We had a Mini cooper S come into us with several fault codes in its ECU (engine control module) relating to different faults and had no boost pressure until high revs when being driven.
Once we had cleared the codes and ran the car up to read some live data it was quite puzzling! we were still getting codes relating to boost pressure control, yet everything we checked seemed to be working as it should.
We checked boost pressure sensors, MAP sensors, MAF sensors, turbo actuator, boost pipes but we couldn’t find a fault with anything. After spending couple of hours checking all these items we decided we needed to check the timing of the engine which meant removing the rocker cover to allow access to the camshafts.
Once we removed the rocker cover we noticed something strange, the top timing chain guide was missing! the mounting bracket was still in place but the guide itself was missing.
On further inspection we noticed that the missing guide had broken off and dropped down in-between the timing chain cover and engine. we removed the broken guide and carried on with checking the engine timing.
When we fitted the engine timing tools we could see that the inlet camshaft was at least one tooth out of alignment. As we started to strip the engine to remove the timing chain and guides we noticed that as the top guide had been rattling around inside the timing chain cover it had caused damage to the other guides!
We removed the sump to check for any other debris from the damaged guides and found quite a few bits, one in particular had managed to wedge itself inside the oil pick up, luckily the gauze filter had stopped it being picked up and thrown around the internals of the engine.
After removing all the debris we fitted a new timing chain kit including new guides and a new tensioner, rebuilt the engine using new gaskets and seals where required and making sure that the engine timing was now correct.
Now that the engine was ready for testing we made sure all codes were cleared from the ECU and started the engine, so far so good, no codes had returned and the engine sounded a lot smoother.
Time for a road test to see if we had cured the boosting problem, the car drove faultlessly and had full boost from the off.
This just goes to show that you can’t rely on fault codes alone, the codes in this car had us chasing our tale for while until we decided to go back to the start and check basics.
What we presume had happened in this case is that the chain guide had broken dropping on top of the crank gear and jamming it enough to allow the chain to jump a tooth which in turn meant the engine timing was out causing our running fault.
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