Vivaro 2.0 M9R-788 Cam/Crank sync issues

rsvr · Post by **rsvr** » Thu Sep 01, 2022 8:54 pm

Hi,

New to Picoscope but just picked up a scope to try and diagnose a no start Vivaro.
I'll keep it short as possible.

Vivaro was working perfectly, driving very well, then one day it wouldn't start.
DFC showed problem with Cam sensor, so swapped for genuine one.
Still the same issue. Using different diagnosing software we also got the crank sensor issue, so replaced that sensor twice over with a genuine part, and still the same fault.

Looks like I have a damaged tooth on the reluctor ring. Voltage is a bit low compared to another engine. So a new battery then I'm going to borescope the reluctor ring, but I think it'll be gearbox off time.

The cam sensor looks to be a 3 pin pull down type. At ignition on:
Pin 1 = ground
Pin 2 = signal wire 11.45v
Pin 3 = feed 12.45v

From what I can tell from others, this is normal ignition on voltages.

Thanks for any help.

Update: Battery has now been replaced as it was 10 years old. Voltages are generally better throughout while cranking, but the crankshaft sensor output still looks low to me. I think the sensor to housing mating surface has been marked a little in the past, due to the difficulty in removing the exceptionally tight fitting ckp sensor. I'm going to clean the mating surface up a little and I think the voltage output will improve. I shall be very careful not to remove much of the surface, just a light sand, as the distance from cks to reluctor ring / pulse generator is critical.

vasek · Post by **vasek** » Fri Sep 02, 2022 8:37 am

Hi.
The main problem is related to the faulty signal of the crankshaft sensor.
This, in turn, is due to a damaged signal disk.
The reduced voltage on the camshaft sensor is due to the fact that when the starter is running, the on-board voltage has decreased.

rsvr · Post by **rsvr** » Fri Sep 02, 2022 10:24 pm

vasek wrote: ↑
Fri Sep 02, 2022 8:37 am
Hi.
The main problem is related to the faulty signal of the crankshaft sensor.
This, in turn, is due to a damaged signal disk.
The reduced voltage on the camshaft sensor is due to the fact that when the starter is running, the on-board voltage has decreased.

Hello,

Yes you are correct.
I just wanted confirmation of what I was thinking.
Because the sensors and wiring checks out fine, and because this anomolly on the ckp sensor waveform is repetetive, we can see that the reluctor ring (signal disk) is damaged, though I have no idea how that has happened. Looking at the signal it is producing, my guess would be that a small piece of tooth has broken away from the disc, not entirely, I think some of the tooth remains.
Next step, gearbox off!

Thank you for commenting.

robbieboyy · Post by **robbieboyy** » Mon Oct 16, 2023 3:39 pm

hi i can see this is an old thread but did you sort your problem? i have a xtrail with a m9r engine and im getting the same outputs at the cam sensor as yours! is that correct? as i thought it should only have a positive a negative and the signal wire returning too the ecu? thanks for eny help you can give!

rsvr · Post by **rsvr** » Tue Oct 17, 2023 6:05 am

Hi,
Only thing to be careful of is that there seems to be some variation, even between the same engine configurations, which is confusing, so I'm not even sure the xtrail will be the same. With that said, if your output looks virtually identical then I guess its probably the same.

What I can tell you is that I resolved the fault and the cam signal is spot on. It was the crankshaft signal that was bad due to a damaged tooth causing the second gap in the waveform. Once the ring was replaced the van ran perfect.

robbieboyy · Post by **robbieboyy** » Wed Oct 25, 2023 11:58 am

hi thanks so much for getting back too me! This is a strange one! when the problem first started it lost all power and the engine was running very uneven on tickover then it wouldnt start at all so we did a diagnostic scan and it was coming up with a cam crank correlation! it was then left for a month till i could get another look at it! so tried starting it again then it started and runs ok but engine light on and wont rev over 3000! plugged it back in and the same code comes back every time for cam sensor! and thats wether the cam sensor is connected or not even fitted a new oem sensor! i think its looking like getting it on a scope is the way forward ?

rsvr · Post by **rsvr** » Wed Oct 25, 2023 5:12 pm

robbieboyy wrote: ↑
Wed Oct 25, 2023 11:58 am
hi thanks so much for getting back too me! This is a strange one! when the problem first started it lost all power and the engine was running very uneven on tickover then it wouldnt start at all so we did a diagnostic scan and it was coming up with a cam crank correlation! it was then left for a month till i could get another look at it! so tried starting it again then it started and runs ok but engine light on and wont rev over 3000! plugged it back in and the same code comes back every time for cam sensor! and thats wether the cam sensor is connected or not even fitted a new oem sensor! i think its looking like getting it on a scope is the way forward ?

A scope would help identify the correlation issue. But for the record, I've had similar issues with these engines that turned out to be a jumped timing chain. I think one van we had showed very similar faults to yours, it had jumped 2 teeth. Once in a while it started but wouldn't run. You need to be careful because if it has done that and you keep turned it over you could jump the chain further. It's a known issue on these engines. The cam chains should last the life of the van, sadly they're made of cheese. Both our vans were done around 80k and they were both slack.

robbieboyy · Post by **robbieboyy** » Thu Oct 26, 2023 10:28 am

yeah i think thats going too be a good starting point! atleast too rule it out! thanks again for your help

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