Hello, I have had intermittently restricted performance mode on my 1999 uk spec xk8 4.0. I pulled the codes which were po352 p0353 and po358. routinely I changed all 8 spark plugs and the coil packs on the affected cylinders from the codes I extracted. The problem is still there. I understand the early xk8 cars had a pair of ignition modules between the ecu and coil packs. i suspected the ignition module as 3 of the cylinders affected are from the same module. I have tried to look for them behind the throttle body on the bulkhead, but cannot see them. is my car considered a later model where the connection to the coil packs is direct from the ecu? Have any other members

 

Did you check the connections to the ECM/PCM and the loom connectors?

Also, what is age and condition of the battery? It should have a minimum of 12.6 volts across the terminals with the ignition in the OFF position for at least ten minutes.

 

Clean the plug leads and housing on the throttle body with contact cleaner. Use about 7x more than you think you need, hose them down. Then put back together and enjoy the money you just saved.
LaRue

 

I suspect your engine is a AJ 27 and the coils are fired by the ECU. The AJ26 ignition modules were quite obvious just under the cowl near the center.

To help identify:

The AJ27 VVT solenoid is in the cam cover, but mounted on the front of the head for the AJ26.

 

First and foremost many thanks for your suggestions and replies. I will address each one with progress to date;
the battery was fitted in Feb 2012. I did the voltage test and initially for the first 5 minutes it read 12.13 / 12.14 volts. This settled down to 12.10 / 12.11 after my last check 20 minutes later. I have followed the loom all the way to the ecm. Popped of the windscreen wiper undercover and opened the housing unit to the ecm. It is all clean and dry in there and the wires look like they have never seen daylight. Even the fan underneath the ecm is spotless. The loom looks fine and undamaged albeit a bit grubby behind the throttle body. The engine is indeed an aj27 unit. Thanks for the heads up on that. All that remains is to spray the throttle body . I can spray the outside with carb cleaner, but can the butterfly and throttle body be cleaned while still in the car? The fault to give more detail is quite intermittent. It will go into restricted performance mode for a few seconds and then clear. Other times it will stay in that mode for 30 minutes or more. The car in that state appears to be running on 4 cylinders. Is there any value in cleaning the ecm contacts with electrical contact spray ? when I replaced the plugs all the wires and coil packs were sprayed with electrical contact spray for completeness . thanks again

 

That battery is dead. It may start the engine but it's too weak for the electronics. I don't think there is any point in pursuing the problem until the battery is either fully charged or replaced.

 

+1 on replacing the battery rather than chasing electrical 'gremlins' that are intermittent.

 

OK good call , I did Have a sneaking suspicion about the battery as there appeared to be similar problems before I bought the car 6 years ago. A new battery was fitted and 6 years of trouble free motoring ensued!

 

I have a 2004 XJ-8 that spends most of its time sitting in the garage. Last year I put 377 miles on it. I drive it rarely.
The other day I took it to the store, on my way home I floored it, temp was in normal range, and the rpm's went right away to 5,000. I backed off and in about a quarter mile the engine stopped. I was fortunate enough to get the car off onto the side road and to safety. It would not start. Acted like only one cylinder or maybe two were firing. I talked to Jag dealer in Denver about 300 miles away and they suggested I call JaguarUS so I did. After about 30 minutes of talking to Jag I called for a wrecker to take me to the local Ford dealer who has been servicing this unit for 3 years. Before the final OK to bring on a wrecker I tried to start the engine again and it started. I went home without further problems. About 2 miles.
Can anyone share a similar experience with me? Car is pristine, has 70k miles, was the wives until she passed and never had a problem of any sort. I take that back, last year I had to replace the battery.

 

The battery has now been replaced on the car and has made no difference at all. The problem starts intermittently and the longer the engine is running for the longer it goes into restricted performance mode

 

Does anyone have any thoughts on a possible intermittent fault with the ecu? Seeing as there are only the wiring between the ecu and coil packs and plugs that have been replaced?

 

Millhouse-corfe,
I had the same problems and the fix was an ECU repair ..... see this thread https://www.jaguarforums.com/forum/x...arning-155799/

 

Thank you Sean,
I will send the ECU away for testing. The test is usually 45 minutes so should show an intermittent fault up in that time. They do repairs as well. May I ask were your symptoms similar as in the the restricted performance came on briefly and went. repeated a few times then spent longer and longer in restricted performance mode?. The codes you cited are exactly the same as the codes my car is throwing.

regards
Oliver

 

One thing I've very rarely seen on this post is the mention of restricted performance warning being tied to the cruise control. Seems the connection at the throttle body can work loose and get a tad dirty. SO, do what I did, disconnect the connection at the throttle body, use some electrical cleaner spray (like mass air flow sensor cleaner), give the connections a good blast both on the harness and the throttle body, let it dry, plug it back in and see if the warning comes back...mine never did.

 

Millhouse-corfe, it would appear our symptoms and error codes were the same. The repair company in the US that I contacted gave me more procedures to test to ensure the problem was with the ECU before I sent it off. Sorry I can't recall what they asked me to check, it could've been related to the throttle body. They also give a life-time warranty on the repair. When I got it back, popped in it and all was well again!

 

Sean, thank you for your reply. it does point to the ECU. I got another ECU with the same code as mine and coded the keys to it but it would not start. Suspect security module intervening. Problem I have is i cannot find any companies in the UK that can properly test and repair the ECU. Most say its too complicated to work on and pass on doing the work!

 

Have you checked the timing? Have you changed the chain tensioners (& related parts)?

It's probably not the PCM ("ECU"). Check everything else, not least codes during RP.

 

Grounding straps might be corroded/ loose...?

 

Millhouse, that amazing there's not a company in the UK that fix these ECU's. I would contact the US company and see what they say as there could be a difference for US and UK ECU's.

 

Hi the timing and tensionsers were changed 6 years ago to the new 4th generation ones. I cam check the grounding strap on the battery. The car does run faultlessly until the intermittent problem reappears. The fault codes that keep cropping up are the ones relating to the 3 coil pack areas and a p1260 which won't do away when cleared. I guess the best option is to contact the US repairers and see what they know of the differences