14 replies to this topic

[Wiggy]

Hello friends,

 

My MPi broke down the other day. Previously running perfectly.

 

For a mile or two before it was down on power and reluctant to rev, intermittently. When it finally broke down, it would run poorly but not rev at all. Literally not at all.

 

Hooked up the ACR with her running and: CAM SENSOR - BAD.

 

Ordered and fitted a genuine brand new one; no change at all.

 

Checked the continuity of the 2 wires from the sensor to the ECU; both check out fine.

 

 

Anyone have any other suggestions as to why the Cam Sensor signal seems to be giving me trouble? 

 

Thanks a lot.

 

 

[Bat]

Hi,

Have you checked for shorts to each other and to ground?

Cheers 

[Wiggy]

I had actually forgotten to check them for a short to earth, ta for that.

 

Both wires check out perfectly.

[pete l]

Isn't the cam sensor only used during start up ?

[Wiggy]

I think its used to sequence the injectors at the correct time due to the Siamese ports.

 

Unplugged the cam sensor completely and it idled a bit higher, and more stably, but still wouldn't rev at all. Still rough though.

[minimat]

Not sure about mpi minis but on modern cars a cam sensor fault can be flagged up by a slack timing chain which throws out alignment of the crank and cam.

[Wiggy]

Interesting. Certainly possible even though it's only done 26k.

Shame it's such a pain in the arse to check.

[Bat]

Hi, 

A sensor sync problem is a fault code on most systems, I can't imagine MEMS being any different.

The problem with "cam sensor bad" is it's not very descriptive.

If you could get access to rover diagnostics you might get a better idea.

Or a dual channel sillyscope to capture the waveforms from the sensors and look for sync issues.

Cheers 

[Wiggy]

I assume it means it's either not getting a signal, or not getting a plausible signal. But the circuit itself is simplicity itself. Cam sensor, one pair a wires straight to the ECU.

Before the comment above, I had a feeling the cam timing could be something to do with it. Or it could be a ECU fault, but they're very rare.

I've searched and searched and not found a single thread that replicates my symptoms.

So I think it's time to pop the timing cover off and take a look. Bum.

Edited by Wiggy, 02 October 2018 - 02:42 PM.

[pete l]

What were the other readings you got from the reader ?

[Wiggy]

I didn't actually take note, because I figured that they'd be all over the place trying to compensate. And it's only possible to run her at about 600 rpm.

I can do, of course.

[Bat]

Hi,

Would be worth having a good look to see if something else is throwing it out before tearing down the engine..

As you say it's not a common problem so extra caution could save time and money!

Cheers 

[Wiggy]

Ok. After some initial investigation, it would appear that the reluctor ring has slipped on the flywheel; retarding the timing by 30° odd.

 

The yellow dot is at TDC on mine.

 

 

With thanks to Sprocket for using his image. Hope you don't mind.

 

[Sprocket]

They don't slip, not that much anyway. the number of teeth you mark out where TDC is, compared to where it should be, looks like the right amount for the wrong type of clutch.

 

what is more likely is that the clutch had been replaced with a non injection clutch.

 

Cannot remember of the top of my head which way the trigger tooth moves when this happens. What makes things worse is I've seen the reluctor ring re positioned to correct this error. Un be known to someone later down the line, they replace the clutch again but this time with an injection type and the trigger tooth moves back the other way and the reluctor ring rarely gets re positioned to correct it, and ultimately put the trigger tooth back to where it should be all along, lol.

[Wiggy]

It hasn't been apart. It was running lovely for a couple of months. Then one day it lost power low down, then within a mile, she'd only just run at all.