just bought my first jaguar! (gearbox fault?)
 

Nice to be here, i am Justas from Lithuania :)

i just bought my first jaguar 1998 jaguar xj8 4liter (with VVT solenoids)

it have 171000km so condition is very good but i noticed that something is wrong with acceleration, when i push pedal to max full throttle it accelerate till 4000rpm and then turns next gear., no difference ir 'S' is on or off.. where is the video below.
i have tried to drive with 3.2 engine for test and it runs well, rpm go to red line 7000rpm. , where the problem can be?? no fault codes coming nothing

On the N/S switch did you get the mode light ?:icon_shrug:

If not check the switch by looking for a ground at the transmission connector car direction pin 12 ( Red / Purple wire ) as you cycle the switch .

no red light on 'S' button no matter if i turn it on or off,

can this be a problem?

Yes , test the switch with a meter at the transmission connector . The light verifies that the transmission has switched as a follow up through the transmission . The meter will go from 0 to 20 ohms as you switch it from S to N . The ground may have been disturbed .

button ground may have been disturbed? that's the Red / Purple wire that goes to gearbox control module under the hood?

I don't have the X308 but mine is under the dash on the passenger side very bottom , very fwd . The Red / Purple wire is not a ground but a point to point wire that you would use to read through to switch to the ground coming out of the switch . This keeps you from removing the switch however hard that would be .

I have tested today 'S' button,. no problems detected.

the problem is when i turn it ON red light lighting everything is okay, but after one hour or more driving red light disappears and and there is no way to turn it on, need to cool down the engine and then all good okay.

can this be a Gearbox ecu problem?

and plus acceleration is not so good with my jaguar.. today i tested friend xj8 4l engine and it starts from stop light like insane.. mine is not,. feels like you start to drive with 2nd gear, but it's 1st gear.

very very sad day today..
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Do you get a 'transmission fault' message in the display? Does it at all change gear? Can you manually select the gears?

From that same transmission connector you can read all the shift solenoids as they should read the same resistance . If you have to replace a solenoid it's easy just drop the pan and plug and play .

no fault messages.. i can manually select all gears while driving.
it just starts so slowly to accelerate, fells like you start to drive with 2nd gear, but i have tested, is starts to drive with 1st gear,

maybe my engine i weak? :(

Hmm, so, it accelerates quite slowly. You can select all gears. Do the revs build up slowly and does it bog out?

Is your spark advancing all the way?
It should be ~4 at idle, then advance to some ~30 degrees at acceleration / higher rpm's.

You can simply check it by using a bluetooth or wifi connector (depending phone) in the OBD plug, and a program on your smartphone.

Maybe a long shot, but I am asking, cause there was a UK member here last year, having same kind of problems of lacking power and strange shifts.
He went through a lot, only to find out his knock sensors were toast, but they refused to throw a code.

His car drives perfectly after replacing the sensors.

Daim - revs are very good , not slow at all,

ericjansen- where knock sensors are located ? i just waked up and driving to buy elm327 bluetooth scanned , i have also purchased torque pro app , maybe there i can see some useful information, but im still not sure what i should search in the app to see " spark advancing"

It is called timing advance in Torque.
And the sensors are located in the V, partially under the intake manifold.
Not much to see though.

sad news.. tried 2 different obd2 bluetooth scanners .., not possible to connect to car ECU :(

You have a Android phone?
Cause Bluetooth does not work with Apple, then you need a Wifi adapter.

yes android , connection to obd adapter was established but with car ECU - not :( was using torque pro

anyway i bought this one few mins ago https://www.ebay.ie/itm/iCarsoft-i930-OBD2-Device-de-Diagnostique-CanBus-Scanner-Pays-Rover-Range/201999939478?ssPageName=STRK%3AMEBIDX%3AIT&_trksid =p2057872.m2749.l2649

hope jaguar will be listed ., because on some youtube videos about iCarsoft-i930 jaguar was lot listed , only rover , look

Look for the 2nd TPS that feeds the transmission ECU separate physically from the 1st that feeds the engine ECU . Have you cleaned the electrical connector on the transmission itself , gets contaminated by a common fluid leak from above as well as the general environmental conditions . There is a speed sensor at the input end of the transmission as well as one in the output end and a error in these signals may error the shifting schedule or sequence .