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During change from first to second gear (after full throttle) car makes small explosion in exhaust system and when engine is properly heated, starts to shut down. Obviously there is plenty of fuel in system. That can be seen also during acceleration, exhaust gases are black.

Did someone experienced this kind of problem?

Lambda probe is new, AFM works like clock and it is on factory settings. Sparkplugs are new (ngk platinium bpr6f), cops are working good and there are no leaks on injectors. Engine temperature sensor is in factory readings. Car runs on modified old type plenum ported to 43mm, along with intake runners. Exhaust system is also custom made and runs on two free flow silencers.

I'm running out of ideas.. Where else to look for eventual solution of problem? Can this be related to old type of plenum?

Nothing wrong with plenum. Sounds like cam overlap. I get it on start up on my one car that has huge overlap. Its not typical of a gotech system as its on my haltec system. Injectors dont need to leak but maybe chech them on injectors machine as maybe one of them is overfueling chronically. I was playing o n ijector machine other day testing all my injectors and its not just a simple leak test. There are four tests you carry out. one of them being leak. With this machine you can set the rpm you want to test at etc. I ended up throwing away three injectors, the others were cleaned on the machine using a frequency agitator.
Put on tdc and check timing marks on back cams. Process elimination.

Timing is ok, checked it twice; once during cam belt change and once after 3000 kms. Strange thing is that this explosion/choking thing happens only when engine is almost fully warm, but all components that could affect that seems to be on factory measures...

I'll test flow injectors - they were only cleaned but not tested.
Thank you for suggestion!

ECU disregards Lambda at WOT, check fuel pressure.

a friend of mine experienced a similar behaviour: he had fuel pressure falling on WOT after 4000rpm (Fuel pump tired)...

Mike, you've found it! Did all measuring and totally forgot about fuel pressure - there was the problem. FPR died and I measured 3.1 - 3.2 bar on rail! In a day or two I'll test the car, but even at the first look at slider on maf there's a change in behavior. Now it hits max value on full throttle, which wasn't the case before.

With the fuel pressure falling off is that a problem with the pump, the return regulator or something else??

Fuel pressure is directly proportional to manifold pressure.
As manifold pressure drops so does the fuel rail pressure.

This is to maintain constant flow rates through the injectors as flow is equal to the square root of delta pressure.

With manifold at atmosphere normal fuel pressure should, for most cars, be around 3 bar (45psi) and could (if you're going foot off at 100mph down a steep hill in first gear) drop as low as 2bar (30psi).

Yeah thats the normal progression of things, bcal....I wanted to know about the reason for the problem that killaz was having.

It's normal thing for fpr to fail, it stands "closed" and gives max pressure (and maybe bit higher) for wich is calibrated - to clear things, measuring was done at idle, where pressure should be from 2.6-2.8 bar, I had 3.2 bar.

Fuel pump makes about ~4.5 bar in system, so it doesn't suffer this malfunction.