2002 Audi A4 Quattro 1.8t Misfire Help

[Drummy]

New member round these parts. Picked up an 02 A4 with the 1.8t and tiptronic. Not my ideal car but it was cheap ($600 cad). Has 262k km on it. I bought it with a misfire and brought it home. It needs a few other minor items looked after.

The previous owner replaced all 4 coil packs and spark plugs, as well as replaced injector 4. He was also trying to figure out a misfire. It had a broken wire for injector 4 so I soldered in a new connector but it's still misfiring. It's only misfiring on 4. I've swapped coils between cylinders and it stayed on 4. That coil delivers spark in other cylinders.

Everything I'm getting from this is that it could be broken wires on my ignition coil harness, where there was already a broken wire on an injector, and it's isolated to cylinder 4. I'm hoping it's something simple and not extremely in-depth but I'll tackle it all.

There's also a coolant leak where the upper rad hose clamps to the coolant pipe. It's all corroded so I picked up another pipe. The serpentine belt tensioner is failing as well and I've ordered a new one.

Anyone able to give some input? Really trying to get this fixed.

[FNK]

Have you scanned the ECU for codes?
1st place to start.

[Dr.B6Banter]

Start with checking the codes with VCDS to get an idea of if the problem is electrical or something more mechanical. What kind of misfire is it? only on cold starts or a consistent miss on cylinder 4? Plenty of VW guys in NS that could check the codes if you don't have it. A generic code reader would show you obvious stuff but VCDS is VW/Audi specific and shows more info.

If it is in fact the ignition wiring you could pull the coilpack out and use a spare spark plug to see if there is spark.

[grayjay]

Failure if the ignition harness wires is very common problem. Search the forum for the many previous threads that detail ignition harness replacement/repair options.

After just a few hundred miles of buying and putting my '03 with 140k miles on the road, the serpentine belt idler pulley failed. Alternator quit charging and left me stranded. If you are replacing the serpentine tensioner, I would highly suggest replacing the idler pulley while you are at it and consider changing the timing belt soon too if maintenance has been deferred and that is overdue.

[Drummy]

Start with checking the codes with VCDS to get an idea of if the problem is electrical or something more mechanical. What kind of misfire is it? only on cold starts or a consistent miss on cylinder 4? Plenty of VW guys in NS that could check the codes if you don't have it. A generic code reader would show you obvious stuff but VCDS is VW/Audi specific and shows more info.

If it is in fact the ignition wiring you could pull the coilpack out and use a spare spark plug to see if there is spark.

I replaced the ignition coil connector with a new one I purchased locally. The old connector had a broken 3rd wire.

However there's still no change. I'm going to replace my alternator and battery together as I am getting tired of having to jumpstart the car every time. Will also replace the serpentine belt at that time

I know a couple people with VCDS but I don't want to drive the car any distance with only 3 cylinders.

It will misfire constantly. Not just on cold start or when warmed up. It is all the time and only cyl 4. Extremely rough idle like the car is about to stall out, sounds like a Subaru. CEL flashing at low RPM but when revved up above 1500ish RPM the CEL stops flashing and the car SOUNDS like it has no misfire.

I've unscrewed the oil fill cap while the car is running and it is not sucked on by vacuum, comes off no problem. Although it feels like there might be pressure pushing against it from the inside.

When idling, the corner lights struggle to stay on, as if there's not enough power being generated by the alternator, which makes me want to replace it. Coupled with the fact that if I shut off the car it will not start on its own and has to be jumped to start again. And seems like the battery can't hold a charge at all as everything dies as soon as the car is shut off. Can't even roll up a window with the power that's left. Potentially could be a bad CCM that's draining all kinds of power. Going to look at that really soon.

I hope that's enough info. Will try to get a VCDS scan.

[Dr.B6Banter]

I replaced the ignition coil connector with a new one I purchased locally. The old connector had a broken 3rd wire.

However there's still no change. I'm going to replace my alternator and battery together as I am getting tired of having to jumpstart the car every time. Will also replace the serpentine belt at that time

I know a couple people with VCDS but I don't want to drive the car any distance with only 3 cylinders.

It will misfire constantly. Not just on cold start or when warmed up. It is all the time and only cyl 4. Extremely rough idle like the car is about to stall out, sounds like a Subaru. CEL flashing at low RPM but when revved up above 1500ish RPM the CEL stops flashing and the car SOUNDS like it has no misfire.

I've unscrewed the oil fill cap while the car is running and it is not sucked on by vacuum, comes off no problem. Although it feels like there might be pressure pushing against it from the inside.

When idling, the corner lights struggle to stay on, as if there's not enough power being generated by the alternator, which makes me want to replace it. Coupled with the fact that if I shut off the car it will not start on its own and has to be jumped to start again. And seems like the battery can't hold a charge at all as everything dies as soon as the car is shut off. Can't even roll up a window with the power that's left. Potentially could be a bad CCM that's draining all kinds of power. Going to look at that really soon.

I hope that's enough info. Will try to get a VCDS scan.

Yeah, probably a wiring issue if you already saw and fixed one broken connection.

Regarding the battery drain issue, you can just follow the normal battery drain test procedure since the process is fairly standardized regardless of the car. A lot of the time people chuck in junk batteries when selling really cheap cars since a decent battery is a few hundred dollars. Before buying an alternator put in a good battery and see if the alternator holds 13v-14v while idling. Really bad batteries make the alternator work harder than normal so it may seem like the alternator is bad even if it's fine. Especially at idle alternators don't put out their peak currents so a bad battery could cause the symptoms you're seeing.

Take it one step at a time because throwing parts at a cheap VAG car is a slippery slope lol.

[Drummy]

Yeah, probably a wiring issue if you already saw and fixed one broken connection.

Regarding the battery drain issue, you can just follow the normal battery drain test procedure since the process is fairly standardized regardless of the car. A lot of the time people chuck in junk batteries when selling really cheap cars since a decent battery is a few hundred dollars. Before buying an alternator put in a good battery and see if the alternator holds 13v-14v while idling. Really bad batteries make the alternator work harder than normal so it may seem like the alternator is bad even if it's fine. Especially at idle alternators don't put out their peak currents so a bad battery could cause the symptoms you're seeing.

Take it one step at a time because throwing parts at a cheap VAG car is a slippery slope lol.

Well for what I paid for the car I really can't complain, and where I'm in no rush to fix, I'm not overly stressed about it. I mean I'm still stressed because of this misfire but it's not ripping my hair out levels of stress. Yet.

I'll start with a battery like you said. I'm also going to replace another ignition coil connector on cyl 1 as the inner plastic where the pins seat has broken although it's not causing cyl 1 to misfire.

[Drummy]

Update: Had my buddy come up to my house with his basic scan tool. Codes were p0304 p0400 and p0688

I've confirmed my coil works and my plug was just replaced by me. Could other broken wires on the harness be causing my issue?

[Drummy]

I stripped back the plastic covering on my coil harness. No other broken wires under the covering (surprisingly) but one ground is broken right at the ground point. So that's gonna be fixed.

I'm also going to start thinking about my injector. The previous owner replaced injector 4, so I'm going to move it to cylinder 3 and vice versa. I will update afterwards. No other broken wires from what I can see.

[Fast4esT]

I just replaced both my injector and coil harnesses for a cylinder 1 misfire and still have it. I do find if I wiggle the coil harness back behind the head the idle changes and gets a lot worse. Guessing my break is further back than I thought. Might be worth poking around further back on the harness and see if you notice any changes. Mine is in storage now so haven’t gotten around to finishing it yet

[Drummy]

I just replaced both my injector and coil harnesses for a cylinder 1 misfire and still have it. I do find if I wiggle the coil harness back behind the head the idle changes and gets a lot worse. Guessing my break is further back than I thought. Might be worth poking around further back on the harness and see if you notice any changes. Mine is in storage now so haven’t gotten around to finishing it yet

Good idea. Next day I get a little free time I'll start poking around back there and see if anything changes

[Drummy]

Well, pulled my spark plug from cyl 4. It's running rich on that cylinder. Like really rich.

So that either points to a bad fuel injector, or a short to ground somewhere in the wiring.
I followed my harness from the injector to where it enters behind the coolant reservoir, and I found no breaks visible.

Getting closer to figuring out my misfire

[Dr.B6Banter]

Could move the injector between cylinders to see if the misfire moves. I figure a break in the injector harness would just stop the injector from working but I've never experienced that problem IRL so it very well could be the issue.

[Drummy]

That's my plan when I get a day off. Going to the local VW dealer tomorrow to pick up injector o-rings. Then will move injectors. I also plan to hit up my nearest junk yard and get 4 injectors dirt cheap. Working or otherwise.

[Gin+]

Why bother with all that. Pull the coil stick a plug in the end of it and see if it sparks when cranking. I'd do the same for the injectors and see if they all spray fuel. If you determine that you have a wiring issue, a pinout diagram of the ecu is pretty easy to come by with a quick google "ME7.5 Pinout" if you want to go straight to the source.

[Drummy]

Why bother with all that. Pull the coil stick a plug in the end of it and see if it sparks when cranking. I'd do the same for the injectors and see if they all spray fuel. If you determine that you have a wiring issue, a pinout diagram of the ecu is pretty easy to come by with a quick google "ME7.5 Pinout" if you want to go straight to the source.

I'm going to bother with it because I've already pulled the coils and stuck a plug in it to check for spark. I'm going to move injectors around and see if the misfire moves with it or stays in cyl 4. And if it moves it's my fuel injector. If not, then I have a short to ground somewhere in the harness, but a lot farther back than I thought.

[Gin+]

Fair enough. I hope you get it figured out.

[Drummy]

It's finally fixed. It was a bad injector. So after a trip to my local junkyard, I have a smooth idle. I feel so relieved. Thank you everyone for the help.

[Dr.B6Banter]

Glad it was as simple as that.

[Drummy]

It could have been a lot worse

[URS4surf]

maybe the O owner replaced cyl 4's injector with the wrong size

Glad you got it figured out for cheap..

[Drummy]

maybe the O owner replaced cyl 4's injector with the wrong size

Glad you got it figured out for cheap..

If I can find the injector I'll upload a picture. It was the right part number and all but it was broke

[Drummy]

Well it would appear things have taken a turn for the worse. I've got low compression on cylinder 4.

So I picked up an engine locally from a 1.8t wagon for about $50 :)

Expect a detailed post soon on pulling the engine

[Dr.B6Banter]

Well it would appear things have taken a turn for the worse. I've got low compression on cylinder 4.

So I picked up an engine locally from a 1.8t wagon for about $50 :)

Expect a detailed post soon on pulling the engine

Solid deal. Just spend some time making sure it's up to snuff and swap out easy things like the RMS