Rev counter drops and hold light flashes

[carloff1]

Hi there, I wonder if anyone can help me with an issue that's recently just developed on my 1996 2.5l auto diesel Ford Freda. A few miles after starting my van, the rev counter sometimes moves erratically and can drop to zero and which point the Hold light begins to flash. The problem often corrects itself and when it does occur it doesn't appear to affect the engine in terms of moving through the auto gearbox. If I stop and start the engine it usually disappears. Any help in identifying the issue much appreciated

[rita]

Sounds like a Crankshaft Position Sensor problem..

Item Number 18-230,

http://lushprojects.com/bongopartsmk2/c ... no=.html#2

[Northern Bongolow]

i would get the alternator checked out, sounds like its struggling. make sure its a gen mazda one for best results as there are some low output ones out there that dont last long.

has it got a split charge system on it for a leisure battery.

[sotal]

We've had a similar issue (always on a wet day).

We were told it was probably the speed sensor / wiring to the sensor.

As you say it doesn't affect gear changes etc - you just don't get the speedo. We just stopped and restarted each time it happened and carried on perfectly happily.

[Simon Jones]

Sounds like a Crankshaft Position Sensor problem..

Item Number 18-230,

http://lushprojects.com/bongopartsmk2/c ... no=.html#2

Actually, this is the sensor for the rev counter which gets the signal from the injector pump rather than crankshaft:

[carloff1]

Thanks for the response and also the photo of the sensor. Does it have a part name that I could order? Am I right to assume that as the gearbox seems to behave normally even during this problem that the van os ok to drive?

[rita]

Sounds like a Crankshaft Position Sensor problem..

Item Number 18-230,

http://lushprojects.com/bongopartsmk2/c ... no=.html#2

Actually, this is the sensor for the rev counter which gets the signal from the injector pump rather than crankshaft:

That's a new one, can you elaborate on where / how the IP drives the CPS.

Good Luck.

[rita]

i would get the alternator checked out, sounds like its struggling. make sure its a gen mazda one for best results as there are some low output ones out there that dont last long.

has it got a split charge system on it for a leisure battery.

Would this not show as being the charge and sediment light on together (Not the Hold light) as this usually indicates an alternator/charging fault.?

Good Luck.

[g8dhe]

Not always it took about 6-9 months of oddities in charging for the alternator on ours to eventually light the CHARGE light! If one diodes fails then the alternator is still producing current but its circulating around internally rather than charging the battery On ours it would be fine when cool and would charge, like when you actually measure the charging current first thing, then after an hour or so it would heat up and start leaking current, charging falls very low, but would recover again after a while stopped so it had me truly confused until the diode actually failed totally!

[rita]

Not always it took about 6-9 months of oddities in charging for the alternator on ours to eventually light the CHARGE light! If one diodes fails then the alternator is still producing current but its circulating around internally rather than charging the battery On ours it would be fine when cool and would charge, like when you actually measure the charging current first thing, then after an hour or so it would heat up and start leaking current, charging falls very low, but would recover again after a while stopped so it had me truly confused until the diode actually failed totally!

Geoff, appreciate that but would this affect the rev counter and the hold light
,as in the OP case.

[Simon Jones]

Sounds like a Crankshaft Position Sensor problem..

Item Number 18-230,

http://lushprojects.com/bongopartsmk2/c ... no=.html#2

Actually, this is the sensor for the rev counter which gets the signal from the injector pump rather than crankshaft:

That's a new one, can you elaborate on where / how the IP drives the CPS.

Good Luck.

The 1997 diesel engine above (currently sat in my garage) had the highlighted NE sensor by the IP. That particular sensor has since been fitted in another engine that exhibited the symptoms of intermittent rev counter & the owner confirmed the replacement sensor resolved the problem. Other engines may have different sensor arrangements, such as the post-'99 drive by wire variants.

Here's a link to a brand new sensor which may be of interest to the OP: http://www.autolinkmx5.com/ne-sensor-ma ... 5961-p.asp

[g8dhe]

Yes it can affect several things especially on a diesel, as the battery volts fall it is only really being used by the display etc. and weird results can appear, whilst on a petrol its more likely to start affecting the ignition way before it starts causing the gauges to play around!

[Northern Bongolow]

thats the way ive seen it geoff, when the sensor acts up or gets oil behind it (like mine last week again) it can affect tick over, or gearbox changing, staling etc, but rev counter fluctuation and hold light can be voltage wandering up and down, or over charging, undercharging usually a sign of early alternator woes or battery probs or even split charge issues.


but hey, ive been wrong before --------- and will be again.

[Simon Jones]

Sounds like a Crankshaft Position Sensor problem..

Item Number 18-230,

http://lushprojects.com/bongopartsmk2/c ... no=.html#2

BTW, that diagram relates to post 1999 models with the drive by wire IP which differs from the '96 model in question.