172 cup developed a missfire

[williams-ant]

I changed plugs for ngk and fitted new OEM leads and car was running fine.

Parked up and just fired it up to go for a drive and it was misfiring from the outset with engine light flashing and going constant. Plugged in my obd and got 300 random/multiple missfire.

Unplugged injectors one by one and 3 and 4 make zero difference.

Any ideas? Is it likely that 2 injectors have gone faulty at exactly the same time??? Seems a bit odd!

 

[White16valver]

Are all the leads definitely fitted firmly to the plugs?

I was going to ask if the right leads were on the right plugs but you've said it did run earlier lol


It's not got wet or anything?

 

[Brigsy]

Flashing eml is usually injector, if leads are all on OK its prob coincidence and one has failed, however check the leads are not crushed by the plenum. Resistance test the injectors if you are unsure which one is at fault.

 

[williams-ant]

Flashing eml is usually injector, if leads are all on OK its prob coincidence and one has failed, however check the leads are not crushed by the plenum. Resistance test the injectors if you are unsure which one is at fault.

Thanks, though as above removing the plug from both 3 and 4 injectors didn’t change anything at all

 

[williams-ant]

Are all the leads definitely fitted firmly to the plugs?

I was going to ask if the right leads were on the right plugs but you've said it did run earlier lol


It's not got wet or anything?

Yes all fitted great, again it would be odd for 2 to have become loose..

 

[Une_Baguette]

Do you have a multimeter handy? My coil pack went yesterday so I tested it and pretty much confirmed the coil pack was to blame.

 

[Brigsy]

Thanks, though as above removing the plug from both 3 and 4 injectors didn’t change anything at all

I found it hard to tell which cylinder was off as mine was missing like f**k when injector went. Itll be spark or fuel related if its been running ok, coil pack might have given up

 

[Ianboom]

1 & 4, 2 & 3 fire together, so it doesn't look like the coil is faulty.
Could be leads not fitted correctly or a wiring fault to the 2 injectors, surprised it ran with 2 faulty injectors though.

 

[williams-ant]

Update, fitted new injectors to 3 & 4 and cured 3 but not 4.

So 4 still misfiring and pulling the injector harness for 4 doesn’t make a difference

 

[william84]

Try cleaning plugs maybe full of sh*t with the faulty injectors ?
I still had misfire after injector change and it turned out to be my spark plug was full of sh*t cleaned and cured it.

 

[Brigsy]

Check the injector wiring with a noid light if nothing is happening on number 4. If it checks out ok, itll be spark, or compression test time. If wiring does not check out, trace it until it you find the break.

 

[williams-ant]

I switched the harnesses over between injectors and the wiring it fine.. might just be a coil pack, dodgy lead or plug or something.
Just a funny one with there being 2 separate faults at the same time

 

[william84]

Did you try and clean your spark plugs?

 

[Ianboom]

How did you swap the harness between injectors?
Thought they all pulsed at different times?

 

[williams-ant]

I plugged 3 on to injector 2 and it ran. I only used to gauge if it was firing the pot, but then disconnecting it to see if there was any change in behaviour

 

[william84]

it's the simple things that get over looked. I've been where you have been.
A full day scratching my head after replacing my faulty injector asking why it was still misfiring. After checking leads coil wires it turned out to be the most simple thing. A dirty spark plug. Just to add my injector that was removed was faulty hence the build up on spark plug.

 

[williams-ant]

it's the simple things that get over looked. I've been where you have been.
A full day scratching my head after replacing my faulty injector asking why it was still misfiring. After checking leads coil wires it turned out to be the most simple thing. A dirty spark plug. Just to add my injector that was removed was faulty hence the build up on spark plug.

I’ll be trying the electrics side through the week hopefully and see what’s what there. I’ll post up my findings!