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Discussion Starter #1
Hey everyone!

So a month or so ago while driving on the highway my check engine light started blinking. So i pulled over and let it sit for awhile. When i started it again, i noticed that the engine vibrates, pulsating sound came from the exhaust, it felt funny. Noticed that there was oil in the spark plug wells near the oil filler cap, sobto be safe, i replaced the valve cover gasket, but the old one seemed still good. So far i have replaced all 8 plugs, checked the resistance of the injectors, swapped spark plug coil locations, but still the vibration remains. When checking the new plugs, i found that the tips of the plugs in cylinder 4 are wet, swapped them over to another cylinder, but still any plugs put to the 4th cylinder get wet. Took it to a car shop to get it diagnosed, only thing they found was that the 4th cylinder was reporting a fault. After letting it sit for a few weeks, i noticed a spitting like sound from the front of the engine, just around the exhaust manifold. I also took the injector of the 4th cylinder to get it cleaned, but the guy who cleaned it said that the injector was ok, the amount of fuel it sprayed was normal and the spray pattern was normal too. I have never really worked on cars, so i really don’t have a clue what it might be. The belts and pulleys were changed 10k km ago, according to the maintenance history book, i got with the car. I changed the oil and filter 5 or 6 months ago and checked it regularly and topped up if needed. I don’t know if a lambda sensor can cause something like this, but a year ago, one of the sensors reported a fault, but didn’t reappear when deleted. Any help is much appreaciated. I don’t have access to the car at all times so it is getting annoying to track down something that was not bad to begin with
 

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I'd check the spark of number 4 cylinder first- just to be sure. Swap the coil and HT lead with one from another cylinder. If the problem goes to another cylinder, the coil and boot is your problem. If not, see below.

Noise from exhaust manifold is probably your problem. Given the engine has a camshaft position sensor and the way it is programmed, I'd expect injector number 4 to inject much more fuel. The reason for this is air getting in to the exhaust upstream of the O2 sensor which thinks it is weak so gets number 4 cylinder to inject much more fuel. Often diagnostic equipment can see this on live data as cylinder 4 fuel trim being a much higher positive value. The other cylinder fuel trims should be as close to zero as possible.

Trace exactly where the leak is. Use a rubber or plastic hose. Position one end close to where you think the leak is. Put the other end right up to one of your ears. Any leaks will be CLEARLY heard.
Fix the source of the leak and your car should run ok.
 

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A "spitting" sound emanating from or seemingly near the exhaust manifold does tend to suggest an exhaust leak. A leak at the manifold (i.e. gasket or perforation of the manifold) can cause an O2 sensor to erroneously detect a lean condition (i.e. an excess of O2 at the sensor that isn't indicative of the in cylinder O2 content). But even if there is a leak I'm not completely convinced that this is what is causing your number 4 spark plugs to become wet (with petrol I assume...?).

Of the two precat O2 sensors, the one that monitors AFR in cylinder 4 is the sensor located physically nearest to cylinder 1 (lets call it sensor 'A'). However, this sensor not only monitors cylinder number 4, but also cylinder number 1 (while cylinders 2 and 3 are monitored by the other precat sensor). If the ECU were enriching AFR because it was getting an erroneous lean signal from sensor A (in this case), then the ECU would be unwantedly enriching AFR not only in cylinder 4 but also in cylinder 1. So, if the ECU were detecting a false lean signal from sensor A, then the spark plugs from both cylinders 4 and 1 would be equally exhibiting signs of excessively rich AFR (i.e. wet, and also blackened with carbon deposits).

A faulty O2 sensor would create a similar issue, i.e. any symptoms arising (such as over-fuelling) wouldn't be isolated to a single cylinder but occur in both cylinders which that sensor monitors (i.e. cylinders 1 and 4, or cylinders 2 and 3).

On the other hand:
If one cylinder were in fact significantly lean due to say an air leak on the induction side, then this would be correctly detected by one of the two precat O2 sensors. Since the sensor monitors two cylinders, the ECU would then enrich the AFR in both cylinders which that sensor is asociated with (both 1 and 4, or, both 2 and 3). The ECU would continue enriching until it 'sees' the exhaust O2 content that it 'wants' to 'see'. Since the sensor is monitoring two cylinders at the same time, it sees an O2 content that is the average of the two cylinders (not each cylinder individually). So, the ECU will equally enrich AFR in both cylinders, but one is being enriched from a too lean base, and the other will be enriched from a 'correct' base.

As a result, even though the ECU enriches both cylinders, one cylinder will still be lean, just less lean than it was. The other cylinder will enriched, but since its' AFR was correct to start with, it will become too rich. This might be enough to cause wetting of plugs etc in that cylinder, maybe...

Regards,
John.
 

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Discussion Starter #4
Thanks for the input, got a opening to take it to a local mechanic who has fixed my fathers car numerous times, lets see if he can find the problem.
 

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So, i just got the car back, and turns out that there is almost no compression in the 4th cylinder. Which is more likely, a worn piston ring or something to do with the valves on that cylinder?
 

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Valves not seating are far more common than worn rings these days (especially wear on a single set of rings)…..but there is always the chance of a broken ring on that bore....with resulting bore damage.
 
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Ah, no compression...

More or less agree with alfaitalia, loss of compression in only one cylinder is probably more likely to be a burnt (or maybe stuck) valve than worn rings (while not ruling out a broken ring as suggested). You can check with a 'wet' compression test:


The 'spitting' sound you heard might be half compressed gas escaping past a non sealing exhaust valve. The seat on a valve could be burnt. Or, a valve might not be fully closing, which could be caused by a slightly bent stem ('cocking' the valve head). Or perhaps carbon build up on the stem preventing the valve from completely closing (i.e. the valve might stick very slightly open, even if it moves normally otherwise). Less than likely but not impossible, perhaps a valve seat insert might have come loose in the head (???).

Or, the head gasket might be leaking (?). Are you losing coolant? This might explain some wetness on the spark plugs? (are you sure that the liquid on the plugs is petrol, could it be coolant?). Note that a head gasket leak doesn't neccesarily always involve the cooling system (or may do only to a relatively minor degree). It is quite possible for a HG to leak entirely or mostly into the crankcase (and / or into the adjacent cylinder, but then there would be two cylinders down on compression) and not at all or only a little bit into the water jacket. So, it is possible to have a major loss of compression with zero or relatively little coolant loss (i.e. little to no affect on the cooling system), maybe just enough to wet the plugs?

If compression is as bad as you say, then the engine is almost certainly running on only three cylinders, which would explain the vibration (and lack of power...).

Regards,
John.
 

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Discussion Starter #8
Just got the car back from a local mechanic, turned out that the valve on the bad cylinder was burnt, got all the valves replaced along with all sorts of other things inside the engine, replaced the belts and pullyes aswell, runs like new, but i don’t think they did anything with the variator, they told me to get the oil pressure checked to sort out the diesel like idle, should i? Or will the variator replacement do the trick?
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You want reasonable oil pressure (to state the obvious), so checking it can't hurt, but unless the oil pressure is pretty low it is more likely that a noisy variator is caused by the variator itself.

Oil pressure will be lowest with hot oil at idle, so thicker oil might help. Years ago I owned an Alfetta sedan that ran about 8psi oil pressure at idle (according to the gauge), but ran well and never gave me any problems (at least not engine problems...).

I'd be more concerned with trying to find out why that valve burnt in the first place. Exhaust valve material is (must be) very resistant to higher temperatures, so obviously it must have been running very hot. So why was that? Does the cause still exist, and will the new valve also run hot?

Maybe a lean AFR in that cylinder, perhaps caused by faulty injector?

Valve not seating properly? Exhaust valves run very hot, and rely heavily on the valve seat to cool the valve head and keep its' temperature within reasonable limits. Whenever the valve is closed (much more time than it is open) heat is conducting from the very hot valve head into the much cooler valve seat. If the valve is not seating correctly then substantially less heat will conduct from the valve and the temperature will rise substantially. The valve can then get so hot that the head will burn.

A slightly bent stem could cause this (valve only seating on very small part of the valve edge).

Or a build up of carbon on the stem (holding valve very slightly open as the stem sticks in the guide), or carbon on the valve seat face (holding valve slightly off the seat, and also conducting less heat than a metal to metal contact).

Or a problem with the tappet (i.e. holding the valve slightly open when the tappet is riding on the cam base circle, i.e. no effective clearance between tappet and cam base circle, for whatever reason).

Weak valve springs could be an issue (not holding the valve strongly against the seat when closed).

Hopefully whatever work has now been done to the head will have rectified whatever may have caused the initial valve to burn, but it would be good to know...

Regards,
John.
 

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Discussion Starter #10
You want reasonable oil pressure (to state the obvious), so checking it can't hurt, but unless the oil pressure is pretty low it is more likely that a noisy variator is caused by the variator itself.

Oil pressure will be lowest with hot oil at idle, so thicker oil might help. Years ago I owned an Alfetta sedan that ran about 8psi oil pressure at idle (according to the gauge), but ran well and never gave me any problems (at least not engine problems...).

I'd be more concerned with trying to find out why that valve burnt in the first place. Exhaust valve material is (must be) very resistant to higher temperatures, so obviously it must have been running very hot. So why was that? Does the cause still exist, and will the new valve also run hot?

Maybe a lean AFR in that cylinder, perhaps caused by faulty injector?

Valve not seating properly? Exhaust valves run very hot, and rely heavily on the valve seat to cool the valve head and keep its' temperature within reasonable limits. Whenever the valve is closed (much more time than it is open) heat is conducting from the very hot valve head into the much cooler valve seat. If the valve is not seating correctly then substantially less heat will conduct from the valve and the temperature will rise substantially. The valve can then get so hot that the head will burn.

A slightly bent stem could cause this (valve only seating on very small part of the valve edge).

Or a build up of carbon on the stem (holding valve very slightly open as the stem sticks in the guide), or carbon on the valve seat face (holding valve slightly off the seat, and also conducting less heat than a metal to metal contact).

Or a problem with the tappet (i.e. holding the valve slightly open when the tappet is riding on the cam base circle, i.e. no effective clearance between tappet and cam base circle, for whatever reason).

Weak valve springs could be an issue (not holding the valve strongly against the seat when closed).

Hopefully whatever work has now been done to the head will have rectified whatever may have caused the initial valve to burn, but it would be good to know...

Regards,
John.
The car had a period a few months ago when i forgot to check the oil level for a month or so, i learned that the twinspark engines tend to burn more oil than other engines, when i checked it, the dipstick was dry, it was running well, but could that have affected the car to a point where the valve was damaged slightly and get worse and worse over time?
Since this is my first car, i have a quite agressive driving style where i do push it to the limits when i haven’t driven for a while.
 

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A 'dry' dipstick is never a good thing, but doesn't necessarily mean that the engine was running with no oil at all (hopefully just enough...). Did the engine ever sound unusually rattly? If not then you may not have done any significant damage, with luck...

I think it is madness to not have an oil pressure guage, especially with AR engines (should have been a standard fitment, like it was back in the day before FIAT accountants got involved, as should an oil level gauge...). Having said that, I haven't fitted one to my car, yet...

At any rate, oil starvation won't cause the sort of damage exhibited by that valve.

Valve stems are lubricated by a microscopically thin oil film (between stem and valve guide), but even if it were to run dry the guide is nearly always made from a bronze alloy which has a characteristic of being 'self lubricating' (most and maybe all bronze and brass alloys are like this, try cutting some brass with a hacksaw or filing it and you'll see what I mean, it is 'slippery'). Because of this self lubricating quality, lack of oil would mean that the engine would 'run' a bearing or seize a piston well before the guides became significantly damaged by lack of oil.

Modern valve heads (and seats) are made from very hard and heat resistant steel (usually 'stellite' from memory) and are unlubricated. Years ago they were made from softer steels that required a lubricant to prevent them wearing out quickly, which was one of the functions of the tetraethyl lead once added to the petrol. When lead was deleted from petrol the valve head and seats had to be made from a much harder material capable of running 'dry' without wearing.

From the photo, your valve shows the signs of having been damaged by becoming severely overheated (despite the carbon deposits looking very black and not having burnt off, the valve probably was not all that hot all the time that the engine was running).This could be a result of abnormally high combustion temperature, but I would expect this to also show up as overheated spark plugs.

More likely it is as a result of failure to cool the valve head (but I cannot guarantee this is the cause, just my strong suspicion). This could be as a result of the valve not seating correctly. This could possibly be due to a bent valve stem (only takes a tiny bend). Or, maybe a valve seat insert has become just a tad loose in the head casting (possible, but not very common, does happen).

The valve head stays cool by conducting some heat up the valve stem and from there into the valve guide and from there into the head casting, but, most of the heat conducts directly from the valve head into the valve seat insert, and from the insert into the head casting (the casting in turn being cooled by the cooling system). If the insert becomes loose (not unheard of) then path of conductivity is interrupted and the insert gets abnormaly hot and consequently so too does the valve head.

Regards,
John.
 

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When i changed the plugs, some of them had white spots on them, they had a massive amount of carbon build up on them aswell, i think that this was the first time that this engine saw a spark plug replacement, since the kilometrage is only 124k, im suspecting that the plugs could have caused such a premature failure on the valve?
 

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"White spots" on the plugs does not sound like a good thing, but I tend to doubt that spark plugs would be the cause of a burnt valve. Very dirty plugs could cause pre-igintion (because carbon deposits can glow red hot and ignite the fuel before the spark plug fires), which is very bad, but any damage is more likely to be piston related.

Be aware that 'reading plugs' isn't as simple as it is sometimes presented as being...

In theory; An engine may possibly be running lean between X and Y rpm at Z throttle opening (i.e. under specific circumstances, e.g. driving on the highway), so that might be when a valve is overheating and possibly burning. Under other circumstances, e.g. when idling or say at low rpm, the engine (or an individual cylinder in that engine) may be running very rich. If the engine is running very rich under certain circumstances then the plug is likely to 'soot up' and become quite black under those circumstances.

This would disguise the appearance of the spark plugs as they might appear under other circumstances, i.e. you wouldn't see any sign of a lean condition that might be occuring when driving at higher speed on the highway.

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I stole the following from this page:

Possible causes of burnt valves are:
Bent-Valves-Caused-By-A-Broken-Timing-Belt-320x200

Bent valves caused by broken timing belt
  • Excessive localized heat
  • Combustion gases escaping past the valve and concentrated at only one point
  • Irregular valve sealing with cylinder head valve seat. Carbon residues generated by irregular combustion (poor mixture) will appear at the seat region and will jeopardize the sealing between the valve and its seat
  • Deficient refrigeration is another factor, due to partial obstruction of the cylinder head cooling. As a consequence, the valve is cooled inadequately
  • Incorrect valve clearance can jeopardize the valve sealing and also cause this type of failure
  • Running a dry fuel such as L.P.G resulting in inadequate lubrication of the valve seat, causing the valve seat to fail and consequently, the valves
    A-Valve-Starting-To-Burn4

    A Valve Starting To Burn
To help prevent this type of failure, there are a few things you can do. Maintain a clean, efficient cooling system so the engine does not run too hot, use good quality fuels to help prevent carbon build up on the valve seats, and have your mechanic regularly check the valve clearances are within specifications.

Burnt-Exhaust-Valve5

Burnt Exhaust Valve

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Regards,
John.
 
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