1999 XJ 2.5TD in limp mode

[M84AB1]

Hi guys,

I was hoping someone had a similar issue before. Basically I was doing a compression test on my cylinders and to do so I disconnected the wiring harness to the bosch fuel injection pump. After reconnecting the wiring harness my XJ is now definitely stuck in limp mode. Loses power around 2,000rpm. I can accelerate past 100km/h but it has definitely lost the 'explosive' power it had prior to compression tests and there is a very obvious power limitation/loss once 2,000 rpm are reached.

Car definitely worked great and had lots of power immediately before I carried out the test. I have checked the on-screen (dashboard) fault codes and only come with 12, 55, 55 (in this order), basically no error codes.

I have tried resetting the ECU (a few times) by:
1. Disconnecting positive battery lead
2. Connecting that lead to a ground (engine block, A/C compressor) for 30 secs
3. Connecting the positive lead
4. Turning key to ON position
5. Turning headlights on/off
6. Turning key to OFF position

I did not touch anything else and can't workout why the ECU continues to keep the car in limp mode although everything is back in place.

Help greatly appreciated. Cheers!

[vernicious]

Go back to what you did... Perhaps a pin bent, or you got some moisture in the plug without realizing it. If you did something and the vehicle was running good prior to that item and not not... Chances are you did something wrong. It's a start at least.

[M84AB1]

vernicious,

I have checked everything and all seems ok. No pins are bent and nothing is disconnected. I get no CHECK ENGINE light and no error codes on the dashboard.

I bled the air from on the low pressure fuel side as according to my service repair manual trapped air can affect the fuel pressure and put the car into limp mode. (see attachments).

I reset the ECU again but am still having limited power. I can rev it up to 3,000rpm in second gear if I really push it. Perhaps if I drive it around for a while it will get out of limp mode on its own?

[layback40]

just for fun & to remove the most common cause. Could you please measure the resistance of the injector #1 sensor. you may have bumped the wire when you did the IP work.

[M84AB1]

Hi layback40,

Checking the no.1 fuel injector sensor was one of the first things I did as I am aware that, that sensor is one major cause where the ECU would trigger limp home mode. Resistance reads 112 Ohms.

Although I did not mention (as I do not think it has caused this) in my first post, prior to the compression tests, I did change the rocker cover gasket. So the chain of events in order

1. Drove car to my brother's garage and car worked great
2. Changed rocker cover gasket
3. With glow plugs removed and Bosch injection pump disconnected, performed compression tests.
4. Put glow plugs back in, connected the glow plug harness as well as the injection pump harness
5. Started driving and almost immediately upon acceleration noticed the lack of power around 2,000rpm.

It feels as if something trips/triggers, it is very apparent. It is not the TURBO or anything as I have installed a turbo boost/pressure gauge and see the TURBO compressing properly.

I find it odd that I am not getting any error codes or the Check Engine Light. Wondering if the dashboard readout shows all faults or if the DRB tool is needed for further analysis.

[layback40]

Originally Posted by M84AB1

Hi layback40,

Checking the no.1 fuel injector sensor was one of the first things I did as I am aware that, that sensor is one major cause where the ECU would trigger limp home mode. Resistance reads 112 Ohms.

Although I did not mention (as I do not think it has caused this) in my first post, prior to the compression tests, I did change the rocker cover gasket. So the chain of events in order

1. Drove car to my brother's garage and car worked great
2. Changed rocker cover gasket
3. With glow plugs removed and Bosch injection pump disconnected, performed compression tests.
4. Put glow plugs back in, connected the glow plug harness as well as the injection pump harness
5. Started driving and almost immediately upon acceleration noticed the lack of power around 2,000rpm.

It feels as if something trips/triggers, it is very apparent. It is not the TURBO or anything as I have installed a turbo boost/pressure gauge and see the TURBO compressing properly.

I find it odd that I am not getting any error codes or the Check Engine Light. Wondering if the dashboard readout shows all faults or if the DRB tool is needed for further analysis.

If its a late model with a MAP on the inlet manifold, that can cause limp mode. I found that out by forgetting to reconnect it once. Dont know what happens with the older ones with a MAF.
I have never checked codes. Couldnt get the ignition key off & on thing to work & dont have free access to a DBR tool.
Sorry I cant be of more help, have had limp a few times. always found the problem soon enough though. Always some thing obvious that I didnt see.

Good luck with your hunt & please post the outcome when you find it. Always good to learn from others problems.

[mud_slut]

might be a bit late on this one but i had an issue with limp home mode once with a bad fuel filter. i do have an after market one fitting and there was a bad seal on one side which put the car straight into limp home mode. im surprised your not getting any error codes though. you did try reading with a drb III reader a normal OBD II will not return you any info.