greetings all

3 months ago I bought a 1998 4.0L Cherokee, all had been going well then last night while driving home it cut out and wont restart.

The fuel gauge was showing empty but I know the tank is at least 1/3 full - despite my doubts I tried adding a can's worth of petrol before calling out breakdown assistance (so as not to look too stupid if it had just run out!) but was still the same - engine was cranking but not starting.

checked fuses which all seemed ok. Then checked and found there was no spark - called for breakdown assistance who blamed the crank position sensor and sent for a recovery lorry to get us home.

Been looking at it today and Im not so sure that is the problem - I noticed that when activiating the ignition the immobiliser light is staying on after all the others have gone out.

Tried disconnecting & reconnecting the battery but its still the same. If the problem was just the CPS then surely my petrol guage would have shown a reading after the battery was reconnected but before trying to start up? (am assuming that before cranking the ECU is not going to know the CPS isnt working).

Have also tried unlocking and attempting to start with the spare set of keys - still the same.

any thoughts on what to try now? Im not a mechanic so quite literally stuck! Any help would be greatly appreciated...

 

could be fuel pump/filter issue. the More you crank it, the more it uses everthing in the lines ones its dead. Itll try hard for a few seconds, but then nothing but crank. That happened to me as I was driving over Mt. hood

 

I did wonder if it was a failed fuel pump as I couldnt hear it activating but would have thought you would still get a spark while cranking?

 

Do you have Spark? No, it's not the fuel pump. Yes, it might be the fuel pump. Pump function has NO affect on spark. No spark then there is a ignition related issue. CPS, CKPS, plugs, wires, Cap, rotor and coils, ect.

 

Pull a plug and ground the electrode to the block to check spark... Also you can check for fuel with the pressure relief valve on the injector rail. Relieve the pressure then cycle the key a few times and relieve it again. I had the exact same thing happen and it was the pump. If it's out or going out you will get little to no fuel coming out of the relief the second time. By the way.... I would check spark before fuel. It's never a good idea to get gas on your engine then add a source of ignition nearby.

 

Remember, if the PCM sees no cam sensor signal it will shut power off to the fuel pump. But you should still hear the pump prime when you first turn the key to the run position regardless if there is a cam signal or not.

 

thanks for all the suggestions - I didnt know there was a relief valve on the fuel rail


good advice!

I checked 2 of the spark plugs last night against the block but no, no spark under cranking.

and when I reconnected the battery today the pump didnt seem to prime at all.

The fact the immobiliser light stays on has me very worried! replacing a CPS is within my limited auto skills but I wouldnt know where to start with an immobiliser problem.

The "check engine" light goes out, if the car had decided to shutdown spark / fuel wouldnt that stay on??

 

Don't think so without the engine running. When it first comes on when you turn the key it's just a procedure to make sure all the dash lights are working. I look into it more

 

HAhaaa..... I just remembered a certain camaro I fixed a year or two back. If your key is coded with a "chip" it is likely a simple resistor. When the key is inserted the correct resistance will unlock the theft system. The camaro had no spark or fuel. I don't know if you have a key like this but if so start by cleaning the key. You can look up your vin and with a little searching find the resistance yours should have. Test the key with a multimeter. If that checks out pull your casing on the column and trace the wires from the ignition. Check all connections. In the case of the camaro the wires to the ignition itself inside the column had worn down. If that's the case you may need to replace the lock and tumbler and have the key coded with the correct resistor. You could try to solder broken wires but these things are very sensitive to the resistance so you're better off replacing. I traced the wires back, clipped them, and made a resistor pack and wired it in to bypass the whole thing. This is a shot in the dark because I don't even know if you have a coded key but if so......MONEY! That stumped me for a minute.. Let me know if that's the kind of system you have or not so I can pack that away for future reference.

 

If the key thing isn't going in the right direction check the voltage at the fuel pump and into the coil. It could be the computer...... How the hell do so many people fry those things?

 

many thanks for the responses - much appreciated

wow, never would have guess it would be that simple! To the greatest accuracy of my multimeter both my keys have 0 resistance so not sure if mine works that way (could just be my meter)

have tried a few more things tonight - checking connections and cleaning up a few things but still no joy:

tried reading the fault codes off the odometer but it just cycles from 0000000 to 9999999 then clears, doesn’t display any other numbers (am I doing something wrong there?)

update of the symptoms

-unlock doors from remote
-activate ignition
-dash lights come on then all go out
-immobiliser light comes back and stays on
-fuel shows empty (has 1/2 a tank)
-battery level shows empty (battery is fully charged, reads 12.9V on meter. Windows, lights etc work fine)
-turn the key again and engine will crank but pump doesnt prime we know there's no spark happening

Does that sound like it could be CPS or is this the immobiliser? Is it normal for the immobiliser light to stay on like that? (as in pic below)

 

Hmmm.....well does your key have a little piece of plastic in it with a wire running through.... I'm not familiar with the immobilizer in these things.

 

Alright I looked it up. This thing isn't that simple. It uses a radio signal to read the key or something pike that. Looks like you're going to have to get with the dealer on this one. You need the original key or you will have to give the dealer your vin to make another one.

 

Good luck with the issue, and please report back when you have it figured out. I'm interested in what actually went bad and what the fix was.

 

UPDATE------------ my Jeep is fixed!!!


Eventually I gave up trying to diagnose the fault myself – had pretty much concluded it must be an immobiliser fault which would be beyond my ability to fix so took it to Silver Service garage, an independent Jeep specialist just a few miles from me.

And the fault was………. the CPS! (which I’d wrongly ruled out!)

At first the garage also thought it had to be either PCM or immobiliser but when they swapped out the CPS the engine started and the other symptoms such as the gauges that read empty and the immobiliser light staying on – all went back to normal.

so Im back on the road and impressed with the garage who resolved the matter very quickly and for a very reasonable fee.

Many thanks for all the help and suggestions from all on here!