Seasons Greetings to All! Noticed that the speedometer starts at 15 mph at idle and works fine up to 60 but will go no further. I know I was doing well over 60 mph on the Blue Route the other day. Checked archives but still don't know where to begin. Sensor on tranny or the gauge itself? Everything else is working including the trip thingy. Any ideas?
Thanks in Advance, MKLAW
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240, 1992, auto
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240, 1992, auto

Hi,

That is strange behavior indeed. I haven't seen it happen, although my experience is limited to those electronic speedos before ABS, which brings some subtle differences to the gauge circuitry and not so subtle changes to the tone ring and sender.

In your case, I would be curious about how this came about. When in its life did you notice this? An easy explanation would place some errant iron filings or other ferrous debris inside the gauge's D'Arsonval meter movement, causing the needle's motion mechanical interference. Usually this only occurs after a bit of tinkering in the area.

If this just came about without provocation, perhaps, as others may have experience, the circuit's decoupling capacitor may be drying up with age, allowing undesired signal from alternator or ignition to be coupled to the sensor input on the speed counter chip. I think there's a suggestion in the 700/900 FAQ list to replace the capacitor, though for differing symptoms.
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Art Benstein near Baltimore

When you've seen one shopping center you've seen a mall.

Art:

I must say I'm impressed, I doubt there are too many folks on this board that know what a galvanic D'Arsonval gauge is! Might I ask what your background is? Needless to say, I am impressed, not just from this post, but a summary of all your other posts. In short, on this Board, I consider you the "Brick Man"! Please take that as a compliment! You deserve it!

I'd love to have an off-line chat, jorrell@qualcomm.com

jorrell
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92 245 245K miles, IPD'd to the hilt, 06 XC70, 00 Eclipse custom Turbo setup...currently in pieces

Way over my head. As the original poster, I pleaded ignorance and decided to do some serious research. Only problem, there is only one university where I live :}.

mklaw
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240, 1992, auto

Sorry about that. I knew somehow that might lead to head scratching, but thought it would be the quickest way to differentiate the internal construction of the electronic speedometer gauge from every other Volvo gauge so you'd know (after a quick trip to Wikipedia) how easily a single hair of iron can mess it up. This type of meter movement ruled electronics before meters got light-up digits.

Back to the practicals. Since this wasn't your car before it happened, there's only speculation possible about who may have tinkered in there, hopefully not ruining things to deceive you on an odometer reading. I doubt it could be the differential sender causing the problem where you have a reading before even moving. The ABS shares that signal as an input (according to my '92 wiring diagram) so you might do some research on testing whether ABS is working and that no previous owner disabled its warning light.

Naturally, you could swap in a new cluster, but I believe 92 have a very narrow range of replacements. I'm sure both variants of the 91 model year are different (ABS was optional in 91 and employed a frequency multiplier module IIRC) and I've no clue about changes for 93. Maybe the behavior you see is a result of someone else swapping in the wrong cluster. I might be able to tell using the manufacture date stamped on the gauge itself; every one I've had apart shows this.

If you find the ABS is using the rear wheel sensor OK, then you might just disconnect the green/white wire leading to the gauge to see how that affects your symptom. The L-shaped connector that mates with the gauge's circuit board can be opened to release the pins individually. At the bottom of my web page http://cleanflametrap.com are a couple pictorials of earlier speedometers to help you envision this before tearing into your dash.

Then again, maybe it is all innocent, and simply replacing the electrolytic capacitor will make it right again.
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Art Benstein near Baltimore

A bicycle can't stand alone because it is two-tired.

Thank you for responding. Although the car was purchased a year ago, this is the first time I have seen and driven it(long distance ebay purchase).
Any guesses on what part to replace first?

Thanks again, Art.

mklaw
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240, 1992, auto