1994 Jeep Wrangler with 6 cyl

Have replaced distributor, spark plugs, coil, and still have very weak, erratic spark. Plugs getting plenty of fuel, won’t start. Anybody have any idea what else I should do?

With replacing all those parts already, one thing that would be a maintenence item that I don’t see on there is plug wires.

Do you think a crankshaft sensor could cause this? or a computer issue?

Yes, a crankshaft sensor can cause this and may not set a computer code. Yes, the computer could be bad too, but typically the computer on a car is extremely reliable and should be suspected last.

When you say the spark is ‘erratic’, what do you mean?

How can a crankshaft sensor or the computer cause a WEAK spark?? I can understand no spark…but how does it cause a weak spark???

When the jeep is cranked it will show a spark several times and then when it is under a crank still, it loses spark and then it will regain spark, but it is a light spark, about as thick as a human hair.

An erratic (failing) crankshaft sensor can cause an erratic spark, but not a “weak” spark. A “weak” spark, one of voltage just barely sufficient to jump the gap rather than of the voltage that the coil should be discharging, can only be caused by shorted coil windings, by a voltage “drop” from the coil secondary to the plug, or by low voltage at the primary.

I think the best way to diagnose what’s going on is with a scope. An oscilloscope trace can show definitively all the essential elements…voltage to the primary, residual voltage if there is any (that would reduce the induced voltage), voltage/rise time/fall time/wave form from the coil secondary, reliability of the spikes (erratic or not), etc. etc. etc.

You’re going to need a good shop for this one.

How was the strength of the spark determined? On an oscilloscope? If so what was the peak voltage and the duration of spark?