Crank Position Sensor... Riddle Me This?

[LPTJoe]

Right, first things first, some time back LairdScooby said I should check the wiring on my crank position sensor.

Turns out that was good advice (Thanks LS!) Today I did, look what I found....

SAM_7029 by [url=https://www.flickr.com/photos/152293344@N05/]

I traced the wires back from the sensor to the plug, shock! Whilst the internal wiring looks ok the insulation is clearly shot. Clearly I need to replace this but as usual I have a few questions

1. Could this be responsible for my odd misfire problem and lazy starts?

if the answer to question 1 is yes, then...

2. To refit does the engine need to be at TDC? Is it necessary to pull fuse 1/disconnect the battery whilst fitting? Anything special that I need to do other than simply bolting the new one on and connecting the plug?

3. Has anyone had any luck with aftermarket parts for these or is it best to stick with OEM?

As always, thanks in advance chaps. Advice/suggestions/tips/musings encouraged and appreciated

[loki_the_glt]

I did mine a while back, with an aftermarket unit, and didn't bother to disconnect the battery. Once the new sensor is installed it should automatically sense TDC - you can always manually crank the engine over (with the gear lever in neutral) and the ignition on - since the engine will rarely be switched off with the flywheel mark and the CPS aligned anyway.

[TonyS9]

When you say 'misfire' do you just mean the engine doesn't idle perfectly? Its fairly normal for red blocks to do this, I have tried all sort of things but nothing improves it. May just be a little difference in compression or the weak spark problem. I think my wasted spark B230FT works well.

They are normally either working or not, but the 940 seems a bit noisey with the disti nearby so its possible if the shield is broken it might get interference occassionally. You can see the crank senor is shielded and the low voltage computer output to the ignition amp, so perhaps Volvo have experienced some problems with this. There are no shielded cables in the 360, but its a Renix system, and the coil is built into the computer.

Most of my 360s ticked over lovely except the low compression GLT which I could never solve. My 940 is like this, random 'futs' during idle.

[lynns hubby]

1.My expeerience of these on ANY car is that they either work or they dont.
2. Just screw the new one in. No need for engine to be in a particular stroke i.e TDC. No need to disconect battery or pull fuse.
3.Aftermarket are fine, Any good motor factor will get one for you.

[LPTJoe]

Originally Posted by TonyS9

When you say 'misfire' do you just mean the engine doesn't idle perfectly?

It's basically an occasional stutter when at low revs and the engine will visibly shake/wobble briefly about once every three of four seconds. Inside the car this translates to a shudder/wobble of the gearstick every few seconds when idling and a slight hesitation when pulling off or driving at low revs.

Meanwhile I've ordered this...

https://www.ebay.co.uk/itm/514-899-0...53.m2749.l2649

At £12.50 it's as cheap as as a takeaway and Meyle is a decent brand IME.

[lynns hubby]

That will do fine.

[Laird Scooby]

That wiring could cause your problems Joe! Had a similar problem years ago with a Mk2 Cavalier that used Hall Effect ignition triggers and a similar result when i eventually found the insulation on the three wires (inside a lead that passed through a moulded-onto-the-lead grommet) into the dizzy.

I shaved the grommet back, cut and remade the connections with heatshrink sleeving and used heatshrink on the whole repair - good as new for a long time after, certainly the rest of my ownership!

Doesn't look like you have that option there, also by the time you've got the old one out it's just as easy to fit the new one.

Meyle are usually good but some parts can be fake - i had to replace a pair of drop-links less than 2 months old that were fake Meyle but sold as genuine.

If it's genuine you'll be fine though.

[TonyS9]

Originally Posted by LPTJoe

It's basically an occasional stutter when at low revs and the engine will visibly shake/wobble briefly about once every three of four seconds. Inside the car this translates to a shudder/wobble of the gearstick every few seconds when idling and a slight hesitation when pulling off or driving at low revs.

Yep sounds like mine on the idle. The hesitation is definately weak spark, can be cured temporarily by cleaning the disti cap, but it doesn't last long, oil vapour gets back in there pretty quick. Permanent cure is the buchka spark mod and convert to DIS (distributorless ignition system). Really helps the torque and pull off.

The 360 (B230FT with DIS) is in dissassemly atm but from memory I think the idle is pretty sweet, certainly torque is great no hesitation. Excellent control for drag racing.

I'm not sure the 2 are connected though. Injection is more of a common thread, the carb cars were more steady, but I need to hear my DIS car again.

[Dirty Rooster]

From the pic it looks like your CPS could do with being replaced, but all problems/cracking with mine over the years have been down at the bottom end ...

Your symptoms ;

Originally Posted by LPTJoe

It's basically an occasional stutter when at low revs and the engine will visibly shake/wobble briefly about once every three of four seconds..

don't sound like a CPS problem according to my own experience.

[LPTJoe]

Thanks all.

Whilst I appreciate it may not be responsible for the misfire/stumble I sometimes get, the old CPS looks to be suspect so better to replace it than find myself stranded at some point.

RE the Meyle part linked, after having a read through that sellers feedback I spotted someone complaining that a CPS bought from them had failed in under a fortnight... Needless to say order cancelled. I've managed to find a Bougicord one that's admittedly around £25 more expensive but should do the job more reliably- Surely a good thing as that sensor does quite an important job