Hi everybody,
I'm new on this forum, dutch from origine and living in Romania., I have some friends here driving Cherokees and always asking me to resolve electric problems. Usually I manage but this time I'm having some difficulties I can't get my finger on:
So the case is a XJ 2.5 diesel that doesn't charge anymore. The car was brought to someone who messed around with it and now the charging problem is still there but I have additional issues on top of that: The glow plug relay doesn't do it anymore and it is not the relay itself, the shut-off valve on the mechanical injection pump (replaced, originally it was electric) is not activated anymore and a 20A fuse keeps on blowing out. The next picture is to give you guys an overview of the engine we are talking about:

So the fuse that keeps on blowing out is shown on the next picture:

Anybody have an idea? What does this fuse exactly protect?
But my main question: Why ain't it charging anymore. So I had at my disposition an exact same Cherokee and I took the different parts out and tested them in this good working car. Both the boxes, under the steering wheel and in the engine bay, the alternator... everything works fine in the other car. I checked the 2 wires going to the alternator, they are okay. Massa connection between alternator and battery is okay. So could there be a sensor or so not allowing the field of the alternator to be powered? I tried to get information about the temp sensor (Mopar pn 56041053) under the battery but don't get the resistor value of it. The company making them doesn't give me any useful information.
I already passed 2 full days on this car and I'm running out of ideas.
Really would appreciate some input here.
Thank you in advance and if more information is required, please let me know.
Bouke

 

You can go to Cruiser54's site here: https://cruiser54.com/?page_id=365 and get the 2000 FSM.

The diagram for the 2.5 Diesel Power Distribution Center indicates that fuse (Fuse #21) powers the glow plug relay, fuel injection pump, and the electric vacuum modulator. It also provides the "fused Auto Shutdown Relay Output to the PCM which appears in the charging system diagrams but seem to apply only to the gas engines. So I'm not sure that it affects your charging circuit directly.

There is a battery temperature sensor so I'd check that too. The FSM will give procedures for testing.

 

Hi Saudade,
thank you for your reaction. Of course, I immediately downloaded the pdf of 2119 pages () and already started studying and have some questions:
Where did you find the fuse 21 in the pdf? I have been looking in the 8W-20-4 'charging system diesel' page 733 and the 8W-21-6 'starting system diesel' page 741 but there I don't find this fuse.
And I did find the batt temp sensor but not where it sais how to test it. Could you give me some page numbers here?
Thank you in advance and have a nice day.
Bouke

 

The box with fuses in the engine bay is the Power Distribution Center (PDC). Section 8W (Wiring Diagrams) Page 8W-10-7 is the layout for the Diesel. That spot is Fuse 21. Once open in Acrobat (or whatever PDF tool you use), you can use the text search for "fuse 21" (without the quotes) and find all the locations that call it out.

Page 8W-10-34 shows the fuse and the connections to the relays.

Just make sure you're looking at Fuse 21 in the PDC and not the Junction Block (JB, under the dash). Also make sure you're looking at the Diesel pages and not the Gas (Petrol) pages.

Page 8W-20-4 Charging System Diesel wiring diagram and does not show Fuse 21 playing here. Doesn't mean there's not a short somewhere that may affect it.

Section 8C is the charging system with the diagnostics.

Since this FSM is in parts, file EXJ_TAB.PDF is the "table of contents:". You can click on any tab and it should open the appropriate section.

Is your Check Engine light on? If so, can you read the codes?

 

Hi Saudade and other readers,
Sorry it has been a while but had some other things on my plate. So I resolved the problem with fuse 21: short circuit of 2 wires going to the fuel pump. The pre-heating plugs work again and the fuse doesn't blow anymore. Remains the fact that the fuel valve (white black wire, only got 2.5V on that lead coming in as a bleu/black line wire)

on the pump doesn't open with the contact put and the alternator isn't charging so I presume fuse 21 hasn't anything to do with that as you already said you thought. As said in my former post, I exchanged both cdi units (under the steering wheel and engin compartment) and the alternator with a similar Cherokee and in that car everything works fine. Also, in that car the battery temp sensor was taking out but the alternator stil charges the battery so I presume a faulty sensor can't be the problem neither. Never got the resistor value of this sensor so I can't put a resistor in place to overrule the sensor to see if this solves my ploblem. No Check Engine light on in the dashboard.
Really gonna need expert inside here
Thanks in advance again for your input or everybody else's remarks.
Bouke.

 

Anyone has a hint please ...?

 

Sorry for the delay replying/ I'm not expert on diesels.. If you have the manual, Section 8C has the changing system diagnostics.

I'm confused a bit. Are you able to get it started and running? If so, what does the battery voltage read when running? Use a volt meter across the terminals.

If you disconnected the battery, or the battery got very low, it would erase any codes. Was your check engine light on when you began troubleshooting the blown fuse?

 

Hi Saudade,
Thank you very much for coming back to this topic, so let me reply to your questions:

If you have the manual, Section 8C has the changing system diagnostics. Yes, I do have the manual and believe me, I've been reading it many times.
Are you able to get it started and running?: Yes the car starts and runs but doesn't charge the battery. If so, what does the battery voltage read when running? Battery voltage reads around 12.2V at all time, so revving up the engine doesn't change anything. It is the voltage of the battery itself. Use a volt meter across the terminals. I did and I also checked all cables involved in the charging system as far as I know and no significant resistance is measured.

If you disconnected the battery, or the battery got very low, it would erase any codes. Was your check engine light on when you began troubleshooting the blown fuse No, the 'Check Engine' light was never on. The blown fuse problem is solved: some wires were short-circuited.
My question: are there any other sensors or possible items that can stop the system from charging? like the battery sensor or other....

 

Thank you so much.

 

The battery sensor reports battery temp to the ECU. The ECU can then reduce the charging when the battery is too hot. So yes, an issue with the battery temp sensor could impact charging. The resistance varies with temp causing the ECU to cycle grounding on the field wire to regulate the charging. So the voltage regulator is part of the ECU.