lgrant

Problem started about a month ago. The beginning: engine dies while running (just like turning the key off) but would start right up. Progressed to not starting right up after it dies - cranks good but no start. I'm fairly sure it's an electrical prob. During one of the no start events, I dumped a little gasoline down the throttle body but could get no firing of any cylinders. That worked back in the 60s - will it work on a computer controlled engine?

Before I became aware of the fact that the pickup coil is necessary to start but not to run (which probably eliminates the pickup coil as the primary problem) I was in the process of replacing the pickup coil based on what seemed like a permanent "no start" situation. When I got the cap off I discovered a corroded rotor. Just as a test I sanded off the corrosion and put it back together and it started right up. Thought I had it fixed. Three days later (yesterday), had another die while running and a subsequent no start situation about 30 miles from home. Desperate, I thought I'd just loosen the cap and then put it back in position and tighten. It worked - it started right up and it seems to be okay for the moment. When it starts and runs, it runs and idles good.

Both times that I played with the Dist Cap, I also looked at/tugged on the wiring around the dipstick. Based on the engine dying while running, can the pickup coil be eliminated? Must be a chaffed wire somewhere - probably involved with the CPS or maybe an O2 sensor? Obviously, there is some kind of a problem involving the distributor or something in the wiring. Any ideas?

Early on before the problem got bad I began reading a lot of "crank but no start" threads. Seemed like there was a tendency to throw a lot of parts at the problems with no permanent good results - seemed like lots of threads ended with no solution. Anyway, I have not thrown one part at the problem - yet.

Thanks to all in advance,
Larry

RTorrez1

By any chance have you checked the code to see if anything comes up? Pulling the code can tell you a lot.
Your problem sounds like a failing crank shaft position sensor CPS. But you say that it runs when you mess with the distributor make me think the cam shaft position sensor. I don't know if it is a coincidence or what? But, I would start by testing both of the and go from there.

lgrant

Thanks for the post Robert. I forgot to mention in my original post that there are no codes, according to my inexpensive Asian OBD II reader. It has worked well in the past with a CEL and a failed O2 sensor.

This new problem is so intermittent that I am inclined to wait until it totally fails and then do a full court press to solve it (comprehensive testing, etc) - that should be more efficient than trying to locate a problem that comes and goes.

My original post was mostly pointed toward the camshaft position sensor and to get some knowledgeable person to confirm that if the vehicle stalls at 60 mph when running normal, then the CMK is not likely my primary problem. My logic on that is: if the CMK is not required for the engine to run, then it's failure would not cause the engine to stall like someone was turning the key off. Something else must be causing that.

Also, I was curious to know if the electronics kills the spark in a low fuel pressure (at the rail) condition. Assume for the moment that the fuel pump is bad and a little gas is poured down the TB. If there is spark, the engine should try to do something. If no spark, then the test would be pointless.

I did change out the fuel filter (Wix) yesterday since it had been at least 130K. Wow, there was some ugly fluid (mostly gasoline) that came out of the fuel pump side of the filter.

I'll keep the thread updated on developments. What do you think about the CMK?
Larry

lgrant

Please refer to the original post wherein I said that the rotor was corroded and that I cleaned it up. Well, I had the radio off and didn't notice the new radio static/interference. Discovered in another post on this forum that, what looks like corrosion, is really something that is applied to the rotor contact to guard against radio static. So don't remove that material with sand paper like I did.

Great forum - you can learn a lot. I wouldn't have figured out that problem on my own in a hundred years.
Larry

lgrant

Bump - anybody want to respond to whether or not the CMK "could" be causing the problem. I'm thinking that because the engine dies at 60 mph, it probably isn't the CMK.

lgrant

Okay, this XJ finally failed "completely" this past Friday morning in my driveway. No spark.

I tested the coil and it tested good. Got 0.00 (not to be confused with infinity) resistance on the primary circuit. Got 12,000 on the secondary (to the distributor) circuit. Both right on the money.

Skipped the camshaft position sensor and went to the crankshaft position sensor. The reason I'm giving the forum this elaborate story is I think there are some new light we can shed on testing the CPS. This "new light" is buried in this (and similar) forums but it is somewhat obscure. The frequent comment is that you can test the CPS but it doesn't prove anything, which is kinda the equivalent of saying you can't test it. I'm not concluding one way or the other on that one but here is what I did:

1. At the CPS connection and with key on run, I back probed with a paper clip and checked the shared 5v circuit that goes to the six sensors for 5v. It had 5v and that is a real decision block. Since it had the correct voltage I didn't have to check any of the other sensors to try to find out which one was shorting out and compromising the voltage.
2. Next I back probed the CPS connection and checked the sensor signal which is on the opposite side of the connector (the ground is in the middle). The reading was 3v which makes the CPS immediately suspect (it was already suspect since experience tells us that most [over half] good crank but no start issues are caused by the CPS).

With engine not turning over, you would normally expect a reading of either zero volts or 5v, depending on the position of the flex plate vs the CPS - again my reading was 3v. I then had a helper crank the starter to see what would happen to the voltage. It stayed right on 3v. If you were using a Digital MM, you could expect about .5v from a good CPS, which is an average of the voltage seen. Apparently the alignment time that creates voltage is only about 1/10th of the non-alignment time and the DMM gives you the average, which is about .5v. If you get a reading on a DMM that is much different than .5v you should be concerned - probably time to change the CPS.

I was using an analog meter and was expecting some movement in the needle but it stayed right on 3v. Changed the CPS and it started right up. I put about 400 miles and 20 starts on it this weekend and no problems. I tried to buy a Mopar CPS last Friday and the dealer couldn't get one in before Tuesday (tomorrow). Then went to NAPA and that turned out to be a "service only" facility and no parts - they could get one to their location by Monday (today). So went to O'Reilly's and bought their BorgWarner product. I will update this thread if it fails anytime soon. So far so good.

Jeep never threw a code.

Again, the reason I'm posting this is I've read a lot of "no start" threads where the CPS was changed and there was no improvement. If testing is done right, I think that experience can be minimized.
Larry

Mealticket

Good call, man. I believe that voltage test from the crank sensor to the PCM is the best test, not that resistance test many use. I suppose you could do both,

Mealtime

lgrant

Early June 2014, I installed a B & W CPS into my 96 Country. I must have 25K miles on it since then (254K total). CPS has performed flawlessly since installation. I would have no hesitation to buy again. I think it was about $65 at O'reilly's.

Cheers,
Larry