yellowxj
NAXJA Forum User
- Location
- Ocala, FL.
put a spark plug in that wire and ground it (like to the block) so you can see spark...use insulated pliers to hold it there...
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91 4.0L Died, cranks, no start
- Thread starter Phil
- Start date
- Location
- Antioch, CA
OK, couple things.
1) According to my search on the Chrysler computer, the CPS sensor part number is 04638128, list price $78.25. My dealership sells parts above the factory suggested retail price, usually at a 100% markup. Cost on the sensor is around $48, so expect somewhere close to $100. The part is the same for the 91-92 XJ/MJ and doesn't designate MT or AT. It will fit both trans types, according to Chrysler.
2) To check for spark, disconnect the wire from the ignition coil to the distributor cap and place the wire near, but not directly on (leave a gap for the spark to jump, maybe 1/4 inch) a really good ground source (like the engine block or engine mount bracket). Now have someone crank the engine and you watch for the spark to jump the gap. If you have no spark, then you may have a bad CPS or ignition coil. If you have spark, then reconnect the coil wire and then pull a spark plug wire and recheck for spark from the plug wire, this will check your cap and rotor for direct shorts to ground. So if you have spark going into the distibutor cap, but not coming out, it is the cap and rotor.
3) To check for a bad ignition coil. You will need a basic 12v test light. Connect the test light to the ground terminal of the battery and then check to make sure the light works by touching the positive battery terminal with the probe tip. Now, disconnect the 2 wire connector at the ignition coil. One of the 2 wires will have 12v with the key on, check this while turning the key to the on position. The other wire will be the ground signal from the computer to make the coil spark. So with you test light, verify which wire has the 12volts. Now, move the ground wire from the test light to the positive battery terminal so you can check the ground signal. While someone cranks the engine, check the other wire for a pulsing ground signal. The test light should blink on and off if the signal is good. This test will verify proper operation of your CPS, the engine controller and the wires going to the coil. If all this is good, then change the ignition coil.
This may sound complicated, but it is exactly what a good mechanic will do when you have your car towed into the repair shop. I still bank on the fact that the CPS is bad. If it was the ignition coil or cap and rotor, the fuel pump would run anytime you cranked the engine. You verified the fuel pump works when you turn the key on, so I would say the pump is good. Max posted about the pump wiring havind 2 circuits, he is correct on the older models, but not sure about the 91+ Chrysler injection models. This might be a problem, but is not as likely as a bad CPS.
Long post to say the parts guys might be mixing up the part numbers for the YJ with the XJ which is very likely. The YJ CPS does differentiate between AT and MT, but not the XJ/MJ.
Hope all this rambling helps. Good luck.
Bryan
1) According to my search on the Chrysler computer, the CPS sensor part number is 04638128, list price $78.25. My dealership sells parts above the factory suggested retail price, usually at a 100% markup. Cost on the sensor is around $48, so expect somewhere close to $100. The part is the same for the 91-92 XJ/MJ and doesn't designate MT or AT. It will fit both trans types, according to Chrysler.
2) To check for spark, disconnect the wire from the ignition coil to the distributor cap and place the wire near, but not directly on (leave a gap for the spark to jump, maybe 1/4 inch) a really good ground source (like the engine block or engine mount bracket). Now have someone crank the engine and you watch for the spark to jump the gap. If you have no spark, then you may have a bad CPS or ignition coil. If you have spark, then reconnect the coil wire and then pull a spark plug wire and recheck for spark from the plug wire, this will check your cap and rotor for direct shorts to ground. So if you have spark going into the distibutor cap, but not coming out, it is the cap and rotor.
3) To check for a bad ignition coil. You will need a basic 12v test light. Connect the test light to the ground terminal of the battery and then check to make sure the light works by touching the positive battery terminal with the probe tip. Now, disconnect the 2 wire connector at the ignition coil. One of the 2 wires will have 12v with the key on, check this while turning the key to the on position. The other wire will be the ground signal from the computer to make the coil spark. So with you test light, verify which wire has the 12volts. Now, move the ground wire from the test light to the positive battery terminal so you can check the ground signal. While someone cranks the engine, check the other wire for a pulsing ground signal. The test light should blink on and off if the signal is good. This test will verify proper operation of your CPS, the engine controller and the wires going to the coil. If all this is good, then change the ignition coil.
This may sound complicated, but it is exactly what a good mechanic will do when you have your car towed into the repair shop. I still bank on the fact that the CPS is bad. If it was the ignition coil or cap and rotor, the fuel pump would run anytime you cranked the engine. You verified the fuel pump works when you turn the key on, so I would say the pump is good. Max posted about the pump wiring havind 2 circuits, he is correct on the older models, but not sure about the 91+ Chrysler injection models. This might be a problem, but is not as likely as a bad CPS.
Long post to say the parts guys might be mixing up the part numbers for the YJ with the XJ which is very likely. The YJ CPS does differentiate between AT and MT, but not the XJ/MJ.
Hope all this rambling helps. Good luck.
Bryan
- Location
- West Sacramento, CA
That's what I needed! Thanks Bryan! I think I'll go ahead and get the CPS tomorrow, and then try to get it in Friday afternoon. Good thing about being a student is the free time. Less good (because you can't really complain about college life) is when that free time is interrupted by homework, tests, labs, stuff like that.
willysnut
NAXJA Forum User
- Location
- Newnan, Ga.
My '93 has died like that twice, both times it was the camshaft position sensor located under the rotor in the distrib. Pull the cap and look below the rotor. There's a little plastic piece that holds a magnet and if the magnet has been broken off, the motor will turn over but not start. Now for the good news- if that's tha case Idiot Zone has a rebuilt distrib for $65. Hope that helps ya. :wave1:
woody431
NAXJA Forum User
- Location
- Virden, IL
OK, my 95 did the same thing a few weeks ago. I took it to a small garage with a diagnostic checker(thing) and it ended up being my CPS. My CPS was only $60. I think there are several places that sell them, Quadratec has them I know. It's scary when it dies like that! I was working when mine went out...D'oh.
xjbmx
NAXJA Forum User
- Location
- Newnan,Georgia
there are two CPS sensors one is the cam shaft position sensor and the other is the crankshaft position sensor. make sure you know which sensor the posts are talking about
- Location
- West Sacramento, CA
Ok, I put in the new CPS this afternoon and unless they sold me a bad CPS, I need to get a test light and check the ignition coil, because it's still not running.
Spectre006
NAXJA Forum User
- Location
- Stamford, CT
- Location
- West Sacramento, CA
Spectre006 said:
Thanks Andy. I already put in a new CPS though. I'm going to check the ignition coil next to see if that's bad because it did not start with the new CPS.
[Edit]Test light is something like this?
Last edited:
- Location
- Antioch, CA
That is the "magic test light." OK so the crank sensor didn't fix it? That really sucks. One quick question. Does the check engine light come on when you turn the key on? What about spark? Any spark at all?
Bryan
Bryan
- Location
- West Sacramento, CA
No on the spark, yes on the check engine light.
- Location
- Antioch, CA
Did you try cycling the key 3 times to get any trouble codes? Since the crank sensor was good after all, I think it would be best to try and check the problem further before changing any more parts. That can get expensive and frustrating for sure. Have you ever pulled codes this way? The check engine light will flash in a series, count the flashes, and look for any short pauses to indicate another digit or long pause to indicate another code. The light flashes should end with code 55. This may give you some direction if the coil test doesn't tell you anything.
Bryan
Bryan
- Location
- West Sacramento, CA
Ok, didn't check the coil yet but I did flash the codes. I got 12, 54, and 55. Searching told me that 12 is disconnected battery within 50 key cycles, so that's cool. 55 is just the end code to tell me I'm done, so that's cool. 54, though,looks like it is "No signal from the Camshaft Position Sensor" right? So I need to replace that CPS now too?
- Location
- Antioch, CA
I can't verify your code number as my on-line info on diagnostics only goes back to 96. It looks like you have the plate style cam sensor in your 91 according to the parts catalog. All you need to do is pull your dist cap and rotor, then just lift off the sensor plate. My info says you need part number 56026817. Swift Dodge in Sac says they have the part in stock. $35.60 list.
I guess I should have steered you to the flash code thing first. :dunce: I have only seen a very small number of cam sensors go bad compared to the large number of crank sensors that have gone bad. The plate style sensors are known to go out on other Chrysler products, but not often in Jeeps. I guess the old "shotgun diagnostics" failed me, and unfortunately you too.
I would trust the code that the computer is setting as being the fault. A good inspection of the wiring and connector would be a good place to start, then replacing the sensor if all is well. I have seen the sensor wire caught between the distributor and cap and shorting out the sensor signal a few times too.
I hope I was at least some help to you at some point. :anon: If not maybe you can take out your frustrations on me in Hollister on the 28th. :twak:
Bryan
I guess I should have steered you to the flash code thing first. :dunce: I have only seen a very small number of cam sensors go bad compared to the large number of crank sensors that have gone bad. The plate style sensors are known to go out on other Chrysler products, but not often in Jeeps. I guess the old "shotgun diagnostics" failed me, and unfortunately you too.
I would trust the code that the computer is setting as being the fault. A good inspection of the wiring and connector would be a good place to start, then replacing the sensor if all is well. I have seen the sensor wire caught between the distributor and cap and shorting out the sensor signal a few times too.
I hope I was at least some help to you at some point. :anon: If not maybe you can take out your frustrations on me in Hollister on the 28th. :twak:
Bryan
I have almost exactly the same Jeep- 91 motor from a 99. I also have the exact same problem... My list of new ignition parts includes: plugs, wires, cap, rotor, CPS, and coil. I have tested the alternator, its good. I don't think the computer is bad because it will do the diagnostic check on itself with the check engine light. I still have NO SPARK. Anyone have any good ideas? Bad wire somewhere maybe? Thanks!
