine ran smooth without any backfiring and had plenty of power.

You have something else going on there. How old are the ignition wires? Check the date code on the wires for when they were made.
 

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Discussion Starter · #12 ·
wires and plugs along with air intake sensor were purchased in July. Who knows how long they were sitting. I'll give a look in daylight. Although this over all issue has been droning on for years pretty much. Until the passed few months, the CEL has not come on. After the first few minutes of rough backfiring driving, the CEL would come on and the car ran great. But when I checked for codes, there was non
 

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Sounds to me that when the engine runs bad and turns on the CEL light, the engine runs smooth again. At this point that would usually mean the ECM would put the vehicle into limp in mode and disregard certain sensors/systems to continue to drive to nearest repair facility. Might have to do with the fire you mentioned or not. More troublshooting needed to find the culpit.
 

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Discussion Starter · #15 ·
Thats why I have been leaning towards an electrical issue and not so much mechanical. I have changed almost all sensors running to pin 28 especially the ones that threw a code. With no luck.
 

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Discussion Starter · #16 ·
ka9yhd, The wires had no dates on them that I could see 7mm double ins. made in usa. each boot had a different number kw 213, kw 237 etc. pulled the crank position sensor. and still no change. Thankfully I am doing this myself. Otherwise I'd be in the $1000s by now instead of hundreds. This needs to be my reliable car to get to work and as I stated I have seen this problem with other Chrysler engines. I cant believe this problem has never been resolved, or at least the fix posted. Could it be coil pack?
 

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Possibly the ignition wires mixed up? If it is backfiring out the throttle body, maybe an intake valve stuck open. Do a compression test and once you find a cylinder with an intake valve sticking open you will hear it out the throttle body.
 

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There is no fix posted because there is no 'one' fix for 'rough running and backfiring'. The challenge is in the diagnosis of the cause. A session with an OBD 1 scan tool may reveal the culprit easier.
It has to be diagnosed in an orderly and methodical fashion. Spark/electrical, Fuel or Mechanical (leaky valves) must be ruled out until the issue is found.
The factory service manual and Powertrain Diagnostic Procedures books were useful for finding the problem and often paid for themselves. Consider them a 'tool' cost.
What diagnostics led the shop to replace the TPS wiring? Were they actually onto something or was it just an educated guess?
 

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Discussion Starter · #19 ·
The shop changed the connector. They said that was the problem and the car ran for a week we'll. Before the shop I would just touch that connector and the car would stall.When the car started aacting up again and I relied those sensor wires shared the same pin I started touching all the other connectors and sure enough the car would stall on the MAP. I didn't have another 300 to spend to change a connector so I just opened it and tightened the female bullets and now nothing changes when that connector is touched. When I did the ignition wires I'd pull one and replace the new one immediately so I couldn't cross them up. I thought the sticking valve and used Lucas on the fuel side and marvel on the oil side. I know it's not a up close inspection. But I am not leaning towards mechanical due to the engine light coming on and the car running fine then in the beginning
 

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I would disconnect the suspect connector, spray both sides with contact cleaner, apply silicon grease and connect it again.
 
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