All cylinders misfiring

And about your misfires?

If these are the original plugs, the ignition coil connectors may have been damaged when they were removed/installed to install the plugs.

Rockauto sells these too.,2001,a8,4.2l+v8,2617,ignition,ignition+coil+wiring+harness+repair+kit,15553


For that price I may as well buy a new set of 8 for $212

Well I would pick the best used one and install in the hole that is easiest to get to. Then order a new one and install it when it comes in. Or if just drive one of my backup vehicles while new one comes in. I live 45 minutes from the closest part store that likely doesn’t stock what I need anyway.

What do you do when a customer is ready to pick up their vehicle?


I only work on my cars

Today I did an Ignition Coil inspection, put dielectric grease on the plug tips, torqued down the spark plugs to 22 Ft. Lbs., and listened for vacuum leaks. The car does run smoother it seems but I still have at least 4 misfires happening. There is a vacuum leak behind the motor near the blower motor but I could not pinpoint it.

It’s probably too late now but I hope you had a plug connected to the wire when you performed this test. Without an appropriate load, that’s a good way to over stress your coils…

I actually decided not to do it that way. Now I’m glad i did. I just did a visual inspection and put grease on them.

First off: Inspect one of the old plugs and one of the new plugs side by side on the bench under good lighting. Measure each for comparison, best you can, referenced to the seating surface. In other words seating surface to top of plug, seating surface to bottom of plug. Next take a close look at the top of the plugs, where the coils attach. Notice any difference? Now take a close look at the part of the plug where the it seats, some plugs are tapered with no seals, some have little rings, crush-seals. What differences do you observe between the two plugs?

Here’s my guess: As long as there are no dimensional differences, the replacement plug should work as well as the original, at least for a short test run; however the replacement plug – if it isn’t recognized by Audi as an acceptable sub – might cause problems later, for example if it was the wrong heat range it might foul sooner. So I don’t think the reason for the misfires is due to the plug. Here’s some ideas

  • Plug wires not replaced on their plug in the right order
  • Something (part, electrical connector, vacuum hose, fuel hose etc) was removed to make room for the job and didn’t get replaced correctly
  • Plugs were left in the engine too long, heat bonded to the head, and removing them damaged the cylinder head threads.

I really hope the threads aren’t damaged. The plugs tightened up fine with no issues. I’m thinking vacuum leak. It runs fine when i give it gas. Only misfire at idle. I think the random misfire is causing the other misfire codes. I might try to run it this weekend and take it for a drive to see if more related codes show up.

Well, looked for my vacuum leak and instead I found the coolant temp sensor. The engine was completely hot so that’s nice. Now I have to order a new retainer clip because that one broke instantly.

I just found my vacuum leak and its pretty big. It was there before but i think it may be my issue. I sprayed carb cleaner on it and it rev’d up nice and was stable for a few seconds. Going to replace it if i can find one and the I should be ok. Ive got a video where you can hear it if anyone is interested. I was using it as a flashlight while recording so its pretty shaky but you can hear everything.

This is most certainly a coil over plug system. You need to be careful when removing the coils and their stubby rubber “wire” to the plug. They dont enjoy being disturbed and they do not suffer any moisture in their plug wells…not at all.

I suspect you are having an issue more with your coils and rubber boots than the plugs themselves. The connections need to be dry and clean…a little di electric grease never hurt anyone here either. Make sure the internal spring that makes connection to the plug and the rubber boot itself is sound and not torn or cracked anywhere as this will allow high voltage leak to ground inside the plug wells.

Might not hurt to buy yourself the coil lowers (the rubber boot and spring) that attach to each coil…some are replaceable…others are not…not sure what Bosch has in store for you there.

Also…an Audi of that vintage smacks of Bosch coil recall to me… Bosch had a widespread issue with coils for a time there, I remember it well. See if your vehicle was recalled for those Bosch coils… My 03’ VW was and were replaced for free a few years ago.

Where was the vacuum leak occurring? If that’s the problem, there’s a remaining puzzle why the misfire symptoms started after the plug swap.

The leak is where the metal breather line from the PCV goes down to the intake manifold. Im thinking that with the old plugs together are causing my misfire. I think its mainly the lack of air though as it runs fine when i give it gas. I could go cross-country so long as i dont have to sit at idle.

I looked and found no recalls. Im putting new plugs in tomorrow so i will triple check the coil overs again. In order to repair my vacuum leak i have to remove the throttle body which I believe also needs a gasket. I also have a hard time believing that the metal breather tube does not need a gasket but i cant find one for the life of me. I will let you know tomorrow if i can finish this up. I might have to order the throttle body gasket from europe like the rest of my stuff.

The vacume leak should only raise your idle speed and not cause multiple misfires…not the likes of which you were reporting anyway.

Also… Im no expert on the 4.2 V8 but that engine was widely used here in the states and parts should be readily available. Go online…even Amazon carries parts for that engine…ebay as welll for sure… The internet will save you money as opposed to local parts gathering and or ordering from Europe

So right after I posted my comment i realized that the breather gasket is part of the throttle body gasket which is metal. Since its metal i might just try to tighten the bolts and see if it goes away. Before i had reset the codes the first time I had intitially had 3 o2 sensor codes. 2 low voltage and 1 lean code. None of them came back. I wonder if it was throwing codes due to the leak and was self correcting but now that i reset them it is throwing the misfire. Also, i think that there is really only one and thats the p0300. I think its causing the other p0301-p0308 codes even though it is not a steady misfire and its all due to a vacuum leak. Just a guess. What do you think?

From memory the 300 should be Random Misfire…301 points to cylinder number 1 specifically and the 308 points to cyl 8 specifically. So 1 and 8 are misfiring.

Any minor intake leaks can be solved with gasket maker…just apply a light film to the existing clean surfaces and the leak will go away.

I think you may have misunderstood. Im getting all codes between p0300 and p0308. So, 01 02 03 04 05 06 07 also. Thats why i think its just a random and not any actual cylinders.

I have gasket maker in the garage. Ill put some in the leak and tighten it up. After maybe an hour ill start it up and see whats what.