--------------------------------------------------- Article in “Professional Motor Mechanic”, December 2005 Issue I have often written about successful jobs through our workshop, so I think it only fair to write about why we enjoy a high degree of success; it's often called experience, or knowing when to stop before failure. Recently we were offered a repair to a Porsche 928 S4 with an ABS fault. Upon first impressions this was not Dr Ferdinand's finest hour: the driver's door window did not operate and the internal trim suggested a catalogue of equally less discerning previous owners. With no serial capability at our disposal we opted to test for the most likely problems: 'the wheel sensors', which, like all Porsche designs, were easy to reach and test. We scoped the outputs and quickly ruled out any problems at the road wheels; however, wiring problems and the need to now concentrate at the ABS module, led us to the n/s foot well. HIGH COST The story that illustrates why electronics would make or break many garages involves a BMW M3 Coupe and contrasts very nicely with the previous Porsche. One of my recent concerns was the influx of the plug and play cowboys, armed with a scan tool, a van full of spares and a telephone diary full helpful friends' phone numbers. (Do not confuse these with genuine highly skilled mobile technicians!) It did not threaten my business directly but undermined our ability to market genuine skill to the public and other garages. However, our recent association with a leading company and the acquisition of their brilliant software platform has allowed to access customers who would normally use the main dealerships or otherwise be turned away because of the complex relationship between serial interface and diagnostic logic. In plain English, using serial data to determine cause and symptoms. SERIAL DATA The next course of action was to examine serial data in detail; we had previously noted no DTC's or obvious serial errors. Moving through to software, we conducted actuator tests to the electro-hydraulic actuators, which appeared to operate normally. However, we noted in the Vanos live data directory that the exhaust cam position, actual vis desired, was in error to the tune of -30° whilst the inlet differential was less than 1°. -------------------------------------------------- Picture referred to [Halfords] contains 5 Scotch Locks and a couple of joints besides... Will post that if required...
Message modified by user UKAT5556 December 21, 2005, 2:31 am
Written by Frank Massey [Trouble Shooter Article]
The module and the main relay fuse panel are accessed on the forward
bulkhead. Removing the wooden floor panel revealed one of my greatest fears -the relay panel looked more like a bowl of noodles, attacked by a plague of enthusiastic, but not so skilful electricians, whose only desire was to use up Halfords' entire stock of scotch locks (see below). So faced with my greatest fear -failure - and with every intention that this vehicle was not one on which I would fail, we refused the work.
Upon ringing the garage explaining the reason we refused to continue – i.e.
high cost, with the probability of uncovering other problems through
poor connections and no doubt being blamed for every fault on the car -I was curious when told, “Oh yes, we know about the problem with the fuse box; I have yet to repair the electric windows.” With that I offered a few words of encouragement: "Good Luck".
The M3 is a high performance power plant using Vanos or variable electro/hydraulic cam timing control. The camshaft sprockets are connected to the camshafts via a helical gear arrangement which in turn are brought in and out of mesh using hydraulic pistons controlled by solenoids (not dissimilar to ABS), thus causing the camshafts to be adjusted independently of each other and the crankshaft (see opposite page).
The vehicle's problem: poor idle, lumpy with excessive emissions but top end performance was normal. So how the hell did we end up looking at Vanos when the problem could have been a dozen other faults?
I served my apprenticeship as a specialist engine builder, so therefore I feel comfortable with mechanical as well as electronic diagnostic procedures. However, in this case my background would have been no help without the expert level of software at our disposal.
Not forgetting our usual and important preparation procedures – ¬inspecting the plugs, scoping the coils and confirming the ignition profile against lambda and air mass meter outputs ¬our attention soon directed us to a mechanical problem: poor vacuum and high HC's. This could, however, have been an injector problem and these symptoms are identical to poor atomisation or fuel quantity error.
This then gave rise to the probability of a Vanos mechanical control error. Removing the Vanos unit, dismantling and examination confirmed a piston and seal failure in the exhaust hydraulic port, allowing the all-important pressure, which drives the piston into the correct mechanical position to leak.
The Vanos assembly, by the way, is £1,000. The customer who had recently been unsuccessful with her local BMW dealership is now a customer for life, thanks to the excellent diagnostic equipment, software, skill and investment. So my advice to genuine businesses out there: set yourself apart from the cowboys and follow our lead; we are only going to get one shot at this technological revolution.
E.
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How you gonna cope with this then? - John Wallis October 30, 2004, 5:48 pm
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