25 Feb 2024

A month in the life of a vehicle technician

Frank’s adventures through the valley of the shadow of random faults as seen at Eldon Street Garage continues
By Frank Massey

The last two months has presented me with a unique and diverse set of challenges. However, I am beginning to think that experience can be a millstone around my neck.

The faults generally fall into two categories; Diagnostic and engineering. One invariably leads to the other. Only last week I had another broken stud challenge. Just to make it interesting, there were two broken studs just below the gasket face. They were at the rear of the engine with a 20-degree list and no direct line-of-sight. Could more pain be added? Oh yes, they were of the alloy head variety with a hardened steel stud.

If I failed it meant a new cylinder head at the very least, or complete engine replacement. No pressure then. That’s the context. On the plus side, I am fortunate in that I had a drilling guide tool allowing for an accurate pilot at precisely 90° to the gasket face. The tool was fixed by an adjacent stud. The catch was ensuring that I hit dead centre with little or no pilot hole. I elected to drill at 8mm and helicoil back to 8×1.25mm. It took two hours with an agreed cost of £400, plus a new turbo with additional reassembly costs.

I had almost given up on engine rebuilds, entirely due to the high labour costs incurred, having just finished a rebuild six weeks ago. This was yet another Vauxhall that had presented itself-having lost its coolant and almost seized up. We agreed a fixed price to dismantle and provide an accurate repair cost.

What I found was that a simple leak at the thermostat housing with a very discrete internal leak from the timing case housing was allowing coolant directly into the sump. Please refer to Fig.1, which shows the thermostat housing, and Fig.2, which shows the rear of the timing cover.

Authority was granted, which was unexpected due to the extensive list of repairs required:
• Complete strip down to the cylinder block
• New pistons
• Cylinder hone
• New big end bearing shells
• New stretch bolts, rods, head, front pulley.
• Full head overhaul new valves, with 0.5mm skim required due to thermal distortion
• Gaskets, hose clips, and fluids.

Please refer to Fig.3, which shows the cylinder block ready for reassembly, and Fig.4, where it has been fully overhauled. £4,000.00 for a 2016 Meriva. I was a little surprised that this later engine variant had cold cracked rods.

A little diagnostic work helped the mix. This came in the form of a Citroen C3 diesel with NOx reduction SCR. The lady owner was concerned with what she described as “smoke” from the exhaust. The vehicle was transported via the RAC. A serial scan suggested a NOx sensor error and CAN communication failure with PCM.

The exhaust was soaking wet with a milky fluid that we finally agreed was excessive SCR additive. There was also a great deal of serial data relating to NOx reduction and DPF regeneration. However, we deemed this unhelpful given the extent of the fault, electing to replace the NOx module and injector, followed by a complete refresh of all adaptions prior to an extended road test. This was a reasonably straightforward repair, although there was the £700 parts value element to consider. Please refer to Fig.5, showing the NOx module with deposits, and Fig.6, where you can see the NOx additive injector.

Flat performance
The icing on the cake was a Mazda CX5 SKYACTIV on a 65 plate. The problem was flat performance with a PCM MIL error. Serial data suggested air mass meter below threshold, with an EGR position error. We were a little ahead of the curve here as we had knowledge of a common problem with carbon fouling of the intake system.
Once again, we agreed to partly strip out the manifold to fully assess the extent of the problem. This was tedious rather than technically difficult. Here is what we found.

Please refer to Fig.7, which shows the intake ports, and Fig.8 showing the throttle valve and MAP sensor.
With my engineering background I don’t take to compromise easily. My preferred option was head off, complete decoke, new injectors, EGR, EGR cooler and DPF. Instead, I was left with the in-situ option. It took an awfully long time and was messy even with great care, and there is always the problem of cylinder fouling even with closed valves.

We received some additional information regarding this problem and vehicle type relating to turbo failure following decoke repairs. In fact, it is confirmed on the manufacturers service repair bulletins. My thoughts on this issue lean towards likely oil fuel contamination due to excessive regeneration cycles. More probable is a restricted map sensor; This would reduce the feedback manifold pressure, possibly causing to turbo to over boost.

The owner did explain that when used as a company vehicle over frequent distance journeys the car performed without any issues. The car was then passed to his wife who only used it for short trips.

Clean diesel technology is theoretically sound. In practical terms though they are very expensive both to service and repair. I always advocate performance fuel B5 not B7 and regular oil changes in keeping with usage profile. We now have low and high pressure EGR valves as well as an exhaust flow regulation valve. Exhaust coolers and additive injectors are often problematic though.

One last word of advice; Always check your urea; 32.5% concentration no more, no less. It needs to be stored in a very particular way to keep it in good health too. Naturally, most retail garages store outside it in direct sunlight, then leave it out in the frost in winter. Then again, if it works for the screenwash, why treat this any differently?