91' Sovereign. Check Engine Light on, OBD1 system. I have a vintage Jag mechanic with a OBD1 device, I'm taking it to him tomorrow (no one has OBD 1's anymore).

It could be many things, as I have heard. IF it's the Oxygen Sensor, he's gonna charge around $250 for parts and installation. Maybe I can do it my self, but where is the sensor on 91's? How easy is the install? (a diagram or pic would be wonderful), as would be any tips on NOT screwing up something. As of now the engine runs fine, no rough idle or missing.

Jagbro

 

Have you tried using the on-board Vehicle Condition Monitor yourself?

This VCM will read the code for you and by-pass the need for whatever equipment you mechanic has - the fault code displayed will display showing either "FF" and a number or "Fuel Fail" and a number.

This code will show up in the mileage window LCD in the dash.

To read any code, you switch on the ignition but don't start the car then press the VCM button to the right of the steering wheel.

The code displayed will guide you to a specific area to investigate, which you can then follow up by reading the engine management .pdf

This is the recommended way of chasing down a check engine light, throwing parts at it, beginning with the oxygen sensor is the other but not recommended way.

Here's a link to the engine management .pdf, download it and compare your displayed code to the flowcharts.

http://www.mediafire.com/file/szzac3...stic+Guide.pdf

BTW you can reset the check engine light by disconnecting the battery but if youu do that make a note of your radio code as you'll need to re-enter it after a battery disconnect.

You could also post the FF code here and maybe we could help you out further.

Cheers

Larry

 

Cool, will do tonite.... Let you know the codes tomorrow...

 

Download and print the .pdf too, great insights in that doc

Larry

 

https://www.google.co.nz/search?q=xj...VFZ1Lj4KKa12M:
Typical o2 sensor location on the ‘40
If you have a digital multi meter you can check if the o2 sensor is bad it returns a value between 0 an 1volt:
https://www.google.co.nz/search?q=o2...osM_9tkL___7M:
The harness runs across the firewall on the exhaust side of the car. Disconnect the harness and run the engine once it gets to temp you will see the value starting to oscillate, if the value stays steady then the o2 needs replacing.
Question when you start the car from cold and start driving do you feel the car stumble after a few minutes and then the MIL appears? This is another manifestation of a failed o2.

 

VCM displays Fuel Failure code 24. What may this indicate?

 

Hi Jagbro,

FF24 indicates a problem with the Ignition Drive circuit between the Engine Control Module (ECM) and Ignition Amplifier Module (the small electronic component mounted on a flat heat sink below the ignition coil).

Referring to page 94 of the AJ6 Engine Management System Manual for which Larry provided the download link, possible causes of FF24 include:

Low Battery Voltage
Poor connection at ECM or Ignition Module
Water ingress at ECM blue connector (White wire with Red tracer line (WR))
Short circuit in WR wire between ECM and Ignition Module
Defective Ignition Module
Defective ECM

Page 95 provides a diagnostic flow chart for troubleshooting DTC FF24.

Note that I have had spurious occurrences of FF24 that were cured by cleaning the ground/earth points referenced by the ECM, which include the two on intake manifold studs and the one on the firewall/bulkhead behind the cylinder head.

Please keep us informed!

Cheers,

Don

 

Great I will inspect and let you know

 

Once done, how to a reset/ turn off the check engine light?

 

Mine usually turn off on their own once the issue is corrected. I think it takes 3 starts to clear. Or you can pull fuse 9 in the center fusebox (fuse 1 is at left side). Or you can unhook the battery If you have the radio code.

 

I would check the battery voltage as a start, then work your way down the list.

 

Thanks Robman... Interesting that this seemed to happen, after while cleaning out the inside of my Jag one late dark 5pm evening, I left the lights on (w/ignition fully engaged to use the cigarette lighter outlet for the car vacuum, THE HEADLIGHTS ON) for about 10 minutes. Once I finished vacuuming I realized the headlights were still on, I rushed to start the car.... The battery dragged for a few seconds, and almost gave out, but narrowly cranked up the engine. I drove it a while to charge the battery up, but this could have weakened the battery. The check engine light came on a few days later. I will do a voltage test.

Question: Can this FF24 code happen at ANYTHING below a 12 volt battery output? Because the engine always cranks strong other than the incident above...