Ms tacho issues

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Richard P6
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Post by Richard P6 »

Mine only switched the relay when the voltage was high enough. Using the internal circuit, which bounced from 0.5V to 9V at 86 on the relay, it would only buzz above 6V or so.

Using the external home made one, the voltage was stable at 5.4V and didn't switch the relay at all :)



DaveEFI
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Post by DaveEFI »

Quagmire wrote:On mine, the relay buzzed all the time with the engine running, but I guess what the relay does is a factor of the spec and brand it is...
As a matter of interest, did it work OK with your rev counter at all revs - and which model rev counter was it?

I've got Richard's MS here and have been having a play. The transistor driving the coil gets very hot indeed very quickly and the pulse the circuit produces reduces in level as this happens. I'd also expect the transistor to fail in time. Also not sure how long a chattering relay would last either.

All very odd, as this circuit is often mentioned on the MS forums as being a fix.
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Quagmire
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Post by Quagmire »

Revs right up the the redline with no issues. I will take a snap of the bottom of my tach tomorrow so we can check its the same model as Richard's.
1974 Rover 3500s
1984 3.5 90
1959 2.25 series 2

Quagmire
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Post by Quagmire »

Dave sorry for the delay - I took a photo but cant get it to upload for some reason at the mo.

My tach has the following text at the bottom:

RVC 2812/OO Made in UK
1974 Rover 3500s
1984 3.5 90
1959 2.25 series 2

Richard P6
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Post by Richard P6 »

Image

Same as mine :)

I hope to get it plugged in tomorrow Dave, so will let you know how it goes.

Cheers

Richard

Richard P6
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Post by Richard P6 »

It works, nearly perfectly :)

Just now and then, it bounces up or down, but only very briefly, but is certainly very useable, so success :)

Only problem is, I now have a slight misfire :?

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Post by Quagmire »

Do the tach blips and misfires occur at the same time?

If so you might have some kind of loss of sync error or MS reset going on.

Try running around and taking a datalog, see if you get anything.

If you do have something like that then its worth checking out the field called "Lost sync reason", the maximum value logged for that field will tell you what the reason is.

For example after rummaging around in my EDIS wiring I was getting what felt like resets, and it was lost sync reason code 15, which indicated I had upset the EDIS. I disconnected and remade all my connections and all was good again.
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1984 3.5 90
1959 2.25 series 2

DaveEFI
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Post by DaveEFI »

It was on soak test here for more than 24 hours driven from a Stim and on-line to the PC. Rock solid.

Where is the tach adaptor mounted? It produces a pretty vicious pulse.

First try with the adaptor disconnected, to make sure the miss fire isn't something else.

If it proves to be the adaptor, I'd mount it as close to the rev-counter as possible (so well away from MS and its wiring) and derive the +12v from the rev counter +12v.
Dave
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Richard P6
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Post by Richard P6 »

Can't find a, "lost sync reason," field anywhere ?

I have disconnected the ign live from the main relay, and wired into the back of the tacho instead. The tach adaptor is sitting at the back of the engine compartment on the top of the heater box, under the front scuttle. I have fixed it there, then shortened all of the wires so it is nice and tidy.

Took it up the road, still misfires, disconnected it, still misfires :(

Took it for a spin and got the engine nice and warm, around 15 minutes popping around town, and the misfire did get a lot better, so drove around for another 30 minutes, and it's all but gone. I do think it just maybe down to not being driven for a while, so I'll try to get out a bit more and hopefully that will solve it :)

The tacho still has a little jump now and again, but it's very useable, so many thanks Dave, your help was very much appreciated.

Regards, Richard

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Post by DaveEFI »

Does the tach kicking co-inside with a misfire? Just that I had it running up to 8000 rpm here and it was stable.

If you want to play, you could try it from IDM on EDIS again - that's what's driving mine. One less stage of reading pulses.

As regards the misfire, there is a tendency to think EDIS bomb proof - which it generally is. But a mate had a coil fail such that it drove one plug of a pair OK but not the other. And are you using resistor plugs?
Dave
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Richard P6
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Post by Richard P6 »

Hi Dave

No, the misfire is fairly regular, but the tach jump isn't, they don't coincide. I'll take it for a few runs in the week and see if it improves at all.

I can try the IDM again, I'll let you know how that goes :)

Cheers

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Post by Richard P6 »

Finally got a few minutes to finish this off :D

Tidied everything up, replaced the front scuttle, put the wipers back (been doing some work getting them to work better), started him up and went for a spin.

He used to just tear up hills from low revs, but when the misfire arrived, this was the worst place, up hill in low revs. Any hard acceleration started the misfire, but from low revs on an incline was not good at all.

Got to a hill, and eased my foot down to accelerate up it, from 1,800 rpm. He took off like a scalded cat, so problem solved :D

I did have the power to the tach fix coming from the main relay in the MS, so I suppose that's what caused it - who knows, he may have been having a bad day.

Tacho is working ok now, little jump now and then, but to be quite honest, it hasn't worked for so long now, I really can't remember if it did that before :?

Thanks for all your help, especially Dave :)
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