Cylinders 1-4 Not Firing

The other day I lost 1/2 the engine when cylinders 1-4 were not firing. Fortunately I was near home when it occurred so the cat did not get too hot before I limped home. Today while driving the same thing occurred (after about the same amount of time). I have deduced that the problem is post coil. I took a piece of spark plug lead and attached it to a spark plug with the other end inserted in the coil output terminal where the lead that normally would go to the distributor goes. Started engine and noted that the plug was firing just fine. Therefore I have to conclude the problem lies in the distributor and is either the rotor or the distributor cap. It could also be the lead from the coil to the distributor.

Does anyone know what resistance should I measure across the rotor? I'd rather not open the rear distributor to check its resistance. Due the cost of these items, I don't want to use brute force and purchase both the cap and rotor if only one of them is bad. I will check the cap under bright light and an magnifying glass but sometimes cracks are difficult to see. Thanks in advance for any assistance.

 

You really can't make a direct resistance measurement as the cap+rotor is an "air gap" device where the spark jumps the air space of a few thousanths of an inch. The more meaningful measurement would be the voltage drop across the cap-to-rotor gap during operation (but, if this is getting marginal, it usually results in occasional misfires rather than having a whole bank blink in and out so I wouldn't go there yet).

I wouldn't be too shy here. It's not complicated, the screws are captive, and it only goes on one-way -- besides, it's the only way that you can check the condition of the carbon button. With the cap removed, you can also make a resistance measurement from the (unplugged) coil wire terminal that goes into the coil -to- the button. But have a look -- more often than not, the problem is so obvious that it's a miracle the darn thing was mostly running so well .

 

Had similar problem recently. After many frustrating weeks, expense (new coils plug wires etc) and false leads it turned out to be the wire from the coil to the distributor. (internally broken) Make a new jumper wire to go direct from the coil to the distributor and try again.

 

Thanks Steve and marankie. I'll take a look at it very soon. Will report what I find.

 

I had just such a problem with a customers 308 QV yesterday. A small amount of oil leakage into the rear distributor along with some moisture fouled things just enough so it occasionally would quit firing. I cleaned it up and polished the cap and rotor contacts and he was good to go. Will replace the distributor seal another day.

 

Dear Ferraristi,

This happened on my Testarossa a few years ago.....except it was 1-"6"


Since your coil ( you say so ) is firing, the lead going to the coil may be bad.

OK, but before you replace the lead, try this:

Open the distributer cap, under the carbon button ( just pull it straight out slowly ) you will see a screw ( pin ) that holds the wire. It holds and passes the current by piercing the wire.

In my TR, the wire filament around the piercing pin just sort of wore away. I snipped a small bit of wire off beyond the old pin hole and re pierced the wire and screwed it down....put back the original carbon button and all was good.


Shamile

Freeze....Miami Vice !

 

I've been away for the past several days - just got back. Plan to look into it this week. Will report what I find. Thanks.

 

my moneys on a bad crank sensor

 

The engine is running on all cylinders. I took it out for a drive this morning. Yesterday I removed the distributor and checked the resistance from the coil end of the coil wire to the spring loaded button in the center of the inside of the distributor cap. At times the resistance would go infinite when button was pressed. I removed the button/spring and cleaned out the hole that the assembly rides in. It was rather dirty. I also removed the set screw and removed the coil wire. I cut the coil wire where it was pierced by the set screw and reinstalled after checking its resistance. Then I checked the resistance to the button again. This time the resistance remained nearly constant as the button moved smoothly in its spring loaded path. I also put graphite under the button. Lastly, the top of the rotor was cleaned. It was quite dirty as well. Rotor showed little resistance and was not shorted out to the cam shaft so I have to assume it is ok.

In doing all this, I noticed that I had used a thicker distributor gasket that I cut myself when I changed the cam belts this spring. I also had used the thicker stuff for the cam cover but it was too thick and allowed oil to get past the two o-rings. I eventually purchased the correct cam cover gaskets which sealed up the cam cover properly but left the gasket at the distributor. It is considerably thicker than the quite thin factory gasket. It's thickness reduced the loading on the springy button in the distributor. Compounding the problem is the fact that the thicker gasket material was also used between the seal plate and block/cam cover. So now I have two layers of gaskets that are too thick. They serve to lessen the load on the distributor button. If the problem occurs again, I'll replace both gaskets.

 

Dear Ferraristi,

What was that?

Thanks to.......?

Ahem Ahem cough cough



Shamile

Freeze.....Miami Vice !

 

Yes, Shamile, it looks like your solution combined by my thicker gaskets was the winner. Yesterday I purchased the thinner gasket material. Plan to cut new gaskets this morning. That will put more load on the distributor button.

Thanks all for the suggestions, everyone.