Thread: Clueless rev issue

Have you tried the stall test as per RAVE? This might tell you if the TC is at fault

Have you confirmed the speedo reading?
Maybe? the transducer for the speed sensor is out and telling the speedo 120K, but you're going faster?

Originally Posted by Marmoset

Have you tried the stall test as per RAVE? This might tell you if the TC is at fault

Thanks, the stall test unfortunately wont tell you anything with regard to lockup on an auto and the clutch. D2's only lockup in 3 & 4 high and above 2000rpm with 0% throttle in Low range.

Tyre size also doesn't make a diff since the speed sensor is electronic pickup off the auto and rev and speed counter's get info from the ECU. Both Discos are running 245's and speedos are roughly 8km/h slower than the Garmin. This makes it even worse ! and one can hear the engine is running high. 255 tyres give correct readings.

My personal D2 is also a mystery regarding this, not that I complain. Lockup in 4th appears at 92Km/h and drops from 2500rpm to 2000rpm !! At 120 I'm only doing 2500rpm? And I'm running 265 tyres.

There does seem to be a vague connection with similar pre facelift Discos running NNN ECU's like mine. They appear to have lower rpm's...

When installing the new Trans did you reset the transmission adaptation?

Sent from my iPhone using Forum Runner

Hi Tombie, nobody our side seem to have a answer for me.

Yes, in both cases it was done, on Deon1's Disco various times with me driving it in S mode afterwards... No diff apart from lockup which shifts ever so slightly.

I'm now down to tyre size. Correct me on the following.
Speedo and rev counter doesn't share any input origins.
So with smaller tyres you would have higher revs, right?
Your speedo would be out showing an over reading.
And the opposite for larger tyres.
BUT what happens if one only look at true speed. (both drivers base their readings on speedos)
Small tyres
You would reach 120 on the speedo and only do say 110 - at 1:1 gear ratio revs would be lower at 110 and go up as speed goes up, so...
Big tyres
You would reach 120 on the speedo and do say 135 - the revs would be higher because you haven't touched the gear ratio?
Am I loosing it?

Changing tyre sizes shouldn't change the relationship between indicated revs and speed, except possibly while the converter is unlocked and you need more slip to maintain the same speed than with standard tyres.

The relationship between revs and indicated road speed will change with 1. alternator pulley size (this drives the rpm signal) and of course 2. the transfer case hi ratio if it has been changed.

Just a thought.

Does the gearbox ECU use the transducer for its road speed input or does it use the ABS output?

HTH
Andrew

Originally Posted by nobbyclrk

Just a thought.

Does the gearbox ECU use the transducer for its road speed input or does it use the ABS output?

HTH
Andrew

Gbox ecu uses the ZF output shaft speed sensor only.

Speedo gets signal from ABS slabs ECU, while tachometer gets its signal from the engine ECU. Tacho does not come from the alternator.