Running problem
Turbo Mini Forums

i have managed to get my 998 turbo running ok now but it will only boost to 0.3bar! driving it along it pulls realy well until the boost goes above 0.3 then it makes a very loud bang!!! it still runs afterwards but just will not stand the boost! any ideas guys? i cant seem to find anything wrong!:$

did you block off the poppet valve in the plenum?

is it a bang under bonnet or a bang out the exhaust as in a misfire?

Edited by Brett on 29th Oct, 2011.

Yes i moved to the darkside

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FPR plumbed in correctly?

Hole in gasket between carb and plenum?

Part throttle lean off pipe in good order?

In the 13's at last!.. Just

Its a misfire! I cant understand why number 1 and 2 plugs are lean and 3 and 4 are rich :s

i have just found a small crack in the inlet manifold on number 1 and 2 cylinder! :( can i use a n/a inlet manifold???

Not with the metro turbo exhaust manifold.

In the 13's at last!.. Just

Ok i have fixed the inlet manifold problem but the engine still backfires down the exhaust under boost! I have spoken 2 a garage and they think that the boost pressure is pushing fuel past an inlet valve due to a weak spring and because i am running a wasted spark system it is igniting on an exhaust stroke!?!?! Help! :(

sounds like balls to me, you'd need loads of boost to push the valve open, about 70 psi, if the spring was weak enough to be pushed open I'd think it'd valve bounce like a bastard alll the time, or would ave droped already.

Any ideas then guys? Im scratchin my head!

pushing the valve, definitely not but what about a crack in the valve seat ?

Anyway, if you get a compression test done, it will confirm this eventuality.

Rusty by nature

Have you checked everything mentioned above?

In the 13's at last!.. Just

Check and re check tappets, could be a valve not quite closing???

What's the fueling like? Could it be going seriously lean on boost? Possibly even the fuel pressure not raising with boost?

Edited by almichie on 1st Nov, 2011.

i have checked all the above and all seems ok! each cylinder is about 190 and compression! it seems to go very lean on boost!why???????
im hoping you are going to tell me something now almichie????

If it is going lean on boot it can really only be a few things:

1) Fuel pressure not rising in-line with boost. This is nothing to do with the FPR, search for T-piece trick as a good check. You say you have checked that the pressure feed to the float bowl is clear and that the gasket between the plenum and carb is not blocking it?

2) Needle profile is incorrect, not allowing sufficient fuel on boost.

3) There is a seperate carb fault, such as a sticking dash pot piston, or a blocked or restricted jet.

The blowing the valve open is hilarious.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

What are you using for ignition - dizzy or megajolt?

Has the carb gasket been changed recently? If so does it have All the correct holes in it?
Does the Plenum have the restrictor in it?

i am running a megajolt system. and i have changed all the carb gaskets today so they are all ok! i have tryed doing the 'trick' will the float bowl vent and that has helped the problem but it still misses and coughs under heavy boost!

Edited by softlad1988 on 3rd Nov, 2011.

oh and wil_h. i have done the trick and it helped so thanks! now it stays rich on boost. i have a bdd needle in the carb and the dash pot is total free! :(

In which case it must just need the needle profiling.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

ok, do you know any good rolling roads? i live in staffordshire if its any help?

You could try mikeanics in congleton.

The other option is to fit a wideband AFR gauge and di it your self. that's all I ever do.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk