1.8 (DX engine) fails when hot

And that's it. I think it works only in 3 cilinders when the car is already warm. It's so hard to drive that is like jumpin'!!

Could it be head gasket and water on spark plugs? Could it be K-jetronic?

Sometimes it gets hard to start also Suggestions where to start?

Thanks!

How old is the ignition side of things, eg spark plugs, HT leads, dissy cap, rotor arm?

What car do you have a tin top or cabriolet and what year?

Are you losing/using and coolant?

Does the fuel pump make more noise when it's jumping down the road?

Cabby from 1985.

New spark plugs and new gas filter.

The car is quite new to me, so the rest i don't know yet

Test all HV leads for Spark.
Take Photos of the Engine, and Diz area and post them.

Model and Year of your car is also nice to know, yes with all the Frankensteining of these guys since they were oem, all things are possible.  

So not starting when hot is different on different years and engines…. ie: Coil, FPR, WUR, 5th injector, Vapor Lock…. Bad ICM or Dizzy HV lead.  I had one car that had 1 bad new out of the box plug (bosch), and my original issue was a bad HV lead….  Try having 2 sets of Bosch NEW plugs with bad plugs in each…. then originally having a bad HV lead so you were really running on one cylinder….

I was glad to have a running Cabriolet as a Spare as when it showed up I changed all over and my bad car ran great.  So I was able to tell the bad plugs as they never fired, but the HV leads I found the bad one…..

So as I stated knowing the Year, Model, and CIS, Carbed or Digifant is all relative to me.  

Check fuel system pressure or co2 mixture ? 

yo said

Check fuel system pressure or co2 mixture ? 

Hard to see it @ home!

Why not take a plug spanner with you and when it misbehaves have a look at the plugs, you should be able to tell if it's only one cylinder, all of them, and if it's rich, weak, or neither. If it's one cylionder try swopping things around, leads, plugs, and if you can the fuel lines but only do one swop at  a time.

What if i tell you guys that when the car starts to fail, if i turn off engine and imediatlly turn it on, everything is OK for 500 ou 1000 meters??

Does it helps? Then it starts to fail again, like if it is working on 3 cylinders or fuel is not gettin' there!

And again, and again….!

Is there a loud whine from the rear wheel arch area?

CIS or Carbed?

I would also think a bad in-tank pump, and or a bad Fuel pump relay . as when the car cools off, it works well?

Fuel pump relays are notorious over here for getting cold solder joints, so when they get toasty 20 minutes or so they fail as the solder doesn't make good connection, cools off reconnects, and runs till it heats up again.  

In-tank pump can do the same thing as they stop up, causing the primary pump to over heat and fail,,, cools off for a while and starts to work…. The think here is that when the main pump starts to over work or heat up, it complains rather loudly about being over worked hence the whine.

In tank pump is brand new! Relay is an option!

Look at the guide for Fuel pump relays on www.cabby-info.com as there are a lot of iffy ones out there.

Have feel of the fuel pump relay, does it get hot when things start to go wrong?

Might be worth carefully removing the relay (easy to pull the plastic top off) and give the connection a good clean.

Thanks for the help guys!

We're talking about relay nr2, right?

Yes fuel relay in slot 2.

What number does it have on it if original VW?

You can try a different relay in the slot, 17, 18 or 100 to see if that works better?

more info here

https://vwgolfmk1.org.uk/forum/index.php?page=topicview&id=technical%2Ffuel-systems-and_3%2Ffuel-pump-relay

The number of the relay is also 2

Bit more info on relays etc here..

View topic: Fuze box wiring layout . Relay locations . Fuze locations . - The Mk1 Golf Owners Club

No 2 relay is early fuel pump relay without rev limiter built in according to info above.

The threads a is bit hard to find a fuse is spelt with a Z..