I have grumbled here, and asked for help, over the past 15 months

I bought a 1997 XJR last year. It stopped running after 5 days and had major intake work to get it going again - new Eaton, TPS, O2 sensors, thermostat, expensive hit-and-miss work because it wouldn't communicate with the X300 PDU Jaguar diagnostic gear.
Then it ran fairy well for a year, in which I did 30,000 km.
A month ago it started missing, losing power, then stalling.

Andy XJREngineer has been really helpful, answering all my emails as we tried to work through it.
The EPROMs were reprogrammed with Andy's software by the previous owner, but the software was put on the EPROMs locally in NZ after Andy emailed it to the local company.
During my ownership, the car has never run in Closed Loop when worked on by my mechanic, and when it failed last month the plugs and O2 sensors were sooted up from rich running.


Over the past month my mechanic has tested sensor voltages at AFM, O2 sensors, etc. the readings at the ECU connection were wrong, but correct at the source of the various sensors. All the earths were checked - first by my mechanic, then an autoelectrician - all fine.

Finally we opened the ECU following instructions in a Jaguar Service bulletin supplied by Andy. The EPROMS were carefully removed - both OK, no bent legs.
Today my mechanic tried a different ECU with my Andy-software EPROMs installed

Bingo !!

good phone call while I was at work - car idling at 700rpm (first time in 15 months), closed loop, normal fuel trims etc etc.
I think for the first time I have owned it, the car is running properly. It always seemed powerful, but not as special as I had hoped. But I don't know what 340bhp should really feel like - I drove a 560 bhp SLS 5 years ago, and it was awesome, but didn't feel like 560 horses.

Anyway, I think we may finally be there.
I will take it to work tomorrow and see how it goes, then report back..

 

Congratulations! And thanks for posting the fix.
However, I cannot understand why you get different readings at the sensors and the ECU if the wiring and connectors are ok, or how changing the ECU fixed that. Since (generally) the sensors are connected to the ECU by a simple wire you would expect the same voltage at each end of that wire, at least at signal levels where currents are very small. Can you give any specific examples?

 

I can't remember exact voltages, but for example:-

same reading at AFM and other end of wiring harness going into ECU, but different reading on the PDU when plugged in to ECU. so some problem in the ECU itself.

no fault codes, ever, from old ECU. Suddenly fault codes from new ECU (only an AFM fault code with new generic AFM, fixed by putting on the tatty old secondhand XJR genuine AFM LNA1620AA part). Able to erase fault code, so PDU communicating normally.
the old ECU never gave any fault codes over 15 months, even when the car would barely run.

 

Thanks, that makes sense.
Have you still got the old ecu? I'd be keen to check out the insides of it if you don't want to keep it.

 

Wow, that's great news that you finally found the problem. I know it can be maddening to methodically chase a problem, never finding it.

The only thing worse is to have a significant problem that mysteriously goes away on its own, never to know if it will reappear.


Specific to your issue, I had the exact scenario with my 1995 Buick Riviera a couple years ago. The problem started as rough idling, then occasional dying, to finally extremely rough idle/running with an inability to take more than part throttle without quitting. We went through all the standard checks over a period of weeks with no success. Eventually my mechanic suggested that the ECU on that series were well known to eventually fail and exhibit these symptoms. I found that hard to believe, but he was right. Fortunately it was easy to find a salvage ECU for about $40 at a pick and pull as the ECU was used on several models. It has run well ever since.


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Al, I got my ECU for NZD 450 plus 15% tax, which was a special price offered by the wreckers as I think they felt sorry for me!
Usual price is 750 plus tax...
a bit dearer than the Riviera, but that's Jags for you

 

The car is going like a rocket now. Yesterday I did about 80 km, gave it a hard time wherever possible, and got 21 mpg (Imp)
I thought it has a hesitant throttle in the midrange and needed a lot of pedal, but today I fiddled with the tortuous throttle cable under the bonnet/hood, and improved the way it curled around (bigger radii), and now it feels way better.
So i am hopeful this XJR is finally going properly.

Now for some extractors/headers..
.. and may be a 3.58 diff instead of its 3.27:1 diff. But honestly, I don't think it needs it.
... and then in the longer term a rebuild of the Getrag 5-speed which has some noisy bearings in some ratios, but good synchro still.

where to stop?

 

OUCH! $450NZD (~$300USD)!? Sorry to hear that!

Not to make you feel bad, but an FYI for anyone looking for XJ computer modules: I just pulled the ECU and TCU from an XJ at the same big pick/pull chain (LKQ, we have three in the area) for I think about $40USD each, or maybe it was $40USD for the pair. And I see the XJ ECUs on the US eBay for $100-200USD all the time. It might take a bit longer to find an XJR ECU, but they are around, and like my Buick I bet you just change the EPROMS over to an XJ ECU and it becomes your XJR ECU. Of course these are used prices.

Reman units I'm sure are more expensive. I think the Buick remans were over $200 versus my $40 for the used one.

.

 

I just took my car for a short blast.
It is pulling like a train, right past 180km/h. Definitely running better than before. The new Bosch IC water pump seems to be helping too - not getting the heat soak, but it is also winter here now, with much cooler intake temps (about 5'-15'C outside, c/w 25'-30'C 2 months ago).

Yesterday I went somewhere with my daughter, did about 30 miles round trip, first half in moderate traffic with a couple of full-throttle overtakes, got 26 mpg(Imp) so the economy is better than before - I remember Andy saying he can get 28 mpg on a cross country run at about 70 mph, so I seem to be on target.

 

Hi is that fuel consumption on motorway..and is that the average cause mine after doing Andy bracket then the alt went and I changed plugs and a ecu reset I'm getting average 10.2 local roads I was getting average 15 1y before and 21 on motorway.to be fair not been on motorway yet.

 

my current tank of gas i am averaging 20mpg (imp) - that is everything - cold running, around town, traffic lights, drive thru's, medium distance runs (13 miles) of which the first 2-3 are cold engine.
Once warm, I can get 25+ if chugging a steady 80-100 km/h in traffic
If the foot goes down, the fuel averages drop pretty fast, but definitely better than before when the ECU wasn't working properly and the engine stayed in Open Loop