[TECH] Rev counter "flickering"

[Guest]

John and Roman
The rev counter flickering occasionally is a "feature" of these vehicles. I've had it from time to time, and when it's in flicker mode my idle revs can be reported as ~400rpm or even lower (and the revs at higher speeds can be garbage too). But there is no change in engine note, and the tachometer is simply telling lies.
It's definitely an electrical and/or sensor problem, and discussion on the 80scool forum suggests that it is not that uncommon. The most credible suggestion I've had is a poor earth connection somewhere on the engine, but I've never been able to track it down.
After three years of this on and off (and mostly "off" lately, I haven't seen a flicker for about 6 months) I'm convinced that it's nothing to worry about, and is quite likely to cure itself. More to the point John, don't adjust your idle speed unless you get some independent confirmation that it is wrong.
Christopher Bell
Devon, UK
1996 1HD-FT
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| Thanks Roman for that, a picture tells a thousand words.
| John C
| 92HDJ 80 1HDT Ireland
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[Guest]

On 5/27/05, Christopher Bell <[Email address removed]> wrote:
just your idle speed unless you get some independent confirmation that it is wrong.
Christopher,
IFRC, speedo pulses are taken from the alternator, but I may be wrong
as I have not the FM to hand.
If John reports "it's been always so", it quite unlikely to cure itself
--
Rgds,
Roman (London, UK)
'92 HDJ80

 

[Guest]

Roman

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| IFRC, speedo pulses are taken from the alternator, but I may be wrong
| as I have not the FM to hand.
Makes sense. My alternator creates quite a lot of electrical noise on the radio, so I can believe it is worn. On the other hand it has been like that for nearly 4 years without getting worse, and seems to produce lots of amps for the headlights without any grief.
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| If John reports "it's been always so", it quite unlikely to
| cure itself
True, but my experience is that it will have a bad month or two with flickers every day, followed by a long flicker-free period. Currently I'm in the latter, so perhaps mine is in what a doctor would call "remission". I wonder if giving the alternator a medium weight tap with a hammer & wiggling the connector about (possibly not in that order) would have any effect?
The main point I wanted to make, since John's mental equilibrium is important to this group, was that flickering tacho =3D unreliable tacho =3D not unknown on these vehicles =3D no need in itself to worry about idle speed.
For what it's worth mine idles at an indicated 650 or so rpm, rising to just under 800 or so when the a/c or steering "idle up" settings cut in, which feels about right to me. Facing upwards on a 1 in 2 slope this drops to about 450 rpm, which I suppose means my injection pump is getting a little tired - but on the principle of "if it ain't broke don't fix it" I'm not planning to do anything about it, as 29mpg on the last tankful (of Morrison's finest*) suggests that it is going OK.
Christopher Bell
* For those outside the UK "Morrison's" is a supermarket group which took over Safeways about a year ago, converting an expensive and fairly nasty supermarket chain into a cheap and very nasty one. They are in the process of booting the boss & founder off the board, and in today's financial news have finally admitted that they don't actually know whether or not their new stores are profitable since they sacked all the ex-Safeways people who understood the accounting system. However my truck seems happy enough on their fuel.