Advice needed: Misfire, Zero Compression in Cylinder 1

[vwgtivr6]

Went through a bunch of repairs to remedy a misfire problem. Changed coils and plugs first. Seemed to fix the problem. Great.

Plugs were fouled and there was oil in the IC pipe so I replaced the valve cover gasket shortly after. About a week later, the misfire problem returned. After searching decided to replace the injectors.

Injectors replaced, misfire continues. Checked compression to find zero compression in cylinder 1. Removed the intake manifold (again) and cleaned as much carbon build up as I could. Wasn’t too bad but just in case it was causing the valves not to seat properly.

Removed the valve cover and checked the valves for cylinder 1. Seems to be seated. No gap or play in the springs.

At this point, not sure what to do next? I’m guessing possibilities are:

- Bent valve
- Rings
- Cracked piston.

Could it be anything else? I think if it’s the bottom end, I’d rather opt for a replacement engine.

Car has about 63k miles. Throwing codes P0300 and P0301

Thoroughly frustrated.

[aluthman]

Went through a bunch of repairs to remedy a misfire problem. Changed coils and plugs first. Seemed to fix the problem. Great.

Plugs were fouled and there was oil in the IC pipe so I replaced the valve cover gasket shortly after. About a week later, the misfire problem returned. After searching decided to replace the injectors.

Injectors replaced, misfire continues. Checked compression to find zero compression in cylinder 1. Removed the intake manifold (again) and cleaned as much carbon build up as I could. Wasn’t too bad but just in case it was causing the valves not to seat properly.

Removed the valve cover and checked the valves for cylinder 1. Seems to be seated. No gap or play in the springs.

At this point, not sure what to do next? I’m guessing possibilities are:

- Bent valve
- Rings
- Cracked piston.

Could it be anything else? I think if it’s the bottom end, I’d rather opt for a replacement engine.

Car has about 63k miles. Throwing codes P0300 and P0301

Thoroughly frustrated.

Leakdown test should tell you whether it is piston/rings or valve related.

[vwgtivr6]

Thanks. I'll have to go pick one up and test.

[vce1232000]

Im gambling its a burnt exhaust valve in # 1 cylinder. thing is youll have to the cylinder head to check thou

[vwgtivr6]

At this point I'm thinking best case scenario is a bad valve. Or a head gasket. Worst case is a bad piston or rings. Either way I guess the head is coming off. Damn.

[kk97]

Never seen a head gasket go like tht or at all in that case on these 1.8t's but once burn a exhaust valve due to maf sensor crapped out

Sent from my SM-G920W8 using Tapatalk

[vwgtivr6]

I think it's unlikely to be a head gasket. I don't see any oil leaks and there's no coolant in the oil. It was more wishful thinking than anything.

[vwgtivr6]

Did the leakdown test and I *think* it's an issue with the exhaust valves.

I wasn't entirely precise with the test so I will do it again although I'm certain the valves are closed despite the engine not being at TDC. Am I correct to assume that's ok?

The oil filler cap was off and dipstick was out. No air from either of those places. Also pulled the crankcase vent hose from the PCV and no air there either.

Tried to check if there was air out of the tailpipe but I couldn't really tell. I'll pull the O2 sensor to be sure.

Is there anything else I should be doing?

Thanks,
Ken

[vwgtivr6]

@vce1232000 called it. Burnt exhaust valve.

[aluthman]

Pop a new valve in and you should be good to go. I have lots of used stock valves if you need one.

[mfdk]

When we say "burnt", does it actually burn completely or is that broken piece still wondering around somewhere...? it quite a big piece, OP did you manage to find that broken piece.

[aluthman]

You won't find it. What happens is that something sticks in the seat of the valve and keeps it from sealing. The hot gasses that then get by will cut/erode the valve itself and the hole gets bigger until you eventually have a hole big enough to lose all compression. It's not like there is a hunk of valve that shot into his turbo.

[vce1232000]

You won't find it. What happens is that something sticks in the seat of the valve and keeps it from sealing. The hot gasses that then get by will cut/erode the valve itself and the hole gets bigger until you eventually have a hole big enough to lose all compression. It's not like there is a hunk of valve that shot into his turbo.

Agree. Mostl likely a piece of carbon deposit dropped down off the valve and jammed between the seat and the valve face. Usually occurs after a hard hot

[vwgtivr6]

When we say "burnt", does it actually burn completely or is that broken piece still wondering around somewhere...? it quite a big piece, OP did you manage to find that broken piece.

Nope. The missing piece is gone.

[vwgtivr6]

Agree. Mostl likely a piece of carbon deposit dropped down off the valve and jammed between the seat and the valve face. Usually occurs after a hard hot

I would expect this to happen after pushing it hard but it was typical daily driving when it happened. I'm guessing excessive carbon buildup just took its toll.

[vce1232000]

I would expect this to happen after pushing it hard but it was typical daily driving when it happened. I'm guessing excessive carbon buildup just took its toll.

Sometimes it takes days for the burnt valve syndrome to show up as a miss depending on how big that piece of carbon was that jammed up or what you stated also too

[bk21]

how easy or hard is it to replace the exhaust valve and how do you diagnose it?? I am having similar misfire issues on cylinder one and have had the intake valves professionally cleaned, new PCV, new camshaft follower, new coils and new plugs but the issue still persists. I do have leaks in my exhaust and a bust engine mount both of which shouldnt really impact the engine firing i would think.

Sometimes it takes days for the burnt valve syndrome to show up as a miss depending on how big that piece of carbon was that jammed up or what you stated also too

[aluthman]

how easy or hard is it to replace the exhaust valve and how do you diagnose it?? I am having similar misfire issues on cylinder one and have had the intake valves professionally cleaned, new PCV, new camshaft follower, new coils and new plugs but the issue still persists. I do have leaks in my exhaust and a bust engine mount both of which shouldnt really impact the engine firing i would think.

Do a compression test. If you have zero compression in cyl 1, pull the head and repair as necessary.

[MrBigglesworth]

how easy or hard is it to replace the exhaust valve and how do you diagnose it?? I am having similar misfire issues on cylinder one and have had the intake valves professionally cleaned, new PCV, new camshaft follower, new coils and new plugs but the issue still persists. I do have leaks in my exhaust and a bust engine mount both of which shouldnt really impact the engine firing i would think.

Possibly not as simple as that, if you have an exhaust leak then your exhaust could be pulling air, the O2 sensor will think you are running lean and add fuel, and there could be more fuel than you need at ignition, could lead to misfires?

How many misfires are you seeing or feeling. Do you have complete loss of compression ; I.e. Have you compression tested? If not what are your fuel trims doing?

[vce1232000]

Do a compression test. If you have zero compression in cyl 1, pull the head and repair as necessary.

x2

[vwgtivr6]

Do a compression test. If you have zero compression in cyl 1, pull the head and repair as necessary.

I did a compression test followed by a leak down test to confirm it was exhaust and not rings or intake.

[aluthman]

Your next step is pulling the head then.

[MrBigglesworth]

Your next step is pulling the head then.

I think there are multiple posters here - so vwgtivr6 was OP with the burnt exhaust valve and then bk21 posted saying he had similar issues - but he hasn't reposted yet so we don't know if he has compression tested etc.

[aluthman]

Yep, just realized that myself.

[bk21]

Possibly not as simple as that, if you have an exhaust leak then your exhaust could be pulling air, the O2 sensor will think you are running lean and add fuel, and there could be more fuel than you need at ignition, could lead to misfires?

How many misfires are you seeing or feeling. Do you have complete loss of compression ; I.e. Have you compression tested? If not what are your fuel trims doing?

Thanks Adam & MrBigglesworth. Sorry vwgtivr6 dont mean to hijack your thread :(

3 Faults Found:
000768 - Random/Multiple Cylinder Misfire Detected
P0300 - 008 - - MIL ON
Freeze Frame:
Fault Status: 11101000
Fault Priority: 0
Fault Frequency: 129
Reset counter: 255
Mileage: 213670 km
Time Indication: 0

Freeze Frame:
RPM: 1110 /min
Load: 44.7 %
Speed: 13.0 km/h
Temperature: 18.0°C
Temperature: 9.0°C
Absolute Pres.: 970.0 mbar
Voltage: 14.351 V

000769 - Cylinder 1
P0301 - 008 - Misfire Detected - MIL ON
Freeze Frame:
Fault Status: 11101000
Fault Priority: 0
Fault Frequency: 128
Reset counter: 255
Mileage: 213670 km
Time Indication: 0

Freeze Frame:
RPM: 952 /min
Load: 37.6 %
Speed: 7.0 km/h
Temperature: 23.0°C
Temperature: 9.0°C
Absolute Pres.: 970.0 mbar
Voltage: 14.478 V

001110 - EVAP System
P0456 - 001 - Very Small Leak Detected
Freeze Frame:
Fault Status: 01100001
Fault Priority: 0
Fault Frequency: 5
Reset counter: 255
Mileage: 229901 km
Time Indication: 0

Freeze Frame:
RPM: 751 /min
Load: 22.0 %
Speed: 0.0 km/h
Temperature: 62.0°C
Temperature: 8.0°C
Absolute Pres.: 990.0 mbar
Voltage: 13.970 V

Readiness: 0000 0000

[MrBigglesworth]

Thanks Adam & MrBigglesworth. Sorry vwgtivr6 dont mean to hijack your thread :(

3 Faults Found:
000768 - Random/Multiple Cylinder Misfire Detected
P0300 - 008 - - MIL ON
Freeze Frame:
Fault Status: 11101000
Fault Priority: 0
Fault Frequency: 129
Reset counter: 255
Mileage: 213670 km
Time Indication: 0

Freeze Frame:
RPM: 1110 /min
Load: 44.7 %
Speed: 13.0 km/h
Temperature: 18.0°C
Temperature: 9.0°C
Absolute Pres.: 970.0 mbar
Voltage: 14.351 V

000769 - Cylinder 1
P0301 - 008 - Misfire Detected - MIL ON
Freeze Frame:
Fault Status: 11101000
Fault Priority: 0
Fault Frequency: 128
Reset counter: 255
Mileage: 213670 km
Time Indication: 0

Freeze Frame:
RPM: 952 /min
Load: 37.6 %
Speed: 7.0 km/h
Temperature: 23.0°C
Temperature: 9.0°C
Absolute Pres.: 970.0 mbar
Voltage: 14.478 V

001110 - EVAP System
P0456 - 001 - Very Small Leak Detected
Freeze Frame:
Fault Status: 01100001
Fault Priority: 0
Fault Frequency: 5
Reset counter: 255
Mileage: 229901 km
Time Indication: 0

Freeze Frame:
RPM: 751 /min
Load: 22.0 %
Speed: 0.0 km/h
Temperature: 62.0°C
Temperature: 8.0°C
Absolute Pres.: 990.0 mbar
Voltage: 13.970 V

Readiness: 0000 0000

That's all quite helpful - errors of it being logged at idle and suggestion of an evap leak. How bad are the misfires - are you feeling them?

Intersting that its all low rpm stuff and the EVAP leak, although it was logged after the misfires. I'm not an expert at this, but from what I read it is possible the misfires are related to the engine mount.

Some further VCDS questions I would have if you can do them are 1) Fuel trim info would be help (block 32 on VCDS - add and mult values). 2) Also once you are driving does the car go ok in terms of boost and hp vs request? 3) if you log misfires, how often are you seeing misfires on which cylinder and are they during idle/part throttle/WOT etc? 4) if you reset codes, how soon is it before you find the error codes coming back?

Some other options at this stage would be 1) check gas cap to ensure its sealed properly and 2) smoke test for leaks 3)you could try changing the N80 as it is a cheap part to change and a 5 min job and can be known to cause EVAP problems. 4) compression test.