A tale of two phonics

Non-runners with no history might be cheap, but usually for a reason

Published:  28 October, 2013

By Frank Massey

The first problem was on a Mercedes E 350 212 Blue Motion. The car had been presented to us from a local independent technician and the initial problem related to a badly blown fuse in the rear signal acquisition module (SAM) and front main power distribution unit, found in the nearside engine bay. It had been replaced but unfortunately with a random bit of electrical cable instead of a fuse.

This bodged job resulted in several components suffering a no-voltage condition during cranking. Adding to the problem, the vehicle had been bought as a non-runner very cheaply in what would I'd describe as a 'speculative venture'. Equally remarkable, the other vehicle, a Golf 2.0ltr FSI, was purchased in identical circumstances.

Before exploring the technical issues relating to the diagnosis, I think all of us, as an independent industry, need to take a step back and take stock. It's obvious that vehicles have become increasingly more complex, demanding huge investment in hardware, information technology, correct tools and (dare I say), the basic ability to swing a spanner with skilful application. Added to this series of demands, a functional knowledge of systems is also required. I mention all of these because whoever initially assembled these two cars clearly possessed none of these skills. I for one want to distance myself as far as possible, as there is a great danger that the general public will judge us equally incompetent.

So, let's pursue the evidence trail and prove there is no such thing as a cheap repair. The power module had been correctly replaced prior to our involvement, so our first step was a global scan with Autologic. We recorded and cleared down previous faults and attempted a crank start whilst monitoring relevant data. The result was no errors, but it still wouldn't start and it had a curious twitchy tacho with an erratic serial RPM count. We suspected a problem with the crank angle sensor, which often does not produce a DTC as may be expected. We decided to scope the profile whilst cranking.

Removing the starter motor on the Mercedes allowed us to see the torque converter flex plate on which is mounted the ring gear and phonic wheel. The photograph above shows the extent to which the reluctor has been physically damaged. This man-made damage has occurred either by someone dropping the gearbox or by insertion of something physical into the bell housing space. In this case, the damage has clearly been caused by someone doing something wrong - but quite what they were doing and how they caused the damage I can only speculate about.

We agreed to make some kind of vernier pointer so that while rotating the engine we could carefully realign the segments. Unfortunately, it turned out that the damage was such that the base crown and individual teeth were distorted, so the owner wants to investigate getting it turned on a lathe.

As for the Golf, I could see the engine was weathered as if it had been sitting somewhere with the bonnet open for a long time. Somewhere, I should think, like a scrapyard... On this vehicle the phonic wheel consists of a series of slots cut in a flange. In this case several slots were totally missing... I have no idea how but I suspect someone attempted to lock the engine via the reluctor for some reason, forgot and then tried to start it... hey ho!

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