Foreward

Wednesday, 1 February 2012

Breakdown


So there we were, happily cruising along with Bob sleeping next to me, probably dreaming of a hot shower that evening, when the engine just cut out! We were travelling around 140 kph at the time, as the road was perfectly flat and smooth so the damper problem did not show much. The car acted like we had run out of petrol. I put the car into neutral and checked all the instrument gauges but everything seemed completely normal. I then pulled off the road over to the hard shoulder and stopped waking Bob up.
We then checked the whole car over and we were both completely puzzled, as we could find nothing wrong with it? After removing the spark plugs they were completely dry, it had a spark as we had connected one of the plugs to the plug cap and cranked the engine over to see it. There was nothing mechanically wrong with the engine and it had plenty of fuel on the gauge. We even passed a rubber hose into the filler cap to check the tank fuel level manually which confirmed there was enough fuel. We were at a loss as to what was wrong? So there we were in the middle of nowhere, not a building could be seen and no vehicles passed us either way. Two leading Porsche mechanics completely baffled!
I then thought perhaps the fuel injection pump drive toothed drive belt had broken so we checked this, but it was fine and we also checked it was still timed correctly, which it was. I was beginning to think the Bosch mechanical injection pump had broken internally, when it occurred to me to open a fuel injector and see if it was spraying fuel. We removed one fuel injector from its cylinder head and connected it up to its fuel line. Bob cranked the engine over and was spraying out its conical fuel mist. This only increased our bewilderment, however as soon as we stopped manual cranking the engine over on the starter motor; the injector was immediately totally dry of any fuel whatsoever. In the UK, if you did this you would have fuel on your hands and it would be deposited on the local area where it was spraying, but in our case at that time, there was absolutely no trace of petrol to be found. This then led us to the problem, as in theory, if you had fuel and a spark, all timed correctly, the engine must fire and run.
I took the warm up thermostat apart; I found the small circlip that kept the expanding washers together had broken and come off, putting the fuel air ration mixture to fully rich. However this did not make sense as this should have flooded the engine and all the spark plugs should have been soaking wet, but in fact they were all totally dry when we had checked them?
After some thought we reinstalled everything and I got Bob to try and start the engine whilst I manually held the enrichment cam with a screwdriver to the normal hot running position. The engine burst into life and ran perfectly fine until I let go of the enrichment cam. This was obviously the problem but why weren’t the spark plugs soaking wet?
When we thought on it for some time I realised two things were totally different from the UK; firstly it was 45c to 50c outside temperature in the shade and the engine was a lot hotter than that; and secondly, we were several thousands of feet above sea level, so the air must have been a lot thinner due to altitude and of course the higher temperature. We therefore knew that the spark plugs should have been flooded, but by the time we have unscrewed these and taken them out to see, the ambient temperature had evaporated all the fuel so they looked dry to visual inspection.
In fact the engine mixture had gone totally rich and with the lack of dense air as well, had completely thrown the fuel air ration out so it would not run at all. Basically a car engine needs 14 parts air to 1 of petrol in round numbers.
I managed to wedge some steel rod in to shim the thermostat to be permanently in the normal hot running position and we were on our way. It would subsequently be harder to start the engine when it was cold, but I assumed it would never be that cold at night in this part of the world.

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