Misfire

Car recentley passed MOT. Bog standard gti 8v..The tester confirmed it had a misfire.He said ignition side of things are ok,sugggested mechanical lazy valve.Got car home & done a plug chop no clues there all looked the same,light tan colour.Since I have owned it 5 yrs replaced filler neck,at least 3 fuel filters,meter head,coolant,thermostat,oil & filter,plugs dizzy cap,leads rotor arm & air filter, fuel pump and cleaned the WUR.The car idles within the limits although it misfires & a strong smell of fuel.After reading  posts and looking at haynes manual.I decided to disconnect the 5th inj.Took it for a 1hr drive up & down the A303 at average speed of 75mph ran great but still misfires when at junctions etc. holding back,hesitating…Returned home temp reading on gauge during trip was just above cold.let it run on drive while opening  garage then the needle moved and fan cut in still misfiring.My question is do I look at the thermostat & thermo switch before looking at injectors etc.?
Anyone with these symptoms in the past or pointers to a cure would be most helpful.

I don't see it being thermostat but as no one as got back to you let I'll BUMP this one!
I'm guessing members are busy with holidays etc…  

Is the misfire consistent, can you replicate it or is it random?

First thing I would do is to replace the Battery to Frame Earth, then the Frame to engine/tranny earth.

Second I would suspect the smell of fuel is because the timing isn't right or that your HV leads are suspect….

Mis-fires are usually electrical in nature and not Fuelish.

Plugs wires Cap rotor,  or clean the corrosion off the rotor and cap.

Bad Earths are the bane of these critters as well as vacuum leaks….

But 5 years and you haven't replace the Cap, Wires, Rotor, and or Plugs?  it's time.

What type of petrol are you using, Super unleaded or normal unleaded?

The 5th injector only fires up for a few seconds when the engine is very cold eg cold weather outside so I don't recon it should be firing with the weather we have been having.
 

OK guys…firstly I'm grateful for the feed back considering our busy lifestyles.
The earth wires I will look at but I did service those a couple of years back.The misfire only SEEMS to be at low revs.I am using SHELL expensive stuff 98 oct?.During the week I took out all the injectors but No.2 had what looked like rust at the top wherre it connects to the line….all the rest were 'clean'.I have put them all in a little jar & filled it with carb cleaner.. who knows it may work.So I will cocentrate on those before anything else is tried.gonna try and eliminate that first.Will update you over the W/end..Thank you all.

Good plan to investigate the injectors, I'm on my 3rd set now and they do transform the engine when working well.
There is a couple of types of injectors, if you have a rubber air hose going to the back of the head between cylinders 3 and 4 then you have the later air shroud injectors but you can fit early type with a bit of modding.
let us now how you get on and check the timing, if the cambelt has been changed and the misfire started check the static timing marks.

Hello..my plan today was to do the injector test…have I got a fuel relay? If so which one? Looking to replace the correct one with17?…

The fuel pump relay is the black one above No 17 with no number on it, it looks like an after market fuel pump relay, be careful pulling it out th fuse box as I've pulled the plastic tops of those sort of relay a couple of times.

Take the fuel pump relay out and No 17 below, turn 17 around till it fits where the fuel pump relay lives and the fuel pump will run when the ignition is on and engine not running.

Thank you for your advice squire..I had already disconnected the correct wires on the coil & had the injectors ready in some bottles.Then the rain came…I dont play with sparks & fuel inside my garage anymore.Over 5 yrs ago my MK1 mex burnt out my garage and 20% of my house….

Flawndooley said

Thank you for your advice squire..I had already disconnected the correct wires on the coil & had the injectors ready in some bottles.Then the rain came…I dont play with sparks & fuel inside my garage anymore.Over 5 yrs ago my MK1 mex burnt out my garage and 20% of my house….

OUCH.

Afternoon ladies & gents…I have done the injector test….my assumption is that fuel side of things ok??? Ready to be corrected…by a knowledgeable forum user. If I am correct where or what do I check next…

I once had a bad miss, so I replaced the wires and plugs (bosch) and it still continued.
Removing the plugs told me that one wasn't firing.
Went and got another set, this time it was worse.
2 plugs weren't firing.

Daughter got home and I swapped cap wire and plugs between my 2 cars and presto it was working.
Put on the original cap and wires misfire.  Unplugged one at a time and found the bad wire.
Put the new wires on and all was still good.

Took the 2 sets of Bosch back and got NGK plats and it loved them…….

So don't discount a bad plug or wire, or both.

Thank you Briano 1234..After sundays test,deep breath & a cup of tea.This was my next step.It sounds like an old diesel engine.I have ordered some new wires(leads)should be with me tomorrow.

 

 Evening all.Found it! Found it! Replaced all the HT leads.The culprit was the one from the coil to the dizzy.Taken positives from this episode.I now have a better knowledge of how the fuel system works,pipes, tubes & bellows checked for leaks.Not to always accept even a mechanics diagnosis.Had a good couple of days driving it around.Still need jobs doing & parts to source but thats what its all about owning classics.

This is a lesson I'm constantly telling my 19 year old son.
Slight exaggeration but if the car doesn't run don't start by ripping out the back axle! 😂

50% of the time it's something basic but finding it is an art. 👍🏼
But we're all guilty of it at one time or other! 😉😂