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Intermittent Tachometer


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7 replies to this topic

#1 KStretch55

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Posted 01 June 2005 - 02:14 PM

My son has a '86 Loyale wagon, carbuerated, 5spd d/r. He told me his tach works sometimes, but not until over 2000rpm. Under 2000 it sits there and bounces between 0 - 2000. I looked around for a loose connection. Made sure it was connected to the right post on the coil, etc. Do you think it could be a weak coil?

#2 Cougar

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Posted 01 June 2005 - 03:19 PM

I think this may mean the disty bearings may be bad.

#3 KStretch55

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Posted 01 June 2005 - 04:44 PM

Cougar, please 'splain. I'm not following your correlation to the distributer bearings. Must be another of the Soob mysteries I need to know. I'm not sure, as that car actually belongs to the ex, but I think they may have put a new/rebuilt/used disty in it a few months ago. So, what you say may be making sense. How would the disty bearings cause this problem? I was thinking at most maybe cap and rotor, if they were really, really worn. Enlighten me, Master Cougar! Thanks, too.

#4 Cougar

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Posted 01 June 2005 - 06:05 PM

I seem to recall from other posts that if the bearings are bad then the alignment for the pickup inside the disty gets to be a problem. I am only going by what I seem to recall and I may not be remembering correctly.

If the disty was replaced not to long ago then I would have to say then that either the tach is at fault or there is noise at the lower RPM's and........ FLASH (mind flash that is). Wait a minute. Maybe there is noise from the alternator at lower RPM's causing this to happen. Perhaps some of the output diodes are bad. The more I think about this the more I think that is what is going on. Forget the disty, check the alternator for noise. If you have a digital voltmeter put it on the AC mode and see if the noise goes down as the RPM's go up.

#5 KStretch55

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Posted 01 June 2005 - 09:18 PM

How will I tell if it's got "noise"? What will I be looking for, erratic voltage output?

#6 Cougar

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Posted 01 June 2005 - 10:08 PM

Yes that's right. If things are ok I would suspect the AC volts on the output lead of the alternator would be less than about .2 volts. If things are not right then you would see more. Check to see what the AC voltage is at idle and then around 2,500 RPM. Let me know what you get for readings.

#7 Ratty2Austin

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Posted 02 June 2005 - 12:49 AM

its the distributor bearings... when they get loose (check for even the slightest play) they can get too close to the pickups, and/or the rotor can contact the cap contacts.. when this happens, it generates a large EMI pulse, wich interferes with the tach pickup-

i suggest fixing it soon, a bad bearing in an old EA81 of mine seized up and stripped the teeth off the cam gear inside the block! :banghead:

#8 Cougar

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Posted 02 June 2005 - 03:08 AM

Thanks for the reply Ratty2Austin. I couldn't remember exactly how the problem occured. I still suspect a noisey alternator could be the problem, with this one at least. One us has the right solution for the problem I think.




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