Hi all,

It’s time to help dad with his xjs again, this time with a suspected faulty gearbox ecu. Symptoms including a bit of a lurch when selecting drive and lurching between gears seem to suggest the gearbox ecu, so dad bought a replacement- I haven’t been able to definitively pin down where it is though, google searches and the manual we have suggest at least a couple of different places.

Where is it on a 1991 J-plated 4.0 facelift xjs? And is there anything I need to know about getting to it- special tools to remove particular trim etc?

If it’s on the passenger side I suspect water ingress through the faulty passenger door seal may be related- that’s the other task for this weekend…

Oddly, I don’t have a photo of the actual car on my phone, but it’s like the one in the attached photo. The photo of the gearbox ecu is the actual replacement one dad purchased.

thanks in advance for any info/suggestions

cheers

 

Lookingafterdasxjs,

I'm not sure about th early facelift 4.0, but I think it might b ein the passenger footwell on the sidewall. If so, there's a carpeted cover to remove and I think you also need to remove the lower A-post trim.

Just as a suggestion before you start swapping out the ecu, there are a few things that can cause exactly the symptoms you're experiencing:

- A faulty or badly-adjusted Throttle Position Sensor. This is notorious for causing a lurch into Drive or Reverse and harsh 1-2-3 changes
- Corrosion of the TCU connector.
- incorrect oil level in the gearbox. This is common to causing lurch symptoms. You must check the oil level in the gearbox only when it's hot and cycled through the gears at rest. IMO, there is absolutely no point in checking it when cold as it can give really conflicting readings. Even 0.5 litre short of the correct amount can cause lurching and even stalling when selecting Drive or Reverse.

I'd start with being sure about the gearbox oil level, and then check the TCU connector.

Good luck

Paul

 

A further note about checking the fluid level on automatics if you're not familiar with them is that the engine must be running and shifter in park. Engine oil is checked with the engine off, transmission oil checked when running.

The fluid expands considerably, so the hot part is important. That typically means a drive of at least 15 miles to warm up the fluid.

 

Great, thanks both- I checked with Dad and the gearbox oil was changed last time it was serviced by Jagutech over the summer, so I’m assuming the oil level was set correctly but it’s easy enough to check.

Will check the connection/connector to the gearbox ecu as part of the investigating, and check the tps- does anyone have a link to a guide to it, before I wade through google?

If the gearbox ecu is under the passenger side a-post trim I suspect it’s full of water… will let you know what I find.

Cheers

 

Behind the rear passenger right side interior 1/4 panel.


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