missfire on higher boost

[RobCrezz]

Weird thing happened today, missfiring randomly under hard accelleration when boost is over 0.9 bar. When I turn off the profec b and run at actuator pressure, its a smooth as butter.

Im gonna change plugs tomorrow as they are pretty black (i think due to my dp being cracked and possibly overfueling), and ive got my shiny new berk DP going on tomorrow.

Any other ideas if its not these?

Could my profec be broken already? (only 3 months old)

[Dangerous]

Could be ignition... also try dizzy cap/rotor arm and leads..

[RobCrezz]

Could be ignition... also try dizzy cap/rotor arm and leads..

Yeah did think that, dizzy cap and rotor arm are only few months old. Ive got a set of magnacore leads that ill try tomorrow too.

[BenF]

My money would be on the ignition too - higher boost shows up any HT weaknesses very clearly.

If it is HT - once sorted you should notice a good improvement.

[Dundee]

I've got the same problem Rob, I've changed everything as far as ignition goes bar the coil (next on the list) also waiting for a timing gun to see if it's that, a guy on mr2oc said that it could be the blitz dump valve thats causing it too. When I get to the bottom of it, I'll let you know

[super]

Could be the knock sensor doing it's job.
Check the timing, as you mention it only happens on upped boost.

[RobCrezz]

I've got the same problem Rob, I've changed everything as far as ignition goes bar the coil (next on the list) also waiting for a timing gun to see if it's that, a guy on mr2oc said that it could be the blitz dump valve thats causing it too. When I get to the bottom of it, I'll let you know

Hmm, ive got a blitz dump valve too.

Im changing my plugs when they arrive, hopefully that will sort.

[Chris.L]

Misfire only at higher boost levels (+ 0.7 bar) will also show up any compression issues that you may have as the effects of blowby will occur more so at higher boost levels.

If this is the cause of your problem droping your plug gap down from 0.8mm to 0.6mm might help.

[RobCrezz]

Misfire only at higher boost levels (+ 0.7 bar) will also show up any compression issues that you may have as the effects of blowby will occur more so at higher boost levels.

If this is the cause of your problem droping your plug gap down from 0.8mm to 0.6mm might help.

I did that a while ago and it fixed the problem, I think my plugs might just need changing now.

Might be worth me getting a compression test too I guess. anyone got one in essex?

[RobCrezz]

Gonna change the plugs tomorrow.

Anything else I can check? Changed the leads, but not king lead. rotor arm and dizzy cap are new.

[RobCrezz]

Ok, done plugs, seemed a bit smoother but still misfired under hard accelleration. Played with the settings on the profec b, brought the gain right down and the set gain and that has helped alot, hardly doing it at all at 1.05bar.

So im a bit confused now...

Could this be some sort of boost leak? or the coil/ignitor?

Not sure what to try next really!

Just to recap,
New:

Plugs
Leads (not king lead though)
Dizzy cap and rotor arm.


How low can I go with plug gaps, as last time I had similar symptoms, i gapped down to 0.7 and that totally sorted it.

[Munnsy]

i have exactly the same problem with mine at the moment,
i also have a blitz valve, was wondering what the prob with that is (leaking??)

I have yet to change all the ignition components but am on the case, but im eager to know why the blitz was a prob?

keep us posted

[RobCrezz]

i have exactly the same problem with mine at the moment,
i also have a blitz valve, was wondering what the prob with that is (leaking??)

I have yet to change all the ignition components but am on the case, but im eager to know why the blitz was a prob?

keep us posted

Ive also got the blitz valve... I wonder if that is the problem?

Is there any way to disable it? I dont have the stock valve or anything.

[RobCrezz]

Just noticed Ive got code 21 (O2 sensor), i wonder if that is to blame...

[BenF]

Is there any way to disable it? I dont have the stock valve or anything.

DIY a blanking plate ?

[BenF]

Just noticed Ive got code 21 (O2 sensor), i wonder if that is to blame...

Not the misfire under boost.

For this increasing / decreasing boost, are you amending the timing to take this into account?

I assume you're using 97 or 99 RON pump fuel ?

[RobCrezz]

Just noticed Ive got code 21 (O2 sensor), i wonder if that is to blame...

Not the misfire under boost.

For this increasing / decreasing boost, are you amending the timing to take this into account?

I assume you're using 97 or 99 RON pump fuel ?

Havent adjusted the timing, always used 99RON.

Cleared the code and hasnt come back.

When it rained, the misfire got worse but after drying out its now alot better than it was even before. I think ill check the Dizzy cap again.

Now I only get a very very small hiccup.

[BenF]

If you're increasing the boost, you definitely need to adjust the timing to suit the peak boost you're running so you don't get detonation ( see the piston at the back of the three at www.modifiedisbetter.com )

Dizzy cap - if you're getting a misfire when it is wet, definitely then sounds HT related - I'd go the whole hog and replace it all.

[RobCrezz]

If you're increasing the boost, you definitely need to adjust the timing to suit the peak boost you're running so you don't get detonation ( see the piston at the back of the three at www.modifiedisbetter.com )

Dizzy cap - if you're getting a misfire when it is wet, definitely then sounds HT related - I'd go the whole hog and replace it all.

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.

[RobCrezz]

Ok, checked my dizzy cap, looks all in good nick, you can see where rotor has been wearing it but nothing major (only few months old).

Weird thing is, I cant make it do it all the time. When I went to see Luke, we could barely make it do it at all, but later on in the day I got some much more noticable misfires when boosting.

Anyone got anything else I can check?

Havent changed the king lead, I guess that would be worth a try.