DTC P3040

The technician who looked at the car has a big advantage over everyone here since he or she was able to examine the general condition of the car and engine.

The tech should have been able to get a general idea about the condition of the rings by seeing if the compression improves in a wet test.

Leaking valve stem seals will not in itself result in lower compression although smoke out of the exhaust is a symptom.

Hi Ray,

Please explain the wet test.

cea1

To take cylinder compression readings, the spark plug is removed, a compression gauge is installed in the spark plug opening, the engine is cranked, and the peak compression for the cylinder is recorded. This is known as a "dry" compression reading. After recording the dry compression reading, the compression gauge is removed and some engine oil is squirted into the spark plug hole, the compression gauge is re-installed, the engine is cranked, and the compression reading is recorded again. This is known as a "wet" reading. If the compression reading increases when oil is squirted into the cylinder, it indicates that the piston rings may be bad because the oil acts to seal some of the leakage.

I understand it completely now, thank you for the explanation.

cea1

You're welcome!

Interesting. Just like Ray pointed out, a worn valve guide seal has no bearing on compression. The problem may very well be poor sealing at the rings, but you can't make that determination from a dry compression test. Like Ray said, you have to do a wet compression test also. If I had this car in my bay and observed the condition you described, I would recommend doing a cylinder leak-down test. They are MUCH more effective in the information they provide compared to a simple compression test, but also more involved. It involves finding TDC on the tested cylinder and jamming air at about 90psi in through the spark plug hole. If there is a compression loss, you will be able to see it on the gauge and see it leaking from the engine. If there are bubbles pouring out of the radiator cap, you have a bad head gasket. If there is air coming out of the exhaust or intake, you have a valve problem, and air in the crankcase would point to a bad ring or two. The problem with compression tests is that they only measure a cylinders sealing relative to the surrounding cylinders. There are a lot of variables (cam lift, cranking speed, etc) that can affect readings. The leakdown test is a pinpoint measurement and should be standard procedure before digging in for a rebuild.

And if the compression on one cylinder is unusually low but the wet test does not improve the readings, there is probably a bad valve or a valve seat problem. Or it's a blown head gasket issue.

To narrow down the problem further, they put another adapter in the spark plug hole called a "Leakdown Tester" that has an air chuck and a pressure gauge.

You put the engine at top dead center for that cylinder and hold it in place, then apply compressed shop air into the cylinder through the adapter. If you hear hissing from the tailpipe, it's the exhaust valve, from the intake manifold and it's the intake valve.

If the radiator starts bubbling it's not the valves... Head Gasket. But this usually reveals itself in overheating issues.

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Bruce,

Thanks for the info. Can I purchase a Leakdown Tester from many parts store, or is this a tool that's generally only available at an auto repair shop?

Oh by the way, do you know what DTC code P01300 means?

cea1

Thanks, qslim!

I have two DTC codes associated with this vehicle, the first you've already addressed, and the second one is P01300. Do you know what's the meaning of the latter?

cea1

I don't think there is such a thing as P01300 - there is one too many digits.

You can check OBD II codes on this site:

Ray, He said in his first post that he has a 1995. OBD II was not used until

As a Toyots mechanic, do you know with any certainty what the application schedule is for OBD II as it relates to Toyotas? I assume that 1996 was the drop-dead year, but some makers made the change earlier.

schedule is for OBD II as it relates to Toyotas? I assume that 1996 was the drop-dead year, but some makers made the change earlier.>>

Yeah, this guys Avalon is OBD2. Same for Camrys of that year too. Toyota was ahead of the mandate then.

BUT if you hear it from the exhaust and the intake; it could still be the exhaust (Leaking into the manifold and finding it's way through another cylinders open valve.

We just did one last week had a chipped exhaust valve; the first time I got to use my leak down tester, and I've had it for 2 years.

Actually, I am not a Toyota mechanic, never was. I did work for Toyota for about 15 years, had various jobs including a district service manager.

Here is a a web page with a list of OBD II implementations (you have to scroll quite a ways down to see the list):

to use my leak down tester, and I've had it for 2 years.