Misfire

[enigma]

I visited WRC back in May and had a quick dyno run. The car was set up conservatively as I was having some problems with boost above 0.9bar. Ran it on the dyno and got the following results

[enigma]

The nice gentlemen at WRC suggested that I had a misfire, which I kind of already knew due to my running problems and because the logging I had been doing showed erratic rpm values.......only mildly but they were there none the less. Recently I have been getting issues with big misfires under load so decided it was time for new plugs and leads.

The plugs have been in the engine for 21 months and were in the previous engine an undetermined amount of time. I got the garage to swap the plugs when they swapped the engine.

I found that I had 2 plugs that looked like this (ie normal ish)

[enigma]

3 that looked like this (ie buggered)

[enigma]

And one random platinum one that the garage must have forgotten to change.

I have also replaced the leads today with some magnecor ones from camskill and done the oil and filter. Maybe I can wind the boost up a bit now without major misfiring. In fact I would settle for misfire free at my current boost! :o

[Wodjno]

Dave ! I don't see any pics.. :o

Anyone else ??

[Paul Beazer]

Cant see the attachments?

You seem to be collecting buggered plugs Dave. Hope the new ones behave themselves!

[enigma]

fixed

[Wodjno]

What the heat e Duck is doing that Dave.. ?? Was it the Nitrous :huh2:

[enigma]

Nope, just 'normal' wear and tear. Each time the plug fires it takes a bit of metal with it. Thats why you need to replace your plugs, because eventually enough wears away to mean that your gap is too big and the spark struggles to bridge it. This is much more apparent with high cylinder pressures when on boost. Pootling about day to day it was not noticeable, but boot it and the plugs said NO! Should be fixed now though.

[Wodjno]

Nope, just 'normal' wear and tear. Each time the plug fires it takes a bit of metal with it. Thats why you need to replace your plugs, because eventually enough wears away to mean that your gap is too big and the spark struggles to bridge it. This is much more apparent with high cylinder pressures when on boost. Pootling about day to day it was not noticeable, but boot it and the plugs said NO! Should be fixed now though.

When i took my last set of plugs out, they looked near perfect apart from the gap being a little to wide(Approx 30000 miles) But nothing like what yours are like :o The only difference between your car Dave and my car is the fact that you have used nitrous ! So was just wondering if this was a contributory factor ??

[SGHOM]

perfect apart from the gap being a little to wide(Approx 30000 miles)

'kin 'ell !! :rolleyes3 I'd get those re-gapped ! :D

[amsoil]

I think with plugs like that you could be just at the point of detonation, just. Half a degree less advance might do it the world of good.

[enigma]

I think with plugs like that you could be just at the point of detonation, just. Half a degree less advance might do it the world of good.

I have tried up to 6 degrees advance and it has no perceivable difference......I also tried up to 6 degrees retarded with much the same effect :o

I have put a new set in and regapped them to 0.63mm rather than the standard 0.8mm.............see how it goes!

[bernmc]

I was under the impression that you shouldn't alter the gap of iridium plugs ( very brittle metal)...?

[enigma]

I was under the impression that you shouldn't alter the gap of iridium plugs ( very brittle metal)...?

The iridium tip is indeed very brittle, but the electrode strap is just your common or garden strap. Yes care has to be taken, but it is far from impossible!

[Wodjno]

I have tried up to 6 degrees advance and it has no perceivable difference......I also tried up to 6 degrees retarded with much the same effect :o

I have put a new set in and regapped them to 0.63mm rather than the standard 0.8mm.............see how it goes!

No Perceivable difference you say Dave ! obviously you are referring to power ? But the long term affect of having your timing advance in this position, as Don states, could be the reason for the state of the plugs. So you don't notice any power difference when advancing the timing, but internally it could be gradually damaging your internals. Also retarding, you say you don't notice no difference.. So retarding the ignition a 1/2 to 1 degree will not affect your power delivery, but may save your plugs and or your engine ... Gotta be worth a try Dave ??

[amsoil]

Might just be worth a chat with Champion. :smash: Yes I know they arn't the flavour of the modern world but they have knowledge in depth and supply plugs for most real racing engines. What I'm thinking about is their plugs that have no electrode bar over the top, the gap is the distance from the center electode to the inner edege of the plug. They are made for just this type of problem.
Think I would try and borrow a boreascope too. If metals vanishing from the plug tips where else might it be going from? Just a suggestion; be interesting to see how it goes.

[psbarham]

. What I'm thinking about is their plugs that have no electrode bar over the top, the gap is the distance from the center electode to the inner edege of the plug. They are made for just this type of problem.

aah surface discharge , i ran a set in the v6 a while back (ex btcc honda) and yes a noticable difference on power , it was a lot crisper throughout , but , once the weather cooled down she became a complete tw@t to start , so its back on iridiums now , acctually thinking about it i got a set for zentac , it might be worth asking him if he's used them in the tyre shredder

[ritch_w]

aah surface discharge , i ran a set in the v6 a while back (ex btcc honda) and yes a noticable difference on power , it was a lot crisper throughout , but , once the weather cooled down she became a complete tw@t to start ,

PSB - i had the same issue with the set you gave me - I ended up going back to normal plugs too

[psbarham]

PSB - i had the same issue with the set you gave me - I ended up going back to normal plugs too
yeh , pain ain't it , shame coz during the summer they were awesome , can't have everything can you ?

[ritch_w]

yeh , pain ain't it , shame coz during the summer they were awesome , can't have everything can you ?

Not in this world matey!

[valmes]

I have put a new set in and regapped them to 0.63mm rather than the standard 0.8mm.............see how it goes!

I did the same with my platinums. No misfire up to 1.4 bar... then hoses start to come off...

[enigma]

I did the same with my platinums. No misfire up to 1.4 bar... then hoses start to come off...

Misfire completely eliminated. However I bought the wrong plugs IK22s rather than the IK27s I have been running for some time.

The result was a destroyed plug, piston and ring on number 5 cylinder.

[Nick Mann]

Ooops. /help

What's the difference between 22's and 27's? Would that difference really make so much difference?

And Valmes - I didn't spot your reply previously - how often do you run at 1.4 bar? There was a thread by Zentac recently where he thought he had found the limit of the engine at 1.3 bar. Or are you running stronger internals?

[enigma]

Ooops. /help

What's the difference between 22's and 27's? Would that difference really make so much difference?

And Valmes - I didn't spot your reply previously - how often do you run at 1.4 bar? There was a thread by Zentac recently where he thought he had found the limit of the engine at 1.3 bar. Or are you running stronger internals?

27s are a colder plug and will more easily cope with the much harsher conditions.

Remember Rich was rinning 1.3 PLUS Nitrous

[enigma]

Taken from http://www.misterfixit.com/


WHAT IS DETONATION?
Detonation (also called "spark knock") is an erratic form of combustion that can cause head gasket failure as well as other engine damage. Detonation occurs when excessive heat and pressure in the combustion chamber cause the air/fuel mixture to autoignite. This produces multiple flame fronts within the combustion chamber instead of a single flame kernel. When these multiple flames collide, they do so with explosive force that produces a sudden rise in cylinder pressure accompanied by a sharp metallic pinging or knocking noise. The hammer-like shock waves created by detonation subject the head gasket, piston, rings, spark plug and rod bearings to severe overloading.
Mild or occasional detonation can occur in almost any engine and usually causes no harm. But prolonged or heavy detonation can be very damaging. So if you hear knocking or pinging when accelerating or lugging your engine, you probably have a detonation problem.

A DOZEN WAYS TO PREVENT DETONATION
1. Try a higher octane fuel. The octane rating of a given grade of gasoline is a measure of its detonation resistance. The higher the octane number, the better able the fuel is to resist detonation. Most engines in good condition will run fine on regular grade 87 octane fuel. But engines with high compression ratios (over 9:1), turbochargers, superchargers, or with accumulated carbon deposits in the combustion chamber may require 89 or higher octane fuel.
How a vehicle is used can also affect its octane requirements. If a vehicle is used for towing or some other application where the engine is forced to work hard under load, a higher octane fuel may be necessary to prevent detonation.
If switching to a higher octane fuel fails to eliminate a persistent detonation problem, it probably means something else is amiss. Anything that increases normal combustion temperatures or pressures, leans out the air/fuel mixture, or causes the engine to run hotter than normal can cause detonation.
2. Check for loss of EGR. The Exhaust Gas Recirculation (EGR) system is one of the engine's primary emission controls. Its purpose is to reduce oxides of nitrogen (NOX) pollution in the exhaust. It does this by "leaking" (recirculating) small amounts of exhaust into the intake manifold through the EGR valve. Though the gases are hot, they actually have a cooling effect on combustion temperatures by diluting the air/fuel mixture slightly. Lowering the combustion temperature reduces the formation of NOX as well as the octane requirements of the engine.
If the EGR valve is not opening, either because the valve itself is defective or because its vacuum supply is blocked (loose, plugged or misrouted vacuum hose connections, or a defective vacuum control valve or solenoid), the cooling effect is lost. The result will be higher combustion temperatures under load and an increased chance of detonation.
Refer to a service manual for the configuration and hose routing of your engine's EGR system, and the recommended procedure for checking the operation of the EGR system.
3. Keep compression within reasonable limits. A static compression ratio of 9:1 is usually the recommended limit for most naturally aspirated street engines (though some newer engines with knock sensors can handle higher compression ratios).
Compression ratios over 10.5:1 may create a detonation problem even with 93 octane premium gasoline. So unless an engine is being built to run on racing fuel, keep the compression ratio within a reasonable range for pump gasoline. This, in turn, may require using lower compression pistons and/or cylinder heads with larger combustion chambers. Another option would be to use a copper head gasket shim with the stock head gasket to reduce compression.
Retarding the cam timing can also lower cylinder pressures to reduce detonation at low r.p.m., but doing so hurts low speed torque which is not recommended for street engines or cars with automatics.
For supercharged or turbocharged applications, a static compression ratio of 8:1 or less may be required depending on the amount of boost pressure.
Another point to keep in mind is that boring an engine's cylinders to accept oversized pistons also increases the static compression ratio. So too does milling the cylinder heads. If such modifications are necessary to compensate for cylinder wear, head warpage or damage, you may have to use a thicker head gasket if one is available for the application or a head gasket shim (a dead soft copper spacer shim) to offset the increase in compression.
4. Check for over-advanced ignition timing. Too much spark advance can cause cylinder pressures to rise too rapidly. If resetting the timing to stock specifications doesn't help, retarding the timing a couple of degrees and/or recalibrating the distributor advance curve may be necessary to keep detonation under control.
6. "Read" your spark plugs. The wrong heat range plug can cause detonation as well as preignition. If the insulators around the electrodes on your plugs appear yellowish or blistered, they may be too hot for the application. Try the next heat range colder spark plug. Copper core spark plugs generally have a broader heat range than ordinary plugs, which lessens the danger of detonation.
9. Check for a lean fuel mixture. Rich fuel mixtures resist detonation while lean ones do not. Air leaks in vacuum lines, intake manifold gaskets, carburetor gaskets or the induction plumbing downstream of a fuel injection throttle can all admit extra air into the engine and lean out the fuel mixture. Lean mixtures can also be caused by dirty fuel injectors, carburetor jets clogged with fuel deposits or dirt, a restricted fuel filter or a weak fuel pump.
If the fuel mixture becomes too lean, "lean misfire" may occur as the load on the engine increases. This can cause a hesitation, stumble and/or rough idle problem as well.
The air/fuel ratio can also be affected by changes in altitude. As you go up in elevation, the air becomes less dense.
A carburetor that's calibrated for high altitude driving will run too lean if driven at a lower elevation. Altitude changes are generally not a problem with engines that have electronic feedback carburetors or electronic fuel injection because the oxygen and barometric pressure sensors compensate for changes in air density and fuel ratios.
10. Remove carbon deposits. An accumulation of carbon deposits in the combustion chamber and on the top of the pistons can increase compression to the point where detonation becomes a problem. Carbon deposits are a common cause of detonation in high-mileage engines, and can be especially thick if the engine consumes oil because of worn valve guides and seals, worn or broken piston rings and/or cylinder wear. Infrequent driving and not changing the oil often enough can also accelerate the buildup of deposits.
In addition to increasing compression, carbon deposits also have an insulating effect that slows the normal transfer of heat away from the combustion chamber into the head. A thick layer of deposits can therefore raise combustion temperatures and contribute to "preignition" as well as detonation.
Carbon deposits can often be removed from an engine that's still in service by using a chemical "top cleaner." This type of product is poured into an idling engine through the carburetor or throttle body. The engine is then shut off so the solvent can soak into and loosen the deposits. When the engine is restarted the deposits are blown out of the combustion chamber.
If chemical cleaning fails to remove the deposits, it may be necessary to pull the cylinder head and scrape the deposits off with a wire brush or scraper (be careful not to scratch the face of the cylinder head or engine deck!).
11. Check the boost pressure. Controlling the amount of boost in a turbocharged engine is absolutely critical to prevent detonation. The turbo wastegate bleeds off boost pressure in response to rising intake manifold pressure. On most late-model engines, a computer-controlled solenoid helps regulate the operation of the wastegate. A malfunction with the manifold pressure sensor, the wastegate control solenoid, the wastegate itself or a leak in the vacuum connections between these components can allow the turbo to deliver too much boost, which destroys the head gasket as well as the engine in short order if not corrected.
Improved intercooling can help reduce detonation under boost. The intercooler's job is to lower the incoming air temperature after it exits the turbo compressor. Adding an intercooler to a turbo motor that isn't intercooled (or installing a larger or more efficient intercooler) can eliminate detonation worries while also allowing the engine to safely handle more boost.
12. Change your driving habits. Instead of lugging the engine, try downshifting to a lower gear and/or accelerating more gradually. Keep in mind, too, that the engine and drivetrain have to be matched to the application. If you're working your engine too hard, perhaps you need a transmission with a wider gear ratio or a higher final drive ratio in the differential.



As you can see a 'hot' plug can easily cause the onset of detonation.

[bradc]

slightly off topic, but we don't have EGR in our engines do we?

Back on topic, for my car would Ik27's be the best plug? It has a full autronic ecu, map sensor, etc etc.

[enigma]

As far as I can tell at the moment your car requires no plugs!

I would certainly go for a cold plug as I suspect you are expecting lots of boost and high power. 27s may not be cold enough depending how far you plan to go.

[Kieran]

slightly off topic, but we don't have EGR in our engines do we?


I Don't think so.

Dave - Ugh, that's not good. Repairable? Another engine to replace? Or are you gonna break for spares?

[enigma]

Dave - Ugh, that's not good. Repairable? Another engine to replace? Or are you gonna break for spares?

Beyond economic repair. Break it for spares? No, I will replace the engine and then probably sell it. Either as standard and sell the bits seperately or as it is.

[bradc]

They are tuning my car at the moment, so it does indeed require plugs :) I'm going to push as much power out of the stock td03's as possible :)

[enigma]

They are tuning my car at the moment, so it does indeed require plugs :) I'm going to push as much power out of the stock td03's as possible :)

With the time and money invested its a bit of a waste staying with stock turbos dont you think?

[bradc]

I'm going to move to GT25R's next year. It was never supposed to take this long of course..

[enigma]

I'm going to move to GT25R's next year. It was never supposed to take this long of course..

Fair enough.................

[bradc]

The main reason for the delay was that noone could get the autronic working with the auto box, so I had to get it swapped to a manual.

Just need to get forged rods and pistons made up in the mean time :)

[enigma]

Just need to get forged rods and pistons made up in the mean time :)

Thats the easy bit.........paying for them is the hard bit!

[bradc]

especially because we have 6 to get, most people get away with ordering 4 :)

[Nutter_John]

Paying for then is not the issue , finding the right ones is the problem ( also rods as well )

[enigma]

Paying for then is not the issue , finding the right ones is the problem ( also rods as well )

We spoke at the weekend................should be easy enough

[Nutter_John]

Yes I remember our conversation further research around the rods as highlighted a short fall in lenght by around 4 mm

[enigma]

Yes I remember our conversation further research around the rods as highlighted a short fall in lenght by around 4 mm

Yes but with the correct pistons and offset grinding the rods you could take up the 4mm with relative ease..............

[Nutter_John]

Sorry Dave think I may have confussed you , our rod length is 138.8 mm center to center the ones we are talking about is 135mm , hence the shortfall . As you say if the pistons had a 4mm higher crown then it may work but then there is the issue of finding a piston with a higher crown

[enigma]

Sorry Dave think I may have confussed you , our rod length is 138.8 mm center to center the ones we are talking about is 135mm , hence the shortfall . As you say if the pistons had a 4mm higher crown then it may work but then there is the issue of finding a piston with a higher crown

Yes, but the big ends are also slightly different which would allow some machine work. A 4mm higher crown would not be too hard to source as it would be a 'higher compression' variant of the piston. Even if you didn't get 4mm the resultant effect would be a lower CR allowing more boost.......

[Nutter_John]

Yep all valid points , and my investigations will continue

Rather not be in the position of having to remachine the rods , so it may end up having custom rods done and using the known pistons