Thread: what are the symptoms of a stuck exhaust valve?

on a few cars i have had i have had a similar thing... on one it was a leaky HT lead shorting with the head.. but only at certain revs.. very wierd.. that was originally diagnosed as a sticking valve... the other car was some high tec spark plugs with a 100k km guarantee suffice to say less than 20k's later they were breaking down and doing very very wierd things to the firing also..

probably wont help... but its all i can manage

Steve

When my Disco stuck a valve it wasn't intermittent, more terminal...

I'd get it checked out, if it is a valve when it finally does stick you may be up for substantial rebuild bill if it bangs into a piston etc.

The exhaust valves on the 3.9s do carbon up and stick eventually normally after 100ks of around town running.

The more I think of it I is more likely to be an electrical miss.
I swapped the rotor, swapped the dizzy cap.
The plugs were only put in a few 100 kms ago.
I did use that dialectric ??? grease on the plug bbots.
May be that has caused the problem.
Will have to check the Dizzy leads to ignition amp.
Wonder if the Ign amp could be playing up, thought it it was it just wouldn't run?

Just went out and checked under bonnet in complete darkness.... nothing appears to be arching anywhere

Good idea on checking under the bonnet in complete darkness - it's a very simple way of diagnosing a problem which is relatively simple and cheap to fix. I have just one question - was the engine missing when you looked? If it's an intermitant problem it's conceivable that there's an arc developing only under certain conditions. If there was no miss it wasn't the right time to look!

The other aspect which you should take into account is that the arc could be happening where you can't see it - under a lead for example -and where it is only jumping a very short distance. I'm thinking here particularly where the HT lead runs across a rubber hose (radiator hose, heater hose, vacuum hose). Rubber hoses are a bit of a trap because we assume that, being rubber, they're good insulators. Not true. They contain lamp black (carbon black) to make them nice and black in colour. See http://en.wikipedia.org/wiki/Lamp_black for more info. It's a conductor - not a good one but a conductor nonetheless and the hoses usually terminate on a metal spigot on the engine block (at electrical ground). So it's a good idea to separate the HT leads from these hoses. If it's difficult to move the HT lead you can tape a small section of clear PVC hose or even a bit of 15mm conduit under the lead to provide some separation as a diagnostic tool.

The HT leads with fatter insulation are better in this situation of course and keeping the leads and the spark plug insulators clean helps too.

What you've described sounds like an electrical miss to me. My philosophy in diagnosing these problem is start with the cheapest things.

Can I slip in a little humour here (it's relevant)?

PILOT SQUARKS
"Squawks" are problem lists that pilots generally leave for maintenance crews to fix before the next flight. Here are some squawks submitted by US Air Force pilots and the replies from the maintenance crews:

My favourite ...

(Problem) Number three engine missing
(Response) Number three engine found on starboard wing after brief search

Originally Posted by GrahamH

Good idea on checking under the bonnet in complete darkness - it's a very simple way of diagnosing a problem which is relatively simple and cheap to fix. I have just one question - was the engine missing when you looked? If it's an intermitant problem it's conceivable that there's an arc developing only under certain conditions. If there was no miss it wasn't the right time to look!

The other aspect which you should take into account is that the arc could be happening where you can't see it - under a lead for example -and where it is only jumping a very short distance. I'm thinking here particularly where the HT lead runs across a rubber hose (radiator hose, heater hose, vacuum hose). Rubber hoses are a bit of a trap because we assume that, being rubber, they're good insulators. Not true. They contain lamp black (carbon black) to make them nice and black in colour. See http://en.wikipedia.org/wiki/Lamp_black for more info. It's a conductor - not a good one but a conductor nonetheless and the hoses usually terminate on a metal spigot on the engine block (at electrical ground). So it's a good idea to separate the HT leads from these hoses. If it's difficult to move the HT lead you can tape a small section of clear PVC hose or even a bit of 15mm conduit under the lead to provide some separation as a diagnostic tool.

The HT leads with fatter insulation are better in this situation of course and keeping the leads and the spark plug insulators clean helps too.

What you've described sounds like an electrical miss to me. My philosophy in diagnosing these problem is start with the cheapest things.

Can I slip in a little humour here (it's relevant)?

PILOT SQUARKS
"Squawks" are problem lists that pilots generally leave for maintenance crews to fix before the next flight. Here are some squawks submitted by US Air Force pilots and the replies from the maintenance crews:

My favourite ...

(Problem) Number three engine missing
(Response) Number three engine found on starboard wing after brief search

She starts and idles fine, it's when she's under load, like at throttle. coasting I don't notice anything out of the norm.
I did rev the engine while I looked in darkness.
The leads are magnacore leads, although a few years old now.
I did have a problem some time back with number 8 spark plug having a strange appearance, on the inner body, ( not the electrodes or tips, but the inner body wall of the plug. It was like it was overheating the metal. It gave me loss of power, After I changed the plug all was well again, but it had a different drivability.
I will pull the plugs on the weekend. Clean that dialectric grease off the inside of the plug lead boots and give it a thorough check.

did you fit a genuine rotor button.......?


if you want to check for leaking spark......use a spray bottle on fine mist setting......
and simply spray a tiny bit of humidity under the bonnet.......no too much.....you dont want to wet things......

this may help you find a dud lead if done in the dark again.......

Hmmmm ... doing the same diagnosis at night, in darkness, under load does present a bit of a problem - unless you've got a rolling road. Mount a video camera under the bonnet perhaps???

Some years ago my old 2a suddenly developed a bad misfire on the way to work. The NRMA mechanic (being an older chap) had the answer. The distributer cap tracked between two posts. His solution? Using a sharp pocket knife, he cut out the carbon track in the cap then he painted it with nail pol;ish remover to seal the cut out section. After that he used a heat gun to dry the acetone. I was advised to buy a new cap but I never had to use it as the old cap never faulteds.