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#548431 - 16/12/18 11:24 PM Plus eight Rev Counter reading double RPM
MJW Offline
New to Talk Morgan

Registered: 08/11/16
Posts: 6
Loc: Southport Merseyside UK
Hi Guys, I have been reading with interest your comments, advice and banter for some time, but this is my first attempt at asking a question. Sorry if it has been asked before as I cannot quite understand how to use the forum yet...not very IT savvy!!.
My rev counter has suddenly decided to read about double the actual engine RPM. Does anyone have any ideas why this may be?
I am assuming that the feed for the RPM comes from the coil.
I have a 1997 Plus eight 4.6
Thanks Martin

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#548433 - 16/12/18 11:41 PM Re: Plus eight Rev Counter reading double RPM [Re: MJW]
+8Rich Offline

Member of the Inner Circle

Registered: 15/12/09
Posts: 19183
Loc: Devonshire
Hi Martin and welcome to TM I don't know what would cause that but to help you find it is a link to the gomog site with the Plus 8 wiring diagrams. The impulse feed is White with a black tracer on the cable well worth checking these connections end to end I would have thought. Plus 8 Electrical

Someone will have seen it before and hopefully come along soon.

p.s. You are better of in future posting technical stuff in the Servicing and Maintenance section as the Malvern Arms is for very general stuff and can be ignored quite often so your query may get missed.
_________________________
Richard
1999 Indigo +8






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#548435 - 16/12/18 11:53 PM Re: Plus eight Rev Counter reading double RPM [Re: +8Rich]
MJW Offline
New to Talk Morgan

Registered: 08/11/16
Posts: 6
Loc: Southport Merseyside UK
Thankyou kindly. +8Rich, very helpfull. Ill check it out after I have finished replacing the rear wheel bearings and seals. Good fun job!!
I just realised I got the wrong Forum. I am new to this type of communication, will do better next time.

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#548436 - 16/12/18 11:57 PM Re: Plus eight Rev Counter reading double RPM [Re: MJW]
+8Rich Offline

Member of the Inner Circle

Registered: 15/12/09
Posts: 19183
Loc: Devonshire
Sounds like you have got your hands full for the time being Martin, my Rev counter was intermittent and it was the Lucar connector in the engine bay. You probably have the only 4.6 that revs to 8,000rpm at the moment..
Good luck.


Edited by +8Rich (16/12/18 11:58 PM)
_________________________
Richard
1999 Indigo +8






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#548465 - 17/12/18 10:08 AM Re: Plus eight Rev Counter reading double RPM [Re: MJW]
howard Offline
Part of the Furniture

Registered: 01/01/09
Posts: 4178
The feed to the rev counter is a pulse electical signal. On some rev counters there is software to allow you to change from 4 to 6 to 8 cylinders and that can become upset if, for example, the car is stood for a long time and settings memory is lost. But more likely its vibration making the signal even more intermittent and therefor higher reading. In that case its likely the rev reading would jump about a bit.

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#548587 - 17/12/18 10:57 PM Re: Plus eight Rev Counter reading double RPM [Re: howard]
MJW Offline
New to Talk Morgan

Registered: 08/11/16
Posts: 6
Loc: Southport Merseyside UK
Thanks Howard, I will check both ideas. The RPM is very stable at double the RPM, so I am guessing it thinks its a 4 cyl engine! I am busy with the rear axle at present but will gladly advise my findings.

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#548590 - 17/12/18 11:05 PM Re: Plus eight Rev Counter reading double RPM [Re: MJW]
Craig Jezz Online   content

Talk Morgan Regular

Registered: 27/03/17
Posts: 866
Loc: Oxon
My 4/4 did this, I was told on here to leave the ignition lights on for at least 10 seconds before turning the engine over. Problem solved for me, but a 1997 Plus 8 might be different.


Edited by Craig Jezz (17/12/18 11:06 PM)
_________________________
Craig Jezz

Morgan 4/4 Sports Sand (Williams & Wolf Tuned)

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#548604 - 18/12/18 12:28 AM Re: Plus eight Rev Counter reading double RPM [Re: MJW]
MJW Offline
New to Talk Morgan

Registered: 08/11/16
Posts: 6
Loc: Southport Merseyside UK
Craig, now that sounds very interesting. Ill try it thanks

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#548665 - 18/12/18 12:09 PM Re: Plus eight Rev Counter reading double RPM [Re: MJW]
sospan Offline
Talk Morgan Sage

Registered: 31/05/10
Posts: 6035
Loc: Llanelli
Delaying starting while ECU boots up is a good idea. It allows the program to go through its checks etc and initialise fully.
I tend to do that (but not always) in any car with ecu. My thoughts are that no external signals will come from the engine sensors during boot up and possibly cause a glitch when picked up.
Maybe not critical in a newer car but an older one may not have the software to cope with it.
Worth trying anyway.
_________________________
Red Plus8

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#548705 - 18/12/18 03:05 PM Re: Plus eight Rev Counter reading double RPM [Re: MJW]
Dave Turner Offline
L - Learner Plates On

Registered: 15/10/12
Posts: 119
Loc: Calgary Alberta Canada
Martin , I also have a 97 4.6 liter .
Last year I changed the ignition coil for a pertronix coil to match the pertronix distributor. Car ran great but the tach read 1/2 engine speed , no amount of checking wiring and even running separate wires from coil to tach would change things so I changed the dip switches which you will find on the back of the tach to the 4 cyl setting and my tach is now ( approximately) correct ?
Made no sence at all .
Perhaps pop the tach out and move the switches around the clean the contacts ?
BTW if anyone has a used tach for sale I would be interested 😊
Cheers Dave

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