Cylinder Numbering?

[Big Jim M]

Twizzler

Actually, Big Jim, I do have a noise that sounds something like an exhaust leak, and its coming from the driver side of the motor. The same side as #5.

What are the chances that the loose plug from last year screwed up the threads or something and is allowing air to escape through the plug hole? Escaped air would also explain the miss, a rather rich mixture.

If the present plug is in there tight there is NO CHANCE! To find that noise why not start the engine cold and raise the hood and apply your hand to varioue places to FEEL for escaping pressure?
If you have an exhaust leak that in itself can cause a burnt valve.. ALL exhaust leaks need to be repaired specially those near the engine.

Stop trying to blame your present miss on yesterdays loose plug. If you are so worried why not simply unscrew the plug and then reinstall it to see if it is wasted or doing it's job. We cannot trouble shoot your miss till you sort it out and tell us what is ISN'T! Give a little help here. Oh, and I would advise installing a NEW plug instead of the old one..
Big Jim

 

[Twizzler09]

I've already stated twice that that plug was replaced last year. The loose plug is an old memory, something I discovered by accident while giving it a tune-up last year.

I only asked about potential damages because of the coincidental circumstances.

I'm going to have a compression check done before long, guy at work is going to let me borrow his tester when I've got time for it. Besides that, I need a good way to test the injector. Pretty sure the injector is still good but I'd rather check it anyway to be on the safe side.

 

[Twizzler09]

Double post, I know. But I've got news.

Borrowed the comp. tester, and when I got home from work I immediately started testing....well I didnt make it very far. Having decided to test 4/5/6 first, I started with 4. Cylinder #4 puts out 135psi....ok that seems pretty spot-on to me. I go to pull the plug wire off of #5....lo-and-behold the connector on the plug wire was loose and came right off! Damn thing was still hangin onto the plug while I was holdin onto the wire! Didn't even have to pull very hard, just a tiny yank. Stupid cheap little metal pieces.... -.-

I did go ahead and check #5's compression anyway....140psi.

I attempted to put the connector back in the wire....and got it *most* of the way back in....but its busted. But I did get a chance to observe it's behavior after I shoved the little bastard back in. Every once in awhile the spark would jump from the wire to the block. Would easily explain the occasional miss....the spark went to the wrong place!

(oh yeah, when I did this is was semi-dark outside, which is the only reason I could see the spark jump)

Thanks for the lifetime warranty, O'Reilly

 

[shadetree]

If you have an exhaust leak that in itself can cause a burnt valve.. ALL exhaust leaks need to be repaired specially those near the engine.

How do you think this could happen??? shady

 

[Big Jim M]

Shady ever notice how a manifold leak shuts up as the rpm increases? The flow of exhaust going down the pipe gets high enough to PULL air into the stream..
The reverse of that is when the air mixes with exhaust as the intake stroke starts and causes an extremely hot flame that can and HAS burnt the exhaust valve..
Big JIm

 

[shadetree]

That explanation doesn't make sense to me. Air in the exhaust on the intake stroke????????????shady

 

[Big Jim M]

Ok Shady... The faucet on your sink has an aerator on it... When the faucet is turned on the air enters and bubbles out with the water.. You do know this doncha?
Now the same thing happens when there is an exhaust leak... The faster the exhaust goes thru the pipe the less comes out the leak hole... Then the leak reverses itself and takes air INTO the hole.. Yes this happens!
Now if the leak is close to the piston...as a manifold leak is.. as the piston descends to pull fuel into the cylinder the exhaust valve is partially open.. this sudden reversal of pressure can and does pull fresh air into the exhaust valve causing a really hot fire on the exhaust valve itself.. doing this time and time again will burn the valve!
This is why all forms of racers have an extension to the engine exhaust that is longer than the amount of air that could enter backwards into the valve area. Running an engine without a pipe/manifold WILL burn the valves of that engine..
There are all sorts of devices that depend on velocity in one tube to pull another product into the tube from a smaller tube.. Have you ever had a water hose with a small leak in it? When the water flows past the leak some may escape at low velocity...but at higher velocity air enters and can be seen at the business end of the hose.
Here's a good example.. A pressure washer.. a container of soap can be placed under the washer and a small tube placed in the soap.. as the pressure is turned on the soap is SUCKED into the flow of water.. I'm sure most of us have used one of these.. Well the same principle applies to the exhaust system.
Big Jim

 

[shadetree]

I have heard this arugment many times before, and as yet have not had the theory proven.

Valve overlap after exhaust is just a few degrees, and the gasses are still moving out of the combustion chamber. Any minute amount of outside air could not get into the chamber, and if it did, it would be mixed with exhaust gasses. If the exhaust system is not working properly, there would be some reversion that would block anything from coming back into the system.

When the exhaust valve opens, gasses leave the combustion chamber with tremendous force.

Gasses are moving out of the combustion chamber not in.

Once in the pipe, the gasses are being pushed down the pipe. Any outside air that could enter the system would be pushed out the exhuast along with the gasses.

Pressure from other cylinders would not allow air to enter the manifold.

An air imbalance would be picked up by the 02 sensor and set a code if it were enough to affect the engine.

Cust brought me a 1992 Toyota Corolla with a cracked exhaust manifold. It had no problems other than the noise. I searched several salvages and found that most all the damned things are cracked. This car was working on 250k miles with no other problems, and the cust said the crack occurred at about 80k.

Currently, my 1996 Ford F150, 302 engine has a leaking manifold flange at the head on #4 cylinder. It has been that way for over a year. No codes, no burned valves.

Valves are burned for many reasons, but not from an exhaust manifold leak.

I also get this argument from some when adding headers to an engine. Many say the headers will cause the valves to burn. This stems from carburetor days when the improved flow thru the system would cause the carb to lean out. It doesn't happen with modern fuel injection systems as they adjust the fuel trim from the 02 sensor data.shady

 

[Big Jim M]

Shady I have heard of cracks causing burnt valves all my life.. The one thing I can see left out of your post is the speed at which the new oxygen would travel in the existing flame.. Yes the gasses you write of are still a flame when entering the maniold adding new oxygen will (can) flame backwards into the chamber as the exhaust valve is closeing.. Which will (can be) as hot as a torch.
Although this has never happened to me I still know it has been taught for many decades.. I never have risked a cracked manifold for more than the time it took to get it off.
Big JIm

 

[Twizzler09]

As nobody has answered my question in another thread.....

Since the plug wires did not 100% solve the problem (it DOES run better now, however). I went ahead and checked the fuel pressure, at the rail.

I got 35psi w/Key "on" and 28psi with the engine running. The specifications call for 40/30. I know the difference is small, but is that enough to cause a problem?