mysfiring nightmare
Turbo Mini Forums

I have passed the entyre past day from 8 in the morning to 4 in the night trying to solve a mysfire on my last builded turbo.
the first time I started it ,wednesday,it was running very fine, good idling, no polution, I made a little road gently to break in it a little and allow the cam and rtings to bed in; comin back at the garage some oil were flowwing under the car.......
The turbo oil return pipe had gone
I dismantled the intake manifold, the exhaust one ;
solved he oil return pipe leak,
reassembly all these yersterday morning,

at 9 the job was finished.......
and impossible to run it on boost, it mysfiring, I have tried an other fuell return line, an other fuell pump, an other fuell pressure reglator setted at 3 psi at idle, and tried 5 psi later, after we have changed the carb two times the last one have been completely striped for inspection and rebuilt, there is no leak in the pressure system between the plenum/carb fuell regulator and waste gate; I have tried two others dizzys, the same number of coils which have worked on a car just five minutes before, we have changed the ignition module; three set of plugs etc etc tc, impossible to make it run ; it seem to lack of fuell each time the turbo make a little boost; I have tried the car with the boost pressure pipe disconnected, it have the same hesitation at 3500 rpm's but allow to go further and rev up to 5500.
I'm misunderstanding or have forgotten something, but impossible to find what , I'll go back to the garage now to try an spi fuell tank and fuell lines, but I'm not conviced that the problem is here..
ideas are welcome
regards
fab

I have had a miss fire in my mini for a year. it goes away as the revs build up.

I finally solved it last week. My 1989 mini has a coil voltage of 9v, and the metro ignition module needs 12v. So i have now bypassed the mini wire and run my own wire from the fuse box.

Have you replaced the plenum to carb gasket?
Some gaskets do not have a hole punched in them that pressurise the float chamber, so the car will never run on boost.

Will feel like lack of fuel when driving.

Fab- connect a small (lamp from the speedo is a good example) across the coil. This will rule out the ignition once and for all.

Aside fromn that, check the fuel pressure rises with boost pressure.
Confirm you have the carb pipes round the right way (mistakes happen). The rearmost pipe is fuel in!
If fuel pressure DOES rise, then put your pressure gauge on the 'anti run on' pipe on the carb (the one normally blocked off). This should also show an increase in pressure proportional to boost. If it doesn't , then you don't have the correct gasket between the carb and plenum, or the internal port is blocked. Whichever one, this can be by-passed by connecting the 'anti run on' pipe straight into the pipe from plenum to fuel regulator with a 'Tee piece'.
I have my mini connected up like this at the moment - i could find NOTHING wrong when i last pulled it apart with a simialr fueling problem!

Hope that helps,
D

I was certainly very tired at this moment, sometimes it is better to let the problem as it is, go back home drink a bear eat soething and have a good night, then solve the problem,
yesterday morning after only a short slip as the car was to be delivered today.
so I come back to the garage, took an spi fuell tank ( as I was ok with my fuell /pressure lines checked many times before to post), and before to continu changing all the parts of the cars ; start to look at what was the real problem , a big lean each time the boost come , the pressure line were ok and the float chamber was connected with the plenum by the vent pipe; the pressure in the fuell line were ok and the pressure rised when some pressure signal was given to the regulator;
decided trying to remove the balance/leaning pipe and plug it .
and:
broooapp broapp ; broooooooooaaaapppppshiiiiiiiiiiiiiiiiiii; rev up to 6500 rpms boost seted at 10 psi's , the bdd needle wasn't perfect so tried a montego one, and the fuelling , reving , boost are strong......

all this work for a little pice of plactic which was leaking.
my comment: I will never assume that this pipe is ok, and will remove / change it each time I will touch a turbo engine

fab

Well, there you go - We've all been caught out with this pipe at some time or other!
The original 'plastic' one is definately asking for trouble.
I just 'assumed' you had already checked this over, as it is the most common source of problems on these carbs...

At least it's done!

Like TurboDave mentioned it is THE main problem with turbo HIF?s. Get rid of it.

Jukka

hi guys

ive had virtually the same problem as fab after building my engine again with my new half engine.

ive been hanging on to see what's suggested to fab before posting my own Question!

can someone just confirm which one the balance/leaning pipe is? is it the short hose that loops out the carb and then back in again?
if so do both holes need to be plugged?

cheers for the help.

You can just replace it with a new piece of decent fuel hose, or block it off.
If you choose the latter, your economy does drop a little, but the stability of your mixture between on/off boost is a lot better.
Credit where it's due though - It was Jukka who confirmed this to me a few years ago!

D

Cheers guys, i'll give it a go.

Wes.

Which pipe is this...

any chance of a photo?

Alex

AlexF

its the pipe that comes out of the top of the carb and back into the side

Team Racing

The very top one of the pipes on the carb, its the one that loops as everybody has said

Its the shiney black one

Edited by iain on 15th Mar, 2004.

So is it just the case that if it leaks it will perform badly or could it become blocked?

I have trouble low down the rev range with it spluttering its way to about 2500rpm then appears to be fine!

Ill check this straight away!

I have a standard metro turbo running the normal 5psi boost.
The problem started a few weeks back. the car runs fine from a cold start but from a hot start it misfires over 2500rpm. It started as a lack of power then a misfire and now it will not fire at all above 2500rpm! its still perfext from a cold start though. One my foot slipped and i stalled it, on starting it a second later again the problem occured stands on its nose at 2500rpm.

Any ideas?

check everything mentioned above...

turbo 16v k-series 11.9@118.9 :)

Denis O'Brien.

When you say that blocking off the pipes you just do like with the anti run on pipe? bolt in the end of a pipe with a jubilee clip on it?

My pipe appears fine so is it worth me blocking it off any way? The fuel economy has never been good is it noticable how much worse it gets?

My understanding was this pipe pressurised the float chamber so that the carb worked like a normally aspirated barb just everything is at a higher pressure. Is this correct and if so am I likely to wreck anything by blocking these points up?

yes bolt the end of the pipe and clamp it, or take sometning which go in the pipe and bock it, then put it at his palce; this pipe isn't used to pressuride , the float chamber, it is leaning the mixture at part throttle , ie stady slow (60/70) speed on the motorway,
the float chamber is pressurised by tunnels in the carb matched to the plenum, and this allow the carb to work as a na one, but make it boost sensitive as the tunnels are before the pressure is reduced by the restrictor ring.
cheers
fab