one piston not firing, not the injector, possibly burnt valve or head gasket?

[sixshooter]

If it's down on compression on one cylinder, it's not going to be the lead or the coilpack.

If you take the word of the mechanic that looked at it...

Thanks hako, yeh he did a compression test and thats what he told me.

just check my example of what my mate was told by his mechanic regarding his LPG !!! :yeah:

Some mechanics are as useful as condoms at a convent !

 

[Famine]

Its not the coil, or leads, already swapped them around. The good thing about this mechanic though, is that he doesnt mind if I hang around to see whats going on, and I can sorta get involved in what hes doing to get more of an idea. This mechanic seems pretty genuine, and I was there when he shifted around the leads etc.

 

[digisol]

I see you mention it's not the coil or the leads, I guess that includes plugs ?

This mechanic seems to be missing a vital criteria here, No SPARK ! it don't matter squat if the piston had a hole in it, the lead / plug will still throw a spark outside the engine when turned over.

Would not matter if the valve was not there at all, it will still spark, perhaps time to change the mechanic for an auto electrician that also has a trade ticket in auto mechanics.

 

[JD]

sorry mate woudln't have a clue now.
my vn was on running on 6 cylinders turned out to be leads and plugs.
thats was i asked if i was firing on occasion

 

[Famine]

It sparks, I was there when he tested it. He even replaced the spark plug to see, and it still did the same thing.

 

[digisol]

I see my bad, I guess you have not yet removed the offending injector ?

Burnt valves usually come from using incorrect fuel and running at high speed, if your a closet racer the faulty valve is possible.

Checking for broken springs is not rocket science, pretty much means having a look,

Neither is doing a compression test, wet and dry, IE; check it normally and if low, then squirt a small amount of engine oil onto the cylinder wall and check the compression again, if it fails to increase, the valve and or gasket may be at fault, however if it does increase when wet the rings may be broken.

Quicker to rip out the injector first, but if found stuffed get em all reco'd at the same time.

Try again, having fun yet ?

 

[Famine]

If I was to dive into the insides of the motor, would a burnt valve or blown head gasket be relatively obvious? If I cant tell whats broken and whats not, it would be a huge waste of time. I was under the impression that when a head gasket blows, the car doesnt run... however mine runs, and is still perfectly driveable, it just lacks power (obviously) and it feels rough.

 

[hako]

When a head gasket fails it will usually just affect one cylinder, so you still have 5 good ones - so you still have 80% good. Additionally, if the gasket fails it means the gases etc which are escaping past the failed gasket then go into your cooling system resulting in lot of excess pressure, bubbles in the coolant and maybe even boiling. So the telltale signs here are signs of bubbling/gases escaping from the radiator when you remove the radiator cap with the engine idling.
With a burnt valve, you would do a compression test (already done by mechanic). He's decided one pot is dead. Only way forward from here is to remove that head. First step in removing the head is to remove the rocker cover which will allow you to inspect the valve springs just to make sure its not a busted spring as previously suggested by Digisol (I think). If no busted valve spring then proceed with removing the head - once off you will have no difficulty in identifying the burnt valve as it may have a crack in it an/or when you insect the valve seat you will easily see that it is not sealing. Similarly with a failed gasket you would easily see where the gasket was busted.
Good Luck.

 

[digisol]

Not always, it can blow into a water passage, it can blow between cylinders, it can blow out the side, all will still run, not well, but will run.

I've seen a red motor run fine, with a miss ? but with a snapped piston, half up the top of the bore, the rest in the sump, with the rod and pin rattling in the bore, it ran good enough to drive it some 100 miles before the rod went through the bore and broke into the water jacket, so a blown gasket is minor, just a PIA.

Oil in the water, water in the oil, loss of compression and a heap of other nasties when it blows into a water passage.

The mechanic "should" be able to tell you if it's rings or valve, the squirt of oil shows piston or valve instantly, and removing a head when it's the bottom end is a waste of time, a hole in the piston will show the same as a stuffed valve, either way it would not run well.

NP there you know what cylinder it is, you won't miss it, BUT if it's broken ring/s the engine has to come out for a rebuild, so don't buy anything until it's inspected, it may be cheaper to grab a cheap complete engine from the wreckers.

The head might be cracked ?

The damaged gasket will have burnt sections where the hot gas passes out, just how much down is the compression compared to the others, the entire engine may be clagged ?

 

[genIIIbandit]

When a head gasket fails it will usually just affect one cylinder, so you still have 5 good ones - so you still have 80% good. Additionally, if the gasket fails it means the gases etc which are escaping past the failed gasket then go into your cooling system resulting in lot of excess pressure, bubbles in the coolant and maybe even boiling. So the telltale signs here are signs of bubbling/gases escaping from the radiator when you remove the radiator cap with the engine idling.
With a burnt valve, you would do a compression test (already done by mechanic). He's decided one pot is dead. Only way forward from here is to remove that head. First step in removing the head is to remove the rocker cover which will allow you to inspect the valve springs just to make sure its not a busted spring as previously suggested by Digisol (I think). If no busted valve spring then proceed with removing the head - once off you will have no difficulty in identifying the burnt valve as it may have a crack in it an/or when you insect the valve seat you will easily see that it is not sealing. Similarly with a failed gasket you would easily see where the gasket was busted.
Good Luck.

best way to check if a valve aint seating is to put petrol on chamber and see if it leaks through, very hard to see if it is seating just by looking. Ask the mechanic to do a TK head check, this will determine if you have combustion gases in coolant. I am a mechanic and worked on many v6 engines, i would suggest you have a weak valve spring/or break.Try pushing colet with screwdriver to check 4 weakness. Sounds like your on to a good mechanic but, keep looking.