Mk1 gti cabrio won't rev properly over 4000 rpm

Has anybody got any ideas why my 1991 mk1 golf gti cabrio won't drive properly over 4000 rpm,it revs ok at standstill,but when driving and accelerating it starts cutting out at about 4000 rpm,and a relay starts to click when it misbehaves,has anyone any idea what could be wrong.i have already fitted a new fuel pump relay,new filler neck and fuel filter !!
help please!

Hi mate just out of interest what was the filler neck like before you replaced it, if the condition was overly bad you may have done the damage to the metering head . Otherwise could be air leak in the vacuum system  or even something as simple as a bad spark plug / lead just a process of elimination

If you post in the right section you may get more help, the cabriolet GTi is a large block injection engine not a small block carb…….

I'll move it now!

Your Moderator Team. 

does the rev counter go dappy at the same time, if so it could be dizzy fault or a problem with the tci unit or spark wiring. the relay requires a rev counter feed to work so if this is being lost it'll start clicking.

as a short term test swap the 17/18 relay to the fuel pump slot, if car runs faultlessly and rev counter reeds fine you need a fuel relay. if not check the spark system as above

Rev counter doesn't  drop  when problem happens,but a relay does start clicking when it happens,drove it again tonight,at approx 4000 revs when accelerating there is a sudden power drop and car won't go anymore unless I back off the throttle pedal slightly,it then drives ok again until I take the revs high again.have now tried another coil,the fuel pump relay is new.any other ideas please ?

Is the new fuel pump relay a genuine VW one?
If not a VW one try putting the relay below 17 or 18 in place of the fuel pump relay and try that, just because it's a new relay does not mean it works as the cheaper ones from GSF, ebay etc sell seem very poor quality. 

No,not gen vw relay,will try relay swap over the weekend,it feels as though it's got a rev limiter rotor arm ,but it hasn't,but that's what the symptoms feel like.

The rev limiter on later cars works via the relay so that could be your problem?
Fingers crossed it's an easy fix of just replacing the relay.

Swapped relays,as you suggested,problem sorted!!,so I then bypassed fuel pump relay by putting a piece of wire into large contacts on fuse box where fuel pump relay fits,drove it ,still ok.brilliant !!
euro car parts replaced the relay for another one today,drove it tonight with the new relay and the problems back again!!the make of the relay is KAE , made in Germany,is this one of the makes you say are poor quality?what are your thoughts please?thanks

maybe clean up the terminals on the coil, oh and while there check wiring the right way round. the black wires should go to coil + or 15, the red/black and green to - or 1

have a good look at the relay socket too, the smaller spade terminal for the rev trigger may be a bit grotty or loose

Thanks to those who posted before on this!
My original "D" suffix fuel pump relay stopped energising and switching (fuel pump would work when I used my finger to actuate switch) so I knew I needed a new relay.  I think it was the original as built part amazingly and lasted 40 years!  Vw branding but manufactured by Siemens. Anyway…
I bought an Automega replacement relay listed as being suffix "F" type but it came without anything printed on it so tried it and it made the fuel pump work so thought that was job done. 
Some weeks/months later when back on the road and MOTd I noticed it wouldn't rev past 4000rpm so started worrying about all sorts and checked fuel tank for crud (clean!) and all lines for kinks/leaks (none),  replaced fuel filter with Bosch quality and cleaned all the airbox, meter flap, throttle etc and then started searching on here and re checked the relay and noticed that the small pin was labelled 1 rather than 31b like the old one. So I wasn't sent an "F". 
Bought a new VAG branded replacement "F" type and resolved the problem!  Happy days. 
Thanks again for the expert forum resource and those posting!