Pulled out the motor for the rebulid and crack it open and find this. Tech says it looks like its been running super rich? How is that possible on a TPI car with O2 sensors? It sould shorten the injector pulse too correct the rich condition no? The car has ALWAYS had a rotten egg smell under load and it has NO cats, could this be related. Even with 94 Octane in 20 degree weather the motor detonates CONSTANTLY, WTF? The tech says it almost looks like a carb car running rich? Any ideas guys? I had a custom chip burned by TPIS but I'm not sure if that will fix the problem? The previous owner installed a Hypertech chip, could that be part of the problem. This car has never run right since the day I bought it.

 

Cant tell from the pics- Is the top of the piston pitted badly or is that just alot of carbon deposits?

It appears to be carbon deposits. Did the motor use oil or was there smoke at start up? If so, the oil in the combustion chamber (on the piston/head) could be contributing to detonation especially with a hypertech chip that just ramps up timing.

Matt

 

Well, even with 02 sensors, TPIs can run very rich. It happened to me when I had a massive vacuum leak a while back. Now, I am no expert, and maybe someone else can correct me or back me up here, but could it be burnt water/coolant due to a bad head gasket? Looks like coolant on those heads to me. Note the green stuff...or is that just from when you pulled the head off?

 

Usually with an oil burner I will see about 1/4 inch ring around the outer edge of the piston that is really clean from the blow by and hot oil cleaning the deposites away. I would say that is just carbon build up from a engine that ran really rich and probably got driven around like a grandma would for all its life. Generally you get more carbon build up if the motor never gets warmed up or beat on. Some of those pictures do look like thay have some clean spots from blow by though. Hard to tell from those pictures.

 

The car has bad rings, it smokes on startup and does burn a little oil, hopefully that may be the cause.
The coolant is from yanking the head off.
I was not aware that oil could increase detonation?

 

Oil in the combustion chamber lowers octane significantly. Detonation increase because of it? Yah probably.

On the flip side of this, your pistons look nothing like mine did/do. Mine were coated with a thick sludge of what looked like a liquid carbon deposit, it wasn't solid but it wasn't liquid either... sludge.

When coolant is being burned in the combustion chambers you'll see this white powdery substance that looks kinda crystalline in structure.

 

deposits on the piston also couse hot spots during compression and will cause preignition so its a double wammy. Smoking on start up only is usually a valve stem problem. When you shut a hot motor off and the valve stem seals are bad the oil can drain down the valve stem into the cylinders and it burns off on start up. I have fixed several "smokes on start up" engines buy only replacing valve stem seals.