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Discussion Starter · #1 · (Edited)
Hello,

I am getting a p0301 code, no other codes, cylinder 1 misfiring.

I have replaced the spark plugs Denso TT, gaped at 37 mil, and the ignition wires NGK and swapped the ignition coil with a 2003 Golf that we have with the same 2.0L engine. The problems stayed with the Bug.

When driving, the rough idle used to happen on an occasion, and would go away just by stopping and starting the car.

At this time, the rough idle and misfire is ongoing, runs good for a few seconds, then for a minute or two is misfiring. The ECL, is ether on, or flashing.

Suggestions to my next step are greatly appreciated. Do I replace some sensor/s, fuel injector/s??

Thank you in advance.
:)
 

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Discussion Starter · #3 ·
Thank you billymade.

Part 1 of the "homework" is complete:

I measured the following pressures at cold start:

Initial pressure idle ~30 seconds = 36.5 psi
Ongoing idle pressure 36.0 psi
Unplugging the vacuum hose to the pressure regulator = 44.0 psi
In gear, brake on RPM 2500, 39.0 to 40.0 psi.

So my guess would be that the fuel filter [ replaced filter about a year ago], fuel pump, and fuel regulator are good.

There was no change in the way the engine run when I disconnected the vacuum hose to the pressure regulator.

On a cold start the engine idles flawlessly for the first ~30 seconds, then as the rpm goes down a bit, the first misfire happens. I tested this 4 or 5 times with at least an hour in between.

Hopefully I can get the compression test done in next 2 or 3 days.

Thank you again.
 

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Here are the testing specs; from the service manual, I would pay attention to the specified value, values when fpr is removed, residual pressure (car turned off for 10 minutes) and possibly volume, the amount of fuel the fuel pump can pump @ the specified time frame. Make sure, your engine code is the same; as noted in the manual.

Volkswagen Workshop Manuals > New Beetle GLS L4-2.0L (AZG) (2002) > Maintenance > Tune-up and Engine Performance Checks > Fuel Pressure > System Information > Specifications > Pressure, Vacuum and Temperature Specifications

From testing I have done; variables that affected the cars I have worked on were: heat and load. The misfires happening (after) the car warmed up and when the car was under load; so, in those cases fuel pressure at idle was not a good gauge of the health of the fuel pump.

I was working on a Jetta 2.0L; that seemed to pass all of the "normal" psi requirements but one test I did not do, was the volume test. In the end; it ended up being the fuel pump and it just could not keep up with the demand of the engine, basically fuel starvation under load (misfiring).

I would be curious; to know, the milage of the car and if the fuel pump is original or if it has ever been changed and what brand/part # the fuel pump was/is. Poor quality aftermarket fuel pumps; have time and again, given member's performance problems. The best performing pumps; have been oem version from VDO/Siemens (the oem for VW) or Bosch.

If everything is ok; a compression or leak down test would be next and then, possibly testing or swapping positions of the specific cylinder injector.

Here is the compression testing info:

Volkswagen Workshop Manuals > New Beetle GLS L4-2.0L (AZG) (2002) > Maintenance > Tune-up and Engine Performance Checks > Compression Check > System Information > Specifications

Here is the fuel injector testing info:

Volkswagen Workshop Manuals > New Beetle GLS L4-2.0L (AZG) (2002) > Powertrain Management > Fuel Delivery and Air Induction > Fuel Injector > Component Information > Locations
 

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Discussion Starter · #5 ·
We purchased the car used about 4 years ago and I do not know the maintenance history.

The engine is AVH code, on GLS model.

Not knowing the history, as soon as we got it, I did the timing belt, water pump, thermostat maintenance. Later I had to replace the ignition coil for random stalls, [ a bit of water spray identified the problem] , crankshaft position sensor for stalls and no starts, the alternator had to be replaced, both O2 sensors and exhaust had to be done.

The rest is just maintenance, oil change brakes..etc.

Recently I did the transmission service, new filter and fluid, as the shifting was getting real clunky, now it shift like it should.

Now the car has 163k miles on it and was running real well until about 2 weeks ago.

Here is what I do not see/understand for the fuel delivery test, it defines the voltage vs volume. eg. 12.2V and 200 cubic cm of fuel in 30 seconds.
What I do not see, is where do I open the fuel line to let to gas escape? Do I need to monitor the fuel pressure while the gas volume delivery is tested?
I would think that there should be some pressure applied, on a volume delivery test..?? unless the gas is released on one of the pressure control valve connectors?

Sorry for all the questions.
As you can see I have been busy fixing this car.

Thank you again.
 

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If the fuel pump; is the original one @ 163K, I would say it is time for a new one. You might pull up your seat; remove the cover plate and see if it looks like a genuine VW part. It is hard to know; the history of the car or if they replace it or if the replacement pump was a genuine VW part.

As for the volume testing; I have not done it myself but I would closely, follow the service manual directions. I have used a couple of different fuel pressure testers; one, that I have, has a valve to open the pressure line and bypass the fuel gauge, so you can to do a volume test. If you look at the service manual; they are using the VW factory fuel gauge and it has a built in fuel bypass valve, to open and allow fuel to divert from the pressure gauge, flowing into a line and finally, into a container.

The manual; has a chart which shows what the flow should be, in relation to the voltage of the battery. The higher the voltage; the more fuel will be pumped. Pressure, in this case; is not what we are concerned with but the volume of gas pumped.

I think; it is possible to make it more complicated than it needs to be. Here is a video; showing the process, in a simple, straightforward way. As you can see from the video; you could make your own adapter or just have it come off the line at the fuel rail, into a big enough container. At that point; taking into consideration the voltage at the battery; you could look at the chart and determine if the volume is sufficient, in factory specs.

https://www.youtube.com/watch?v=FzTz4Z90kgI

As noted before; I would also, check the residual pressure and make sure that is in spec as well (e.g. engine turned off; fuel pressure should remain in spec after 10 minutes).


Here is the service manual; showing a 2001 New Beetle with your AVH engine code:

http://workshop-manuals.com/volkswa...essure_vacuum_and_temperature_specifications/

According to the manual:

After 10 minutes there must be a residual pressure of at least 2.0 bar (29 psi).

At the end of the testing procedures; they ALSO, do a "deadhead" test, when they actually cut off the flow of fuel and see what the pump can do at that moment. This is a stress test; that also, has a spec for the pressure to rise to a certain point.

Here is a good little article; discussing a overview of testing and why they are done.

http://www.motor.com/magazinepdfs/052003_12.pdf
 

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Discussion Starter · #7 ·
Part 2 of fuel delivery test:

Pressure gauge inserted right at the pressure control valve.

  • 30 seconds delivered 260CC of gas, using the bypass on the pressure gauge.
  • Deadhead test, 4 seconds, steady at 92psi
  • Leak down test: When engine stopped, immediate drop from 36psi to 34 psi, ten minutes later still at 34 psi.
I would say that the gas pump gets a pass and the fuel filter is still clean..

I also re-seated the connector on the fuel pump, it is clean, no corrosion of any kind.

I sprayed about 1/2 a can of carburetor cleaner into the intake manifold through the port that has the vacuum for the pressure control valve, as this is right at cylinder 1.

The car stopped misfiring at idle, so I took it for a drive.

  • Misfiring during acceleration
  • Running good between 40 and 50 mph on flat terrain
  • Misfiring at the slightest incline
  • When I got back it was misfiring at idle again.
So I do not think that I achieved anything with the carburetor cleaner and the test drive.

I will do the compression test in next one or two days. At the same time, I will move all injectors 1 position to the left, with the injector on cylinder 1 going to cylinder 4.

I am starting to "feel" that the fuel injector on cylinder one is not delivering the required fuel, however I have no proof for it.
 

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Good testing and troubleshooting! Here is the section for testing fuel injectors:

Volkswagen Workshop Manuals > New Beetle GLS L4-2.0L (AZG) (2002) > Powertrain Management > Fuel Delivery and Air Induction > Fuel Injector > Component Information > Locations

You might consider getting a specific LED/ECU safe probe to test the injector pulses or a noid light kit.

Computer Safe Automotive Logic Probe

Cen-Tech - Item#98709

https://www.google.com/search?q=har...Automotive+Logic+Probe++Cen-Tech+-+Item#98709

Bosch injector noid light kit

https://www.google.com/search?q=har...rome&ie=UTF-8#q=bosch+injector+noid+light+kit
 

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Discussion Starter · #9 ·
Compression test:
Cyl 1: 195
Cyl 2: 180
Cyl 3: 180
Cyl 4: 190

I would guess that the compression is good.

I pulled off the intake manifolds, all looked good, did not look like there were any leaks, the intake valves looked good and clean.

Resistance on injectors, 7.8, 2.4, 2.6. 2.6, ohms.. So i am pretty sure the 7.8ohm injector from cylinder 1 is the culprit.

I ordered 4 refurbished injectors from FCP, real good deal, the car should be on the road next weekend - I hope.

Two of the latches on the injector connectors are broken, one broke on me, one was broken before. I wonder if these connectors can be replaced?
 

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Hmm, that seems to be your problem! Always nice; when, your troubleshooting directly points to your problem! Connectors, are sold at the VW dealership; if you look at the connector, look for a part number. Then you can search for the connector; that way. They are sold; at many places online: ebay, amazon and even fcp euro, etc.: (splice in or just replace the body of the connector):

https://www.google.com/search?q=VW+...9i60j69i61l2.775j0j4&sourceid=chrome&ie=UTF-8


https://www.google.com/search?q=new...rome..69i57.9462j0j7&sourceid=chrome&ie=UTF-8

vw fuel injector plug connector | eBay

The kits with all four new connectors; aren't too expensive, maybe replace them all, while your are in there? Be sure; to replace all the injector seals and any other gaskets you need. I look forward to hearing about your results; when you complete the job! :)
 

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Discussion Starter · #11 · (Edited)
Well, the mystery goes on:
New fuel injectors are in [2.6 ohms on all across the leads], the broken fuel injector connectors are replaced, still misfiring... :mad:
I was so sure that this was going to be the fix.
I even pulled out both computers, re-seated the connectors, cleaned and greased the grounds.
 

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Bummer!

Out of curiosity, when did the misfire start in relation to when the crankshaft position sensor was replaced? What brand sensor did you get?

It is probably about time to replace the fuel pump preemptively anyway, maybe that should be next.
 

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Have the trouble codes; changed or are they still the same? :confused: As noted before; If the fuel pump; is the original one @ 163K, it would seem it would be time for a new one. Looking at the fuel trims; in live data, could be helpful:

http://wiki.ross-tech.com/wiki/index.php/Fuel_Trim_Info

It might be good; to go over the coil aspects again, to see if those could be a issue:

Here is some info; about a tech bulletin concerning ground problems and how to update the coil ground:

http://workshop-manuals.com/volkswa...rical_mil_on/dtcs_p1355/p1358/p1361_or_p1364/

coil testing and checking: do you know for sure, the used coil you swapped, is good?

http://workshop-manuals.com/volkswa...esting_and_inspection/with_generic_scan_tool/

http://forums.vwvortex.com/showthre...eshooting-Coil-pack-on-2-0-AZG-AVH-BEV-or-BBW

As for the injectors; you could rent or purchase, a Bosch noid light kit and see if the pulses are normal/consistent: if the pulses are having problems, it may end up being a ecu issue:

http://workshop-manuals.com/volkswa...tors_for_leaks_and_quanity_injected_checking/
 

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Discussion Starter · #15 ·
Wow.. lot of info to digest...

The error code is the same P0301, if anything the misfire is solid now, it used to get occasional smooth idle periods before I took off the intake manifolds and replaced the fuel injectors and the connectors.

I was just scrolling the output of my code reader looking at all data. I noticed that the the "fuel system 1" is showing as "open2", I wonder if something is stuck, or it is a leftover from no pressure when I replaced the injectors. There is no gas leak that I can see or smell.

I did put on a timing light on the #1 plug, it was flashing. However I think it would be hard to tell if there were missing sparks, as these pulses are too fast.

The other VW that got the ignition coil from this car is working flawlessly, as it was before the ignition coil swap - I think its safe to assume the coil is good.

If I was to take it to the dealer, would they be able to tell within a matter of minutes what is wrong if they connect it to their diagnostic system?
Thank you again.
 

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Hmm, that is a good question; I don't know or can tell, how competent their techs are. The VW factory tools; have some diagnostics features, ability to access modules, display factory vw codes and bi-directional controls (turning components: on/off), that a typical generic obd II scan tool does not.

What scan tool are you using? Looking and seeing live data; viewing a misfire counter, would be nice. When viewing that; moving the wiring and plugs, to see if the misfires change their frequency, would be something to try as well.

For a factory like scan tool; you could check out the vag 401 on amazon ($50) or the higher end VCDS by Ross Tech $250-$350).

Did you ever hook up; some noid lights, to the offending injector/cylinder, to see if the pulses are working and seem normal? You might be able to rent one from a auto parts store or buy one for not too much. If there is a issue; I would check the wiring to the ecu and if that is ok, then possibly the ecu is the problem. Check the factory testing procedures: I linked to above. While ecu's don't seem to fail that often; if it was bad, rebuilding/repairing the ecu, could be the next step.

Bosch Noid Light kit:

https://www.google.com/search?q=Bos...rome..69i57.7958j0j7&sourceid=chrome&ie=UTF-8

I think you are getting close; I hope, a little more testing will find the problem!
 

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Discussion Starter · #19 ·
At this time, I feel the problem is in wiring. Would be nice to have a schematic I could test the wiring from the #1 injector to wherever it goes, and from the ignition connector to where they go.

I did a visual check on the wiring harness in the engine area - I did not see anything obvious. The VW manual is using a test box to accomplish this continuity check on wiring.
 
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