missfire on higher boost

[BenF]

I have never heard that the timing needs to be adjusted for 1.2bar. Everyone else normally says the standard 10 BTDC is fine for the base timing.


Luke checked my timing and its at 10 BTDC as normal.

No, that's very wrong

Basically the problem is that as you increase the boost pressure, the charge temperature in the cylinder rises on the compression stroke.

It can rise to the point where the air/fuel mix will spontaneously explode at the same time - this is bad as it causes a large pressure spike, rather than a smooth, gradual increase you get with a normal flame burn away from the spark plug.

This is called 'knocking' - it sounds like someone tapping a spanner on your engine block gently in time with the engine.

If you've got the standard ECU and boost control still fitted, it will knock the timing back to stop this, and if that doesn't work, cut the boost.

What you want to do is to advance the timing as far as you can at the highest boost level you run whilst avoiding detonation.

Lots of detonation will kill ringlands and hotspots buildup - Valves, piston heads will eventually fail.

That's why running high octane Super unleaded is better than normal unleaded - the high octane rating fuel will be more detonation resistant.

To give you some idea - on my old Rev2 I could run 10deg BTDC and 10-11psi of boost. For 16psi, I had to advance the timing to around 14deg BTDC for 97RON fuel.

A rev3 starts with a base of 13psi and 10DBTDC - to run 17psi / 1.2bar safely you probably want to bring the timing to 12deg BTDC if you're running 97 RON fuel - but it will vary from car to car. You may get away with 10deg BTDC and 17psi if you're running 99RON fuel ( V-Power / Tesco 99RON ) and your particular engine is less fussy.

Either way, I'd get it checked on a rolling road.

You done a compression check?

Have a read back to Jeremy's post on the Inner workings of the Rev2 ECU, and what the ECU in particular does when it detects knock :

http://www.imoc.co.uk/forums/viewtopic. ... ght=timing

[RobCrezz]

Right, I was aware of most of that, but I have never heard anyone else say that 1.2 bar on a rev3 needed the timing set differently. I only run 99octane, and normally it is only set at 1bar anyway. And I do have a better intercooler, which should bring charge temps down more than stock.

Im not saying your wrong, but noone else has said this? And even luke said my timing was fine for 1.2bar.

Im pretty sure im not getting knock anyway, it doesnt seem like knock.

[BenF]

Rob, I'd get it checked on a rolling road - a good outfit will have someone listening to the engine to detect knock and advise. Its dead easy to adjust if needed - just rotate the whole distributor slightly, when using a timing light.

[RobCrezz]

Rob, I'd get it checked on a rolling road - a good outfit will have someone listening to the engine to detect knock and advise. Its dead easy to adjust if needed - just rotate the whole distributor slightly, when using a timing light.

Ive got it booked in at Pacific works soon, so Lukes going to get it sorted for me.

Went drag racing yesterday and the car performed well, no misfires all day, and that was in the baking heat.

Weird!

[Dundee]

Rob, are you still having problems?
Mine ended up being the coil pack, it had a split all round the back

[RobCrezz]

Rob, are you still having problems?
Mine ended up being the coil pack, it had a split all round the back

Yeah, it comes and goes, some days its fine, sometimes it does it more.

Its going to Pacific works week after next, and lukes going to check out all the ignition bits, so I will just leave it to him, or ill just keep buying parts in an attempt to fix it

[Marf]

I had a misfire that manifested itself on full(std) boost and above 6000rpm.

Replaced plugs, leads, dizzy cap and rotor arm and that cured it.