Compression/Leak down

JHP · 02-22-2019, 03:55 PM

Engine is an efi 3.3.
The issue: ---Glowing header and white exhaust port on cyl #6.

I am attempting to determine if I have a burnt exhaust valve/tight valve issue.
I did a compression check on that cylinder and it was good.
Does that conclusively mean there is no exhaust valve issues? Or would a leak down test uncover an issue undetected by the compression test? i just don't have a leak down tool.

pors1968 · pors1968's Garage

You might have fuel delivery issue.

JHP · 05:21 PM

thanks, but I already did all of the other checks;
swapped injectors
swapped injector connectors,
checked for vacuum leaks,
check for play of the valve lash although I was not on tdc,(if that makes a difference)

So now I am down to exhaust valve being burnt. If the compression test is sufficient to check the exhaust valve then that would be good news for me.

Superman · 02-22-2019, 05:17 PM

One of the benefits of a leakdown test is the ability learn more about the source of a compression leak. If you get #6 at TDC and pressurize it, then you will know whether it is holding that pressure and, if not, some information about where the leak is. If the exhaust valve is bent, the hissing will be in the exhaust.

Superman · 02-22-2019, 05:19 PM

* If the exhaust valve were bent, then I think that would have been reflected in the compression numbers. If that cylinder is turning the exhaust manifold orange, then I would suspect...as some one mentioned....a lean mixture or some thing of that nature. I know you have looked into that.

yelcab1 · 02-22-2019, 06:51 PM

A burnt valve produces zero compression so that is not it.

Superman · 02-22-2019, 07:28 PM

Listen to him, JHP. Your other two choices are fuel and ignition. Your demon is there.

JHP · 02-22-2019, 08:46 PM

Ok great! Im glad its not a valve issue. I will try swapping spark plug wires although a resistance test revealed they were within specs. And i will try using a smoker to check for leaks although starter fluid and water did not show any signs of a leak.

Thanks alot guys!

JHP · 02-22-2019, 08:57 PM

brighton911 · 02-23-2019, 03:04 AM

Wow, that is one hot header. I'm thinking a big air leak leaning that cylinder out. Is it idling OK? Best to solve it soon before expensive trouble happens.

JHP · 02-23-2019, 03:52 AM

Yep, idles good, runs strong. I would not have noticed it but by visual. Occurs within minutes at just 1500 rpms or more. Will Try to get my hands on a smoker test. Hoping it is just intake manifold gasket.

pors1968 · pors1968's Garage

Check if you have some débris on cylinder 6 you will have to check with camera.

spuggy · 02-24-2019, 08:58 AM

Quote:

Originally Posted by brighton911

Wow, that is one hot header.

It's all relative.

Yeh, that isn't right and should get addressed before driven. But these motors don't melt as easy as you might think - 930 headers glow orange on the dyno, and a cast iron turbo "hot-side" will glow a much brighter red than that... Can make you kind of agitated the first time you notice it though...

Might be worth swapping injectors between cylinders and see if the issue follows the injector - could just be a bad one. Although that supposedly usually causes rough or uneven running as well.

pampadori · pampadori's Garage

What is the intake setup? Itb's or Carrera manifold?

My entire exhaust glowed like that on the Dyno when we were tuning it. But that was under big load for many minutes straight.
Your header glows like at while under no load???
Are you using distributor or COP with fully adjustable timing? (I'm hinting at the cyl6 timing being off from the others).

JHP · 02-24-2019, 01:19 PM

Tried swapping injectors, did not cure.
Headers glow under no load. Just raising rpms to about 1500 and about 30 seconds later, it starts to glow.
Using a coil pack with the 3.2 manifold. Not individual coils on plug.
The plug is sparking for sure, whether or not its on time, I don't know. Is there an easy way to check that or is that a tuner issue?

Hoping tommorow i can get a smoker to rule out any leaks. Although it seems unlikely after the amount of starter fluid and water I tried spraying in that area.

thanks

Walt Fricke · 02-24-2019, 02:42 PM

Water? Starter fluid, brake fluid, carb cleaner, all are supposed to increase the idle RPM by getting in the combustion chamber via the source of the air leak. But water? Wasn't water injection used on some special application motors to reduce cylinder head heat? Would water vapor cause a drop in RPM?

Superman · 02-24-2019, 03:03 PM

This problem is vexing. You swapped injectors. Is there a fuel line to #6 that you can also swap. I would swear you have a lean mixture problem and if you have swapped injectors and squirted starter fluid and water at the intake, then I just wonder if that injector is not getting fuel.

JHP · 02-24-2019, 06:13 PM

It is my understand a mist of water would cause the engine a distinct sound, nevetheless,i tried start fluid and carb cleaner as well.

I am using the stock 3.2 fuel rails so there is not a specific fuel line to #6.
There is always the possibility that when I switched fuel injectors, I might have accidentally mixed them up and installed the same one back in. That is stretching it but ya never know.

T77911S · 02-25-2019, 02:51 AM

did you check for a broken head stud,

do you have it set up to fire each injector individually.
don't know much about mapping EFI but if so could that one be different than the others.

if set to fire as banks can you swap injector wires.

do the leak down on a hot engine.

Knockdown · Knockdown's Garage

Have you pulled #6 spark plug to see if it is running lean?