A little background (Little longer, please excuse):
Few days before while we were driving Maruti Suzuki Dzire vdi (Engine: Fiat Multijet 1.3 DDIS, CRDI engine) around 40kmph. All of sudden there was a noise from engine and while we attempted to pull over to the side, the engine started to run away. We parked the car on the road side and removed the key but still the engine was running at its peak RPM with plumes of white/grey smoke covering the entire road. At the time of this happening it was our first experience and I was not aware of diesel runaway. We opened the bonnet (engine hood) and was literally frozen due to panic.
I thought the throttle pedal has stuck and hence tried to tap it with my hand and magically engine died. I do not know how it stopped. The coolant boiled over the expansion tank and the engine was hot and smelly and with huge crowd gathered around pouring in advice. We could not think anything wise. I reinserted the key and switched on the ignition (engine not started) thinking the radiator fan could run.
The car was towed away to an authorized service center and they were puzzled about this. Apparently none there were aware of diesel runaway. First they reported that the high pressure diesel pump had failed and was just hanging on to the engine on loose fasteners. Then they said the pump did not fail. They cleaned EGR valve, intercooler. Intercooler was flooded with engine oil, engine oil topped up and started white smoke spewed out for few minutes and then became normal.
Meanwhile I read about diesel runaway (see this video of a similar incident in YouTube) and understood that in my case the engine oil was acting as a fuel. The only way it could go in was through breather pipe or turbo charger seal failure or extremely worn out piston rings. With the noise heard just seconds before runaway and with the observation of having engine oil inside inter cooler I quickly came to conclusion that turbocharger should be the source of problem.
After few days the service center staff performed a compression test and said 2 cylinders achieve compression ratio of 18:1 and other two achieved only 12:1. The white smoke is gone but still could see some trail of smoke (seems normal for a diesel engine). I thought I should have written off the engine, but to my surprise they charged me half of what they charge during normal service. They charged for EGR and intercooler cleaning and oil topup. While driving now there is a significant power loss.
- How did the engine runaway would have stopped? If it had stopped by consuming the engine oil significant damages should have occurred. But this was not the case reported by service centre staff. I have not blocked the air intake and the smoke was only spewing at the rear of the car and front (engine bay) remained clear.
- What would have caused the runaway? If it is the turbo seals, then the car should have trouble using afterwards.
- The loss of compression is not analysed further as we do not want to open up the engine causing high cost. Leak down test could have been done to identify whether the poor compression was due to valve or piston rings. Service center staff were not aware of this test and so do I until after reading further. What could have caused the loss of compression?