'88 Mondial tachometer...

Hi Urs that really helps as I also need to fix both my rev counter and Speedo which show slower speeds than they should. Did the adjustment fix both instruments?

Did you first try to clean the potentiometer as posted above? If so did it not work?

Thanks.

 

Hi Peter

I needed to adjust the speedo as I recently noticed that my usual travel times came down...
I sampled some modern cars with the Car Performance App on an iPhone and found it consistent with their speedos readout at constant speeds. I calibrated my speedo with that app and it is spot on at legal road speeds now.
I haven't double checked the rev counter yet since the low readout incident, but will do so soon. It seems close to reality though (double the rev readout equals the speed in mph). Let you know when I have done so.

Cheers

 

Sounds great, i will hopefully do it when the weather improves. I tried a few of the GPS apps but were not very accurate or had a time delay. I will try the one you mentioned as well as cleaning the potentiometer and see how its goes.

Thanks very much.

 

An update on the speedo and rev counter issue:

I did the above recommendation and cleaned the potentiometer in the 2 instrument mechanisms and the speedo and rev counter are is still the same, i.e. they are displaying slower that they should, very lazy.

I did however try Afterburners advice too and turned the potentiometer clockwise and the speedo now works perfectly, however i have not adjusted it accurately yet as i need a reference to compare with such as another vehicle driving next to me or a gps speed app on my mobile phone, but by turning that adjustment screw it is the solution to the problem.

I also want to try the same with the rev counter but i have no way of knowing what the revs should be at any point in driving, there is no reference, or is there? Is there a tool or something or do some timing guns display the correct revs?

Thanks.

 

Peter, most engine tune sets comprise a timing gun, compression tester and a multimeter that allows to check V, A, Ohms, dwell and rpm (often with a fine position for setting idle and a normal position covering the entire range). This hooks up to 12V power and has an induction connector that you attach around one of the spark plug cables. Depending on the instrument and the setting, you might have to double the reading for an 8 cylinder if the instrument is for a 4 cylinder, for ex.

 

Thanks Urs, I will see what I can find. I have a regular timing gun which I purchased a while ago to check spark on the wires and that's all it does, very basic. I wouldn't trust myself to tune it up as I don't really know what to do but something that shows me the revs simply with an induction wire sounds good.

Thanks again, slowly we are getting there once again

 

This is really great DIY guide!!

i just fixed my tachometer!! I don't know how to calibrate the rev too..

switch off engine, the needle rests at 500rpm. Warm engine idling at 1000rpm.. Mine is 3.2 & I have stock TRX tyres. Any one can tell me what's the correct rpm at 5th gear 100kmh? I can use GPS to calibrate the speedo.. thanks..

 

2'975 according to my information... no guarantee though.

 

Thanks AB.. at least I have a reference now

 

Welcome. My tach is a tad low (-200rpm) too so I am going to trial and error it as well.

 

Hi AB, at 100km/h (speedo), my rev is a tad lower, ~2800rpm (vs 2975). So it's ~200 lower too. When GPS shows 100km/h, speedo shows 100km/h, rev ~3000rpm.. time for trial & error when I have time Thanks.

 

Hi F-car ... there is an inconsistency in your post ;-):

at 100km/h (speedo), my rev is a tad lower, ~2800rpm

next sentence:

When GPS shows 100km/h, speedo shows 100km/h, rev ~3000rpm..

 

Oops.. sorry. GPS 100km/h, speedo 110km/h, rev ~3000rpm.. too much alcohol

 

Hope after the driving ;-)

 

For adjusting the speedo: CW increases the readout
For adjusting the tach: CW decreases the readout

 

Thanks AB! Looks like our readings are identical, at 5th gear speedo 100km/h, rev ~2800rpm. Is your speedo reading matching GPS reading?

 

Welcome. Yes, my speedo is matching the GPS at 100km/h (that is how I set it), and over-reporting about 2km/h at 50km/h, which is a welcome speeding ticket anti-measure.

 

My Tach problem is a little different under 3000 +/- rpm it has a tendency to want to double the RPM, over that it seems to read correctly vs speed in gear. Ideas? 1982 Mondial 8

 

Hi Frank

I am not familiar with your problem of lower rpm over-reporting... my advice would be, just to start, to make sure that all the connections are fine, incl. at the ignition ECU. Pull the multiplug and make sure there is no corrosion. The tach is easy to pull, so undo and clean the connections behind it to assure there is proper contact.
The next thing I would do is take it apart, mark the position of the potentiometer, and then move it back and forth a few times, using some contact cleaner spray. Put it all back and see it the problem persists.

Good luck
Urs

 

Zombie thread resurrection...

That's why I love FChat! My tach is doing the same thing and now I know how to fix it!

Thanks to all past, present and future members for sharing knowledge!

James