Last summer, when I was out driving, my Eos went into limp home mode, so I pulled over, checked everything, restarted the car and all was fine. Checked the fault memory, noticed a code for overboost, didn't think anything of it, and since it didn't recur, more-or-less forgot about it.
This summer, when I was doing about 120 on the motorway on a hot day (around 30C), it came back with a vengeance. Cutting the engine and restarting would remove limp home mode, but only briefly, and it would return to limp home mode after a short period of driving. After it happened three times, instead of the flashing glow plug light, the engine light came on and stayed on - although again, restarting the car would remove the flashing glow plug light and limp home mode. On the home journey later that day I took it easy and managed to avoid limp home mode.
Given that the problem seemed a bit more serious, it was time to do some research. Here's a summary of what I've learnt: these engines have a variable vane turbo, which means that the turbo has vanes that alter the air flow to change the amount of boost. The position of the vanes is controlled by a solenoid that creates a vacuum that moves an actuator. Several things could go wrong here: the various air hoses could leak; the air pressure sensors could go wrong; the solenoid could malfunction; or carbon can build up on the dirty side of the turbo. (The dirty side is where the exhaust gases flow through a turbine, which drives a fan on the clean side that pushes more air into the engine.) In the case of overboost, the most likely cause is that carbon buildup has caused the vanes to stick, and the turbo cannot respond to a decrease in turbo pressure quickly enough. And what is overboost? It's when the turbo gives more boost than the car wants it to. The engine computer decides how much boost it wants to deliver and adjusts the solenoid's position to change the amount of vacuum which moves the vanes. Later cars have the vanes electronically controlled rather than having the vacuum bit in the middle - I guess the vacuum-operated turbos can work entirely mechanically rather than having the computer controlling how much they suck.
The turbo vanes can be tested using your diagnostic tool of choice: start the engine, then go into the engine module, basic settings, channel 011 - this will start a test that will spin the engine up to 1400rpm then move the vanes from minimum boost to full boost and back. Here's a video of what it should look and sound like. I checked the frequency of the whistling sound on that video, and the tone of my turbo is around 10% lower, which suggests that the vanes are not fully opening. Unscientific I know - the ideal would be to know what boost pressure numbers I should see - but all I have to go on there is that someone on the internet wrote that it should be around 150mbar and I get more like 100.
So, first step is to stick a bottle of Wynn's Turbo Cleaner in the tank, and after a few hundred km trying to keep the revs around 2000 to ensure decent exhaust gas temperature to help burn the carbon off, see if there's any difference in the measurement. If that doesn't work, sounds like the turbo needs cleaning.
Unless one of you has a better idea, of course...?
This summer, when I was doing about 120 on the motorway on a hot day (around 30C), it came back with a vengeance. Cutting the engine and restarting would remove limp home mode, but only briefly, and it would return to limp home mode after a short period of driving. After it happened three times, instead of the flashing glow plug light, the engine light came on and stayed on - although again, restarting the car would remove the flashing glow plug light and limp home mode. On the home journey later that day I took it easy and managed to avoid limp home mode.
Given that the problem seemed a bit more serious, it was time to do some research. Here's a summary of what I've learnt: these engines have a variable vane turbo, which means that the turbo has vanes that alter the air flow to change the amount of boost. The position of the vanes is controlled by a solenoid that creates a vacuum that moves an actuator. Several things could go wrong here: the various air hoses could leak; the air pressure sensors could go wrong; the solenoid could malfunction; or carbon can build up on the dirty side of the turbo. (The dirty side is where the exhaust gases flow through a turbine, which drives a fan on the clean side that pushes more air into the engine.) In the case of overboost, the most likely cause is that carbon buildup has caused the vanes to stick, and the turbo cannot respond to a decrease in turbo pressure quickly enough. And what is overboost? It's when the turbo gives more boost than the car wants it to. The engine computer decides how much boost it wants to deliver and adjusts the solenoid's position to change the amount of vacuum which moves the vanes. Later cars have the vanes electronically controlled rather than having the vacuum bit in the middle - I guess the vacuum-operated turbos can work entirely mechanically rather than having the computer controlling how much they suck.
The turbo vanes can be tested using your diagnostic tool of choice: start the engine, then go into the engine module, basic settings, channel 011 - this will start a test that will spin the engine up to 1400rpm then move the vanes from minimum boost to full boost and back. Here's a video of what it should look and sound like. I checked the frequency of the whistling sound on that video, and the tone of my turbo is around 10% lower, which suggests that the vanes are not fully opening. Unscientific I know - the ideal would be to know what boost pressure numbers I should see - but all I have to go on there is that someone on the internet wrote that it should be around 150mbar and I get more like 100.
So, first step is to stick a bottle of Wynn's Turbo Cleaner in the tank, and after a few hundred km trying to keep the revs around 2000 to ensure decent exhaust gas temperature to help burn the carbon off, see if there's any difference in the measurement. If that doesn't work, sounds like the turbo needs cleaning.
Unless one of you has a better idea, of course...?