Stuck Quantity Control Valve

MercTech20 · Post by **MercTech20** » Thu Nov 30, 2023 5:39 am

Here I have 2 waveforms, one from a stuck quantity control valve and the other I took after cleaning the valve and it made it to work again. This is from a Mercedes W212 with om651 engine where the diesel was contaminated and there was still no rail pressure after cleaning the system.
Are those irregularities in the waveform of the working valve caused by the mechanical movements of the valve. If so, then its possible to confirm a fault in this or the rail pressure regulator valve using the waveform.
Does anyone have other testing methods without having to remove half the engine compartment to get to this valve?

picowight · Post by **picowight** » Thu Nov 30, 2023 10:44 pm

I often use the current waveform of rail pressure regulating valves, solenoids, position motors etc - pretty much anything you would expect to move smoothly, to detect if it is sticking from a current anomaly. In the case of EGR and VNT the ECU will often cycle them stop to stop at ign on/off. Even if they are on a fuse that has a bunch of other things on you can use a fuse loop and command it with a scanner - if it's the only thing moving you can see it.

This was an intermittent stall on a CRV, had pages of this

Then finally the IMV /QCV showed up sticking - this did not actually stall the engine but it was enough to show that it was the issue.

MercTech20 · Post by **MercTech20** » Fri Dec 01, 2023 2:34 am

Initially this vehicle wouldnt start and when I first scoped out the Valve it was a very smooth waveform. This was when it was stuck. After reinstalling it, the vehicle started back up. But the waveform is not smooth at all.

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