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Discussion Starter #1
Trying to fix my new beetle with my Dad. Here is what we have done so far.

2002 Turbo S. It is running rough, check engine light comes on. Keeps throwing code for P0301 cylinder 1 misfire.
We have done the following:

1. Swapped ignition coils between cylinder 1 and 2. Still cylinder 1 misfire.
2. Installed new NGK plugs. The VW part number supersedes to a new E3 style plug so no gap to deal with. Still cylinder 1 misfire. (Even swapped new plugs just in case we had really bad luck.)
3. Checked for proper voltage to ignition coil. It is within specifications. Hooked up diode test light to proper terminal and it flashes when car is turned over.
4. Checked cylinder 1 injector resistance. It was just over 12 ohms, same as the other three.
5. Checked cylinder 1 injector voltage and activation. It has proper voltage and it flashes when engine turned over.
6. Pulled fuel rail and swapped cylinder 1 injector with cylinder 2 injector. Still cylinder 1 misfire.
7. Checked compression in cylinder 1.

Hoping someone has had a similar problem or is a genius. We have exhausted the factory shop manual diagnostics for code P0301. Don't know where to go from here.
 

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Ross Tech Wiki: 16685/P0301/000769 - Ross-Tech Wiki

16685/P0301/000769 - Cylinder 1 Misfire Detected


Possible Causes
Ignition system
Fuel injectors
Fuel pressure *
Running out of fuel *
EVAP canister purge valve *
Evaporative emission system *
Low compression
Base engine problems
Control Module damage *

Special Notes
This feature search for engine misfire in a specific cylinder. Most of the time the cause for a misfire is a lack of combustion in a cylinder due to absence of spark, poor fuel metering, or poor compression.


You seem to have tried; most of the typical things! Reading the above: have you done a fuel pressure test? Evap and ECU; seem to be at the end of the troubleshooting process, in the list you haven't done.

Got any history on the car; anything change before the problem started; any variables, that you haven't mentioned?

What was the compression in #1 and the others (any variation)? Did you test the wiring; from the coil/injectors all the way to the ecm; how do the wires/connectors look (coil/injector) and have you tried unplugging/plugging the ecm back in? A common problem; is the wiring harness to the coil packs, the heat gets to them and they crack, causing misfires. Many, have replaced the whole thing with a replacement VW sells; google "1J0971658L". Take a moment; inspect the wiring harness for cracks or anything that doesn't look like it should.

Inside the #1 spark plug "hole"; did you notice, any leaking oil from the valve cover gasket or water from a engine wash (could cause a misfire; from grounding)?

What scan tool are you using and just for the heck of it, try a hard reset (remove battery cables from the battery; then, touch the positive/negative cables together for 30 seconds). You guys are really close; hopefully, you chase down this misfire gremlin! :)
 

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Discussion Starter #4
Dad here. Unfortunately for my daughter I have a full time job that is not wrenching on her car:D

Compression was 150 give or take a couple psi on these.

I think I will try the ecu/harness issues first. I have wondered about fuel problems (water, gunk, etc.) but wouldn't that affect all the cylinders intermittently? Hope to have time tomorrow to work on it. I will try the plug/unplug ecu and hard reset first, then look at the harness. I did not realize the wiring harness for the coil packs was removable independent of the full harness. I will take that out and check the harness for damage, resistance, etc.
Thanks for the info and will update soon.
 

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Dad. the wiring harness to the coil packs is not removable per se; the part number listed above, is a splice in repair harness. I can only assume this is the case; because. this is such a common problem. The engine gets really hot and the turbo just makes it worse; the wiring gets cracked, causing this mid fires.
Many of the wiring harness repair kits; come with a optional wiring harness insulation/cover that protects it from the heat in the future.

Here is a interesting bulletin for the misfire/harness replacement:

Ignition Coil Overlay Harness, Installing
Date: 2001, 2002
Group: 97
Number: 04–02
Golf, GTI, Jetta with 1.8L Turbo Apr. 8, 2004
(eng. code AWD, AWP, AWW)


http://www.uspmotorsports.com/downloads/vw.tb.97-04-02.pdf

1.8T Coil Pack Wiring Harness Replacement: VW Part #: 1J0971658L
 
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