2000 V70XC SE crankshaft position sensor

[monty]

Hi,
If no response by the tach when cranking indicates a bad crankshaft sensor, what sensor does the tach use when the car starts?

thanks, monty

[Ozark Lee]

Your question is a tad confusing but, in general, the Camshaft position sensor controls spark and triggers the injectors. This is done in concert with the RPM / Crankshaft position sensor. The RPM / Crankshaft position sensor is the primary determinate of engine speed for the tachometer but it also serves as a check for Camshaft position sensor signal. The ECU checks the Camshaft position signal and the Crankshaft position signal to make sure they are synchronized.

In the case of a 2000 with CVVT it also takes the combination of those signals, as well as signals from the throttle position and the MAF signal, to make decisions on where to position the camshaft to for optimum engine performance.

If you have no signal from either the Camshaft position sensor or the Crankshaft position sensor the engine will not run.

I'm not sure if that answered your question or not.

...Lee

[monty]

Hi Lee,
Thanks for the reply and sorry for being so vague in my question. I've read numerous posts on various forums that suggest if your tach does not register the cranking rpm then a faulty crankshaft position sensor should be suspected. In the case of my car the tach does not move during cranking, but operates normally once the car starts. So what I was trying to understand was which sensor inputs the tach responds to.
I can't say for sure that the tach ever showed the cranking rpm because I've never used the car as my daily driver, as my son's have used it over the years. Right now it's sitting 750km. away with a suspected failed fuel pump (no start, no pressure at rail, no pump sound, no pump sound when bypassing pump relay). With an local estimate of $2300. to do the repair in mind, I will be going to pick the car up on a trailer and bring it home to work on.
In addition to the fuel pump, and the fact the car has 230,000 miles on the clock, I am considering replacing the crank sensor at the same time. It has had some starting issues lately (die immediately after starting then fine on re-start, and what sounds like rich running on cold start that smooths out as soon as gas pedal is pushed only to load up again when pedal is released).
Any info you can share would be appreciated! Thanks
monty

[Ozark Lee]

Both the crank and cam sensors are easily replaced and they will post a code if they get flaky. When they quit suddenly they don't always post a code but you loose spark and the engine won't run at all.

It sounds like you have the fuel pump properly diagnosed so that is the place to start. It could be that the fuel pump was starting the death dance earlier and that led to the intermittent stalling. The tachometer while cranking test isn't that definitive.

Its too bad they never figured out a better way to design the fuel pump access on the XC.

...Lee