Intermittent power loss (crank sensor related?)

[willmears]

Dear all,

As mentioned in the title I'm having some intermittent total power loss with my 1990 CQ 7a.
When driving along the power will suddenly cut out and then jolt back in, this can happen repeatedly unless I do something to change the rpm i.e downshift.
It mainly seems to happen around the 2-3k mark.
When it cuts out the rpm gauge drops rapidly to zero (obviously engine is still turning over) and then recovers, creating a bucking bronco.
I therefore am beginning to think it is most likely the Crank position sensor or the crank rpm sensor?
Starts every time no issues. It does seem to happen more often when the ambient temp is lower.

Anyone got any ideas? If it is one of the crank sensors, is that a relatively easy swap?

[John.]

.....power will suddenly cut out and then jolt back in,
When it cuts out the rpm gauge drops rapidly to zero

It could be as simple as a dodgy king lead ?

[willmears]

Surely you wouldn’t expect the rpm on the clocks to lose sync with the engine (go to zero).
Not sure it is relevant but when cranking the car the rpms on the dash go all over the place up to 7k rpm

[John.]

Surely you wouldn’t expect the rpm on the clocks to lose sync with the engine (go to zero).
Not sure it is relevant but when cranking the car the rpms on the dash go all over the place up to 7k rpm

If it was arcing at the coil tower it might?......interfering with the switching side if the coil.

With the engine running , earth a wire to the engine/battery and then use it as "feeler" along the HT lead(s) and other HT components , if the insulation is gone at any point you'll see spark jump to the earthed wire and engine will falter.
Worth doing at least to rule out the above !

[Crasher]

The rev counter dropping to zero immediately says crank speed sensor to me.