# 1994 Jeep Wrangler with 6 cyl **URL:** \ **Category:** Maintenance/Repairs\ **Tags:** wrangler, jeep\ **Created:** [January 25, 2011, 1:51am UTC](https://community.cartalk.com/t/1994-jeep-wrangler-with-6-cyl/60439 "2011-01-25T01:51:41Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![Todd\_Sam](https://avatars.discourse-cdn.com/v4/letter/t/46a35a/32.png) [@Todd\_Sam](https://community.cartalk.com/u/Todd_Sam)\ **Post date:** [January 25, 2011, 1:51am UTC](https://community.cartalk.com/t/1994-jeep-wrangler-with-6-cyl/60439/1 "2011-01-25T01:51:41Z")
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? ---
**Author:** ![system](https://global.discourse-cdn.com/cartalk/original/3X/1/d/1d47c66a543aa6c5a7873bb2320858f978ff52ed.png) [@system](https://community.cartalk.com/u/system)\ **Post date:** [January 26, 2011, 4:12am UTC](https://community.cartalk.com/t/1994-jeep-wrangler-with-6-cyl/60439/2 "2011-01-26T04:12:31Z")
With replacing all those parts already, one thing that would be a maintenence item that I don’t see on there is plug wires. ---
**Author:** ![Todd\_Sam](https://avatars.discourse-cdn.com/v4/letter/t/46a35a/32.png) [@Todd\_Sam](https://community.cartalk.com/u/Todd_Sam)\ **Post date:** [January 26, 2011, 7:07am UTC](https://community.cartalk.com/t/1994-jeep-wrangler-with-6-cyl/60439/3 "2011-01-26T07:07:59Z")
Do you think a crankshaft sensor could cause this? or a computer issue? ---
**Author:** ![oblivion](https://avatars.discourse-cdn.com/v4/letter/o/3ab097/32.png) [@oblivion](https://community.cartalk.com/u/oblivion)\ **Post date:** [January 26, 2011, 11:37am UTC](https://community.cartalk.com/t/1994-jeep-wrangler-with-6-cyl/60439/4 "2011-01-26T11:37:15Z")
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? ---
**Author:** ![MikeInNH](https://avatars.discourse-cdn.com/v4/letter/m/a587f6/32.png) [@MikeInNH](https://community.cartalk.com/u/MikeInNH)\ **Post date:** [January 26, 2011, 1:16pm UTC](https://community.cartalk.com/t/1994-jeep-wrangler-with-6-cyl/60439/5 "2011-01-26T13:16:35Z")
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??? ---
**Author:** ![Todd\_Sam](https://avatars.discourse-cdn.com/v4/letter/t/46a35a/32.png) [@Todd\_Sam](https://community.cartalk.com/u/Todd_Sam)\ **Post date:** [January 28, 2011, 5:03am UTC](https://community.cartalk.com/t/1994-jeep-wrangler-with-6-cyl/60439/6 "2011-01-28T05:03:18Z")
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. ---
**Author:** ![the\_same\_mountainbike](https://avatars.discourse-cdn.com/v4/letter/t/c89c15/32.png) [@the\_same\_mountainbike](https://community.cartalk.com/u/the_same_mountainbike)\ **Post date:** [January 28, 2011, 6:59pm UTC](https://community.cartalk.com/t/1994-jeep-wrangler-with-6-cyl/60439/7 "2011-01-28T18:59:42Z")
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. ---
**Author:** ![Rod-Knox](https://avatars.discourse-cdn.com/v4/letter/r/a183cd/32.png) [@Rod-Knox](https://community.cartalk.com/u/Rod-Knox)\ **Post date:** [January 28, 2011, 7:06pm UTC](https://community.cartalk.com/t/1994-jeep-wrangler-with-6-cyl/60439/8 "2011-01-28T19:06:40Z")
How was the strength of the spark determined? On an oscilloscope? If so what was the peak voltage and the duration of spark?