3SFE Loss of Cyl Compression

[lionheart03]

A little disclaimer, I'm not a highly experienced mechanic, just a DIY'er, so sorry if I ask any dumb questions.

Have a 91 Camry ( 170K miles) with a 3SFE engine. Bought the car at 150K, did quite a bit of easy work and general maintenance to it. Had been a great car until now.

Last week while driving 70 on the interstate, car started missing. Got home, found nothing obvious. Had a more mechanically inclined friend help me look at it today. Found out while doing a compression test, there is nothing on cylinder 3. The other three look fine. Pulled valve cover, valves seem to be operating like normal, nothing sticking. Turned the motor until all valves in that cylinder were closed, and pumped some compressed air into that cylinder. It was leaking somewhere, but not through the intake or exhaust that we could tell.

Also hooked a vacuum gauge to the intake. Vacuum seemed to be holding fine, nothing jumpy or erratic that could indicate a bad valve, that we could tell.

Any other ideas before I have to tear the motor down? Given the severity of the problem, this will most likely be a spring project when I have more time and the weather improves.Thanks for any and all help!

[JMSports]

My idea would be a bad valve, but you stated that it did not have any vacuum issues. Have you checked that the plug is getting spark? Have you checked the points on the magneto? Have you checked the rings and seals? When we had a low compression on my brothers engine (totally different engine but similar problem) we tried it a few times and the compression deficiency alternated between the second and third cylinder meaning there was a leak somewhere between those two cylinders, which would prevent either one at any given time to fire.

[new echo owner]

Not even a reading on #3 cylinder, just zero pressure? Where do you hear the air escaping from when you put air to the cylinder if not from the intake or exhaust? What is the vacuum reading? Broken piston or rings? Did you do a wet compression test?

N.E.O.

[Doctor J]

My camry has leaking exhaust valve in cylinder #1, the engine runs smooth at no load idle but slightly skips after I put it in gear especially when hot.
While dooing leak down test verify that the #3 cylinder is in TDC compression, not EXHAUST stroke.
Statistically, the exhaust valve is most likely to leak, however make sure that the spark plug threads are in the good condition as it may cause bad compression and cylinder pressure leak.
I saw the similar problem with not tightened spark plug on V-6 camry

[lionheart03]

Plugs are good. Was getting a good spark on the bad cylinder. Spark plug threads are good. Car was running fine and has had no recent work on the motor before this cylinder suddently went out.

While turing over the motor, it does slightly jump to 20 psi+/-, but it does not hold there, may just be due to vibration from the car. The cylinders on both sides seem to be building up and holding pressure fine.

When compressed are was pumped into the cylinder with the valves closed, I could hear it escaping. Didn't think it was going through the exhaust, but there is a good chance it may have been. I couldn't feel or hear it coming out of the exhaust pipe, then again, the pressure of the air wasn't that great (didn't want to turn the motor over).

The vaccum gauge was hooked to a vacuum port on the top rear of the intake manifold. Was this a good place test? I couldn't give the exact readings we got, as I didn't write anything down.

Could I have a bad piston? Nothing is clanking around inside, and the car was not buring oil or smoking before this happened. Also, there isn't any excess oil in the cylinder.

Could a valve be stuck open for some reason? Bad spring, held open by carbon deposit, etc?

So far most of the indications are pointing to a bad valve, most likely exhaust. On average, what would a garage cost to fix this? If I did do a valve job, would I be better off replacing all of the valves while I had it apart, or just replacing the entire head?

Thanks for the help so far!
Jeremy

[Doctor J]

I think many would agree that bad piston rings will not give you 0 compression.
At this point removal of exhaust manifold with cat attached to inspect exhaust valve ports for leaks will not be a bad idea..
Most shops using at least 100 psi to do a leak test.
to rule out the hole in the piston leak, plug the crankcase vent hose and apply air to the cylinder. Build-up up pressure in crankcase , forced out oil level dipstick would indicate damaged piston

[new echo owner]

If you have 0 compression reading in #3 cylinder, turn up the air pressure and see when the air is escaping to. Unless it is a hole in the piston, a broken valve spring, or drop a valve, there would be some compression. Even with a burnt valve, there should still be some reading. For the compression to go to 0, it has tobe a pretty good size leak. Do waht Doctor J said and see what you find.

N.E.O.

[fredk]

take the plug out and look at the piston

[new echo owner]

Originally Posted by fredk

take the plug out and look at the piston

It is hard to look at the piston, unless he has a borescope; pretty dark down there.

N.E.O.

[fredk]

nah, a small flashlite or a lite on a stick works well, those little lites on keychains do well too

[Doctor J]

At near TDC you can easy see the center portion of the piston [I used flash light on mine]

[lionheart03]

Dropped the car off at a local garage to find the problem ( I don't have the time to mess with it right now.) They did some tests and found that a valve is causing the trouble. Piston and rings are ok. Needless to say, the labor cost are rather high for a repair like this, so I'm going to do the job myself, with some help from a mechanic friend if needed.

The shop was saying a burnt valve. Is this common on a car with only 170K miles? The motor was running fine until it suddenly lost a cylinder one day. Would a burnt valve just go out all of a sudden like that? What are the chances that a valve spring could have broken? Can you replace valve spring without removing the head? I'm just trying to think of anything else I can check before doing a major motor disassembly.

My oil pump gasket/seal is leaking badly, so either way I was planning on fixing that. The timing belt, main seal, and cam seals were all replaced a while back. Not many places left for oil to leak on that side of the motor.

[fredk]

burnt valves happen slowly, thats not it

[new echo owner]

I agree burnt valve won't happen just over night, and it would at least have come compression reading. If the piston is good, I would lean more towards a broken valve spring.

N.E.O.

[Doctor J]

Broken valve spring will show up as 'collapsed' lifter top with the cam lobe facing up; remove valve cover and bring cylinder 3 TDC compression stroke [cam lobes facing up] then using the screwdriver push each valve down The one which will be the lowest one has broken spring It is possible to replace spring without taking the head out but the skilled person and special tool is needed for this job.