misfire under boost
Turbo Mini Forums

Well not like a normal water in the dizzy misfire.

its a difficult one to explain so bear with me.

When i floor it it feels like the engine is holding back, then when the boost builds up as soon as it gets to about 5psi it's like the whole engine just cuts out and theres a bang which kinda sounds like its popping back through the carb. if you keep your foot down then it just starts spluttering and will hardly accelerate.

But if you just lightly push the pedal down a bit you can take it up to 6k no prolems.

Any idea's what it could be? cant afford to go on the rollers till the end of the month, it feels like its too rich and is flooding or something. i'm using 3 in 1 in the dashpot at the minute, you reckon its could be too thin, or is not likely to be something that simple?

mines like this too, i think its that bi metal strip

i changed from 3in1 to 20w50, but it made no difference

fitted the megajolt and no difference too

yup, just swapped to 20W50 aswell and its still the same.

been having a bit of a play though and its fine with the bleed valve closed running about 2psi (my actuators a bit weak) i can give it WOT and it just goes.

If i try to bleed some off to raise the boost with WOT then it starts popping and spluttering and i get a strong smell of fuel.

Its really confusing me now, it just started happening out of the blue, was fine at avon park.

i've checked for split pipes and leaks etc and its all fine. its definately the right plenum gasket aswell.

Might give the T piece trick a try seeing as its a miracle cure lol

Have you checked your fuel pressure to make sure that is OK?

just about to go and give it a check.

Might drop a standard nedle in it for now to give that try, seeing as spamspeed was the last one to tune it.....

Change the plugs.........

they're new plugs dude, put fresh ones in after the rebuild. checked them and they're looking a good colour aswell as per haynes.

fuel pressure is fine at 3.6psi aswell.

put a standard bdd needle in aswell and its still the same.


I'm at an RR shootout tomorrow so i might find out whats happening then. other than that it'll be off to a decent RR operator after payday.

Edited by Nick on 14th Oct, 2005.

just tried running it with the dump valve off and plugged up and still no improvement. Still getting the smell of fuel though when you back off the gas.

I think i might aswell rebuild my spare carb and give that a bash after payday.

Could it be ignition related?

Have you got a spare known good ign module/dizzy/coil you could try?

no i haven't at the minute....although megajolt is looking like a good idea come payday (its gonna be anotehr expensive month for me!)

Is fuel pressure rising with boost properly?

thats next on the list, just been digging out a T piece and a length of fuel hose.


I know its going to end up being something stupid, i can feel it. grrrr

jimmys did this for the day i had it when i drove it to the docks exactly the same problem, but i never tried it with the bleed valve closed.
anyway he sent it to america like that and the guy said it was fine when he got it so a month on a container and your problem should be fine lol j/k
i read a bit later on that there something about the float bowl that causes it but it was a while ago i read it so cant remeber much, sorry. might have been the stop valve type thing?? lol

Dan

the only thing that made a slight difference on mine, is as jon says changing the plugs

i dont know if this fixed it, or if its just coinsidence as it doesnt always do it

on mine it always does it at 5 (i think) psi, so i was wondering if it is spark plug starting to fail as the get old, thats another thought of mine

again another is a faulty regulator

but im lazy and havent really investigated it too much

im running ngk bpr7es, what do you others run

sounds like float valve is leaking when pressure is building.

try blowing down the fuel feed ipe with a air line then try again.

if not fit gauge inline with fuel feed take off dash pot then screw in fuel regulator screw and see if you get any fuel coming out of main jet if so float needle is leaking buy i would sugest it will get to about 7 or 8 psi and it starts to leak hense smell of fuel when booting.

always looking for them bigger bunches of bannanas

Its a good theory from hogster, worth checking out.

Needle valve and seat are cheap and easy to change as well, also could just be some shit blocked in there?

cheers, i shall try it today

well i've just got back from the rollers and its a little better now.

Changed the plugs this morning cos i'd dropped a cylinder at tickover but it made no difference.

Then i fired it up with the front off and saw a cloud of smoke come out between the inlet and head. Gasket was shagged somehow so i replaced that at the side of the road while waiting for the RR which cured my tickover misfire.

Then i looked at the ignition again and noticed my mate had put the fooking leads on the wrong way round when we were fitting the engine last thursday night at 2am! it was firing 1-4-3-2!!!

told you it'd be something fooking simple!

Got it on the rollers and it still misfires under boost but thats cos its overfuelling massively, only made 103 banana's @7psi and the graph looked like everest!


Still gonna rebuild my carb, and fit megajolt, then i can get it set up properly. this chap in brum seems quite good though. really clean place and all the top notch equipment, plus he's got a turbo in there at the minute which is always a good sign :)


Cheers for all the help dudes :)

Metro turbo weekend driver,Mini turbo in the making again!

I had the same, changed coil, and PURRfect. :)

put little cable ties on your leads so you know which plug they go on. i know its not hard to work out wear they go but when there numbered you dont even have to fink a bout it, just make sure your mate knows which side number one is

no longer a series, but still 1.3 turbo.