Hello all.
The tranny on my 1992 is not shifting so I am posting here to get some advice.
Here are some observations:
1. The transmission light on the dash is not lit.
2. The Sport mode light does not turn on.
3. Fluid level is good. I plan to drop the pan and change fluid & filter.
4. I am not sure what gear it is stuck in as take off from a standstill is perfect so its either 1st or second gear.
5. ?? Limp mode should be 3rd gear therefore taking off from a standstill should be sluggish. or so I have read on this forum.
6. Since I am not feeling any shift, I look at the Tach to see if there is any RPM change associated with a gear shift. There is no RPM change.
The car accelerates in the same gear and at around 50 mph the tach is reading 2200 RPM.

Previously as mentioned in one of my posts:
When I purchased the car, it was not running.
I found that the Neutral safety switch (rotary switch) had a burnt harness and the shifter cable was very stiff.
1. I repaired the harness.
2. I replaced the gear shifter cable.
3. I replaced the tranny mount.
Since I do not know whether the shifting problems were happening prior to me doing the above, I am at a loss as to where to start diagnosing the shift problem.
I am going to be putting the car on jack stands to review what I did with the N/S (rotary) switch and change out the fluid and filter.
In the meantime any and all advice will be entertained.
Any questions to add clarity to the issue will be responded to promptly.
Thanks in advance.

 

Hi sanchez,

As you know, the rotary switch is mounted on the gear selector shaft on the gearbox. It not only contains the start-inhibit switches, but also electrical connections for all the gear positions available at the J-gate, which are communicated to the Transmission Control Module (TCM) via the electrical connector at the rear of the transmission. Problems with the rotary switch, the transmission electrical connector, or the cable adjustment can definitely lead to gear shift malfunctions.

Gear shifts also depend on communication between the ABS Control Module and ABS wheel speed sensors (vehicle speed), engine speed signal (Crank Position Sensor (CPS)), engine load signal (Mass Air Flow sensor/MAF), engine Coolant Temperature Sensor (CTS), Throttle Position Sensor (TPS), the Engine Control Module (ECM), Transmission Control Module (TCM), etc. Have you checked the Vehicle Condition Monitor for any stored diagnostic trouble codes that could indicate a problem in one of these circuits or components?

I know you don't have the transmission warning lamp illuminated, but John Ping at the Jag-Lovers forum authored an excellent procedure for the 4HP24 that might be trying anyway:

Jag-Lovers XJ40 eBook Transmission Troubleshooting

Cheers,

Don

 

Thanks Don.
I read and printed out John Ping's article.I will perform some of the tests that I think are relevant to my issue.
Just to recap.
I bought this car in the following condition:
1.No start. I used a car carrier to move the car to my house.
No start issue resolved by replacing the fuel pump and filter.

2. Car would not shift out of Park.

Cause: Burnt shifter cable and Rotary switch harness.

Replaced shifter cable and repaired Rotary switch harness.
The round connector that goes to the transmission was not damaged.
Following the procedure of putting the transmission in neutral and the shifter in neutral to set up the shifter cable, the car would not start in park.
I did some adjustment of the cable at the transmission end and it now starts in P and N.
The plastic piece in the J gate where the shifter resides was broken. This is the piece that also allows you to manually shift the transmission.
I have that piece on order and in the meantime, I just flipped it upside down so now the broken portion is where the manual shift pin is.
I also replaced the rubber parts of the transmission mount, but I am sure something is wrong there. The transmission is sitting too high and is touching the tunnel.
Now the shifting issue.





Broken plastic thingy
I will be going back under the car to see if anything is askew with the round connector at the transmission. I read that the rotary switch has nothing to do with transmission shifts.
Is that correct?

 

Hi sanchez,

Don't rush to second-guess John's diagnostic procedure. Some of the tests that may seem irrelevant may be more important than you realize due to the complexity of the system.

Well...the transmission is electronically controlled, and the rotary switch is a central communication point for the system. Here's what the Technical Guide has to say about it:



So, for example, if the rotary switch tells the electronics that you have selected 2nd gear at the J-gate, then the transmission will be prohibited from shifting beyond 2nd gear. So from that perspective, a problem with the rotary switch or oil contamination of the transmission electrical connector can cause shifting problems.

You can download the Technical Guide here:

Jaguar XJ40 Technical Guide New Model Introduction 1990

Cheers,

Don

 

Note that the order of the components shown in the diagram above is correct. If you refer to the Haynes manual, the photos show an incorrect assembly order. Haynes shows parts 5/6 fitting on top of Part 7, but that is incorrect. As the Jaguar diagram above correctly shows, the locating weight, Part 6, fits inside the spring cradle (a metal cup), Part 5, and the foam buffer, Part 7 fits on top. If you follow the Haynes instructions, the mount will not perform correctly.

Based on the above, the order of components in the pic below will not be correct.

incorrect?



Foam buffer inserted before the spring cup. Item #2 should go under the foam buffer??

 

Hi sanchez,

Sorry, I was going to mention the problem with the Haynes assembly instructions in my previous post but forgot. This error has been well-known since the Haynes manual was first published in the '90s.

Did you mean to include the exploded diagram from the parts catalog in your post? If so, here is the diagram for the cars up to roughly 1992:



And here is the diagram for the 1993-94 cars, with the "check cable" or travel-limiting strap shown as part 19:



Cheers,

Don

 

My car is a 1992. I have not seen part#s 14 thru 17 on the car.
The way I have the mount assembled seems to be incorrect as per the above diagram.
I believe I have Parts 5 and 6 on top of part 7.
I will disassemble and reassemble the way it is above and post the results.
The question I have is whether the assembly to the left in the image above (Parts 9 thru 12) just goes thru the top of the assembly to the right( parts 2 thru 8)
If so, it means that the transmission just floats on top of part 5 via the small spring and is not bolted in any way to the assembly. See attached pic.

this is what is connected to the transmission. This part just sits on small spring
I am also going to the JY this morning to get the rotary switch and the transmission module from a 1990 XJ40.
I am hoping that they would be the same as the 1992

 

@ DONB: Thany you so much for your input.
I removed and reassembled the transmission mount as per the image you posted above.
Result: The transmission no longer touches the tunnel.
One problem resolved.
I also replaced the Rotary switch, but I had to de-pin the 1992 connector(Brown) to put it on the 1990 Rotary switch(yellow)
The 1990 switch had the same number of wires (15) as the 1992 switch and the wires were all of the same color, just in different locations
The connectors can come apart from the back (wire) side and I used a GM tool to de-pin the wires.
Now I have to see why the tranny is not shifting. Now to under the passenger side dash.
I will drop the pan and replace the fluid and filter in the next couple of days.
Thanks again.

 

Transmission:
Replaced the shifter cable.
Replaced the rotary switch.
I disconnected the transmission lines and used 10 quarts of tranny fluid to flush out the system.
Having done that, I dropped the transmission pan and replaced the filter and gasket.
Transmission still not shifting.
Resistance reading at TPS was 4.75 ohms at closed throttle and 1.8 ohms at WOT.
Removed throttle body and replaced and adjusted TPS. Readings now as shown below.
Transmission still not shifting.

Closed Throttle

Wide open throttle
Now that the TPS is at specs, what else can I check?
I swapped out the Transmission ECU DBC6328 but still no shift.
Note: The transmission is not in LIMP Mode. No transmission light 'on' in dash.
What kind of readings should I see at the round connector going into the transmission?
Anyone?

 

Hi sanchez,

Do you have any diagnostic trouble codes (DTCs) stored in the Vehicle Condition Monitor (VCM)? I'm wondering about things such as a code for the ABS or any ECM code. It's possible you have a problem with a solenoid or pressure control valve in the valve body, but I still think an electronic issue is more likely.

Cheers,

Don

 

I hope you don't need it, but I have a NOS valve body with soleniods here.

Good luck,

Rob

 

Thank you Don for this: Jaguar XJ40 Technical Guide New Model Introduction 1990
Using the transmission electrical schematic from the above and the one from the 93/94, I did some sleuthing around this morning and the problem of No Shifting has been resolved.
Doing some electrical checks, I realized that I had a common issue at the Transmission Relay, TCU and Decoder module.
There was no power at the Brown/White wire at the Transmission Relay therefore no power at the TCU or Decoder module.
Tracing the Brown/White backward ended up at C3 of the left hand side fuse panel.
On the fuse side I had power on both legs of the fuse.
Removed fuse panel and there was practically no solder on the output wire (Brown/White) which goes to the Transmission Relay, TCU and Decoder module
Re-flowed the solder and power was back.
Transmission now shifts as it should.
Now it on to the final electrical issue.

 

Way to go, Sanchez! Your persistence paid off!!!

Congratulations!

I will mark your thread RESOLVED.

Cheers,


Don

 

@DONB: Thank you again for your interest in this post.
FYI, I reflowed the solder on all the connections behind the fuse panel.
Tomorrow, I will remove and inspect the right side fuse panel to see if anything is looking funny there.

 

Usually both are kaput.

Larry

 

Awesome! Great job with tracking that down!!

But now this is making me worry. I have literally had ZERO issues (touches wood) with the fuse boxes in my '92. Now I'm wondering if I should check them out before something like this happens.

Nick

 

Thank you Sanchez for closing the loop and adding to the collective knowledge of this forum. Great work!

 

The center console fuse box can also have bad solder joints.....

 

Yes, I agree. I also removed and inspected the center fuse box and all looks good there.
Note: Prior to resolving the gear shift issue, as stated in an earlier post, the car would stay in one gear.
When placed in reverse it would bang as if the RPM was too high and you had bad U-joints.
Upon the resolution, with all gears shifting, the reverse is also nice and smooth.
I installed four new tires today and took it for a test drive. The gear shifts are so smooth, you barely notice them.
The "SPORT" mode also works as it should.
Now, if I could only let people know when I am turning. (See my post "No hazard/Turn Signal)