One of two faults, your boost is blowing the spark out or boost pressure on the injectors causing leaning of the fuel due to lack of pressure.
Fuel starvation is VERY dangerous on a turbo engine,
You need access to a fuel pressure gauge and do some load testing on boost.

Denso iridium plugs and Magnacore leads is a great start.

Have you check the MAF of your PuntoGT?

ave jus got some new ht leads and ive been told to get ngk iridium plugs and ive also just bought new air flow metre

done a quick test befre a went to work and i got the code 1421 injector 1 so im gunna buy 4 350cc injectors webber ones

I have a suggestion: 335cc Fiat Coupè Turbo 20v .... same impedance of original

cant get any of them just the 270cc 315cc or 350 cc

What worries me is that I can't see why a duff injector would cause a backfire. It surely has to be a valve or timing issue -- air/fuel mix entering exhaust gasses and igniting.

But why not simply have the injectors cleaned and tested? Cheaper than buying new ones. Or even swap the injectors round -- see if the fault follows the injector?

claudio's point is a good one. Injectors have 3 main characteristics -- length between O rings (try using weber Pico ones instead of Bosch ones and you'll come unstuck), flow rate, and impedence. Use ones of high impedence with an ECU designed for low impedence injectors (or vice versa) and either the ECU won't handle them correctly or you may even damage the ECU.

done another blink test the code this time is 2133 - which is thu pbv pierburg valve

and are you using the pierburg valve?? and if not is the electrical connector still attached to it? You have to leave it attached even if your not using it

yeah i am using it we disconnected the boost controller thing cos it was happening on that aswell

not sure how you check the operation of the actual valve but worth checking the wiring for continuity and the earths etc. At least chack the connections are free of dirt etc and nice and clean.

can't see how the pierburg could cause misfires etc though tbh, there's something else going on here.. How is the car at idle, does it drive properly if you go really slow and try keep off boost??

if i slowly put my foot down its lumpy but ok if i go with a nit speed it feels like cars gunna blow up

I would be getting compression test done asap, but think that has been said already - you can do it yourself, you don't have to buy a really expensive bit of kit - £15 should get you one.

And don't drive it! You could cause unrepairable damage if say the timing is out slightly.

compression test is fine 3 injectors runnin at 120 and 1 at 110 ive fitted a pierburg boost valve from my old gt3 onto gt1 and problem still persists i was speaking to a kid that knows of turbo cars and he said it could be the acctuator cos that controls your boost n ****

puntogt 94 said:

compression test is fine 3 injectors runnin at 120 and 1 at 110 ive fitted a pierburg boost valve from my old gt3 onto gt1 and problem still persists i was speaking to a kid that knows of turbo cars and he said it could be the acctuator cos that controls your boost n ****

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I don't understand the first bit. What were the compression readings and are you really running the poor car with one injector nearly 10% down?

Common faults I've dealt with on turbo cars --
1,if the car boosts and then you get a crackle sharp loss of power then let off throttle and you get a power surge with sometimes a bang, that is normally weak/faulty ignition system, (boost extinguishing the spark)
2, if you get a feeling like it's holding back/lack of power worse under more load, it's a sign of weak fuel pressure,
3, if once hot you get a hesitation/misfire feeling it can be a sign of the injector windings failing/going to open circuit due to heat, had this once on an 90's escort tried/tested everything and always came up with correct readings, until we heated the injectors one by one, a watched as the resistance of one of the windings fall and fall the hotter we got it, but it totally felt and sounded like a misfire.

Without sounding negative it sounds as though you are way over your head with the car.

Either give it to someone who knows the Punto GT like the back of their hand to get it running properly or revert the car to standard parts and start from scratch.

As soon as something like fuelling is changed - this has effects on a lot of other critical parts.

It sounds to me like the boost is set too high for the fuel setup, but this is a rough guess.

Once the boost is sensible I would be looking at replacing the AFM with another Bosch item and replacing the spark plugs, ignition leads and fuel filter.

ive changed the leads plugs cleaned afm it musnt have too much boost cos ive got it running off standard piersburg boost valve not maanual one wen u accelerate and get above 3k it pops and bangs so ive got it on low boost on the pierburg valve atm

In this case change your fuel filter and check the fuel pump for operation / pressure.

If you can rule out a fuel system problem the next step is the coil pack or ignition module if the rest of the ignition system is up to scratch!

J.R Racing said:

In this case change your fuel filter and check the fuel pump for operation / pressure.

If you can rule out a fuel system problem the next step is the coil pack or ignition module if the rest of the ignition system is up to scratch!

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also worth taking the cam cover off for a look. Mine had a worn lobe on the camshaft, it ran lumpy but really popped and held back when coming on to boost. easy to rule out but not such an easy fix.
I replaced mine with a Fiat X19 cam and its running well.