Hesitation and CEL (Cylinder 1 Misfire)

[CJM_RVA]

Car's been running fine, stock 1.8T w/117k miles, had a bit of a shudder a couple times yesterday on the way to work, then noticeable hesitation/stumbling on the way home and the MIL lit up. I don't have VCDS/OBDeleven but the cheap universal code reader I do have gave me P0301 - Cylinder 1 Misfire Detected. This morning it behaved itself (mostly) on the short trip taking my kids to school but then when I tried to drive to work a little later it was so bad that I turned around and came home. Almost undriveable with the A/C on and still bad when I turned that off to reduce load.

I've never been the best at diagnosis so I was wondering where to start. Coil? Plug? Don't do anything until I borrow/buy a VCDS setup and get more info? Don't want to just blindly throw parts at it but at the same time I'm willing to do a limited amount of experimenting to get it running right again.

Also is cylinder 1 the front or back of the engine? LOL. Thanks in advance.

[Cybersombosis]

Cylinder 1 is the front of the engine. It could be a plug, coil or the wiring harness. To check if it’s a coil, swap coil 1 and 2. If the misfire goes to 2, it’s the coil. If it stays on 1, swap your plug. If it follows, it’s the plug. If it stays on 1, it’s most likely the wiring harness. Pull back the rubber boot on the cylinder 1 connector and inspect for cracked insulation. If there is, a quick fix is to use some black tape to isolate the wires so they don’t short out. Ultimately you’d need to change the wiring harness if it’s in really bad shape.

[CJM_RVA]

Thanks! Will try that later today and report back.

[CJM_RVA]

Results: Inconclusive as the MIL has not yet come back. I swapped both the coil and plug (coil to 2, plug to 3). Plugs looked absolutely awful so they need to be replaced in any case, I'm wondering if I should preventatively replace the coils as well? Do they have a general lifespan or go bad? I've had the car 1.5 years but I don't know if the coils have ever been replaced. Not necessarily trying to spend $120 but...

Also I'm assuming there's no point to upgrading coils on an otherwise stock motor, correct?

[Puddin Tane]

Plugs looked absolutely awful so need to be replaced...

99.99 percent probability that's all it is. I totally recommend these Denso plugs. My 2005 1.8t has liked them just fine for 30K miles which is 1/3rd of their lifespan. Only buy them direct from Denso; Chinese counterfeits are everywhere. Dicking around pulling coils and changing plugs more often is half of why these harnesses fail. The insulation ages and gets brittle, sure, but careless flexing is what cracks it. You want to do that as little as possible and treat the harness like it's made of frickin glass. I remove the ground bolts, then unlatch all four connectors, then gently move the whole harness to the left before touching the coils. 170K miles, no cracks.

[CJM_RVA]

99.99 percent probability that's all it is. I totally recommend these Denso plugs. My 2005 1.8t has liked them just fine for 30K miles which is 1/3rd of their lifespan. Only buy them direct from Denso; Chinese counterfeits are everywhere. Dicking around pulling coils and changing plugs more often is half of why these harnesses fail. The insulation ages and gets brittle, sure, but careless flexing is what cracks it. You want to do that as little as possible and treat the harness like it's made of frickin glass. I remove the ground bolts, then unlatch all four connectors, then gently move the whole harness to the left before touching the coils. 170K miles, no cracks.

Thanks for the harness tip. The coil connectors might as well be made of glass; the clip on #1 was already gone, #2 the clip shattered as soon as I put any pressure on it, and #3 clip cracked despite my being strenuously careful. But the connectors seem to still fit snugly on the coils despite the missing clips. So you'd say those plugs are superior to the OEM NGK units?

[Puddin Tane]

I consider the Denso plug superior because the center electrode is iridium (more stable than Platinum in this application, virtually non-reactive). Both plugs have platinum ground electrodes, I guess. On the Denso there's a visible platinum pad laser-welded to the tip so I know it's there. On NGK PFR6Q I'm like "where's the beef?" I have never used it however. I have used NGK BKR6EIX thinking it was the OEM plug. I was very disappointed by its short life. What a waste of iridium!

About those brittle coil connectors, mine were like that too so three years ago I bought this kit of replacements off eBay that includes a de-pinning tool. Worked perfect and the connectors still work great. You don't have to replace the harness to renew the connectors.

[CJM_RVA]

I consider the Denso plug superior because the center electrode is iridium (more stable than Platinum in this application, virtually non-reactive). Both plugs have platinum ground electrodes, I guess. On the Denso there's a visible platinum pad laser-welded to the tip so I know it's there. On NGK PFR6Q I'm like "where's the beef?" I have never used it however. I have used NGK BKR6EIX thinking it was the OEM plug. I was very disappointed by its short life. What a waste of iridium!

About those brittle coil connectors, mine were like that too so three years ago I bought this kit of replacements off eBay that includes a de-pinning tool. Worked perfect and the connectors still work great. You don't have to replace the harness to renew the connectors.

Went with the NGK plugs because that's what I could get my hands on at short notice. It seems happier now and even idles a little better than it did before the whole issue started (not surprising I guess). Still waiting to see if a code comes back, and if so, I just may replace all the coils as they look kind of rough at the plug end. The connector on #3 cracked further when I tried to put it back on, so it's probably hanging on by a prayer right now - I'll definitely redo the connectors in the near future. Saw the connectors themselves on FCP Euro but I was having trouble finding just one depinning tool (they had a set of 20 or something for different applications that was $80 or so, not paying that!) Thanks for the link.

[Puddin Tane]

Are your present coils revision D (the part no. ends with D)? If so, you don't want to "throw parts" at that unless you confirm they're bad by swapping them around. Previous generations of coils were notoriously bad but with revision D Audi finally got it right.

[old guy]

Are your present coils revision D (the part no. ends with D)? If so, you don't want to "throw parts" at that unless you confirm they're bad by swapping them around. Previous generations of coils were notoriously bad but with revision D Audi finally got it right.

I put in a set of revision D coil packs 14 years ago. Clicky click®️. Still running strong.

[walky_talky20]

I put in a set of revision D coil packs 14 years ago. Clicky click®️. Still running strong.

Wow. I can't believe the Rev D's came out 14 years ago. I need to go lay down.

I was not aware these were that good. I got a free set for my 2001 as part of the recall way back then, and I quickly swapped them for the Oh-So-Trendy Red R8 coils. I can confirm the R8 units *definitely* do not last 14 years, especially when dwell is not adjusted to suit. I just found my Rev D's in a box the other day. I should probably quit messing around and run them already.

[Puddin Tane]

I put in a set of revision D coil packs 14 years ago. Clicky click®️. Still running strong.

Yes, it was you who told me they're solid and I should stick with them when I was tempted to switch. Still going strong.

[CJM_RVA]

Are your present coils revision D (the part no. ends with D)? If so, you don't want to "throw parts" at that unless you confirm they're bad by swapping them around. Previous generations of coils were notoriously bad but with revision D Audi finally got it right.

They are revision D. Since replacing the plugs, it's running well with no MIL, so I'll leave well enough alone unless a code comes back. Whenever the replacement harness connectors get here (apparently could be as late as July 7...) I'll get those swapped out and should be good.

I did discover a probably unrelated issue with the belt tensioner, which I'll be making a new thread about shortly.