Rattle under Boost
Discussion
Need some advice on a strange sound that my car is making. It’s now been in 2 different garages for investigation, but nothing has been found.
It sounds to me like a rattle as if something is loose, or a bolt has been dropped onto the block and got trapped somewhere but it only happens on full boost. An air leak was suggested, but to me it's too loud and too 'mechanical' for that. The car is a sequential twin turbo, so when the primary turbo gets to full boost, the noise will start, and then boost drops, sound disappears. When it gets up to full boost again on both turbos, the sound comes back. Apologies for the poor video, I’ll try to get a better one.
The engine was fully rebuilt a few months ago (crank, bearings, piston rings etc due to big end failure) and was fine for about a month, then the noise started. The turbos were obviously inspected when it was rebuilt, and they were both in perfect condition (car has done 110,000kms – 68k miles).
Performance doesn’t seem to be affected, but it’s not a nice noise none the less. Anybody have any ideas on how to track the source down or places to look? Thanks
https://www.youtube.com/watch?v=UuY_zXy57IY
It sounds to me like a rattle as if something is loose, or a bolt has been dropped onto the block and got trapped somewhere but it only happens on full boost. An air leak was suggested, but to me it's too loud and too 'mechanical' for that. The car is a sequential twin turbo, so when the primary turbo gets to full boost, the noise will start, and then boost drops, sound disappears. When it gets up to full boost again on both turbos, the sound comes back. Apologies for the poor video, I’ll try to get a better one.
The engine was fully rebuilt a few months ago (crank, bearings, piston rings etc due to big end failure) and was fine for about a month, then the noise started. The turbos were obviously inspected when it was rebuilt, and they were both in perfect condition (car has done 110,000kms – 68k miles).
Performance doesn’t seem to be affected, but it’s not a nice noise none the less. Anybody have any ideas on how to track the source down or places to look? Thanks
https://www.youtube.com/watch?v=UuY_zXy57IY
Well thats not good news. Looked up a few videos of detonation, and it does sound similar.
What would be the cause of this (especially after an overhaul), and are there any remedies?
I can't change the map, as the car is standard. All the advice I've read online is for very old cars with very primitive systems, or highly tuned stuff. I'll pull the plugs at the weekend and have a look.
Thanks for your thoughts
What would be the cause of this (especially after an overhaul), and are there any remedies?
I can't change the map, as the car is standard. All the advice I've read online is for very old cars with very primitive systems, or highly tuned stuff. I'll pull the plugs at the weekend and have a look.
Thanks for your thoughts
Yes, it is the Legacy. Knock sensor is a possibility, I asked about this when the engine went the first time - but we decided that this was most likely due to the previous owner running it low on oil as all but one of the bearing surfaces were as new (I had only owned the car 2 weeks before that happened).
Pumaracing, the sound from the pickup is different, but definitely similar. There is a big exhaust on the car, so that may be helping to mask certain sounds. I'm in SW Scotland, Ayrshire but willing to travel for someone who knows what they're doing. I had the engine built by someone in Edinburgh because he came highly recommended. I pointed the noise out to him once the car was all back together and had been run for a week (took it up for a check over), but he didn't say anything about detonation, which I am surprised at as he seemed to know what he was doing.
The heads were lightly skimmed and acid dipped, used mls head gaskets instead of composite, so that I had the option of turning the boost up slightly in the future. The same pistons were used, as they were found to be ok (the bores were wet when the engine came apart - so he thought that the ringlands had gone, but amazingly the pistons were fine). Compression tests & strobe lights are out of my comfort zone experience wise, and anyway I agree that someone experienced should look at it. Going to be so angry if it has turned to swiss cheese after what I've spent on it.
ETA: just checked the car for error codes - all clear. I suppose this could still mean that the sensor is playing up though?
Pumaracing, the sound from the pickup is different, but definitely similar. There is a big exhaust on the car, so that may be helping to mask certain sounds. I'm in SW Scotland, Ayrshire but willing to travel for someone who knows what they're doing. I had the engine built by someone in Edinburgh because he came highly recommended. I pointed the noise out to him once the car was all back together and had been run for a week (took it up for a check over), but he didn't say anything about detonation, which I am surprised at as he seemed to know what he was doing.
The heads were lightly skimmed and acid dipped, used mls head gaskets instead of composite, so that I had the option of turning the boost up slightly in the future. The same pistons were used, as they were found to be ok (the bores were wet when the engine came apart - so he thought that the ringlands had gone, but amazingly the pistons were fine). Compression tests & strobe lights are out of my comfort zone experience wise, and anyway I agree that someone experienced should look at it. Going to be so angry if it has turned to swiss cheese after what I've spent on it.
ETA: just checked the car for error codes - all clear. I suppose this could still mean that the sensor is playing up though?
Edited by Viperz888 on Monday 24th November 21:23
Pumaracing said:
Ach so yer a bloody heathen lowlander are ye? I'll no help any bloody heathens wi their poxy engines when there's plenty of god's own highlanders needing my advice so they are.
It's worse - I'm a pasty at heart! I'll give them a phone tomorrow to see when I could head over; thank you. Who should I say sent me?Until then, just stay off the boost, right?
BG5 EJ20H.
I'll try some octane booster, that might at least tell us something. I thought Tesco stuff was the best you could get here other than race fuel.
Surely the likelihood that the knock sensor has failed in such a way that the car doesn't notice though the diagnostics is incredibly small, otherwise I'd start there. Unfortunately it's a right pig of a job on a TT.
I'll try some octane booster, that might at least tell us something. I thought Tesco stuff was the best you could get here other than race fuel.
Surely the likelihood that the knock sensor has failed in such a way that the car doesn't notice though the diagnostics is incredibly small, otherwise I'd start there. Unfortunately it's a right pig of a job on a TT.
stevieturbo said:
Is it definitely only under boost ?
Who rebuilt it and how long ago ? and why ?
I'm very confident it is only under full boost (approx 9-10 psi). It would be harder to attribute if it wasn't twin, as it would only be under high rpm, but it happens twice in one gear, due to the turbo changeover.Who rebuilt it and how long ago ? and why ?
It was rebuilt in September due to a spun bearing - we determined this was most likely due to a previous owner running it low on oil and it just deteriorated in the time I had it. The rest of the bearings/surfaces were as new, so not in line with the car being thrashed constantly or from cold, and that I was very careful with oil level & grade, and it never overheated.
I’m actually on UKL and have asked there already, but had no real luck.
I have put some Octane Booster in it, just going to give it a few days to come through fully (using it as little as possible at the moment, for obvious reasons) and see if there is a difference. Have been in touch with the builder, and he is going to have a look at it – I think it’s only fair he is first, if the problem still exists I’ll go elsewhere for an opinion.
Problem started about a week or two after the rebuild. It definitely wasn't there immediately afterward.
Boosted LS1, its a standard engine. The only thing that is modified is that it has an exhaust and the aforementioned mls head gaskets. When it was rebuilt, that was the first time the engine had been split.
Boosted LS1, its a standard engine. The only thing that is modified is that it has an exhaust and the aforementioned mls head gaskets. When it was rebuilt, that was the first time the engine had been split.
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