Help from VW/Seat gurus required for mystery problem

[Bora Sport]

An unusual and annoying problem has developed out of the blue. My son parked the Cupra in the carport about 2 weeks ago and it was running perfectly at the time. In fact he had been driving to Gladstone and back once a week a round trip of around 1,100k's.

When he started it up to drive it away it has developed an unusual misfire. It will run almost perfectly up to 2,400 rpm where it develops a random miss. The missing continues to about 3,500rpm when it clears and will rev cleanly to the red line. It is there every time and will even do it when free revving the engine ie not under load. It consistently starts at 2,400 rpm and you can drive it up to that point and you would not know there was a problem.

Hopefully someone will have come across this before and have an answer. Any assistance will be greatly appreciated as we have spent over 4 hours swapping bit over from my Cupra with no solution. My Vchecker could not find any trouble codes.

[ORD10]

I would be looking for an ignition HV fault like a spark plug lead or a distributor cap arcing across.
In a dark garage with the bonnet up look for blue arcing around the leads or cap or coil do it night if you have to

[Greggles4]

I agree, my cordoba did the same thing last year. changed the spark plug leads and distrubtor cap and ignition coil. problem gone after that..
I believe the igition coil was worn out and I think that was the main problem, she would get to 80km and then just couldn't get her to go any faster

[Jmac]

Yep , put the vchecker back in the tool box and start with the basics. Major problem these days people relying solely on a scanner, seen it many times in the dealerships guy scratching his head looking at a scanner saying no codes and the car misfiring. His response was the scanner says there is nothing wrong. Really???Ok customer must have been needing a car park in the dealership for the day. Take all the fancy systems away and you have an internal combustion engine that needs fuel air and a spark at the right time to run right.
Good luck
Jmac

[Bora Sport]

Thanks for the suggestions guys. As I have a second Seat I have swapped most things over from the one going well and so far no luck. My mate has had a car computer guru to have a look at the ECU and he reckons there is a problem with it. I am dubious because I had a spare non immobilisered (is that a word?) ECU. We put that in and it changed the problem. It still had a miss but lower in the rev range which made it a bit easier to drive at 80-100 kph. After I put the repaired ECU back in it if isn't right I will put a new coil in it and see what happens.

Special thanks to Gav for his assistance in scanning and other fiddling that we tried.

[h100vw]

Thanks for the suggestions guys. As I have a second Seat I have swapped most things over from the one going well and so far no luck. My mate has had a car computer guru to have a look at the ECU and he reckons there is a problem with it. I am dubious because I had a spare non immobilisered (is that a word?) ECU. We put that in and it changed the problem. It still had a miss but lower in the rev range which made it a bit easier to drive at 80-100 kph. After I put the repaired ECU back in it if isn't right I will put a new coil in it and see what happens.

Special thanks to Gav for his assistance in scanning and other fiddling that we tried.

But I never fixed it.

[Bora Sport]

Well the saga continues. I sent the ECU off to get looked at. It will not log codes even when you deliberately unplug sensors etc. I have put a new coil in, changed the distributor including cap and leads. No change. It is very annoying. My mechanic says he wishes it would just stop. Then we might know where to look.

The thing is once it gets past 3,000rpm it will pull cleanly to the red line, at ;east in 2nd and 3rd. Anyone who knows a Cupra will know what sort of speed 7,000rpm in third is and I don't have a road that I can try it in 4th or 5th.

[mikinoz]

Try changing the O2 sensor? ECU Relay?