lordbenny
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| posted on 3/9/12 at 06:24 PM |
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Will A Dodgy Crank Sensor Effect My Rev Counter?
As the title says....I have other issues, mainly that my car has real problems starting from cold. I've been told that it could be the crank
sensor, but I have also notice that at around the same time the car had starting issues the rev counter started playing up.
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Davey D
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| posted on 3/9/12 at 06:55 PM |
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It is definitely possible as my gear indicator uses the signal from the crank sensor for the engine rpm
[Edited on 3/9/12 by Davey D]
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scudderfish
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| posted on 3/9/12 at 07:01 PM |
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It depends. What engine? What ignition system? (coil? EDIS? ECU?). What drives the tacho? How does it play up (goes to zero, goes to max revs,
dances around like a mad thing)? Does it only do it whilst cranking or is it the whole time? Things go wrong for a reason, but you need to approach
it methodically rather than guessing at a component and swapping it (unless you have a very large wallet and a lot of time)
Regards,
Dave
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lordbenny
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| posted on 3/9/12 at 07:12 PM |
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quote:
Originally posted by scudderfish
It depends. What engine? What ignition system? (coil? EDIS? ECU?). What drives the tacho? How does it play up (goes to zero, goes to max revs,
dances around like a mad thing)? Does it only do it whilst cranking or is it the whole time? Things go wrong for a reason, but you need to approach
it methodically rather than guessing at a component and swapping it (unless you have a very large wallet and a lot of time)
Regards,
Dave
Thanks for your reply Dave,
2.0 Zetec
Twin 45mm Dellortos
Easimap ECU Software
I hope that helps.
The tacho is fine to 3000rpm then bounces down to 0 whilst driving
The engine starts fine when warm
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motorcycle_mayhem
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| posted on 3/9/12 at 07:31 PM |
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A faulty sensor will certainly affect a few things, you need to effect an analysis of the problem.
I'd say a malfunctioning tacho (or more correctly an intermittent signal to it) may well be a good clue to a faulty crankshaft sensor - assuming
the sensor feeds the tacho.
Certainly the case with my old Volvo. The sensor failed intermittently, only when hot, really difficult to track it down. The clue was the tacho
needle behaviour, along with a study of the wiring diagram. New sensor (£26) no problem.
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lordbenny
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| posted on 3/9/12 at 07:52 PM |
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Im pretty sure the sensor feeds the tacho and the fact that the cold starting issue happened around the same time as the tacho playing up suggests
that this is the problem....does it not
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scudderfish
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| posted on 3/9/12 at 08:23 PM |
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The sensor won't directly feed the tacho. Normally the tacho is fed either by it seeing the voltage spike from the coil as it fires, or by a
digital signal from the ECU (or EDIS) controller. If the sensor fails to provide a signal to the ECU then the engine will stop as it won't know
when to fire the spark plugs. The sensor tells the ECU where the engine is on its rotation; if there is no signal the ECU thinks the engine
isn't turning and it won't bother firing the spark plugs.
I would carefully examine the connection between the tacho and the ECU, the power and earth of the tacho and the shielding of any signal cables. My
tacho had a habit of going wild during cranking which I traced down to a poor 12v feed to it, and I also suffered RPM spikes in data logs which was
down to induced noise from my low impedance fuel injectors.
Regards,
Dave
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