XJS 90, Speedometer Reads 20 MPH low
#1
XJS 90, Speedometer Reads 20 MPH low
The issue I'm having is that the speedometer stays at zero till I reach about 40 mph (Guess based on rpm), and then it reads about 20 mph below the actual speed. The odometer shows movement although the speedometer shows 0
So far, I cleaned the contact-points on the 2 plugs in the back of the speedometer housing. That did not solve the problem.
Has anyone had this or similar problem?
So far, I cleaned the contact-points on the 2 plugs in the back of the speedometer housing. That did not solve the problem.
Has anyone had this or similar problem?
#2
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#4
Thanks for your quick response.
I have already sanded all the contact points on those 2 big plugs on the back of the speedometer housing, using 600 emery paper.
No change.
I have not seen a specific ground cable, possibly the ground is at some points on either of those 2 big plugs.
About the ABS, it seems that a new pressure ball container will be necessary.
I have already sanded all the contact points on those 2 big plugs on the back of the speedometer housing, using 600 emery paper.
No change.
I have not seen a specific ground cable, possibly the ground is at some points on either of those 2 big plugs.
About the ABS, it seems that a new pressure ball container will be necessary.
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#8
Having driven at freeway speeds (California) as recognized by the speed of the traffic alongside, the speedometer registered around 30 mph. The average speed on the TC showed 25. After the reset the TC showed 0. Seems like the speed pick-up unit. How would one test this unit?
If the interface unit is outputting pulses then it is working, it is impossible for it to output a different number of pulses. It uses a digital counter so the output is directly proportional to the number of input pulses. It is possible for the diff VR or cable to be faulty causing the number input pulses to be incorrect.
Did you reset the TC while driving if you reset while stopped then the TC will average 0mph to 70mph which can significantly effect the average, the average of 0 and 70 is 35.................. not saying this is the reason but just be aware.
Best way to check speed is to drive car over a known distance and check the miles traveled on the odometer. If you mark out a mile on a deserted road reset the odometer and drive the car over that mile at ANY speed the odometer should read 1mile. Or you could get a friend in another car with good speedo both of you reset the odometer and drive a few miles and compare the readings. If the odometer reading is within 5% then the speed interface is working correctly and the problem is in the speedo needle drive mechansim. This is the way I would approach this problem.
Last edited by warrjon; 06-27-2017 at 05:31 PM.
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