D3 Start issues with a twist (maybe??)

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Originally Posted by Graeme

Graph live values, engine, engine rpm, which is taken from the crankshaft position sensor. The rpm should increase in a couple of steps from turning over prior to firing, then the first fire increases the revs substantially then proper idle revs. Any dips or zero moments indicates a faulty sensor.

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:ohyes: huh, yeah. That makes perfect sense now ..... [bighmmm]

Yep, I regularly have engine RPM showing, where else would that value come from, I'll setup graphing next start.

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Originally Posted by josh.huber

Be good to graph it against the rail pressure too

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Great suggestion, thank you.

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Originally Posted by swiftnets

I'll setup graphing next start.

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As I found when chasing another issue, graph or display as few variables as possible when you are looking for short events. The more you have subscribed, the slower the update rate.

Just another thought completely away from injectors etc. Maybe ask the mechanic who did the pump and belt if he removed the starter to lock the flywheel, or if he eyeballed it to line up the hole above the starter, then ask him if it is possible to recheck the timing marks once it is all lined up. These can be a pain if the timing is out, as with all cars. I have had many cars where they will run start fine when cold, but not when hot.

Also another question, when did you get fuel before or after the pump was done?

Hi team,

So I have 4 start processes on the logs and most of them do show the RPM intermittantly dropping to 0 along the way.

I take it from this discussion, that would suggest the sensor is either going or the connection is having issues?

I'm going to work on uploading the graphs some time today.

Thanks again, looks like I have some work to do [bighmmm]

Michael

The sensors eventually fail, usually slowly getting worse so it's time to replace it. At least you now have proof rather than replacing it on a hunch or chasing other dead leads.

I feel vindicated! Sorry to hear. Mine cost nearly a grand to get replaced as it’s a ***** to get to and they also found a split CV boot along the way that’s included in that cost.

Here are some of the log graphs

Attachment 179852

Attachment 179853

Sometimes it doesn't show the drop in the start sequences, I guess that happens too quickly then?

Attachment 179854

Anyhow, other than access and time, does this job need any specialised tools?

Michael

Not that I recall when I was looking to do mine. Mine was on the 3L but much the same. Access is from the LHS wheel arch with an access point in the bell housing. A lot of things in the way though to get to it so a bit of work involved.

The sensor must be very close to not working at all!

Sorry, I can't advise on the required tools.

We replaced the sensor on my dads ML350 and it was the easiest job ever. Drove onto his ramp , bent a small shield out of the way, undid the 2 torx bolts, remove and replace, bolts done up and shield bent back - done in less than 5 mins.