S2 lost power funny exhaust noise, Help

[colin944]

Keep going. You'll find it. And when you do you'll feel a lot better about it than you would if you let someone else fix it.

 

[JamesO]

For what it's worth the fuel injector only opens when it's circuit is completed. the injector has a coil in it which when powered pulls the injector open alowing pressurised fuel to squirt into the cylinder.
The eight valve cars have the injectors wired in pairs and are batch fired, I believe the 16 valve cars are the same and don't use sequential injection.

If you do start Removing injectors, remove the fuel pump fuse and try to start the car to depressurise the fuel rail before trying to remove one.

Also if the spark plug has been soaked with fuel it may be ready for the bin despite looking fine.

 

[jamieda]

hi Guys,

thanks again for all your help, i ended drawing a blank with the fuel so took the car down to Porsche Byfleet.

They did a leak down test which didn't read well so then looked inside the cylinder with a borescope. One if the inlet valves was ever so slightly dropped!!!!

Suspected snapped spring and bend inlet valve.

To whip the head off change the valve and all the springs, new head gasket etc they quoted 10 hours plus parts. all the belts chain and tensionr have just been done.

All this at the Porsche classic car discount it was coming in at the same price as the independents i called so I've left it there.

They took the valve cover off today to see if its just a snapped spring, if so they were happy to change the spring without removing the head which surprised me, anyway they couldn't get the valve to close so its bent. heads coming off tomorrow.

once the head is off i'm going to make a decision about skimming and re porting the valve seats.

Again thanks for all your help, i should have the car back in a week or 2.

its making me think twice about tracking it again!

 

[Monkeythree]

I'm puzzled as to why your compression test didn't pick that up? Bent valve stuck partially open should result in zero compression on that cylinder?

 

[jamieda]

so was i and that was my first question.

they said the leak down test (and i'm not really clear how its measured) read at 75% then dropped to 60% and then 50%. Apparently its different to compression test as if the gap is very small we would still get a read on the compression gauge.

the valve only just doesn't push all the way home its very very slightly bent, or so i'm told, there is no major marking on the cylinder head.

They showed me the snapped spring, that was clear to see.

I will get a photo of the valve when it comes out so we can see how bent it actually is.

ORIGINAL: Monkeythree

I'm puzzled as to why your compression test didn't pick that up? Bent valve stuck partially open should result in zero compression on that cylinder?

 

[bmnelsc]

Well - at least its an answer. I understand a broken valve spring but what causes a valve to bend (even slightly) without some kind of contact? Is your fuel too thick [] Once the head is off they will be able to tell if you suffered piston contact on that valve - perhaps the broken spring allowed that to happen at high RPM.

This means all springs and guides should be checked whilst they have the head off just in case there are some more fractures on the way.

A leak down test determines how the cylinder holds the pressure generated by the compression stroke so it should show up valves that are not seating or worn rings. As with a compression test - a squirt of oil will usually improve the seal on bad rings but will not affect valve sealing - so if you test once and have a sizable drop then you repeat with a little oil in the cylinder and the you still get the same drop - then its almost certainly valve related.