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Rich H
Joined: 10 Jun 2007
Posts: 2665
Location: Preston, Lancs, UK
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 Posted: Mon Nov 17, 2008 10:07 pm Post subject: curing the rattles and failing to fix my Tacho |
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Spent an hour or so playing cars (Her words) on Saturday. I was attempting to fix my Tacho that only seems to show the revs when the indicators or wipers are on (it keeps time with them) No clue as to why so I gave up. 12v supply is good, but no reason for the cross talk 
Any ideas? Its wired to the Clean Tach Out on EDIS.
So instead I spent some time taking the center console and radio out and re-looming the wiring with fiberglass tape. One of the POs had been in there and left it all loose. 20 mins later - a rattle free dash! 
Combined with the replaced engine mount, Leda shocks turned to soft and relatively recent wheel bearings its fast becoming comfortable and practical...
Just need to revisit the ECU wiring now and tidy that up...
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1994 Lotus Esprit S4 - Work in progress...
1980 Porsche 924 S2 DITC Turbo - Original spec
1978 Homo-Sapiens - Tired spec
1953 Landrover S1 - Pensioner Spec |
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RC
Joined: 25 Mar 2007
Posts: 2637
Location: Australia
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| Posted: Mon Nov 17, 2008 10:49 pm Post subject: Re: curing the rattles and failing to fix my Tacho |
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| Rich H wrote: | Spent an hour or so playing cars (Her words) on Saturday. I was attempting to fix my Tacho that only seems to show the revs when the indicators or wipers are on (it keeps time with them) No clue as to why so I gave up. 12v supply is good, but no reason for the cross talk
Any ideas? Its wired to the Clean Tach Out on EDIS.
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That`s a strange one.
Sure you have the correct green wire? Not cross wired or bridged?
If you have a DMM with frequency or duty cycle (tach) capability check the EDIS output signal. May be in the market for a new tacho though. |
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Rich H
Joined: 10 Jun 2007
Posts: 2665
Location: Preston, Lancs, UK
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| Posted: Mon Nov 17, 2008 11:31 pm Post subject: |
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The full symptoms are a bit more complicated:
It works fine with the indicators (on-off-etc), wipers (on-off with intermittant) and lights on, when hot under gentle loads, at 50% reading with the rear heated screen on and then cuts when accelerating hard and over 4k rpm
Power is 12v (or over) all the time, but no Tach on my DMM. I suppose it could be the tacho being old and needing exactly 12V to run perhaps? Getting cantankerous in its old age probably...
Can I get it apart without removing the bezel?
Maybe the gremlin is on his last legs?
_________________
1994 Lotus Esprit S4 - Work in progress...
1980 Porsche 924 S2 DITC Turbo - Original spec
1978 Homo-Sapiens - Tired spec
1953 Landrover S1 - Pensioner Spec |
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Vince Ponz
Joined: 02 Nov 2002
Posts: 3581
Location: Florida
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| Posted: Tue Nov 18, 2008 1:09 am Post subject: |
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Maybe someone wanted to know how many revs the wipers run at. I should talk my wipers run at 1 rev a minute. Why, I don't know but they are slow. Any answers would be appreciated.
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"Never let them see you sweat"
77.5 924 modified track car
79 931 Euro stock
88 924S SE
87 911 Targa stock |
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RC
Joined: 25 Mar 2007
Posts: 2637
Location: Australia
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| Posted: Tue Nov 18, 2008 1:15 am Post subject: |
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| Rich H wrote: | The full symptoms are a bit more complicated:
It works fine with the indicators (on-off-etc), wipers (on-off with intermittant) and lights on, when hot under gentle loads, at 50% reading with the rear heated screen on and then cuts when accelerating hard and over 4k rpm
Power is 12v (or over) all the time, but no Tach on my DMM. I suppose it could be the tacho being old and needing exactly 12V to run perhaps? Getting cantankerous in its old age probably... |
Sounds like it may be a power problem, voltage drop. Remember the earth (ground) completes the circuit to - Ve. If you are positive the 12V line is OK (measure while switching on/off a good load, lights, heater) then measure the voltage between a GOOD earth and the earth terminal on the tacho. Should be less than say 0.1V. Run jumper wires to both + (from battery or fuse box) and from - to a good earth to double check.
Was it working fine off the coil or TIU before the EDIS?
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Can I get it apart without removing the bezel? |
Sure you could but I don`t think it would go back together too well. 
Bezel job like the speedo.
| Quote: | | Maybe the gremlin is on his last legs? |
Doesn`t matter. Have you seen how they breed.
The little bastards love these cars. |
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Rich H
Joined: 10 Jun 2007
Posts: 2665
Location: Preston, Lancs, UK
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| Posted: Tue Nov 18, 2008 2:00 am Post subject: |
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Thought of that, checked both +12V and grd. All I can think is that EDIS is doing funny stuff instead of switching direct to ground, maybe its giving zero crossing signal instead of a normal on-off coil pulse which foxes the Tach at high revs? Worked fine on TIU/coil signal and it works when there is electrical load and mid-low revs.
Maybe the load brings the voltage down enough from 13.8V for something old and crap in the Tacho to work properly, high revs/accel then pushes the voltage back up again. Maybe a 12V voltage regulator would work on the +12V?
A second hand Tach might be worth a squirt. I'll borrow one next time I go to a meet. Its no great problem (rev limiter is set to 5.5k as I haev a stipped block thread on one bolt) have hit it on occasions and it sounds like a POS (Ign cut to 10 deg)
_________________
1994 Lotus Esprit S4 - Work in progress...
1980 Porsche 924 S2 DITC Turbo - Original spec
1978 Homo-Sapiens - Tired spec
1953 Landrover S1 - Pensioner Spec |
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RC
Joined: 25 Mar 2007
Posts: 2637
Location: Australia
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| Posted: Tue Nov 18, 2008 1:31 pm Post subject: |
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| Rich H wrote: | | Thought of that, checked both +12V and grd. All I can think is that EDIS is doing funny stuff instead of switching direct to ground, maybe its giving zero crossing signal instead of a normal on-off coil pulse which foxes the Tach at high revs? Worked fine on TIU/coil signal and it works when there is electrical load and mid-low revs. |
OK mate, logic tells me the fault is the signal from EDIS is not what the tacho needs, a 0 - 12V squarewave twice per crank revolution. Not that simple with dual coils and wasted spark.
Have you read the instructions? 
http://www.megamanual.com/ms2/EDIS.htm
They suggest building a simple circuit with a few diodes so the tach gets a signal from both coils:
1N4746 is a 18V, 1W zener diode and 1N4004 is a 400V, 1A, general purpose rectifier diode. Few coins at the local electronics shop. They`re polarized, symbol`s arrow points to line which corresponds with white band (black on zener) on diode.
Here`s a thread started by board member Nick when he discovered the same problem:
http://www.msefi.com/viewtopic.php?f=89&t=25794&p=163714&hilit=edis+tachometer#p163714
More reading here:
http://www.msefi.com/search.php?keywords=edis+tacho&terms=all&author=&sc=1&sf=all&sr=topics&sk=t&sd=d&st=0&ch=1000&t=0&submit=Search
Playing broom broom this weekend too eh?
| Quote: | | Maybe the load brings the voltage down enough from 13.8V for something old and crap in the Tacho to work properly, high revs/accel then pushes the voltage back up again. Maybe a 12V voltage regulator would work on the +12V? |
No, don`t do that. Sure the tach is internally regulated by at least a zener. Three terminal voltage regulators all have some voltage drop. Common 78xx series is about 2.5V so this will reduce output voltage BELOW 12V. |
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Rich H
Joined: 10 Jun 2007
Posts: 2665
Location: Preston, Lancs, UK
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| Posted: Tue Nov 18, 2008 6:34 pm Post subject: |
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OK. never thought of the EDIS output not being high enough.
I'll lash up the diodes and take a signal from the coils. The whole loom needs work anyway.
Ta
Rich
_________________
1994 Lotus Esprit S4 - Work in progress...
1980 Porsche 924 S2 DITC Turbo - Original spec
1978 Homo-Sapiens - Tired spec
1953 Landrover S1 - Pensioner Spec |
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