Ford Scorpio Forum - Print Page


    
      
        Ford Scorpio Forum
        (https://www.fordscorpio.co.uk/cgi-bin/yabb/YaBB.pl)
      

        General >> Problems >> Tachomter fault
        
(Message started by: pinto on Dec 22^nd, 2009, 8:42pm)

Title: Tachomter fault
Post by pinto on Dec 22^nd, 2009, 8:42pm

Poor old cossie has been (for various reasons) parked up for 4 months now so on sunday I decided to just nip out and take a peek over her - battery as flat as a pancake :(

Soooo.... 2 day charge later, i connected it up, turned her over WOT until i had oil pressure and then started her up - chain slap for about a second (but i guess thats to be expected - it is a cossie ;D) before sweet, level tickover

All good :)... so I guess i should take it round the block to make sure its all ok.....

11 miles later and i'm in love again ;D you forget just how good these things are !!! ::)

Anyway...i digress....

When i bought her from amigafan, it had a slight fault on the tacho - it consistantly read about 1k rpm lower on the dial than the true engine speed; this didnt bother me much at the time, but now its deteriorated to a huge extent - tickover to redline shows as 0 - 1k rpm on the clocks !

The VSS must be supplying correct data to the ECU as the shift speeds and kickdown are all good...so.... any advice where to start looking ?

thanks :)

Title: Re: Tachomter fault
Post by gozz on Dec 22^nd, 2009, 8:59pm

Pinto.
Is the VSS not the vehicle speed sensor ? not too sure about the 24v,but most modern rev counters are energised by the alternator or the ignition pulse.
Someone is about to pop up and enlighten you I'm sure.
GOZZ.

Title: Re: Tachomter fault
Post by tlundkvi on Dec 22^nd, 2009, 9:59pm

Gozz is right, the VSS is just for measuring speed and used for various things but not rev counting. Did you check if the rpm error is just in the dash or does odb report the same error?

Title: Re: Tachomter fault
Post by pinto on Dec 23^rd, 2009, 12:11am

dash was a replacement unit just before i bought it (for this reason), and an OBD scan reveals no fault codes.

Alternator is functioning, so im unsure if this would throw a fault - only other thing i can think of is a fault on the EDIS 6 unit - i'll have to dig out my spare and try it.

Any other thoughts ?

Title: Re: Tachomter fault
Post by Tompion on Dec 23^rd, 2009, 12:54am

On the ENGINE CONTROL 2-9 24V EFI IGNITION.pdf it looks like WH/BK wire from pin 2 of the eloctronic DIS module, also links to WH/RD pin 48 of the PCM.

Title: Re: Tachomter fault
Post by amigafan2003 on Dec 23^rd, 2009, 7:39am

For the record - I tried two didfferent dash unit in it trying to resolve the fault - both were exactly the same - so it's deffinately not the clocks at fault.

Hope you get it sorted - I'd love to know what's wrong with it!

Title: Re: Tachomter fault
Post by Jonnycab on Dec 23^rd, 2009, 10:12am

Do you have the correct dash unit for a cossie ?

Also, as far as I know, the tacho works off a signal from the alternator.....so possible alternator diode fault :-/

Title: Re: Tachomter fault
Post by amigafan2003 on Dec 23^rd, 2009, 11:35am

Quote:

Do you have the correct dash unit for a cossie

It does (or did). I also tried another two clock units in it, both taken from a 24v Ultima - nothing changed.

Interestingly though - it always read 50% high when I had it. And when checking the type on the dash unit - it showed type 3 - i.e. 2.3 4 cylinder (for all three clock units). I can only guess the "type" isn't actually held as part of the clock unit but in the ecu/edis unit somewhere.

Another interesting fact is that the mileage didn't change on the clocks. i.e. I took a clock unit out of a 60k Scorpio and put it in my 130k+ Scorpio - the new clocks continued to show 60k. I always though the mileage was held in the ecu.

Title: Re: Tachomter fault
Post by pinto on Dec 23^rd, 2009, 8:22pm

Just read what i put and amiga was right - it did over-read, not under :-[ my mistake lol

I think i'll start by looking at the multiplug to the DIS unit.

Title: Re: Tachomter fault
Post by Stixy on Dec 23^rd, 2009, 8:59pm

I thought all rev counters were the same but depending on which engine a wire is either grounded or ungrounded

pin23 plug C470b instrument cluster

( the wire is earthed through the engine loom via pin 8 multiplug C120 )

4 cylinder ungrounded
12v v6 grounded through an engine type code resister
24v v6 grounded

Title: Re: Tachomter fault
Post by amigafan2003 on Dec 26^th, 2009, 7:14pm

You could be onto something there stixty.

Many a faulty has been traced to a faulty gound.