1995 S420 spark plug #8 not firing at all.

[Patrick 95]

Just finished replacing spark plugs, wires, dist. cap, rotors. All original Bosch quality. Reason to replace was that the car was idling rough at idle and sluggish uphill performance. Fired her up hoping all is fine and has a very slight shake at idle (600 rpm). Checked spark on all 8 wires using the strobe timing light and discovered spark plug #8 had no spark at all. I did a resistance check on the #8 wire and showed 2K resistance, good. I replaced the spark plug for another of same ( I ordered 10 of them ) still no spark. I swapped wire form the right bank cylinder #4, same story, no spark. I can only think of 2 things. Can the coil be bad as causing one particular plug to not fire at all and how can I check it with a ohmeter ? or 2, can a bad EZL cause same ?
Any help would be welcome and appreciated.

 

[gsxr]

have you swapped caps left to right? I had a defective Bosch cap out of the box years ago... rare, but it can happen.

Never heard of an EZL only failing on a single cylinder.

 

[TerryA]

IMOP it has to be the Dist Cap! I would be looking hard at that cap. Maybe where the wire plugs into the cap there is something insulating the spark from passing. Maybe the plastic in that particular hole is covering the brass somehow.

Put the old cap back on and check the spark again.

 

[Patrick 95]

Did not have a chance check the car yesterday as it was pouring rain all day, but this morning I managed to take out the cap and did a resistance check on each terminal and they all measured consistently at 1k ohms. The wire to the plug is checked at 2k ohm like all the others. The wires, caps and rotors are new. I tried the old cap back on and still got that #8 not firing up at all. I will check and substitute another new plug F8DC4 as I have several of them on hand after which I will swap new the caps and let you know what happens.

 

[Patrick 95]

OK, I have found the problem. When I was using the strobe light I was looking just for the activity in plug #8 as that was the first one I tried it on an I was assuming that was the ONLY plug that was NOT firing. I did not even bother to check all the plugs as the engine was running without stalling but rather shakey. Today I thought that maybe other plugs were not firing as well, so surprise, 3 other plugs were not lighting up as well.
I checked one of the coils and was flashing much faster than the firing plugs. But as soon as I put the strobe on the OTHER coil, nothing.
Yes indeed, the this V8 car can run on only 4 cylinders WITHOUT stalling.
The defective coil turned out to be the one on the right as seen from the front of the car.

 

[Patrick 95]

I was thinking if there is perhaps a fuse/relay that supplies voltage to the primary of the coil before I go purchase a new coil. How does one check if a coil is good ?

 

[gsxr]

I was thinking if there is perhaps a fuse/relay that supplies voltage to the primary of the coil before I go purchase a new coil.

Nope. It's either the EZL or the coil.

How does one check if a coil is good ?

Swap coils temporarily and see if the problem moves to the opposite cap. If so, the coil is bad. If not, the EZL is probably bad.

 

[Patrick 95]

That was it ! the coil. one coil was bad. I recieved 2 new coils this morning ( Bosch ) brand new. Installed both new ones and she fired up on all 8. I was worried about that EZL but that was not the case here. Thanks everyone for the tips.