Mk2 gti 8v PB intermittent split second misfire/judder/power-loss!

[mk2daz]

Hi all iv got a 1991 mk2 8v gti and its recently been developing a very strange misfire type judder when driving in gear.

It used to do this a while back and when it did it would completely cut out eventually, then start back up fine.  SO i changed the ignition switch and the coil and cleaned up all my ground terminals and it has been fine for the pas couple months.

Now the past couple days it has returned however this time the car does not cut out it just judders for a split second at completely random times. 

To best describe it its as thoiugh someone has cut off the power to the car for a split second and so it feels like it has misfired.  Im not convinced its timing related though as the car can run sweet for hours then this will happen randomly and the timing has been set and most of the spark related components have been changed (coil, dizzy, leads, plugs, TCI unit etc)

There has been a fair bit of rain lately so i was initially thinking there was water getting into the fusebox causing some intermittent behaviour, dropped the fusebox today and the carpets and everything in the fusebox area is bone dry, took out the scuttle and cleared any debris, dried it up and made sure sunroof drains were cleared also.  CHecked each relay and fuse for water damage but nothing that i can see.

Its almost as if the fuel supply has been cut for a split second or iv lost a spark for a split second or as i mentioned the power has been cut for a split second.

The car can run forever at idle but when its under some kind of load it seems to happen randomly

DOing my head in as use this car everyday and the fact its intermittent is very frustrating! :thumbd:

Can anyone shed any light on the situation?

Heres the car in question :



cheers, daz

[lemski]

Has ignition amp been checked? Fuel filter been changed recently? Fuel pump under car noisy
Blue temp sensor

[mk2daz]

Has ignition amp been checked? Fuel filter been changed recently? Fuel pump under car noisy
Blue temp sensor

hi mate, it's due a fuel filter so gonna do that on Wednesday when I'm off work, ignition amp has been swapped for another second hand one but I may just order a new one from eBay. The fuel pump is not noisy or anything and works as should but I'm gonna check wiring underneath when I do the filter, I done the blue temp sensor about 2 years ago when I unplug it the idle changes so I believe it to be working fine.

Cheers for your help Iv got a few things to check

Daz

[mk2daz]

Little update on the scenario:

Drove the car yesterday and again today as needed it for work, it juddered again on the way home and both on the way in and way home today. This time i managed to floor the clutch so it was crusing at idle when it hapopened again, basically the revs just blipped for the split second, no dash lights and there was some clicking from the fusebox, as if it was the relay going nuts.

The fuel pump relay is a 167 one and it was brand new fitted about a year ago. Im going to put on a new fuel filter, add some redex to clean up the injectors, check the pump wiring, maybe try a new relay, try source a good working fusebox and ensure all my vac lines are good

I think the CO should be okay as its been around 1% and below the past 3 MOTs, the ignition switch is aftermarket and was new 2 months ago but surely it wont be going already?

Getting quite frustrating trying to diagnose this

[mk2daz]

Went out to start the car today, the left headlight was on! keys were out the ign, headlight switch was off, rear light was off, it wasnt parking light either as indicators were off!

When i went to start it i got lots and lots of clicking from the fusebox, video in the link below

I think i can quite confidently say its electrical, im about to give the fusebox a thorough inspection and i also have a spare one to swap over

https://www.youtube.com/watch?v=nMagebXpytc

daz

[lemski]

Whuch relays going mad as thats where id be starting

[mk2daz]

found some water seeping in ever so slightly from the corner of the windscreen so dried it up and seal the windscreen with some vaseline for now, then i swapped over to my old fusebox (cant remeber if it was working 100% either) and il see how it goes next couple days, in the meantime im gonna get my hands on a good working fusebox, hopefully it'll be alright

[mk2daz]

well the other fusebox didn't last very long as I experienced the same clicking and juddering just there, hmmmm....

[Brighouse-gti]

Did you swap the relays from the fuse box you took out to the one you put in? Would suggest one of the relays is at fault if you did.

[mk2daz]

Did you swap the relays from the fuse box you took out to the one you put in? Would suggest one of the relays is at fault if you did.

Yeah I used the same relays, that could be true.

The thing is most of these relays (certainly the ones relating to ECU, fuel pump etc) were brand new on the car within the last 12 months! And they are all genuine VW items