8 replies to this topic

[Jupitus]

Hi folks, especially dklawson whose posts about voltage stabilisors and such I have already read, and who seems to be VERY knowledgable on this area!

This has been puzzling me for a while now, so suggestions or ideas welcome!

My '85 998 city E has a centre speedo with integrated petrol gauge. I have added to this a temperature gauge and revcounter.

I have the revcounter on a direct 12v feed from the fuse box. The petrol gauge and temp gauges are both being fed from the positive feed of the inbuilt voltage stabiliser.

Symptoms:

When revving, the temp and petrol gauges both go downwards, so if I'm humming along at 50 they might read about half what they should (at a guess). When I slow down and the car is idling, they both go back up to approximately what I would expect....

The revcounter is an old smiths one.... I am confident it is connected ok (followed one of dklawson's posts/advice) and it reads the revs, BUT I don't think it is reading correctly. At a 'slow idle to the ear' it reads over 1k RPM, and then at higher engine speeds it seems to be about on the mark, i.e. at a reading of about 5,500 I am wanting to change up as more might start to sound a bit painful for her. Are there any suggestions, hints or tips people have for testing how accurate these readings are or things to try to improve it?

Help and advice most welcome!!

Edit: I see my timing was fortuitous!!

Edited by Jupitus, 18 May 2007 - 12:50 PM.

[dklawson]

At least temporarily you may wish to hook up an analogue volt meter to the contact on the stabilizer supplying your fuel and temp gauges. That means one lead of the meter to the "I" terminal on the stabilizer, the other meter lead on chassis ground. Keep an eye on that while you're driving. Use an analogue meter, not digital. The analog meter should show a more or less constant 10V. If it is dipping below 10V, this could indicate a problem with the stabilizer OR that you're supplying the stabilizer from a questionable source. Move the hot lead of the meter over to the "B" terminal on the stabilizer and repeat your test. The meter should show a voltage anywhere from 12 to 14V or so. If you see this dropping way down while driving... look again at what's supplying the stabilizer. The stabilizer's "B" terminal should always see the car's operating voltage and if it drops below 12V this would indicate a problem with the car's charging system OR that you've tapped into a very questionable supply to power the stabilizer.

As for the tach, which type have you installed, RVI or RVC?

[Jupitus]

At least temporarily you may wish to hook up an analogue volt meter to the contact on the stabilizer supplying your fuel and temp gauges. That means one lead of the meter to the "I" terminal on the stabilizer, the other meter lead on chassis ground. Keep an eye on that while you're driving. Use an analogue meter, not digital. The analog meter should show a more or less constant 10V. If it is dipping below 10V, this could indicate a problem with the stabilizer OR that you're supplying the stabilizer from a questionable source. Move the hot lead of the meter over to the "B" terminal on the stabilizer and repeat your test. The meter should show a voltage anywhere from 12 to 14V or so. If you see this dropping way down while driving... look again at what's supplying the stabilizer. The stabilizer's "B" terminal should always see the car's operating voltage and if it drops below 12V this would indicate a problem with the car's charging system OR that you've tapped into a very questionable supply to power the stabilizer.

As for the tach, which type have you installed, RVI or RVC?

Thank you sir! I just spoke to a colleague who possesses an analogue voltmeter he will lend me next week, so I'll try your suggestions.

The tacho... I forget... it has a single long wire which loops round a block on the back of the unit, which is wired in serial to the coil. Is that enough info?

[dklawson]

Hi,

The tachs that use the loop of wire on the back are RVI type (current sensing). They are very old and they don't always (or often) work with electronic ignitions. The RVI type was phased out sometime in the early 1970s. I don't want to discourage you... but I wouldn't spend a lot of time trying to fix or resolve operating problems with an RVI tachs. Some have calibration pots on the inside that you can access by taking the unit out of its case. However, the gauge is almost 40 years old. The electrolytic caps inside may be drying out. If you're running an electronic ignition I wouldn't waste ANY time trying to make this tach work. The later RVC tachs use a single wire connection to the black/white wire connection point on the coil/distributor. They are voltage sensing, newer, and more reliable in general.

I have an article on tach conversions at:
http://home.mindspri...nversion-R1.pdf
I converted an RVI tach using a circuit board from a donor tach. Others I know have converted the RVI tach by transplanting a complete RVC movement into the case. Either option is possible, both require a fair amount of work.

[Jupitus]

Hi,

The tachs that use the loop of wire on the back are RVI type (current sensing). They are very old and they don't always (or often) work with electronic ignitions. The RVI type was phased out sometime in the early 1970s. I don't want to discourage you... but I wouldn't spend a lot of time trying to fix or resolve operating problems with an RVI tachs. Some have calibration pots on the inside that you can access by taking the unit out of its case. However, the gauge is almost 40 years old. The electrolytic caps inside may be drying out. If you're running an electronic ignition I wouldn't waste ANY time trying to make this tach work. The later RVC tachs use a single wire connection to the black/white wire connection point on the coil/distributor. They are voltage sensing, newer, and more reliable in general.

I have an article on tach conversions at:
http://home.mindspri...nversion-R1.pdf
I converted an RVI tach using a circuit board from a donor tach. Others I know have converted the RVI tach by transplanting a complete RVC movement into the case. Either option is possible, both require a fair amount of work.

Thanks dkl - as I said I have seen your articles on them before, and I don't fancy the challenge of a conversion.... I am soon to upgrade Nala to electronic ignition anyway so I'll start looking out for a suitable replacement tacho too.

Thanks again for your help and advice.

[dklawson]

Any updates after the weekend?

[Big_Adam]

I wish to throw in something here.

Make sure the pcb to multi plug is still good. Mine was shoring so the gauges they go mad! Now It's fixed (+ added ground for stabilizer) and all is well.

[Jupitus]

Any updates after the weekend?

Not yet dkl, was a tad busy as we decided to drive down to Brighton and back! A colleague here has an analogue voltmeter but he forgot to bring it in with him to work...

Regarding the revcounter, I had a chat with speedy cables (www.speedycables.com) and they can take my existing Smiths gauge and refurb it with new innids for less than it will cost me for a new one. Given that it's the design and size I like I am going to package it up and send it off to them so I will have a newly calibrated one for Nala, especially with a new engine going in in the near future;)

[dklawson]

I'm glad they can do the conversion for you for a "reasonable" price. I've converted a couple of the RVI tachs by installing a circuit board from a newer, voltage sensing tach in the RVI case. With that conversion I've still used the Smiths d'Arsonval movement... only the control circuit changes. It's clean and surely looks the part.