I have a '94 Skoda Forman.  Recently the engine has developed a misfire which I traced to the #4 cylinder. I replaced the #4 plug wire and plug, and the motor ran perfect for about an hour or so, and then began to misfire again. I replaced all the plugs, plug wires, distributor cap and rotor. No improvement. I performed a compression test per the factory service manual instructions, and all cylinders are within spec. No broken valve springs and the valve lash is spot-on.

I need to test the distributor. Is there a way to do this on the bench ??  I suspect that there is a problem with the reluctor's #4 leg, but do not know how to test this. I have an oscilloscope , if that will help.   If the distributor tests good, what am I missing ?? I don't want to tear down the cylinder head unless I absolutely have to. Thanks for any help.

 

- JAMES

Edited 30 July, 20196 yr by JAMES399

Is your car on carburetor or injection?

 

Also how the issue started? Gradually? Sudden? Try to give more information as you know all about your car.

Edited 30 July, 20196 yr by RicardoM

The problem appeared suddenly. Engine is carbureted. Another thing ... When I connected my inductive timing light to plug wires 1, 2, & 3, the light fired normally on those cylinders. On #4, the light was flashing all-over the place. I am going to Medellin tomorrow. Maybe I can find a distributor.

 

-  JAMES 

@JAMES399 - I presume this is a "Kettering arc" system, whether with a coil or electronics providing the sparks? If so, then I'd start by examining the distributor cap both inside and outside. If there are any cracks in it, it's scrap; replace it. Otherwise, clean it inside and outside, and clean the #4 plug lead.

 

That might cure the issue(s); otherwise my next step would be to replace the spark plug leads.

On 31/07/2019 at 04:55, JAMES399 said:

I am going to Medellin tomorrow. Maybe I can find a distributor.

Judging by your avatar, I am sure you will find 😎

UPDATE:  I was unable to find what I considered a "decent" used distributor for my Forman. So, I got out my jeweler's eyepiece and checked out my distributor as best I could. I disassembled it down to the advance weights, and blew it out with an air gun, cleaned everything, and reassembled it.  Installed it back on the engine, fired it up and it ran perfectly. My wife has been driving it every day for a week with no problems. I knew that the problem was somewhere in the distributor, yet I have no idea what I did that fixed the misfire. But ... it's good to go and that's the bottom line.

 

- JAMES 

I suppose you know that the distributor has to be lubricated in some specific places once in a while.

Also there is an air gap that has to be set between rotor star and each of the 4 posts of the rotating plate.

My guess is that something went back to right place or correct operation simply by disassembling/assembling it.