TVR Chimaera Speedo and Tachometer *repair advice*

[brubaker19]

For a couple of years my Speedo hasn’t registered until about 25 mph (I understand it’s a common fault) but when the tachometer started to do an intermittent random dance during travel I decided to get both fixed.

My mechanic took them out of the dash and I decided to send them to Speedy Speedos (aka Speedy Cables). They phoned me yesterday to tell me they don’t *repair* these anymore because they can’t get the parts and stand over them. The only option was to convert the Speedo counter to digital. As an aside it will take 20 weeks

All that notwithstanding my question I guess is what do you think about changing to digital. Trevor is absolutely original and my gut is to try to keep him that way.

Also I’ve heard mixed reports about other repair companies but if anyone has had good experiences with them I’d love a sound recommendation.

Any other thoughts or comments appreciated.

Many thanks

Peter

[GreenV8S]

It may just be wiring + sensors taking the signal too far out of spec for the gauge to handle. If you think it's worth the effort, the approach I'd take is to scope out the signals you've getting from the physical sensors and see whether the gauges work properly when given a cleaned up signal. The electronics for an amplifiier to clean up the signal would not be particularly complicated relative to repairing the gauge itself.

If you decide4 to go the 'new gauge' route I assume you'd be aiming to use a digitally driven analogue gauge with the original faces rather than bodging in something completely different.

[brubaker19]

Thanks very much. Yeah if I go for the electronic version it would be just replacement into the original dial. I think I’ll just have to suck it in and go for it. Speedy Speedos want to know what type the *sensor* is? I wouldn’t even know where to look and the car won’t drive without the instruments as they are clearly part of the ignition circuit. Any advice appreciated.

Peter

[GreenV8S]

brubaker19 said:

the car won’t drive without the instruments as they are clearly part of the ignition circuit.

I wouldn't have expected that. The only instrument with any direct connection is the tacho, and that's a voltage sensing type (driven off the coil LT -ve) which should have no effect when disconnected. Is it possible the problem is caused by a wiring fault and that's also causing running problems?

[Mutley00]

Have you tried these chaps Peter?

http://www.speedograph-richfield.com/html/inst_rep...

Cheers, Andrew

[Polly Grigora]

Does disconnecting the instrument cluster remove the 14CUX Engine ECU Pin 6 speed signal?

If answer is yes then there could be a problem if cluster is still out of the car

[spitfire4v8]

If you get anything back in 20 weeks from speedy cables consider yourself very lucky indeed.

The speedo not working until 25mph is likely just air gap too big on the sensor.

The tacho is more interesting, but common issues for bouncy / inaccurate tachos are HT circuit with too little resistance (non resistor extenders / "performance" (cough) HT leads and low voltage to the tacho itself ...

My advice is DON'T send anything away unless you are absolutely sure the instrument is at fault.

[ukkid35]

There may be two different faults here

The dancing tachometer is typically due to a failing 'Big Fuse'

The insensitive speedo/odo is typically due to a failing speedo sensor

Check the PH classifieds and you may find a suitable replacement is available at a fraction of the usual cost

[keeling54]

Not sure where you are in the country but I have a spare Tacho and speedo from a 93 Chimaera you can borrow to test your wiring.

The digital display on my original odometer had failed so I replaced them both with a matching pair from ETB instruments in Southend.

[brubaker19]

I always appreciate the help and expertise of fellow TVR owners. You guys are amazing. Couple of things to point out and then I need someone to actually just tell me what to do next.

My expertise is limited to tinkering, so I will freely admit some of the suggestions I don't even understand. I also have a young family and not much free time.
The only TVR mechanic in Northern Ireland closed up shop last year, so I'm struggling there.
I have a wife who wants me to sell the car because 'its been nothing but trouble'.
Trevor is now in my garage (she won't start without either the tacho or speedo) - well that's what the mechanic told me.
My bits are currently with Speedy Speedos.

I actually feel overwhelmed by this. Since I've had Trevor (nearly 10 years now) he's had been subject to a court case, had full body off chassis repair, been resprayed and nearly burn out. He's a survivor, but I honestly don't know what to do next.

Do I get the instruments back from Speedies and get the garage just to put them in (as is) and try to solve the issue with a new speed sensor?
Do I get them serviced first by another company now they are out - getting them out by a mechanic was a hassle.

I honestly don't know what to do and advice is appreciated,

Peter

[ukkid35]

brubaker19 said:

Trevor is now in my garage (she won't start without either the tacho or speedo) - well that's what the mechanic told me.

Sorry, but no

Admittedly I haven't tried running my Cerb without dash, but I'm certain that there's nothing in the engine management that would prevent it from running without instruments, that is not TVR philosophy

[ukkid35]

I was going to suggest that you might be better off bringing the car to a GB specialist, but I had no idea that it's £500 minimum each way - WTF?

[brubaker19]

Yeah it’s expensive to get to the mainland.

I’ve tried a couple of folks and none wanted to service the tacho so I’ve gone to caerbont (the manufacturer) to see if they will do it. I’ll feedback to the forum as it might be useful if others have similar problems in the future.

[geordiepingu]

I've no faith in Caerbont at all for servicing instruments. I wanted to get mine converted from kmh to mph a couple of years ago, was quoted a 12 week lead time. I get by with Waze and arithmetic instead with a lead time like that.

A Cerbera I look after has already had its speedometer sent back to Speedy twice with the same odometer sticking fault. The owner just lives with it now and gives it a whack on occasion.

Joolz is on the money for your first ports of call. Check the gap on the speed sensor on the diff, and make sure it's clean. As for your tach, do try someone's known good leads and plugs first before looking down the avenue of chasing ignition amp faults.

[Polly Grigora]

Check out the following with the mechanic before getting too concerned or involved

Further to this

Polly Grigora said:

Does disconnecting the instrument cluster remove the 14CUX Engine ECU Pin 6 speed signal?

If answer is yes then there could be a problem if cluster is still out of the car

brubaker19 said:

Trevor is now in my garage (she won't start without either the tacho or speedo) - well that's what the mechanic told me.

Is the whole instrument cluster out of the car?

Loss of the speed signal won't stop the engine from starting

Perhaps the mechanic meant the car won't perform as it should

See this http://www.britishv8.org/Articles/Rover-Hot-Wire-E...

it tells us

The ECU in turn detects vehicle movement from the road speed input and ensures that idle speed control mode is disengaged. If the speed transducer fails, the ECU idle speed control will become erratic.

[GreenV8S]

Is that a picture of a road speed sensor? It looks suspiciously similar to a lambda sensor.

[geordiepingu]

that is indeed a lambda sensor

[geordiepingu]

Polly Grigora said:

Is the whole instrument cluster out of the car?

Loss of the speed signal won't stop the engine from starting

Perhaps the mechanic meant the car won't perform as it should

Further to this, the Speed sensor actually connects to a black box inside the dashboard, a transducer unit if you will. If memory serves it has two separate outputs, one to the 14CUX ECU and the other to the speedometer. The car should idle ok without a speedometer I'd have thought, though I've never tried it.

The nerdy detail: the 14CUX used road speed as a parameter to enable fast idle - if the speed is 0, then closed loop idle with the stepper motor will kick in.

[keeling54]

My Chimaera will run with neither the speedo or rev counter fitted. It also runs with the old and new speedo fitted at the same time.

[Polly Grigora]

Bravo, car should be usable then

Comes across as you need to find someone else to look at the problems

brubaker19 said:

The only TVR mechanic in Northern Ireland closed up shop last year, so I'm struggling there.

Find a good auto electrician to do the work