I concur that this is the sensible thing to do at this point.

 

There is a clue in the engine kicking to 3000 rpm as if a hard reset
was done.

In fact, unintended hard resets may be happening. All that has to
happen is for the ECU to lose power momentarily which causes the
KAM (keep alive memory) to drain. At that point, a hard reset has
been effectively performed.

You have a fresh and presumably fully bench charged battery. I routinely
charge new batteries for 72 hours on an auto regulating charger set at
12 amps to get them to peak condition. These are big batteries and a
2 amp charger will just sit there and spin without ever getting to full
charge.

The first thing to do would be to monitor voltage during those moments
before the kick to 3000 rpm. If you see any kind of drop at all you will
have a good sign that you need to look at both power and ground main
circuits.

The best way to monitor voltage is to backprobe all power supply pins
on the ECU directly while the engine is running. Alternatively, run a
piggyback circuit to keep the standby power pin supplied. If the behaviour
disappears then there is a problem there. If the behaviour continues, but
the overall voltaqe drops at any point, then you are back to looking for
and inconsistent power supply to the ECU.

Of course by this time your ECU could be enroute to ASI and they may
find a intermittent open in the power supply circuits. That would be the
cause of the phantom hard resets.

 

I have very good experience with this:

Jaguar XK8 XJ8 Denso ECU ECM - LJA1410AK - *$100 Exchange Deposit in Shipping


Cheaper and real "plug and play"

 

Thank you for your advice. You are right the increase in RPMs was caused by a hard reset which I performed after installing the new TB. It has not done that since as far as accelerated RPMs are concerned. I would love to test the voltage at the ECU while the engine is running but the engine only runs for a minute or two before shutting down.

The battery is less than a week old.

One interesting note is that after sitting all night I can turn the key to START and there will be no codes or dash errors. The engine will start perfectly and run smoothly for a minute or two before it sputters and shuts down. Then it will display codes and errors. Even after a few hours of sitting, the codes and errors will still be there. The car needs to sit all night before they go away.

My gut tells me that whatever is causing this situation "resets" or defaults back to normal after many hours with the ignition off.

 

Thanks Toaster!

For the same price, I think I want to know what happened/happening to my ECU if anything. If it tests out OK it costs me $55 and shipping and I am back to the drawing board.

Not to save money but to find out what the heck is wrong.

 

That`s a little bit like roulette, whether the ECU is the culprit or not.
My ECU was definitely scrap, so saved time too.
Scrap out, replacement in, done.

PS: Have a second look at the marked capacitor and conductive path, there seems to be the mistake (but maybe my eyes are growing old)

 

I will check that capacitor when I pull the ECU out again. Right now it's snowing and the car is under 2 layers of covers to stay nice and dry.

 

I was going to ask what your evening temps were as if it's cold overnight that may explain why it's all good first thing. Then I saw you're in CA and thought nah.

Toaster might well be on to something. It's dificult as it always seems to be in shadow, but I clipped this from your video. It's blurry but there does seem to be something around the base of that cap.



Mike

 

AND THE EAGLE EYE AWARD GOES TO .......

Toaster and Michaelh you guys caught it. I was packing it up before sending it to ASI and thought I would check the area you guys found suspicious and sure enough, there it was. A bleeding, moaning capacitor! Good eyes! I am still sending it out for troubleshoots and repair.

 

For a test, you can clean the conductive path with a Q-tip and alcohol or aftershave (for good smell),
but this is not a steady solution.
Nothing against ASI but order an exchange-ECU (current software and 5 years warranty) and till it arrives you can still use the car.


See the before and after photos below.

 

You guys are the absolute best! Cleaning that tiny piece of the circuit board fixed the problem. The car started up - ran smooth - threw no codes. I decided I had not much to lose so I went with it after your suggestion. I'm going to test drive it and will still get the ECU overhauled as that capacitor WILL leak again but for now I have a running little kitty.

 

I don't know how to changed the title to "RESOLVED" but I am happy to be able to write it! Thank you to everyone who helped - it was a great group effort.

 

Love to claim credit, but I only saw it after the prompt by toaster, although it was well hidden, m'lud.

Glad you got a temporary fix: wise decision to send for refurb as where one cap has gone others wil surely follow. I would hope that ASI would replace them all as part of the rebuild.

Well done that man

Mike

 

Exchange ECU's for a 97 are going to be pretty rare. When ASI does the repair they also replace components that are likely to fail in the future, and since they are sending your original unit back it' plug and play.

 

Congrats Brad, glad you figured out your problem. Your car is too good looking to not be on the road. Maybe we can do another Jag run this year.

RJ, I might be mistaken but I thought the 97 was the only year that the ECM was plug and play. I thought the 98 MY on were the ECM's that had to be introduced to the car.

 

Hey Bob!
I'm driving down to Chico for some meetings next week and I plan to buy some capacitors and slowly just change them out if the rebuild doesn't do it (which I don't think they will) in the next 3 weeks or so I will then re swap my TB with yours and hand deliver that sucker back to you!

Thanks again for your generous help!

 

Great news. Glad you found it. I would hope and expect that ASI replaces the caps. If you DIY, make sure to get automotive grade or better replacement caps or they will not last long under the hood.

 

I took it out for a test drive and the engine ran great - then..............

I got a check engine light - restricted performance - and was able to get home in this rain.

Codes were P0170 and P0171 - I looked them up and they seem like fuel trim or O2 sensor. I'm thinking ECU burping after a 10 day rest. Ugh

 

Brad,
Bear in mind that this cap has leaked its contents, so can't be doing its original job properly. You may see all manner of spurious messages until the ECM is repaired.

Mike

 

Chin up! It´s often only an ordinary air intake leak, check the vacuum hoses.