For an engine to run smoothly you need three things, alll at the correct times - spark, fuel, and compression. I seem to remember you ran a compression test and although not stellar they were pretty good, so we can rule that out. I had a D2 once with only 80psi compression on one cylinder, ran smooth as butter but would throw a code. Not a flashing code, just lit the lamp. On the compression front if it jumped time it would be low on compression which it is not.

On the fuel side, D2 injectors almost never go bad and unless you mixed up the wires to the injectors which is hard to do because of the wire lengths then the injector timing is coming off the ckps which fails in an on-off manner, they don't jump time. I think I have had one bad injector across 23 trucks and it only threw a lean code, not a misfire condition. MAF affects fueling slightly but never causes a hard misfire which is what you are describing.

That leaves spark. To fire the spark in the cylinder takes considerable more power than to fire the spark in the open air. Any breakdown in resistance in the components means the spark goes somewhere besides the plug. 99% of the time a hard misfire is spare related. You are describing hard misfire i.e. dead cylinder. You have codes on 3,4, 6, and 7. So we can assume the other four are fine. First step is to swap the plugs with the other four. Known good with suspected bad. If we still have 3,4, 6 and 7 then we know it is not the plugs. If it moves then we know those are bad and we replace those. So if three goes to 1 and 1 goes to three and it now misfires on 1 we know the plug was bad and we replace the plug. If it still misfires on three we know it was not the plug. The next step is coils and wires. 4&6 are on the same coil (coils are siamesed as I wrote in my blog post here: https://extinctmotorsports.com/the-e...g-perspective/) so I immediately suspect those. We can swap the coils left to right and 4 and 6 will be in 3&5 position. We swap wires 3&7 with wires 4 and 8. After the swap if 8 misfires and 7 does not then we know that wire was bad. If 7 misfires and 8 does not then that coil is bad at 7. If 3&5 misfire we know that coil is bad. Now because we swapped both the coil and the wire at #4 &6 that gets more complicated. If 6 still misfires after swapping the coil you have a bad wire at 6. If 4 still misfires after swapping both the wire and the coil (coil and wire are now in #3 position) then we have somehting truly weird going on, like mixed up wires.

Often times we get so close to a problem we cannot see the forest for the trees. If someone near you could swing by and have a look they might see something you are not seeing.

 

Well, I FINALLY got around to swapping ignition coils. I didj't touch anything else.

My misfires from cyl #3,4, and 6, to #2,4, and 8.

Two things I find interesting.

#1- cyl #4 was consistently misfiring after switching coils.
#2- that I don't have groups of 4 misfires. Since the coils feed 2 cylinders each, on each side of the engine, I would expect it to be, for example- cyl 3, 4, 6, and 5.

Anyway, there's an update. Finally got a day off where it was snowing, raining, or whatever else.

 

The fact you still have a misfire on 4 means the plug or wire on 4 is bad. However 3 and 6 moving to 2 and 8 does not make any sense. I suspect you have mixed up the wire locations.

 

It is unlikely that I have them backwards, as I followed each wire 1 at a time, from the spark plug, back to the coil....

If I just flipped the coils, doesn't cyl#7 become cyl #2? #4 is weird, I agree...

But I have never ever ever, not once, on any of my vehicles, ever.....lol... never had a bad NGK spark plug. That was the first cylinder I tested for spark, and the plug is indeed sparking.... so do you suppose the wire would be bad somehow, out of the box? They are also NGK plug wires. I'll go mist the wires here shortly once the light goes down a bit, and see if I spot any arcing.

 

Well the thing to do is swap plug #4 with one that is not misfiring, like #1. And if it still misses on #4 then swap the plug wire with #3 or 5. Yes, when you flip the coils 2&8 become 1&7. Try to eliminate one misfire at a time if you can. Then you move on to the remaining. Because 4 is persistent you know something is going on there, plug, wire, fuel, or compression.

 

GoootchAaa!! Thanks so much for the help and your patience haha. I've already done compression, so that's good thankfully haha.

 

Regarding your question about coil failure in groups of four, there is a possible explanation. The wiring diagram for the coils show the coil pack is not just one component. If memory serves, there are actually two wound coils in there, along with some diodes to direct the primary current. So if a diode fails, for example, or one of the coils fail, for another example; then less than four cylinders would be affected, for example only two. Hope this clears things up a bit.

 

Interesting! Good to know, thanks!

 

Yes, siamesed coils as explained in the blog post linked above.

 

Well, turns out I found the one single wrong diagram for the coils/wires. Had cyl #4 and 6 swapped.

I was putting everything back together AGAIN and just stopped. I had the manifold on, but not bolted down, and thouhht "this is just stupid!' So I googled again, but got more specific search terms.

Anyway, it drives 95% better. I have had thr MAF sensor lpw voltage code come and go on it's own twice today (been doing a lot of neighborhood drives, testing everything) and p1129 code which is weird... but it has also come and gone. Also, I have a pending p0300 and p0302 code, but the CEL has not yet come on. Is my MAF on it's way out, causing the misfirres maybe? I did get video of live data both warm and cold engine. How can I best make use of that information? Thanks so much!!