Rymanrph Posted July 31, 2017 Share Posted July 31, 2017 So, I've had some intermittent problems that I'm struggling to solve. It first started a couple months ago when I started up the truck and as I was pulling out of the driveway, it just died. It happened one more time and then it was good for the rest of the day. Fast forward the next time I drove it and it was awful. It would die sitting still, moving, almost die and come back, etc. The motor would always crank back up though. From everything I read, it sounded like the crank position sensor, so I replaced it, along with a new front oxygen sensor, distributor cap and rotor (those were things that were not replaced when I did the '97 conversion and I have over 214k miles on the engine). The next time I drove it, it did fine for about 10 minutes and then I couldn't keep it running. It would run for a bit and then die. Each time it died, it would get harder and harder for it to start again. It would still crank fine, but just wouldn't get going. I barely got it home that night - after a while I got it to start and had a very stressful drive home. Did some more research and found that the plug on my ignition coil was broken, so I replaced it. Again I drove it for about 10 minutes and it cut off on me twice. I checked all my connections and drove it again with no problems. Yesterday I went to drive it and a quarter mile from my house it started chugging (learching?) so I got out of the gas and if I'm not mistaken, it looked as if the revs hung for a bit before coming back down (it was hard to tell with the chugging and I was more concerned about getting out of the way of traffic as I wasn't moving very quickly). After I turned around, I had no more issues, but I just parked it back in the driveway. Any ideas? My next thought was maybe a failing fuel pump, but I was under the impression that when a fuel pump goes, it just dies and you get nothing. My problems are sporadic. Link to comment Share on other sites More sharing options...
Rymanrph Posted July 31, 2017 Author Share Posted July 31, 2017 The crankshaft position sensor I bought was not a Mopar one and I have read that some of the aftermarket ones aren't very good. I've read that I should get infinite resistance between terminals B and C on the sensor, but that test would only fail if I get a crank no start condition. I've never gone out to the truck and had it not start. Sometimes I've had to give it a little gas to get it going, but it never just didn't start. Link to comment Share on other sites More sharing options...
Eagle Posted July 31, 2017 Share Posted July 31, 2017 The resistance test is to be run at operating temperature, and I've never been able to determine how the people who wrote the FSM expect you to get the CPS to operating temperature if the engine won't start. The better test is the actual output from the CPS, which can be tested when cranking. Your symptoms definitely sound like CPS. I know they are susceptible to heat soaking -- that is, the performance deteriorates as the sensor heats up. Link to comment Share on other sites More sharing options...
Potterman42 Posted July 31, 2017 Share Posted July 31, 2017 The resistance test is to be run at operating temperature, and I've never been able to determine how the people who wrote the FSM expect you to get the CPS to operating temperature if the engine won't start. The better test is the actual output from the CPS, which can be tested when cranking. Your symptoms definitely sound like CPS. I know they are susceptible to heat soaking -- that is, the performance deteriorates as the sensor heats up. It might be a good idea to freshen your ground system, there are a few good post for that, even if it doesn't solve your problem. You could also check you TPS and your air idle valve those could also cause the same symptoms. Eagle is right about checking your CPS. After that I would refreshen the grounds on the oil dipstick tube and in the rear tail light housing. I hope this helps, good luck. Sent from my SM-G935V using Tapatalk Link to comment Share on other sites More sharing options...
HOrnbrod Posted July 31, 2017 Share Posted July 31, 2017 The resistance test is to be run at operating temperature, and I've never been able to determine how the people who wrote the FSM expect you to get the CPS to operating temperature if the engine won't start. The better test is the actual output from the CPS, which can be tested when cranking. Your symptoms definitely sound like CPS. I know they are susceptible to heat soaking -- that is, the performance deteriorates as the sensor heats up. If this rig is a full OBD2 97 conversion (is it?), you can't check the CPS output with a meter. If full 97, can you check for codes? Link to comment Share on other sites More sharing options...
Rymanrph Posted July 31, 2017 Author Share Posted July 31, 2017 It's a full '97 conversion. No codes. Link to comment Share on other sites More sharing options...
HOrnbrod Posted July 31, 2017 Share Posted July 31, 2017 I've had both ignition coils and a distributor cam sensor go bad w/o throwing codes causing similar symptoms. Unless you see something obvious, like a frayed/crushed distributor low-voltage wire harness where it goes into the dizzy under the cap, there's really no foolproof way to check the coil or cam sensor except by replacement. Link to comment Share on other sites More sharing options...
Eagle Posted July 31, 2017 Share Posted July 31, 2017 I missed the important fact that this is a '97 conversion. I just had my late wife's 2000 XJ die in the middle of the road after having been stopped for about ten minutes while I met a guy to sell an old laptop computer. Had it towed home and, 45 minutes later, it started right up. No codes. I talked to the shop foreman at the dealership (he's a long-time friend) -- turns out, the CPS doesn't throw a code when it goes tango uniform. Link to comment Share on other sites More sharing options...
Strokermjcomanche Posted July 31, 2017 Share Posted July 31, 2017 I would get a fuel pressure tester and see what happens to the fuel pressure when it starts acting up . I just changed a cps in a 00 XJ , it died on me when I was doing a brake job on it . How I determined the CPS was bad was by hitting the CPS with a piece of pvc pipe while cranking it immediately after it died and it fired right up and ran great for another 5 minutes. It may not be the most scientific test but it worked in that case . Link to comment Share on other sites More sharing options...
Potterman42 Posted July 31, 2017 Share Posted July 31, 2017 Didn't realize it is a 97 conversion. Unfortunately my comment is for the RENIX. Not familiar with the 97 up. Good luck Sent from my SM-G935V using Tapatalk Link to comment Share on other sites More sharing options...
Rymanrph Posted July 31, 2017 Author Share Posted July 31, 2017 When I got home today, I decided to retest both crankshaft position sensors. The new one tested bad and the old one tested good. It's possible that the coil was really my problem since the plug was broken, but I replaced the CPS first. I can't send the new one back because it's been too long; I could have it warranted through the manufacturer, but I don't want another one of their's. That's $50 down the drain. I did find a Mopar one on Amazon for about $72, so I might go that route. First I think I'll swap the old CPS in and see if I still have issues. Link to comment Share on other sites More sharing options...
gogmorgo Posted August 1, 2017 Share Posted August 1, 2017 Hopefully that's your problem. Ive had CPS-failure symptoms because my bellhousing bolts went AWOL. Hard to read the flywheel when it's moving around in the bellhousing. Just something to think about. Link to comment Share on other sites More sharing options...
Rymanrph Posted August 10, 2017 Author Share Posted August 10, 2017 I put in a new Mopar crank position sensor and I can get the truck to fire with a little bit of gas, but it immediately dies even if I continue to give it gas. I'm a little stumped. Link to comment Share on other sites More sharing options...
HOrnbrod Posted August 10, 2017 Share Posted August 10, 2017 What was the CPS Mopar part number you used? Link to comment Share on other sites More sharing options...
Rymanrph Posted August 11, 2017 Author Share Posted August 11, 2017 What was the CPS Mopar part number you used? 68281273aa - it's what the Mopar website said fit a '97 Cherokee. Link to comment Share on other sites More sharing options...
HOrnbrod Posted August 11, 2017 Share Posted August 11, 2017 A quick search reveals this info: Crankshaft Sensor, 068281273aa, Sensor-Crankshaft Position Description:THIS IS FOR 2.5 4CYL JEEP and DAKOTA. IT WILL NOT FIT A 4.0 INLINE 6 OF ANY YEAR. IF YOU HAVE A 4.0 AND YOU HAVE A 97-99 JEEP CHEROKEE(xj) YOU NEED PART# 56027866AC. 94-96 4.0 AUTO PART # 56026921. 00-01 PART#56027866AE Please provide VIN at time of check out for confirmation. The correct p/n for the 97 4.0 in the parts manual is 56027866AB. Yet Chrysler Parts Direct says p/n 068281273aa has been superseded to 68281273AA. :hmm: I think I'd go with p/n 56027866AB as it says in the 97 parts manual. Link to comment Share on other sites More sharing options...
8valvehero Posted August 11, 2017 Share Posted August 11, 2017 Do a fuel rail leak down test. My '99 XJ had a tank return check valve that went bad with similar symptoms. Link to comment Share on other sites More sharing options...
Jeep Driver Posted August 11, 2017 Share Posted August 11, 2017 2.5s and 4.0s use the same CPS. I agree with the fuel problem. Link to comment Share on other sites More sharing options...
HOrnbrod Posted August 11, 2017 Share Posted August 11, 2017 2.5s and 4.0s use the same CPS. Oh, okay, I guess THIS SITE is lying then. This is true AFAIK for the Renix and OBD1, but not all the OBD2 stuff. Link to comment Share on other sites More sharing options...
Rymanrph Posted August 11, 2017 Author Share Posted August 11, 2017 "Fit" is probably the wrong word to use. The parts look identical from what I can tell, so it actually "fits" in the vehicle, but there must be some difference if there are different part numbers. Regardless, I was still experiencing problems with the non-mopar crank position sensor I bought from Rock Auto. I can't even get the truck to start with my original one anymore - that leads me to believe it wasn't the culprit. I'm going to stop on the way home and rent a fuel pressure tester; I'll go ahead and pick up a distributor pickup coil too. It's a $40 part and if it doesn't solve my issue, it's really easy to swap out and I can take it back. Link to comment Share on other sites More sharing options...
Rymanrph Posted August 12, 2017 Author Share Posted August 12, 2017 The distributor pickup coil made no difference. I rented a fuel pressure tester. The first time I connected it and put the key in run, the pressure was low, but after trying to start it, the pressure went to around 40 psi. I still can't get the truck to start, but when cranking I'm only seeing about 28 psi. Is that too low? I know when it's running it should be around 49 plus or minus 5 psi, but I didn't know if cranking pressure was different. Link to comment Share on other sites More sharing options...
HOrnbrod Posted August 12, 2017 Share Posted August 12, 2017 I have the larger 97 Mopar fuel injectors in my stroker running at 49psi. I have monitored the fuel pressure while cranking and it is ~30psi until it starts, then jumps up to the set regulator pressure pressure of 49psi instantly. So I'd say lower pressure while cranking is normal. Link to comment Share on other sites More sharing options...
Rymanrph Posted August 12, 2017 Author Share Posted August 12, 2017 So if I have fuel and air, then all that is left is spark. I'll have to wait till I have a friend around to help crank the motor while I check one of the plugs. Link to comment Share on other sites More sharing options...
8valvehero Posted August 13, 2017 Share Posted August 13, 2017 I didn't diagnose my fuel issues until a leakdown test. I pressurized the system then turned it off and let it sit. Lost 20psi in 30 min. Not normal. Link to comment Share on other sites More sharing options...
Rymanrph Posted August 15, 2017 Author Share Posted August 15, 2017 I made a little progress last night. I had read that these rigs don't like low voltage and I had been cranking the truck a lot, so I put the battery charger on it for quite some time to get a full charge on it. I also read about the asd relay giving some people issues, so I swapped it with the cooling fan relay. I was able to get the truck to run, but not without issue. I ran the truck for probably 10-15 minutes and it cut off on me probably three or four times - each time starting back up with no issue. Interestingly enough, the electric cooling fan never turned on (Is there a temperature that it automatically cuts on, or do I have to be running the AC or something?). The temperature gauge went to just shy of 210 and stayed there. While the truck was running, the idle wasn't perfect. There was a slight hesitation occasionally - sometimes very minor and other times it lead me to think it was going to cut off again but didn't. I think I will go back and rent the fuel pressure tester again. That way I can get an idea of what the pressure is reading while idling. I can also do the leak down test as well. Link to comment Share on other sites More sharing options...
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