General Too much compression?

[dgdsm]

As part of tracking down a recent cooling systems problem that cropped up, I did an engine compression test to check the HG. The numbers came out similar to what I got last time: 200-210psi. It’s possible that I need a new compression tester, but how much is excessive cylinder compression a problem and where does this come from? I guess the shaving off of a few mm of aluminum when the head was resurfaced could be a part of this, and I think the 4g64 has normally has a slighter higher normal compression than the 4g63. One problem that is happening is that I have some leak at the spark plug well gaskets, and oil is pooling up in the spark plug wells. I usually try to soak up the excessive oil with a paper towel, but I know some is getting into the combustion chamber in the compression test. Could oil in the combustion chamber raise the compression by 50+ psi ? My LTFTs have been running at around +7 to +10 at idle, so running lean might be a bit of a problem.

The good side of this is, I’m reasonably satisfied that I don’t have a leaking HG and replacing the ECT sensor has taken care of most of the cooling system issue. It’s possible I have a cracked overflow reservoir and the engine is losing coolant there.

But I’d like to track down this possible excessive compression issue and whether it might be affecting engine performance.

 

[1990TSIAWDTALON]

If its pooling in the sparkplug wells you more than likely have a blow by problem with excessive crankcase pressure. Is the PCV system working properly or a catch can setup?

 

[dgdsm]

I replaced the PCV valve about 1+ yr ago. I haven't checked it out recently. There's no catch can setup. It passed CA emissions in January which I don't think can happen with excessive blow-by.

 

[1990TSIAWDTALON]

Well the well seals are leaking into the sparkplug wells and there isn't any way for that to get in there other than pressure or bad seals. Maybe you have old well seals that are brittle.

 

[lasthope05]

Spark plug wells on the 64 are notorious for leaking oil even with brand new seals. I always use permatex #2 on the inside where they attach to the tubes and on the top face that sits on the actual over itself.

As for compression results it is only a little higher than stock (190ish) so I dont know what you are worried about. Its sound like you have a perfection healthy engine.

 

[chrysler kid]

My 4g63 with torn up intake an exhaust valve seals tested 179 across the board from all the oil build up in the chambers. Basically every compression test was a wet test. After the new seals went on the dry test showed 157 range across the board which is more normal for a car with 180k miles

 

[dgdsm]

Spark plug wells on the 64 are notorious for leaking oil even with brand new seals. I always use permatex #2 on the inside where they attach to the tubes and on the top face that sits on the actual over itself.

I took the head off twice when I did the engine work, now 3yrs ago, and some components I reused from the 1st time, and these well seals were one of them. I don't recall what gasket sealant I used. I'm pretty sure this is the problem, and I'll find some permatex #2. Thanks for that.

As for compression results it is only a little higher than stock (190ish) so I dont know what you are worried about. Its sound like you have a perfection healthy engine.

Well I think the engine is fundamentally doing OK, but I don't think "perfection" really describes it. There are lots of little things, that I don't know the cause of. In the past week it's been reeking of engine oil in the passenger compartment. I don't know what it takes for oil odors to get through the firewall etc and into the passenger compartment. I think it's stopped now.

The way this started is that after months of short-distance driving, I took the vehicle for a "spirited drive" and when I came back to where I had parked the vehicle about an hour later, I found a pool of coolant, right underneath where the overflow reservoir is. The coolant was low and there was lots of air in the system. All these problems are gone now, but I'd really like to find out how the system could be losing that much coolant.

Also there's lots of oil around the exhaust manifold at cylinder #4. I'm planning to replace the exhaust manifold gasket (another component I reused), but this wouldn't explain how oil is escaping out there. With the wrenches I was using 3 yrs ago, I don't know that all the head studs are torqued to the correct specs, so I think there could be some "head lifting" under heavy load going on.

The vehicle did pass emissions in January, but just barely on the 15mph NOx. I'm right now driving around with a P0421 CEL code (warm-up catalyst below threshold). From my O2 sensor logs, the front cat is almost dead. I think the main cat is OK. It won't pass next time unless the front cat is replaced. With all the short-distance drives and the front cat issue, I'm wondering if there might be some exhaust backpressure going on.

 

[lasthope05]

I would suggest getting started on working each of those individual issues then. Are you asking for testing procedures you can run? For a start, to diagnose the cooling system, run a pressure check. For the oil leak, after fixing the valve cover issue, use a uv dye. For the catalytic converter efficiency check the differential operational temps with an IR thermometer between the inlet and out.... Etc..

Any burning smells will automatically come into the cabin when the HVAC is set to fresh air since the intake vents are on the top of the firewall.

 

[dgdsm]

I would suggest getting started on working each of those individual issues then. Are you asking for testing procedures you can run? For a start, to diagnose the cooling system, run a pressure check. For the oil leak, after fixing the valve cover issue, use a uv dye. For the catalytic converter efficiency check the differential operational temps with an IR thermometer between the inlet and out.... Etc..

Any burning smells will automatically come into the cabin when the HVAC is set to fresh air since the intake vents are on the top of the firewall.

Between the FSM and alldatadiy.com, I can pretty much find all the diagnostic tests (recommended by Mitsubishi).. though these documents were written 20 yrs ago and experienced dsmers have some different ways of doing things. Like most people I don't have access to all the specialty tools that Mitsubishi techs have. I guess Pepboys rents a coolant system pressure tester, though I'm not sure what this will tell me that I don't already know. There are not too many ways for coolant to leak right underneath the overflow reservoir.

The oil smell was not a burning smell, just an excessive oil smell. I think I just put too much oil into the engine.

I did a lot of stuff with IR thermometer readings around the front and main cats when I was prepping for emissions tests, so I have a good idea of what's going on. The front cat takes too long to get to lite-off temperature, and even after 1 hr it's not really working. I'll probably go ahead and clear this P0421 code, but I know it'll come back in a few weeks or in a month. It's possible that if I take the front cat off the exhaust system and clean it that might do something.