M177 Compression test results 150psi on Cylinder 5. Rebuild due?
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⏱️ 700HP Facelift converted C63 S Coupe with Drexler 3.06 plated LSD
M177 Compression test results 150psi on Cylinder 5. Rebuild due?
Who's done a comp test on their C63 here?
Got a workshop to do my car today before installing injectors on cylinder 5 & 6. Results where 195 to 210psi on all cylinders EXCEPT cylinder 5 which had 150psi (they said over the phone).Workshop said they checked cylinder 5 with a borescope for damage but was in good condition with no scoring however they said it's "time to think about a rebuild".
Car is a 2017 Coupe with a mild stage 1 tune for the last 2 years - 600bhp on a good day nothing drastic and it runs like a dream.
🔹Coil packs recently changed
🔹Spark plugs changed last week
🔹Both injectors changed today for Cylinders 5 & 6 (after the compression test was done)
Car runs beautifully and can't fault it.
Should I get another compression test was done as a second opinion?
Sort of pissed off about this as I've always been on top of maintenance but what do you do.
Who else has done a comp test on their M177? What were your results?
Last edited by Jimmy_c63s; May 18, 2022 at 01:51 AM. Reason: Added a pic
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From: Maryland
2018 C63s
*****The above are good suggestions. If the car runs well, and there is no evidence of excessive oil consumption, or other related issues I would just drive the car. Prepare to grab your ankles if you go the rebuild route, and a 150 compression is NOT *that* bad. I'd recheck that cylinder especially if the borescope turns up no scoring and do the oil test. It could also be a leaky or poorly sealing valve due to a scored valve seat or any number of other things, like the compression tester itself was not inserted properly or tight enough and it leaked itself (happens..) Rebuilding a head or the heads is a LOT easier than a full rebuild, but it is totally up to you as it is your car.
Anyway, just stuff to think about. Sorry for the news, but it doesn't sound terminal or anything. If the car runs ok, drive it. These are really nice cars.
Good luck
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From: Australia
⏱️ 700HP Facelift converted C63 S Coupe with Drexler 3.06 plated LSD
If it comes down to a rebuild I've got two options here in Australia:
$20,000 AUD for rebuild - 3 months off the road
$35,000 AUD forged - 6 months off the road
I'd recheck that cylinder especially if the borescope turns up no scoring and do the oil test. It could also be a leaky or poorly sealing valve due to a scored valve seat or any number of other things, like the compression tester itself was not inserted properly or tight enough and it leaked itself (happens..)
What spun me out is that the car drives so well, no oil loss what so ever and no plumes of smoke or anything of that nature. That's why I was tripping out when they said "low comp on cylinder 5..... 150psi but all other cylinders are immaculate - should start thinking about a rebuild and if you want we can look for an engine for you for around $20,000"
Here's a clip I did the other day just for myself to test the stock exhaust sound in comfort and sport+ and it drives so well (sorry about the low quality clip and blurring etc.)
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C63 amg edition 1
Thanks Ryan, yeah man that would be the next step after I get a second opinion. I'll keep this topic updated.
If it comes down to a rebuild I've got two options here in Australia:
$20,000 AUD for rebuild - 3 months off the road
$35,000 AUD forged - 6 months off the road
Thank you bud, I will now enquire about a leakdown test as well. This wasn't suggested to me by the tuner/mechanic after this compression test was done. It was basically "you've got low comp on Cylinder 5 you should think about a rebuild, we can start finding you an engine".
You're right mate, the engine was warm at the time as I had driven the car there (12 miles). It was there for injectors and he didn't explain how the compression test was done. Whether it was via Xentry or with a gauge. I do know for sure that the spark plugs weren't removed because they weren't replaced. And the spark plugs in our cars are a one use only, right? Due to the indexing?
Thanks a lot Max. Encouraging words and I like your posts man - you're one of the helpful ones on here.
What spun me out is that the car drives so well, no oil loss what so ever and no plumes of smoke or anything of that nature. That's why I was tripping out when they said "low comp on cylinder 5..... 150psi but all other cylinders are immaculate - should start thinking about a rebuild and if you want we can look for an engine for you for around $20,000"
Here's a clip I did the other day just for myself to test the stock exhaust sound in comfort and sport+ and it drives so well (sorry about the low quality clip and blurring etc.)
https://www.youtube.com/watch?v=US_KRtjTzuE
If it comes down to a rebuild I've got two options here in Australia:
$20,000 AUD for rebuild - 3 months off the road
$35,000 AUD forged - 6 months off the road
Thank you bud, I will now enquire about a leakdown test as well. This wasn't suggested to me by the tuner/mechanic after this compression test was done. It was basically "you've got low comp on Cylinder 5 you should think about a rebuild, we can start finding you an engine".
You're right mate, the engine was warm at the time as I had driven the car there (12 miles). It was there for injectors and he didn't explain how the compression test was done. Whether it was via Xentry or with a gauge. I do know for sure that the spark plugs weren't removed because they weren't replaced. And the spark plugs in our cars are a one use only, right? Due to the indexing?
Thanks a lot Max. Encouraging words and I like your posts man - you're one of the helpful ones on here.
What spun me out is that the car drives so well, no oil loss what so ever and no plumes of smoke or anything of that nature. That's why I was tripping out when they said "low comp on cylinder 5..... 150psi but all other cylinders are immaculate - should start thinking about a rebuild and if you want we can look for an engine for you for around $20,000"
Here's a clip I did the other day just for myself to test the stock exhaust sound in comfort and sport+ and it drives so well (sorry about the low quality clip and blurring etc.)
https://www.youtube.com/watch?v=US_KRtjTzuE
they have to remove the plugs to do a typical compression test 🤷♂️ I have seen a lot of variance in cars that are done cold but you usually see it in more than one cyl due to some of them being warm and others getting cold by the time the plugs are pulled and cyl is tested. They can also add oil and retest the individual cyl to see how that affects the compression or if the issue is still present. There’s a lot of variables in how these are done. Leakdown is your best bet. I would not panic too much. I had a shop tell me I had low compression on 2 cyls when i was deciding to boost my v8 2017 mustang and after testing it myself they were identical to the others. I went on to boost the car and it ran beautiful for 30k miles on 800whp. Until I sold it 🤷♂️. Sometimes there is human error. I’d breathe and leak down test it for sure man 👍🏼
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Who's done a comp test on their C63 here?
Got a workshop to do my car today before installing injectors on cylinder 5 & 6. Results where 195 to 210psi on all cylinders EXCEPT cylinder 5 which had 150psi (they said over the phone).Workshop said they checked cylinder 5 with a borescope for damage but was in good condition with no scoring however they said it's "time to think about a rebuild".
Car is a 2017 Coupe with a mild stage 1 tune for the last 2 years - 600bhp on a good day nothing drastic and it runs like a dream.
🔹Coil packs recently changed
🔹Spark plugs changed last week
🔹Both injectors changed today for Cylinders 5 & 6 (after the compression test was done)
Car runs beautifully and can't fault it.
Should I get another compression test was done as a second opinion?
Sort of pissed off about this as I've always been on top of maintenance but what do you do.
Who else has done a comp test on their M177? What were your results?
wait how much mileage can your car have that it needs a rebuild??
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⏱️ 700HP Facelift converted C63 S Coupe with Drexler 3.06 plated LSD
Yeah exactly and I know the plugs were not removed because I wasn't charged for a new set of plugs and seeing as our plugs can't be removed and reinstalled due to the spark plug indexing, they couldn't have removed them
Thanks for the encouraging words too. That bit about human error is true and quite a feat seeing your car made 800whp after. My car makes 505rwhp right now (dyno'd a few months ago) I couldn't imagine what 800whp would be like haha 😖
I'm on 90,000km now bro which is (55,000 miles).
My old rust bucket E39 M5 I had for years was at 200,000 miles without issues haha and my wife's Audi S3 is at 210,000 miles 🤷♀️
Thanks for the encouraging words too. That bit about human error is true and quite a feat seeing your car made 800whp after. My car makes 505rwhp right now (dyno'd a few months ago) I couldn't imagine what 800whp would be like haha 😖
I'm on 90,000km now bro which is (55,000 miles).
My old rust bucket E39 M5 I had for years was at 200,000 miles without issues haha and my wife's Audi S3 is at 210,000 miles 🤷♀️
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C63 amg edition 1
Yeah exactly and I know the plugs were not removed because I wasn't charged for a new set of plugs and seeing as our plugs can't be removed and reinstalled due to the spark plug indexing, they couldn't have removed them
Thanks for the encouraging words too. That bit about human error is true and quite a feat seeing your car made 800whp after. My car makes 505rwhp right now (dyno'd a few months ago) I couldn't imagine what 800whp would be like haha 😖
I'm on 90,000km now bro which is (55,000 miles).
My old rust bucket E39 M5 I had for years was at 200,000 miles without issues haha and my wife's Audi S3 is at 210,000 miles 🤷♀️
Thanks for the encouraging words too. That bit about human error is true and quite a feat seeing your car made 800whp after. My car makes 505rwhp right now (dyno'd a few months ago) I couldn't imagine what 800whp would be like haha 😖
I'm on 90,000km now bro which is (55,000 miles).
My old rust bucket E39 M5 I had for years was at 200,000 miles without issues haha and my wife's Audi S3 is at 210,000 miles 🤷♀️
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Joined: Jan 2020
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From: Sydney
C63 S Coupe
Exactly dude i'm betting they didn't even do the compression test..... plugs weren't even pulled & old jimmy is being led down the garden path for 20k and 35k......
second opinion that sh*t & oust the mechanic/shop if the real comp test shows cylinder 5 is fine!!
second opinion that sh*t & oust the mechanic/shop if the real comp test shows cylinder 5 is fine!!
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C300 4Matic
Compression test on that engine are done through a scan tool, not pulling the plugs.
Compression tests on these engines are done through a scan tool. The leak down is the only thing you have to pull the plugs for
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⏱️ 700HP Facelift converted C63 S Coupe with Drexler 3.06 plated LSD
Etuners
In the end the car had no issues with compression... so I don't even know how they got those low compression readings. Luckily I stopped going to that shop after they did a rush job install on my LSD that caused me to go back and forth to fix a mysterious loud knocking sound that appeared after they fitted the LSD and they had no idea how to remove the electronic differential inoperative dashboard error without disabling my exhaust flaps hahaha 😂
I fuken dodged a bullet with those Etuners blokes never again.
Last edited by Jimmy_c63s; Mar 7, 2023 at 09:19 AM.
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From: Sydney
C63 S Coupe
Etuners in Sydney was the shop that told me I had the "low compression" and started quoting me for rebuild $30,000 haha.
In the end the car had no issues with compression... so I don't even know how they got those low compression readings. Luckily I stopped going to that shop after they did a rush job install on my LSD that caused me to go back and forth to fix a mysterious loud knocking sound that appeared after they fitted the LSD and they had no idea how to remove the electronic differential inoperative dashboard error without disabling my exhaust flaps hahaha 😂
I fuken dodged a bullet with those Etuners blokes never again.
In the end the car had no issues with compression... so I don't even know how they got those low compression readings. Luckily I stopped going to that shop after they did a rush job install on my LSD that caused me to go back and forth to fix a mysterious loud knocking sound that appeared after they fitted the LSD and they had no idea how to remove the electronic differential inoperative dashboard error without disabling my exhaust flaps hahaha 😂
I fuken dodged a bullet with those Etuners blokes never again.
George Lisciandro
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From: Australia
⏱️ 700HP Facelift converted C63 S Coupe with Drexler 3.06 plated LSD
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C63s
Who's done a comp test on their C63 here?
Got a workshop to do my car today before installing injectors on cylinder 5 & 6. Results where 195 to 210psi on all cylinders EXCEPT cylinder 5 which had 150psi (they said over the phone).Workshop said they checked cylinder 5 with a borescope for damage but was in good condition with no scoring however they said it's "time to think about a rebuild".
Car is a 2017 Coupe with a mild stage 1 tune for the last 2 years - 600bhp on a good day nothing drastic and it runs like a dream.
🔹Coil packs recently changed
🔹Spark plugs changed last week
🔹Both injectors changed today for Cylinders 5 & 6 (after the compression test was done)
Car runs beautifully and can't fault it.
Should I get another compression test was done as a second opinion?
Sort of pissed off about this as I've always been on top of maintenance but what do you do.
Who else has done a comp test on their M177? What were your results?
hey, what was your reason for replacing the injectors on 5&6?? I’m having some issues and wondering if what you were dealing with might be the same as mine. If you still have those codes that’d be great.
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⏱️ 700HP Facelift converted C63 S Coupe with Drexler 3.06 plated LSD
Check engine light, ECO Start/Stop button wouldn't illuminate green anymore or let me use that feature (tell-tale sign it's the injector). Replaced the faulty injector and car never missed a beat again. And compression returned to normal then I installed larger hybrid turbos and been running 700HP for almost 3 years now without a problem.
Last edited by Jimmy_c63s; Jun 15, 2025 at 09:05 AM.
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C63s
Check engine light, ECO Start/Stop button wouldn't illuminate green anymore or let me use that feature (tell-tale sign it's the injector). Replaced the faulty injector and car never missed a beat again. And compression returned to normal then I installed larger hybrid turbos and been running 700HP for almost 3 years now without a problem.
thanks that’s good to know, I’m dealing with a mixture is irregular on cylinder 4 and also it saying injector injection excessively lean mix on cylinder 4, makes me think that the injector needs to be replaced so ordered 4 new ones to replace that whole bank. I’m hoping that’s the reason.
