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1993 Dakota - weak spark

3 replies to this topic

#1 valiant67


    Rich, Corinthian Leather

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Posted February 18, 2013 at 07:22 pm

Truck in question is my old 1993 Dakota that a neighbor now owns. Around 135k on the truck, Magnum 3.9 auto, 2wd.
It quit on him and the shop told him the computer was bad after some "diagnostics" and replacing the coil would not make it start. So he had it towed home. It appears to be getting fuel, but doesn't seem to be firing. We pulled a plug and the spark was orange, not bright. The cap and rotor are worn, but not the the point I'd suspect they would kill the spark. He's gonna grab a new cap and rotor. Plugs were newer as are the wires. But the plugs are now fuel soaked so he's gonna clean them up.

It hasn't skipped time as it turns over smoothly, no popping (plus I put a new timing chain in it back then I had it with 120k miles). I've never had a crank sensor fail on these. Would one make the spark weak? I'm also gonna look the grounds over for problems. I hooked my scanner up to it and the scanner reads the part number from the computer, so I don't suspect the computer.

Anyone got anything else that I may have overlooked? I thought about a worn distributor but I assume that would have chewed the cap up inside if that was the case.

#2 Bob Lincoln

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Posted February 18, 2013 at 10:12 pm

First of all, this engine does not tolerate aluminum contacts in the distributor cap.  They oxidize quickly, as evidenced by the white powder that is found on them.  So the cap has to be one with brass inserts.


Next, I replace the ignition rotor every 15K miles, because they char more readily these days.  You might get away with 25K miles, but at that point I replace the rotor, cap, plugs and wires.  If there are more miles on them than that, it's the most likely cause of poor spark.


Also make sure that the ignition wires don't cross and touch each other or the valve cover, as that can cause misfires.  There are plastic wire guides to prevent this.

Edited by Bob Lincoln, February 18, 2013 at 10:13 pm.

#3 dana44

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Posted February 19, 2013 at 12:21 pm

A loose wire around the coil and distributor, or, more likely, a weak battery or battery cable can do this, too. Corroded interior cable, especially the ground cable, or even a weak alternator may be the cause. Definitely weak connection somewhere causing the problem from the description, or oil/corrosion contamination in a connection. Quite a few little things to check, but I do agree with the distributor cap (et al) items above as a possibility.

#4 valiant67


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Posted February 20, 2013 at 05:19 am

I did find one ground disconnected when we first started. Prior to that the truck wouldn't even light up my scanner (and I guess that's why the shop said to replace the computer). Once I fixed that, it immediately lit up my scanner and let me run the tests with it. We didn't get to work on it last night, if it's not runnign by this weekend, hopefully the weather will cooperate and we can work on it in better ligth.


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