Geeto67 Posted July 27, 2015 Report Share Posted July 27, 2015 Trying to diagnose this issue that has been driving me nuts. Here are the basics: 1995 Jeep Wrangler YJ. 1 owner. 4.0L Six with OBD I computer, NV3550 Rubicon Trans (swapped), Borla Full stainless exhaust header to tailpipe. Giant Aluminum 2 core radiator (purchased for future v-8 swap, operating temp dropped from 190 to 180 degrees with no other changes). Otherwise stock. When the outside ambient air temp is above 65 degrees and the car has been run up to operating temp it will not hot restart. Engine just cranks and cranks but no fire. Tested the original 20 year old Crank Position Sensor and was seeing thermal failure (pins B and C were showing continuity which they should not be doing). Replaced with duralast unit from autozone because no jeep dealer has this part in stock. cured the issue for about 3 weeks then started again.... Verified that the coil had no spark when hot with spark tester. Replaced factory coil Saturday (Thanks Clay for the loan of your 10mm box wrench and smaller hands). Original 20 year old mopar coil had many cracks, most not visible until the unit was removed. Replaced with a brand new Accel unit. Tested all day Sunday without issue. Drove the truck this morning to downtown and issue re-appeared. Was having vapor lock issues with the fuel rail, insulated the fuel rail with some aluminum high heat tape and high temp foam. Tested fuel line pressure and the line showed 40 psi cold and 45 psi hot (factory rating is 38-45psi for pump). Pump is priming when key is turned and rail is full of fuel indicating no bleed down. Jeep runs fine when running, no stumble, rock solid idle. has never stalled or died. Cap, wires, and rotor are kinda old but otherwise fine, no massive scoring or anything weird. The kid's daycare parking is in an underground garage that is typically 80+ degrees in summer and also on an incline. I will usually park for 15 minutes and when I return the car will just crank and crank and not fire. I didn't test it today but usually when I get this issue there is no spark coming from the coil. I waited 20 minutes and the the jeep restarted. I have noticed that sometimes after waiting for it to cool and restart the speedometer/odometer will not work and the CEL is on. Once the car is fully cooled down it will start normally as if nothing ever happened. Thoughts on what to check next? I know duralast parts aren't exactly known for quality but I find it odd that I would get the exact same behavior out of the new one as I did out of the old. I am kind of leaning toward it being the CPS again since they are known for thermal failure, but my multimeter has gone missing since VMD Mid-Ohio. I can check continuity but not voltage. Quote Link to comment Share on other sites More sharing options...
Skinner Posted July 27, 2015 Report Share Posted July 27, 2015 If it starts and doesnt stall its not the crank position sensor. It will kill the engine when bad (had it happen to me). could be the cam postion sensor. Quote Link to comment Share on other sites More sharing options...
Grudes Posted July 28, 2015 Report Share Posted July 28, 2015 I ran into a similar issue on a 96 Cherokee with the 4.0L and it was the distributor. Quote Link to comment Share on other sites More sharing options...
Geeto67 Posted July 28, 2015 Author Report Share Posted July 28, 2015 I forgot all about the cam sensor. At this point I think I am going to just replace it since I am chasing the gremlin around the car and have replaced pretty much everything else. And it is a $36 part. Quote Link to comment Share on other sites More sharing options...
Geeto67 Posted July 30, 2015 Author Report Share Posted July 30, 2015 Replaced it two days ago and so far have had no issue. Tested it with a multimeter before replacing and it showed power and continuity and no real issues. Since this was heat related as well I am thinking it was an issue with the wire increasing resistance when heat soaked but not breaking full continuity - it was tough to replicate the conditions and even then didn't test out as having failed. Frustrating when the part that was really the problem was hiding in plain sight. Quote Link to comment Share on other sites More sharing options...
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