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  #1  
Old 08-29-2007, 04:09 AM
jimmy jimmy is offline
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Running rough when cold

My 96 3.9 dakota has just recently begun to start acting up, when its cold it barely stays running and backfires through the intake, if I floor the gas it will rev up but anything less than full throttle and it pops and sputters.

Once its warmed up it runs fine, I replaced the coolant sensor thinking it must be the cause but still does the same thing and its not throwing any codes except once in a while I get a code 31 evap sol.

Also has had a complete tune up, new timing chain and water pump.

Only other symptom is long cranking time like 3-5 seconds but it has always done that.

I was just hoping somebody else might have had a similar issue and could point me in the right direction
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  #2  
Old 08-29-2007, 05:30 AM
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O2 sensors. If they've never been replaced, might as well do them all.
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Old 08-29-2007, 06:22 AM
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Your best bet without blindly throwing money at it is if you can get a scanner and look at the "data stream" to tell you what computor is seeing and doing. Almost sounds like a fuel pressure or volume problem. It's gonna be real hard to diagnose this without data or pressure data.

Bryan
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Old 08-30-2007, 04:18 AM
jimmy jimmy is offline
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It seems to be going down hill quickly, now its doing it for longer periods of time even for a min or two after its warm by the gauge at least.
I dont have a obd II scanner yet but I can see im going need one. I do have a fuel pressure gauge so i can try that but I figured since it will take off when its floored that it was unlikely the pump is bad.

If the crank or cam sensor is going bad the scanner probobly wont do much good though, just cant figure out why no codes when its running so badly for such a long period of time
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Old 09-01-2007, 04:10 PM
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Originally Posted by Little Blue Guy View Post
Your best bet without blindly throwing money at it is if you can get a scanner and look at the "data stream" to tell you what computor is seeing and doing. Almost sounds like a fuel pressure or volume problem. It's gonna be real hard to diagnose this without data or pressure data.

Bryan
I agree with the fuel pressure theory. Should check it just to be sure. Also check to make sure it holds, at least for a while, after the key is shut off. The only other thing I can think of, as you mentioned an evap solenoid code, is if the purge valve is stuck open it COULD cause a lean condition, similar to a large vacuum leak, or if the canister is full of fuel vapor it may cause a rich condition as the vapor is sucked from the canister at cold idle. I know that;s a long shot, but it is a possible cause. Also, just like LBG said, you need to look at PID data and see if any inputs are not what they should be, or if the PCM is commanding the correct outputs and are the commanded outputs actually being done. Just because the data says for example AIS65%, doesn't necessarily mean it's at 65%.
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Old 09-01-2007, 06:16 PM
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Got a scanner on the way, I had extra sensors from my old engine that i kept for spares so I replced just about everything one at a time besides the o2 sensors wich i am about to try a used one in the upstream sensor.

My gas milage has just gone to crap too, im lucky to get 10 mpg and the truck is running worse every day
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Old 09-01-2007, 09:20 PM
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Ok found the problem as soon as I took the connector off of the Main o2 sensor water came out and one of the pins was only half way in the socket and there was a burn mark on the plastic so I cleaned it up, dried it out and pushed the pin in all the way till it clicked in and its running good.

Somebody replaced the sensor sometime back with a bocsh brand and they must have bungled the job... So thanks for everybodys help !
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Old 09-01-2007, 09:56 PM
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Good job....

See? That was easy, huh? (now try doing it for a living like I do)

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Old 09-02-2007, 12:16 AM
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Good job....

See? That was easy, huh? (now try doing it for a living like I do)

Bryan
Oh, so you're one of "us" I see! Ever wonder how professional auto tech's don't sometimes run amok and end up in the rubber room? Somedays, I think it would be a short trip over to "the other side"! Hey, try working on new Ford products. Give me 5 minutes alone in a room with the engineers that designed some of the stuff. Two go in the room, but only one will come out!
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Daily driver: 1996 Dakota Sport 4X2, 3.9L, Auto, a/c, cruise, stereo. Stock except hi flow cat, and those darn rust holes in the rear wheel openings, bottom of the doors and rockers that are increasing in size everytime I look (sucks), 126,000 miles and change.
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Old 09-02-2007, 12:41 AM
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Woohoo. +1 for me.
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Old 09-02-2007, 12:53 AM
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Originally Posted by aspen79 View Post
Oh, so you're one of "us" I see! Ever wonder how professional auto tech's don't sometimes run amok and end up in the rubber room? Somedays, I think it would be a short trip over to "the other side"! Hey, try working on new Ford products. Give me 5 minutes alone in a room with the engineers that designed some of the stuff. Two go in the room, but only one will come out!
Yea...no shit!.....like the idiot who designed the plug & coils on the 4.6 & 5.4 liter Fords.....especially in the trucks & vans....the jerk who set that system up should have to work on all of 'em. I say the engineers who designed all the new crap should have to work on them until they design them with us techs in mind.

Bryan (ready for the "rubber room"....where is it!)
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