Classic Rev counter / tacho has stopped working

[jwrrc]

Sorry if this has been answered before (I had a look on search but I'm not the best with technology, Luddite springs to mind)

Red Rover - 1988 Classic, engine swapped for a 200TDI

My Rev counter has worked for the 18 months I've had the car. Sometimes it would stick at 0 on startup, but it'd jump to life when you touched the loud pedal.

Last night it decided to stop altogether, and the charge light is illuminated (red battery light)

Am I right in thinking thetefore:
Problem is electrical and at the alternator end of things?

Thoughts on a postcard!

Many thanks in advance to anyone who can point me in the right direction

 

[Lezley]

Don't know your car but on my last 300tdi disco rev counter was driven by the alternator. I guess it gets an output based on speed it is spinning. If the battery light and rev counter are out then my guess would be goosed alternator. Easy tested with a volt meter.

 

[jwrrc]

Don't know your car but on my last 300tdi disco rev counter was driven by the alternator. I guess it gets an output based on speed it is spinning. If the battery light and rev counter are out then my guess would be goosed alternator. Easy tested with a volt meter.

I think it's probably wiring for the Rev counter, seems to charge OK (never has problems starting even on a cold day). I'll check alternator output tomorrow though, as it's a very valid point. Thanks!

 

[Disco1BFG]

Tacho is driven from the "W" terminal of the alternator - which is a half wave output from the rectifier - so, your rectifier is almost certainly kaput, ... unless the simple fact is the wire has fallen orft .. this happened here not that long ago - you can ask SWMBO how she knows !

Mid ulster rotating electrics have the spares for your alternator - BUT, i'd make damn sure you get the right regulator - it's par for the course now for regulators to allow rather silly voltages - like 15.3 ... and this will not do the relays and such any good on your RRC - if you have an MFU or an alarm, it will toast it nicely.. you can ask me how I know this too

I now use Hitachi regulators which limit voltage to 14.2, and, when they come off load - like when you switch your lights off, they drop the voltage instantly ...

And, yes, this has become something of a soapbox for me

 

[jwrrc]

Tacho is driven from the "W" terminal of the alternator - which is a half wave output from the rectifier - so, your rectifier is almost certainly kaput, ... unless the simple fact is the wire has fallen orft .. this happened here not that long ago - you can ask SWMBO how she knows !

Mid ulster rotating electrics have the spares for your alternator - BUT, i'd make damn sure you get the right regulator - it's par for the course now for regulators to allow rather silly voltages - like 15.3 ... and this will not do the relays and such any good on your RRC - if you have an MFU or an alarm, it will toast it nicely.. you can ask me how I know this too

I now use Hitachi regulators which limit voltage to 14.2, and, when they come off load - like when you switch your lights off, they drop the voltage instantly ...

And, yes, this has become something of a soapbox for me

You're a bloody star!

Thanks for preempting some seemingly unpleasant lessons for me!

I've checked and the wire hasn't just fallen off (it was my first tbought!). Time to get things taken off and bench tested tomorrow, that'll be fun

 

[Disco1BFG]

You're a bloody star!

Why thank you.. - it's funny you say that, because I do actually have a star named after me! Our kids did that for me as a chrimbo pressie some years ago ..

If you have a decent DMM, measuring the AC voltage across the battery terminals should give you a good guide - ideally you'd want to see 5mV ... certainly no more than 15mV

If Mid Ulster can't supply the correct set point regulator, then www.buycarparts.co.uk - who are actually based in Germany should be able to. Assuming it's a Lucas Marelli A127x, then the reg will either be (Hitachi)130799 or 130820 - The rectifier is a Lucas 131304 ..

Here's a link to the mid ulster A127 page:-

https://www.rotatingelectrics.co.uk...or-rectifier-regulator-hd-vr-lc111-mob-rl-01h

As I mentioned before, watch the set point of the reg like a bl**dy hawk!!

 

[Ratae]

Tacho is driven from the "W" terminal of the alternator - which is a half wave output from the rectifier - so, your rectifier is almost certainly kaput, ... unless the simple fact is the wire has fallen orft .. this happened here not that long ago - you can ask SWMBO how she knows !

Mid ulster rotating electrics have the spares for your alternator - BUT, i'd make damn sure you get the right regulator - it's par for the course now for regulators to allow rather silly voltages - like 15.3 ... and this will not do the relays and such any good on your RRC - if you have an MFU or an alarm, it will toast it nicely.. you can ask me how I know this too

I now use Hitachi regulators which limit voltage to 14.2, and, when they come off load - like when you switch your lights off, they drop the voltage instantly ...

And, yes, this has become something of a soapbox for me

Regulator failed on mine last summer (2021) in deepest darkest Cornwall.
19+ volts.
Blew the aftermarket radio fuse, the aftermarket immobiliser fuse and cooked the battery.
Consider myself lucky that was all & it didn't set the thing on fire!

 

[Datatek]

Battery light staying on plus no rev counter equals alternator failure.

 

[jwrrc]

Much obliged to all of you for your help. I hate electrics if I'm honest, it's part of why I love the 200TDI so much, there's not much electricity involved in the process!

As I daily drive the old girl, I've purchased a replacement alternator and will order a rectifier. Then, like the intercooler, I can run one and rebuild the other as needed and keep her on the road.

 

[Datatek]

Much obliged to all of you for your help. I hate electrics if I'm honest, it's part of why I love the 200TDI so much, there's not much electricity involved in the process!

As I daily drive the old girl, I've purchased a replacement alternator and will order a rectifier. Then, like the intercooler, I can run one and rebuild the other as needed and keep her on the road.

The fault in your alternator is more likely to be the regulator or brushes than the rectifier pack.

 

[jwrrc]

The fault in your alternator is more likely to be the regulator or brushes than the rectifier pack.

Noted, with thanks, I'll probably buy a complete rebuild kit, then I know I have a fully functioning one on the shelf if and when I need it. I'm planning to keep Red Rover for as long as I can (not like Brown Rover, which I'm hoping will be gone in the next 12 months) so having spares can only be a good thing!

 

[Disco1BFG]

I'll probably buy a complete rebuild kit,

Good call - Just make sure the reg has the right set point - ask them - or just buy the Hitachi one!

 

[Disco1BFG]

Regulator failed on mine last summer (2021) in deepest darkest Cornwall.
19+ volts.
Blew the aftermarket radio fuse, the aftermarket immobiliser fuse and cooked the battery.
Consider myself lucky that was all & it didn't set the thing on fire!

I agree you were lucky on that one too - I'm told that the Hitachi regs fail safe, or at least are designed to do so - given the low price it's a complete no brainer for me. Viz:-

https://www.buycarparts.co.uk/hitachi/7825663

Set point 14.0V

 

[Datatek]

Good call - Just make sure the reg has the right set point - ask them - or just buy the Hitachi one!

Set point should be 14.7 volts

 

[Disco1BFG]

Set point should be 14.7 volts

Sorry, but this is in your opinion - mine is somewhat different, and my experience is that D1 electronics will not tolerate either 14.7 V OR the SOP of all the regs I have tested ( except the Hitachi ones )

The others allow the voltage to rise to very silly levels when a load is removed - I saw 19.4 V on removing a 25A load from one reg - thus it was hardly surprising my MFU was completely toast.. IIRC this reg was a Mobiltron, supposed set point was 14.7, and it was new.. Calibrated Fluke DMM too....

Bear in mind that I did not want this knowledge.. but it was forced on me given the lack of availability of new MFU's, AND that I couldn't find anyone to repair same either..

My MFU is long gone, replaced by a series of relays - I've lost some functions,intentionally, but they are completely unnecessary IMO.

 

[Datatek]

Sorry, but this is in your opinion - mine is somewhat different, and my experience is that D1 electronics will not tolerate either 14.7 V OR the SOP of all the regs I have tested ( except the Hitachi ones )

The others allow the voltage to rise to very silly levels when a load is removed - I saw 19.4 V on removing a 25A load from one reg - thus it was hardly surprising my MFU was completely toast.. IIRC this reg was a Mobiltron, supposed set point was 14.7, and it was new.. Calibrated Fluke DMM too....

Bear in mind that I did not want this knowledge.. but it was forced on me given the lack of availability of new MFU's, AND that I couldn't find anyone to repair same either..

My MFU is long gone, replaced by a series of relays - I've lost some functions,intentionally, but they are completely unnecessary IMO.

Lead Calcium batteries require 14.2 to 14.7 volts to fully charge. Removing a load if the battery is connected cannot let the voltage rise as you describe but a bad earth can. All vehicle electronics of that era were designed to operate with 13.8 volts, it's highly unlikely that the regulator chips used would fail at 14.7 volts and certainly not with 14.2 volts.

 

[Disco1BFG]

Lead Calcium batteries require 14.2 to 14.7 volts to fully charge. Removing a load if the battery is connected cannot let the voltage rise as you describe but a bad earth can. All vehicle electronics of that era were designed to operate with 13.8 volts, it's highly unlikely that the regulator chips used would fail at 14.7 volts and certainly not with 14.2 volts.

Several of the transistors on the MFU PCB were black - let the smoke out IMO.. to my knowledge there are no regulator chips in it.. Note that these units are >25 years old, "made" by the prince of darkness, and not available new in any way shape or form.. nor repairable to my knowledge ( I did ask a few - even a few on here ) - so, what could I have done differently ?

In terms of charging - all the batteries are are relatively new, essentially all replaced at the same time, and AFAIK all PbCa. They're all charged (now) using Hitachi regs, and none of them give any trouble,, and all test as good using my TopDon BT50, as do all the charging systems..

As you say, this vintage of vehicle electronics were designed to run on 13.8V, so 14 is as close as I can get without going remote regulator, which we very seriously considered given the cost of getting this knowledge in the first place..

We're years into this experience now, and the problems have gone away, so whilst it might not work on a P38, it works on 2 D1's, and 4 Perkins engined vehicles

The crazy/shocking voltage rebound was evidenced on a test rig I built for the purpose, using old sealed beam units as a switchable load bank.. so it's genuinely really hard to see how this contained a bad earth.

 

[jwrrc]

Slight query re the wiring:
I have two small "boxes" connected to the wiring for the alternator.
One on the bottom of the alternator, shown by the light grey wire

The other floating around the engine bay

Am I correct in thinking there should only be 1 of the two connected?

 

[jwrrc]

Slight query re the wiring:
I have two small "boxes" connected to the wiring for the alternator.
One on the bottom of the alternator, shown by the light grey wire
View attachment 277878

The other floating around the engine bay
View attachment 277880

Am I correct in thinking there should only be 1 of the two connected?

The one on the alternator has 39 93 on
The other has 35 93

 

[Jayridium]

I do actually have a star named after me!

You're telling porky pies, I've just looked up a star chart and there isn't a Disco1BFG in any constellation...

Lead Calcium batteries require 14.2 to 14.7 volts to fully charge. Removing a load if the battery is connected cannot let the voltage rise as you describe but a bad earth can. All vehicle electronics of that era were designed to operate with 13.8 volts, it's highly unlikely that the regulator chips used would fail at 14.7 volts and certainly not with 14.2 volts.

Most informative Kieth, thanks for sharing your knowledge again.