1g tsi miss fire

[Mark E Brooks]

I cant figure out this miss i put spark plugs wires cleaned the injector i did a compression test it was 119psi just a hair under 120 that seems pretty good to me i have a guy that has built alot of these motors he says thays past the service point the car did sit for about 8 years when i got it in February i did a tune up oil changed check the timing belt everything was good ran great now it stutters when it hits about 6-8 pounds of boost only does it under boost it seems did a fuel pressure test it was 30 psi with regulator vacuum on 40 off what am i missing or am i wrong to think that 119 120 on the compression test is good please help

 

[Vegas Smith]

Damn, that was a long sentence. Sounds like a clogged fuel filter. Fuel pressure should be 37.5 with vacuum line removed.

edit: if the cylinders are indeed hitting 119 then that's below the service limit and a likely cause.

 

[Sniffbooger]

120 seems really low, i would recommend a cylinder leak down test...that will show where the problem is...a leaky head gasket could cause a misfire under boost...had the same thing happen to my '87 Toyota turbo pickup...I ended up doing a coolant block test with the liquid and it showed combustion byproducts in the coolant... replaced the head gasket and fixed it! The reason i chose that coolant block test initially was because I suspected it might be a head gasket...took off the radiator cap and it smelled like combustion vapors a little bit...
You can also check the engine oil...is there any coolant in the oil? Take off the oil cap and if it looks milk chocolate color thats a problem! However this doesn't always happen with a faulty head gasket...

 

[Mark E Brooks]

Thanks ill check that today

 

[ThunderChild]

Compression is quite low. And do a boost leak test you have classic symptoms.