Engine miss fire

Tiny
SHARPSHORTS
  • MEMBER
  • 1999 DODGE DAKOTA
  • 6 CYL
  • 2WD
  • MANUAL
  • 115,000 MILES
Have a missfire that occurs on cold mornings. Happens shortly after a cold start - major bucking on accelleration or cruise and very rough idle. Then the check engine light comes on and it it stalls. The code set is for 'missfire'. After a while I can drive it with the check engine light on and it seems OK.
Have changed cap, rotor and ignition pickup in distributer (plugs and wires have less than 15k miles.
99 Dakota 3.9L 5 speed, 115k miles. This problem 1st occured 3 years ago on a cold morning (cold in florida is 40 degrees) then did not occur again until recently.
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Monday, January 24th, 2011 AT 2:47 PM

6 Replies

Tiny
CARADIODOC
  • EXPERT
Check the spark timing with a timing light. If you see it bouncing around, replace the distributor. The bushings develop wear that lets the shaft wobble. That changes timing and will cause misfires when timing pulses aren't detected intermittently.

Caradiodoc
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Monday, January 24th, 2011 AT 3:49 PM
Tiny
SHARPSHORTS
  • MEMBER
Thank you cardiodoc.
Was looking for something like this answer that is specific to my motor.
Will check the timing - though when it's miss firing it's hard to keep running, will find a way. May just pull the distributor and inspect it.
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Monday, January 24th, 2011 AT 4:30 PM
Tiny
SHARPSHORTS
  • MEMBER
BTW cardiodoc- The tach jumps crazily when the miss fire occurs so your fix makes sence to me. Will check and report back. Thanks again.
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Monday, January 24th, 2011 AT 4:39 PM
Tiny
SHARPSHORTS
  • MEMBER
So far so good with the new distributor. Though it did missfire on the initial test drive, it was parked (before changing the distributor) with the check engine light on and it was still on on the test drive. After several shut downs, waiting then restarting, the check engine light went out and has stayed off since. And the truck runs fine.
BTW - I could detect no looseness (axial play) in the old distributed shaft nor any wear on it's drive spade (I hate when that happens but am glad that the missfire seems gone).

Thanks cardiodoc
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Saturday, January 29th, 2011 AT 1:05 AM
Tiny
SHARPSHORTS
  • MEMBER
The missfire/bucking turned out to be a bad crank senser, located on the trans bellhousing. I did replace the distributer before I replaced the crank senser and now the problem is I can't set the ignition timing. Thereare no specs. On the underhood sticker and a timing light does not show the balancer/front cover marks. .I've set it by ear by moving the distributer throughout the entire range that it'll rotate (and stay running) but the fuel milage is off by 2-3 mpg (power-wise it seems OK) and the check engine light occationally comes on (without affecting performance). I disconnect the battery to turn off the check engine light but it returns.
I've read that ign. Timing is set by the ECU and a dealer must re-set it. Is there no way to set base timing?
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Monday, July 25th, 2011 AT 9:28 PM
Tiny
CARADIODOC
  • EXPERT
Ignition timing is not adjustable. It is determined by the crankshaft position sensor. The Engine Computer can't advance the timing because it can't get a pulse from the sensor, then fire a spark plug before that. Instead, there is a lot of advance built into the sensor by way of the holes in the flex plate. The computer gets a pulse, then waits a calculated amount of time before firing the coil. By waiting less time, it in effect advances the timing.

The dealer can't change the timing. They can "flash" the computer with updated software but anything that affects ignition timing for any given set of conditions would have been programmed in at Chrysler. They take into account performance, fuel mileage, spark knock, and most importantly, emissions when they write the software.

Turning the distributor only affects the camshaft position sensor which determines when an injector will fire. If you get that set wrong, it might fire while the intake valve is partially closed. The fuel will just sit there until the next time the valve opens but that can cause some of the fuel to condense on the cold back side of the valve. Liquid fuel doesn't burn or contribute power. What doesn't vaporize quickly just goes out the tail pipe, wasted.
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Tuesday, July 26th, 2011 AT 2:26 AM

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