I have a 1988 XJS with a TH400 but have converted to a 5 speed and am trying to get the speedo to work with the rear end of a 1994. The 5 speed Tremec does not support the DAC4569 impulse sender. I can make the speedo spin when I twist the small paddle at the end of the DAC4569 with it wired up in my hand. Now I am trying to use the pulse signal from the differential. Unfortunately I missed the cut off In 1988, the pulse generator DAC4569 on the transmission was eliminated. The speedo interface and diff mounted speedo transducer began with VIN 144263, about half way thru the '88 model year.
I can see the diff signal in the trunk across the red and blue wires looking at resistance an voltage changes with wheel spinning by hand. I have been sending the output from the trunk to where the DAC4569 was connected.
I have a used speed interface that should send a signal to the speedo connections but the speedo does not move.
Any help would be great.
Thanks
Chris
Do you get any reading on the trip computer by the radio - if yes, then you may have to change the dash instrument to be able to get a reading - maybe from an 89 model.
If I am not mistaken, the earlier speedo is looking for a 12v square wave at 8000/mile; late ‘88 is 5v square wave at same rate. Differential sensor is a 2wire VR sensor, so produces a sine wave type signal that varies in amplitude with speed, hence the need for the interface module.
If you know a little about electronics, you could make a MOSFET amplifier with a small number of components and a 12v feed…they are also available online.
You could try feeding the speedo with the signal that feeds the traveler…at your own risk!
I have the opposite problem. I lost the sensor in the rear diff when I swapped in an earlier diff to get 3:54 gears. I plan to experiment with one of these as a solution: Summit Racing® GPS Speedometer Sending Units - Free Shipping on Orders Over $99 at Summit Racing
Maybe it will work for your situation. I don’t have cc or trip computer so I am only worried about Speedo.
There’s a video somewhere where a guy strapped a couple of magnets in a ring around the drive shaft and mounted a magnetic pickup nearby.
I did that decades ago. Not my design. I bought a trip computer. Audovox sounds familiar. Magnet strapped to the drive shaft provided Rpm.
And, then cruise control. Same source. I used the same magnet or the speed signal…
I added lots of gadgets added to that base model 70 IHC Scout II. CB, stereo, etc… Twin spot lights ala cop car. They actually came from a derelict Mopar x cop cruiser. It ended life as a jalopy racer.
Dakota Digital has a line of devices used to provide instrument signals. My Jaguar has one. I used the wrong wires. It works but not quite correctly…
That’s the idea I am using on my MGB V8; 2 magnets epoxied to the output flange of the transmission with a reed switch sensor.
Next generation that I am in the process of building is a Hall effect sensor with a MOSFET switch to invert signal to what the ECU is looking for.
Biggest problem with either is getting the pulse rate to be what you need…my ECU just needs A signal to detect whether the vehicle is moving for idle control.
I’m being a little facetious here by saying … the response of engineering of electronics discussion is too much overkill… Just someone tell him how to make it work
Here i where Dakota digital comes in… Good tech support for projects as well/
no trip computer changing with the diff input sensor but when I spun the paddle blade by hand with it wired to the system (no longer connected to the on the trans speedo) it was working and the speedo worked.
but that was fore the early1988 when it was connected to trans.
I guess I have to recreate the 8000 pulses to the yellow speedo signal.
Hi Robert
I was looking at some gps speedometer 4000 pulses 8000pulses and 16000pulses.I may have to go that way or hire some mice and put some cheese in a wheel. Not givebn up yet.
Maybe I will just tell the officer that I was going 110
because the mice in the wheel drank too much coffee with there their cheese
The GPS is probably the easiest route, but contact that Dakota Digital for their .02; they probably have run into this before.
I wonder if John’s Cars in Texas would know of a solution, their conversions to 4L60 transmissions must have a work around.
Hi Robert
Today I had my early 88 with a 3.54 diff with wheels up I connected diff sensor to the to speed interface then powered it up. I turned on the car and put in 1st gear, with wheels rolling I got a 10.2v signal output to blue and red wires
then I used my meter with the frequency function. I got 17-18 HZ at about 850 RPM bouncing a bit. So the amp works and I will do more testing when I have a helper since I am in the trunk. The question is where should I apply the red and blue wires. My transmission speedo was up front in the transmission. Where is those dam mice when you need them.
Hi Robert
Today I had my early 88 with a 3.54 diff with wheels up I connected diff sensor to the to speed interface then powered it up. I turned on the car and put in 1st gear, with wheels rolling I got a 10.2v signal output to blue and red wires
then I used my meter with the frequency function. I got 17-18 HZ at about 850 RPM bouncing a bit. So the amp works and I will do more testing when I have a helper since I am in the trunk. The question is where should I apply the red and blue wires. My transmission speedo was up front in the transmission. Where is those dam mice when you need them.
Don’t know the colors of the trans-mounted speed sensor, but one should have 12v with key on; the other is the signal, which would be connected to your blue. Red is to travel computer. The signal wires are unbalanced shielded (single wire) relative to vehicle ground.
If I recall, 133hz = about 60mph. Was 17hz at idle rpm in first or top? I think I am at 2200 at 60 mph…which would be the 133hz. You will be about 2600 in 4th.
Robert and Chris,
The speed interface unit is normally mounted in the trunk, behind the trim, and over the left rear wheel arch - like the area used by the ABS ECU if you have one. Attached is the relevant schematic from the '89 XJS we had a number of years ago. You can see the connections and wire colors to the speed interface unit, as well as the coaxe shielding.
1989 XJS Speedo Circuits.pdf (284.1 KB)
Thanks for the info lockheed and Robert I think I am getting close.
My problem is that there is no Speed Interface in my car. I was to early
to get this. So I bought a used 96 interface put it in the trunk and connected it to the diff sensor. Found a ground and hot wire fired it up. Lifted the rear and took measurements. at 1000rpm had 18 HZ
at 1500 rpm had 29 HZ
at 3000 rpm had 50HZ
I wired up 2 wires from the trunk thru the sunroof and into the area where the old sensor lived. Took a drive and things were working but not quite right. Speed was low the trip computer had some info so I am going in the right direction. I am not sure about the shielded wires. That may be what the problem is.
Perhaps I should use coax cable for the red and blue wire.
Keep in mind that none of this speed interface existed in my trunk. My speedo was in the TH400. BTW thanks for the help back in October with the rear end swap. Your pictures and info were extremely helpful.
Thanks
Chris
The frequency is off, should be in mid hundred hz at 3000 rpm. What part number is your interface? There are a couple of part numbers, but I assumed that the difference was the connectors. How far off is the speedo? If exactly half, you might be able to use a circuit to double the rate.
Measure the frequency at the differential sensor leads under same conditions. If it is the same as measured before, you may need to see if someone makes a correction device. Or go GPS.
You indicated that you measured the same signal level on blue and red; try reversing- red for speedo…