(G) misfire/loss of power with my uno turbo mk1

I am experiencing an annoying misfire/loss of power with my
Mk1 turbo between 3000-4000 rpm.
If I accelerate gently and progressively I get no misfire, but if I induce harder acceleration or am going uphill, a pronounced misfire cuts in.

It sounds like it’s only firing on 3 (and sometimes only on 2), and feels like
An ignition advance problem, the car juddering with the loss of power.

If I downchange 2 gears, when this is occurring, I put the revs above 4500 rpm and power returns, although a little flaky with slight popping.

The car is normal at idle and generally smooth in lower / higher revs.

I have fitted new Bosch plugs, 8mm silicon HT leads, dissy cap and rotor,
Ignition fuel relay, power module (not Marelli).
I suspect the power module but I would like to eliminate other possibilities.
The old ignition switch fell apart and I have fitted my own starter button arrangement with an aftermarket key switch, in the centre console.
I have noticed that the key gets quite hot, and I have wondered if the fault lies with the integrity of the key switch?


I have swapped ECU and coil, so I don’t think it is those.

the LT leads off the coil were flaky at the connectors, so I have replaced those also...no difference !

The exhaust is looking a bit sooty and I reckon the fuel use is a bit heavy.

I have uprated fuel pressure regulator and in-car boost adjuster, although I
am being very careful with it whilst problem persist.

Any Ideas ?

My first thought was 'too lean', and air flow meter, in that order :-)

Particularly when you say "a little flaky with slight popping". It sounds as though you have pretty much eliminated the ignition system.

I could be wrong, of course. Although I have a Mk1 Turbo myself, I haven't had that problem (in fact I haven't had any problems; far more reliable than a standard Uno!)

So my hypothesis (trust it at your own risk ;-)) is that the airflow meter flap has taken a hammering from the high boost/off boost transitions, and has become a little sticky. I would be trying to take it apart and clean the resistance track myself. Or you could just try a known-good spare from a specialist wreckers.

As for the key getting hot, I notice that the keyswitch is a different design on my Turbo compared with standard Unos. So I wonder if there is a greater-than-usual current flow through it, perhaps due to the ECUs. What it should have is an 'ignition controlled relay' as my bigger cars have had, and you might like to rig up one yourself. Basically, just arrange it so that the keyswitch turns on a relay - well I don't need to tell you, you've obviously worked out all your wiring for the switch!

-Alex

Yeh the switch was a bugger ! could I get a circuit diagram that made sense anywhere.......I have my own neat little diagram now....
It puffing a lot of unburnt fuel smoke out the back at hi revs and interestingly
you mentioned the air intake flap...I have heard this making it's shutdown sound in amongst the misfire noises. I have a spare so I will swap that out as well.

I have checked the air hoses for integrity and they all seem fine...
I will get the mixture checked...don't know what pressure it is set at..

Ok Alex, swapped the air intake meter...It was oily as hell, but you couldn't see it from the intake side.....The car sounds proper again...going to give it a drive and see...promising anyway....

yeh, makes sense if ignition and hoses all ok...must be air/fuel problem.
fingers crossed then....

cheers mate.

Thanks for the update - let's hope it's cured. I'm keen to learn about common Turbo foibles; but another place for you to try for advice is the Turbo Collective forum (MSN groups) which has a link from http://www.turbocollective.co.uk

Cheers,
-Alex

yeh, thanks Alex...been usin turbo collective for while now.

swapped the AFM and took cover off potentiometer : slight wear (2 grooves)
about 140 000 miles worth i guess. didn't look dirty unless grooves are dirty ?

problem not cured yet though....dissy & rotor cleaned a couple of days ago and look pretty suspect now....rotor looks worn down and may be missing in midrange ? the throttle switch may be compensating mixture's setting at idle and full throttle settings ?

turbo collective boys have suggested she is running a bit lean, but everything
is so sooty only after 250 miles or so, since new plugs etc.

couldn't find any induction leaks...

keep ideas comin all...tis a good learnin experience.!!

mike