My ECU is being shipped off to Automotive Scientific this morning.

Steve, in my case they say my ECU must be repaired and rebuilt, and returned to me. They don't have other rebuilt units available. So I'm hoping they've done enough of these with my particular kind of damage to do the job properly.

Turnaround time once they receive the unit is supposed to be about 5 business days. Cost is $ 289 (although it appears they're raising their price soon to $ 389). I'll keep everyone posted.


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These are the same two capacitors. It would be interesting to see a circuit diagram as this could possibly be a common failing, but it would be nice to find out why.

 

This appears to be more common than one might think. A google search of "leaking capacitor" and ECU comes up with plenty of stories.

My unit arrives at Automotive Scientific later today...I'm hoping for a call from them by tomorrow with a prognosis.


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Good news...Automotive Scientific called this morning. My ECU has already been repaired, and will ship today. Ideally, I'll have it back in the car by the weekend.

The tech there told me that the leaking capacitor, along with several others, had been replaced and the board and circuits cleaned up well. He said that this kind of failure is something they see every day, and that sometimes leaks are bad enough to literally eat into the board...those are the ones difficult or impossible to repair properly. He said that my leak didn't cause that kind of problem, and that everything tested 100% on the money once the clean-up and repair was made. The work is guaranteed as long as I own the car.

When I get the unit back, I'll take a close-up photo of the circuit board again, in the same spot, so everyone can get a look at the repair possibilities.

Who knows if this repair will solve my new idle problem, but it was something that needed to be addressed regardless. I'm glad I got it done.

Price is $ 311 including shipping...but they're raising their prices now. I just squeaked through with the old price.

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I would love to see it, but I'll bet they put a tamper seal on the case so you will lose the warranty if you open it up.

 

Keep us posted on your results. I hope you can indeed open the case and see the circuit board....

Is this a problem only on the early XK8/XKR models or does it strike the later models as well?

 

If this was a Jaguar repair and warranty worth several thousand dollars, I'd leave it sealed. But since I'm only in danger of losing $ 311- worst case scenario if I lose the warranty- I'll probably crack it open and take a look.

I'll keep you posted.


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This does bring up a valid point on the throttle body however. When cleaning it you also must clean the air bypass port in the throttle body which controls idle. They get dirty and plug up too.

 

OK guys,

My ECU has arrived back from Automotive Scientific, after a clean up and replacement of several faulty components. I'll probably crack it open later and take a look, but for now its back in the car.

Took it out for a spirited run, and in the first ten minutes, the idle / RPM problem was gone. Then as I came off the freeway, the problem returned, exact same behavior as before. The ECU needed to be serviced anyway, as seen in the photos from previous posts. But the clean-up and rebuild didn't solve this particular problem.

While I was on the test drive, I pulled into a parking lot to perform the MAFS test as posted by Gus HERE. Gus, would you please tell us where you got these test numbers...I can't find them in any of my documentation.

I can read real-time ECU readings on my Android through the Torque app. My MAFS numbers were all low in relation to the desired numbers in the chart Gus has posted. Here's a look:


Car in PARK Engine at IDLE.......................MAF should be 5.1 gm/s (mine is 3.4 to 4.1, 66 - 80% of normal)

Car in PARK Engine at 2500 RPM...........MAF should be 17.0 gm/s (mine is 13.5 - 14.2, 80 - 84% of normal)

Car in DRIVE Engine at IDLE.....................MAF should be 5.9 gm/s (mine is 4.4, 75% of normal)

Car in DRIVE Engine at 1500 RPM.........MAF should be 39.3 gm/s (mine is 35.0, 89% of normal)


MAF and its connectors were cleaned last week. I do not have significant vacuum leaks, as all short and long-term fuel trims are showing normal levels (less than 6%).

Here's a short video showing the tach behavior as I come to complete stops:

IDLE DROP at COMPLETE STOPS


Please help! I gotta figure this out.

A few reminders from the first post:

1. RPM drop and possible stall only happen when in Drive or Reverse...NOT when I put the car in Neutral. So in other words, only under a bit of load from the torque converter when stopped.

2. Same behavior with the Air Conditioning on or off.

3. Re-start after stall is normal.

4. Acceleration, RPM, etc is normal in all other driving conditions.

5. Throttle body and connections, MAFS and connections, crankcase breathers were all cleaned. No change in behavior.

6. Fuel pressure at the rail is about 42 psi with ignition on and engine off, and drops to about 38 when engine is running.

7. Short and Long-term Fuel Trims are all good...less than 5%...so there don't appear to be any significant vacuum leaks.

8. No codes.


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Check your PM.

 

MAF problems were common on Kim's last car a TT, the best quick way to check for a MAF problem was to disconnect it, the engine ecu would then change to a lambda driven map, if the car drove ok then it pointed to the maf being the problem.

Is it possble to easily disconnect the maf on these cars?

 

Is it typical behavior for the issue to be gone for the first few minutes of driving?

If it is not, then does disconnecting the battery fix it for a few minutes repeatedly?
If it is not, does disconnecting the battery and unpplugging the ECU again fix it for a few minutes repeatedly?

 

I agree with the suggestion of the MAFS but the Throttle Body is also part of the equation.

 

Steve- I'll do some testing and post up the results. Truth is I haven't done a lot of driving since the issue cropped up. Thanks for the suggestions. I may also try to do some of the pinpoint diagnostic tests listed in JTIS for both the MAFS and throttle body.

Related point, maybe, maybe not...when I put the pedal to the floor, Torque indicates only 76% throttle percentage. I've looked at the throttle cable adjustment, but haven't been able to make an adjustment without raising the idle RPM too much.


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I took the car out tonight, same behavior. First 8 minutes of driving, all was normal. Then an RPM problem at complete stops. Might be related to the engine coming to temperature, might not.

As the RPM's drop suddenly and the engine tries to catch itself (usually succeeding), the lights flicker just a bit...I suppose as the alternator loses RPM as well. Even the Torque OBDII data flickers for an instant, with some dials showing "no data" for just a split second before the engine rights itself and RPMs return to normal.

Volts as shown through Torque are at 13.8 with the engine running. No other electrical weirdness.

I'm stumped.


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I am with Gus in suspecting the throttle body. The inability to set 100% throttle also seems to indicate this.

Problem is it is an expensive item to guess at.

Is there any known history of your throttle body being rebuilt before?

 

I got the throttle body (TB) today but I did not get it on the car I will do that tomorrow. The TB I got was not the one I sent in the replaced it because it did not pass tests they put it to so they sent me another. I can put this one in but I am missing the accelerator cable bracket that I left on the old TB. I hope to get it soon! I can install it and get it to run but unable to drive it until then.

 

Hmmm. Yeah, maybe. Tonight I ran the JTIS pinpoint diagnostic tests on the MAF - ECM and TPS - ECM circuits. Everything checked out fine, as far as I can tell with my limited electrical experience.

The throttle body for this car was replaced within the first couple of years - an official Jag recall. Since then, this unit has only been cleaned, never rebuilt.

I don't know if the low WOT throttle percentage is my not getting things right with the cable, or a TPS issue.

Price at Automotive Scientific is $ 589 for a rebuilt unit. Wish I could know definitively whether or not I needed it.

Gus, get that bracket! We're waiting to hear about your new unit.


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I can start it and let it idle but unable to drive it without the bracket. I will give you an update.

 

One more clue, developing just this evening.

On normal startup, the RPMS go to about 1200, stay there for a minute and then evenly drop down to the normal idle of 650 RPM.

This evening, a few times on startup, the RPMs will go to 1200 as normal but then SUDDENLY drop down to 500 - 600...a quick and sharp drop compared to normal behavior...then even out at 650.



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