Technical punto mk1 elx 16v 98 firing on 3 cylinders

[wpisme823]

Hi all,
After a long process of diagnosing the misfire I got new plugs and new coils on my punto to find that 3 of the plugs are black and one is completly clean. can smell petrol on the plug though.

I have also changed the HT leads and rotated them around to see if that solved the problem but with no success.


anybody have any idea what this could be caused by?


thanks

Will

 

[thelad]

Try takeing the spark plug out, put the HT lead on and hold the plug onto the metal rocker cover and check its sparking, use some pliers and thick gloves to hold the plug as it make give you a shock that will make you jump.

 

[Ziggy122]

well its simple - with the engine running
Pull a Plugs HT lead off - if the misfire gets worse = Not that cylinder
Pull a HT off - it dont make a difference = That cylinder

As for 3 black and 1 clean = Potential Problems like compression and Injectors

Compression Test - Dry then Wet

ziggy

 

[wpisme823]

cheers yeah ive done the spark test and thats fine. the misfire stays the same if that plug is disconnected.

i know it sounds pretty obvious but i just wanted to double check as ive wasted a lot of money on things which were not actually the solution!

ill check the injectors today. Could it simply be a case of it being broken or clogged?

as for compression im going to struggle to test it without buying a compression testing kit as i cant take the car anywhere/dont want to ruin the new cat!


thanks for the help

 

[DaveMcT]

Its most likely not the injector - the clue's in the fuel soaked spark plug.
Try swapping the plug and see if the problem moves.

Compression testers are about £15 on ebay.

 

[DaveMcT]

Its most likely not the injector - the clue's in the fuel soaked spark plug.
Try swapping the plug and see if the problem moves.

Compression testers are about £15 on ebay.

Bear in mind the plugs are fired in pairs 1 & 4 and 2 & 3. Dont disconnect both plugs on the same pair as you risk the back emf blowing the ECU coil driver.

 

[wpisme823]

thanks, yeah theres definetly fuel on the plug.

theres no obvious sign of a head gasket failure at least (no water in oil or water loss) but if its not that could it be the valves? or inlet manifold gasket maybe?

 

[wpisme823]

also yeh ill get hold of a compression tester asap

 

[DaveMcT]

If the petrol soaked plug is clean it might be the head gasket. Steam blasts the carbon off. Compression test will prove it.