Full boost, then BAM: running on 3 cylinders? (with pics)

[Yan]

Hi!

Today, when entering on highway, I decided to go full boost from 40 to 70 mph... At the very end, I saw a small puff of black smoke coming from the exhaust and the car began to run on only 3 cylinders. It stopped to smoke right away, but it continued to run on 3 cylinders.

I tried the spark plugs wire test, and it doesn't change anything when I pull it on/off on the 3rd cylinder starting from the radiator side. There's fire, the plug is ok, but the cylinder doesn't run. Changing the spark plug didn't change anything. I know that there are alot of possibilities (exhaust valve, ring, injector and so on), but what is the usual culprit for a 951 to suddently fall on 3 cylinders at full boost (there's a wastegate shim: about 14 PSI)?

Thanks! I'm waiting for bad news

[Lawrence Coppari]

Is that oil on the non-firing cylinder sparkplug or is it fuel?

Is your injector firing?
Is there compression in that cylinder?
Is the plug sparking?

You could get a spare plug, attach it to the spark plug wire. Then take jumper cables and ground the plug to the engine. Crank engine to see if there is spark at plug. Obviously, don't hold it in your hand. Leave other plug in cylinder so there is no fire hazard.

If the plug sparks and there is compression, then it probably is an injector problem.

[fast924S]

I bet you where running to lean at higher boost levels and burnt a hole in your piston, I bet #3 has very little compression and you have alot of blow by. Well I hope thats not it, but you need to run some tests. Do a compression test and then a leakdown test.

[Yan]

Ok guys, here's a better summary:

1) I got fuel
2) I got sparks
3) Cylinder #1 = 140, #2 = 140, #3 = 0, #4 = 125

There's no weird noise, everything is turning fine, no smoke, the spark plugs don't show any bad sign.

What's the easiest way to diagnose a bad valve or holed piston? Can we check the piston with a small light thru the hole of the spark plug?

I know that I'll have to open it anyway, I just want to start shopping for the necessary parts. What are the next steps and how much am I looking to spend for each of the possible culprits?

Ho by the way, yes I was running a bit lean.

[fast924S]

Ok thats not good. High boost+ High load + lean mixture = Very high combustion temps and hot spots. Again not good. Do you have a EGT gauge?? if not when you rebuild the engine I would install one, just to keep a eye on whats going on. As for whats wrong. If you can go and buy the gauge set to do a leak down test on the #3 cyclinder. When you do this and if you hear air or feel air comming from the exhaust then there is a bad exhaust valve. IF you hear or feel it comming from the intake then you have a bad intake valve. If you remove your oil cap and feel and hear it from there then you have a bigger problem, eather a hole in the piston or bad rings. If you take the cap off the radiator and its comming from there then you have a head gasket problem. As for how much it will cost it all depends on whats wrong, but I bet for just bearings,rings and some machining and new valves, ect... full stock engine rebuild I would think like $1200-$2000 if you do the all the work.

[Yan]

Here is the culprit:




The right most valve also has a really weird color, it looks like it overheated. Do you think that it REALLY needs to be changed or if it'll run a good amount of miles without problem?


It looks like the valve guide is pretty worn. We don't this really well on the pic, but will the new valve come with this guide?


:cheers:

[SoCal Driver]

So a decent valve job. Valve guides and new exhaust valves. Bad practice to grind used sodium filled valves.

[ae1969]

Has that head been rebuilt before or is that the original ? What is the mileage ? What boost do you run? What chips are you running? etc...

At this point I would check all those valves very carefully..... You need a full rebuild...

Now what you should also look at is what that piece of metal did to the exhaust turbine on your turbo...... that is a pretty big piece and it could make a pretty big mess....

[Brando]

Probably caught in the turbo turbine.

Sounds like an expensive learning experience... ouch.

[Yan]

When the car began running on 3 cylinders, I didn't hear any turbine desintegration noise and the turbo kept spooling pretty well. It's just when I slowed down that I heard (and felt) the missing cylinder.

Wouldn't a really worn turbine have been more noticeable?

Where can I find the best prices for sodium valves?

[ae1969]

Uhmmm I would pull of the down pipe and take a look.... You would not notice any ill effects unless you tried to build boost.....and since you were running on 3 holes that wasnt going to happen.

[Yan]

I'll take a look at it!

What are the best prices for:
- sodium valves;
- head gasket;
- misc. engine hoses?

Thanks!