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Discussion Starter #1 (Edited)
2001 - 197,000
Recently replaced (within the last 2 years)
  • Automatic Transmission
  • Fuel Pump
  • Fuel Regulator
  • Catalytic Converter
  • Spark Plugs
  • Timing Belt
  • Water Pump
  • Alternator
  • Fuel filter
  • Fuel/Emissions Purge Valve

About two years ago we had a problem with the engine briefly dying on the highway but it would quickly recover. No error codes issued. We found if we just didn't let the gas tank go below a 1/4 tank the problem would not occur.

So for at least a year it ran without issue but recently it has begun losing power for longer stretches and well above the previous 1/4 tank trigger point. It feels like someone threw a switch and cut out two cylinders. The engine would idle very rough, if you revved the engine it sometimes clears up the issue. It's a sporadic failure. When this happens the CEL actually flashes. I do get misfire codes for only #2 and #3 cylinders.

Letting it sit seems to allow it to 'recover' to being stable again.

This makes the car unfit for commuting naturally and the error codes have not given me anything to work with.

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16684 - Random/Multiple Cylinder Misfire Detected
P0300 - 35-10 - - Intermittent
16687 - Cylinder 3
P0303 - 35-10 - Misfire Detected - Intermittent
16686 - Cylinder 2
P0302 - 35-10 - Misfire Detected - Intermittent
16684 - Random/Multiple Cylinder Misfire Detected
P0300 - 35-10 - - Intermittent
16687 - Cylinder 3
P0303 - 35-10 - Misfire Detected - Intermittent
16686 - Cylinder 2
P0302 - 35-10 - Misfire Detected - Intermittent
Readiness: 0010 1101
-----------------------

I'm checking all vacuum hoses but so far haven't found any problems.


So anyone solve a similar problem?


I've really come to loathe the heavy emission controls that these cars have to use.
 

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We seem to have a rash of intermittent misfire issues with the 2.0L lately; they typically break down into ignition or fuel delivery related failures/problems.

I won't list the definitions for all the misfires; as they are all pretty much the same as this one:

16684/P0300/000768 - Ross-Tech Wiki

Start fresh and remove ALL preconceived notions from your mind about troubleshooting the problem; just because the all those parts are "new", replaced, doesn't mean they are not failing and causing the current misfire problem.

What quality parts did you purchase and install? We have a particular problem with poor quality aftermarket fuel pumps (Airtex, O'Reilly Import Direct brands, etc); prematurely failing and causing drivability problems. In that case genuine VW, VDO (who makes the pumps for VW) and BOSCH; oem quality fuel pumps are recommended.

I would start with fuel pressure; do a fuel pump test, paying attention to the various types of testing modes: pressure while running, pressure with engine off (residual), volume and dead head (max pressure capability of the pump). Fuel pumps are typically sensitive to thermal issues; many times working fine, until they get hot and then act up. The fact that you had issues; below 1/4 tank, would also point to the thermal problem exacerbating the problem (less gas to cool the pump) and limited pressure capability, when gas is low.

Volkswagen Workshop Manuals > New Beetle GLS L4-2.0L (AVH) (2001) > Maintenance > Tune-up and Engine Performance Checks > Fuel Pressure > System Information > Specifications > Pressure, Vacuum and Temperature Specifications

I would say; start with that and then we can move on to ignition related issues. We have seen bad coil packs, bad grounds (vw tech bulletin) and believe it or not... BAD ecu's with the onboard ignition chip being fried.

Here is a long drawn out thread; where we finally got the testing of everything down to the ecu, NOTE: that the misfires were pretty cylinder specific and your random, multiple misfires makes me think of fuel delivery more than ignition related. That is speculation on my part and troubleshooting using the correct testing procedures; will result in hard cold FACTS about each component and we can go down the list, a process of elimination. The end result; finding the cause of the problem, make the needed repairs and confirm, the issue is repaired correctly with testing, post repair.

Here are some other helpful links:

coil pack troubleshooting with water to confirm coil isn't cracked:

VWVortex.com - DIY/Troubleshooting - Coil pack on 2.0 AZG, AVH, BEV, or BBW

misfire thread:

intensive testing and troubleshooting steps, ultimate conclusion: bad ecu> sent out for repair:

http://newbeetle.org/forums/2-0-liter-gas/123858-p0301.html

Start with the fuel pump testing; tell the results from that and we can go from there! Thanks! :)
 

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Discussion Starter #3
Thanks Billymade!

Great detail - I do have my suspicions about the pump but I should have mentioned as a test I took the new pump out and put back in the original 'factory' pump. (I had kept it). The same problem occurred. True I could have two bad pumps but I would think the odds are low.

I will do the pressure test on it, pretty easy and I have the testing gauge.

This may be a vacuum thing as I did also have a problem with the Evap canister where I made a repair to it (I also forgot to mention this). My wife had bumped a poll with the left rear and it cracked the canister. I thought I repaired it but maybe that's not holding up.
 

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Hmm, we can speculate ad nauseum; it is best to troubleshoot the problem, by doing a process of elimination and work down the list, shown on the ross tech wiki:

Possible Solutions:

Check Misfire Recognition
Check Air Intake System
Check Fuel Supply
Check Injector(s) and Injector Sealing
Check Ignition Cable(s) and Spark Plug(s)
Check Ignition Coil(s)
Check Exhaust Gas Recirculation (EGR) Valve (N18)
Check Camshaft Position Sensor (G40)

As for the damaged evap parts; it maybe better, to just replace them with good used parts from a junk yard?

Let us know; what the results of your troubleshooting and testing is. We can go from there. Thanks! :)
 

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Discussion Starter #5
Thanks - yes, just finished the fuel pressure test. It went from From 38 psi (2.6 bar) down to 30 (2.0 bar) after 10 minutes.

I wish there was a close by pick and pull for the evap tank. Just because it's easy to do, I'm going to review the repairs I made to it, just to double check.
More as it unfolds.
 

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Discussion Starter #6
So I bit the bullet and ordered a used evap tank from Ebay - I doubt the one I repaired is the problem but ****, may as well replace it just to be able to eliminate it.
 

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Your residual pressure; sounds like it is in spec. What was the fuel pressure; when the engine was running? Specified value: 3.5 to 5.0 bar (50 to 72 psi). Did you happen to notice or remember; the brand of fuel pump, you installed?

Good call on the evap tank; best to eliminate, that from the list. Good work troubleshooting; keep on going! :)
 

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Discussion Starter #8
This is the pump

If the pump is the problem then the 'new' pump has the exact same problem the original does as I've swapped them out and the same problem occurs.

The people who sell this pump are real good at customer service, I had a problem with the first pump they sent me with the guage being WAY off, they sent me a new one right away.

This doesn't mean the pump is cleared and I didn't do a pressure test while the engine was running - just static. I'll review that in the morning.

BTW - Have you ever seen anyone solve the '1/4 tank stall' problem?
 

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Hmm, a classic cheap aftermarket fuel pump (anything non oem quality under $100 and a no name brand is suspect!); we have had continual problems with drivability issues, when non oem pumps are installed. The thing is, they typically "work" or "run" but they just cannot maintain the level of fuel volume/performance levels, needed under load, for the car to run correctly.

The "1/4 stall", is most likely a fuel starvation issue; e.g. the pump cannot maintain enough fuel for the engine to run right.

Try to bypass any assumptions and ideas you have thought about your in your repair history; do "real world" testing and view the results, then make repair choices, based upon the resulting data from correct testing procedures. We have problems with aftermarket fuel pumps; they just don't work right, period. This is why I always ask people what brand they install in their VW's; there are some things you can save money on but crucial things like a fuel pump, is not one of them. If you can return the pump for a refund; I recommend you do so or get store credit, etc. and after testing confirmation, get a high quality oem pump from VDO or Bosch.
 

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Discussion Starter #10
Yeah, but the stall only happens briefly and usually once. It's a weird problem (that I've seen others mention). To me it reminds me of my 60 Beetle that didn't have a gas gauge, just a reserve valve on the forward kick panel. The stall only lasts long enough for the new flow to engage.
 

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You said you replaced the plugs, but didn't mention the coil and plug wires. If they've never been replaced, the coil likely has all sorts of cracks in its exterior case (ours did). Original plug wires ought to be replaced as well, in my opinion, due to age and miles. They may "look good" on the outside, but that might just be hiding interior deterioration due to years of heat and vibration.
 

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Discussion Starter #13
Right, I've not replaced the wires or coils.

I wasn't able to put some time in on the tests until today and have some interesting new twists.

1) I put a fuel pressure gauge on the system and positioned it to where I could see it while driving. The fuel tank has maybe 4 gallons in it. I cleared the codes and took it for a drive. About 4 miles out the CEL started flashing and the performance decrease occurred all the while the fuel pressure was good, near 40psi, only moved a little every now but not note worthy.

The codes were for the usual misfires on cylinder 2 & 3

2) Because in the past the problems with misfires usually subside when the tank is full, I filled the tank and took it for a drive. No misfires, no flashing CEL, it felt fairly normal. Upon return I check the codes and had a pending
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16806 - Main Catalyst; Bank 1
P0422 - 35-00 - Efficiency Below Threshold
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I'm going to look into how to properly test this and will hopefully find something. It's a (relatively) new cat converter. But maybe the sensor is failing or has a fault connection.


It's SO annoying that the problem should change with the filling of the gas tank. It makes me think the emission system is in a different mode when the tank is full and changes when the level gets like to 1/4 tank or so.

This **** is why I've come to loath gasoline powered cars. :(
 

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16806/P0422/001058 - Ross-Tech Wiki

Based upon the factory specs; your fuel pressure is low:

Fuel Pressure:

Specified value: 3.5 to 5.0 bar. (50 to 72 psi)

You could do more fuel pump testing; volume and "dead head" max pressure the pump is capable of, would be the next steps in that process.

Volkswagen Workshop Manuals > New Beetle GLS L4-2.0L (AVH) (2001) > Maintenance > Tune-up and Engine Performance Checks > Fuel Pressure > System Information > Specifications > Page 1780

I was working with a Jetta 2.0L; that was acting the same as yours, it ended up being the fuel pump and it maintained what seemed to be "normal" fuel pressure but it was the VOLUME, of fuel that was the problem! Under load and eventually; even at idle, is was rough and misfiring. I never did the volume test but only did a running and residual pressure test. It is possible the volume or "dead head" (maximum psi capability test); would have shed light on the weakness of the pump. At idle; the engine isn't under load and so, that is not testing, how the fuel delivery system, acts under load (stress).

I cannot stress enough; how the fuel pump you installed is a aftermarket pump, that are KNOWN, to have problems with these VW's. We have helped a bunch of people/members of this site, troubleshoot drivability problems and every time, they install a aftermarket pump, it causes the car to run badly and with all kinds of misfire issues. Aftermarket pumps are INFERIOR quality; they just are not up to the performing level needed, for these cars to run correctly!

The FACT, that you reference problems; when the fuel tank is low, is by definition a fuel delivery problem and a fuel pump, gets hotter and has to work harder, when the gas levels are low.

Please, seriously, considering getting the correct oem quality fuel pump and returning your aftermarket one, as a defective part and get a refund or credit, towards a Bosch or VDO. The Bosch, is nice; as they have integrated the fuel level sending unit into the redesigned pump (included) and they include a fuel tank seal (everything is included to do the swap; I would recommend installing a new fuel pressure regulator and fuel filter as well).

Bosch Fuel pumps:

https://www.boschautoparts.com/en/auto/fuel-pumps/fuel-pump-assemblies?partId=69740

Key Features:

Replacement fuel pump dimensions precisely match those of the old part to ensure a perfect fit
Improved cold-start ability and interference suppression
Compatible with a wide variety of fuel types
Bosch impeller ring ensures smooth fuel flow and reliable performance
Aftermarket fuel pumps follow the same rigorous standards as Bosch OE fuel pumps


Engine code: APH, AWV

Bosch Part Number: 69740

https://www.google.com/search?q=Bos...40&aqs=chrome..69i57&sourceid=chrome&ie=UTF-8

At this time, I would be less concerned; about the catalytic converter efficiency problems, until you get the basic drivability issues handled (other problems; could contribute to this issue). Then, after you get the car running well; you can look into "detailed" performance of the emissions and how the fuel trims are and go from there. Let us know; what your next steps are! Thanks! :)
 

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Discussion Starter #15
Wow - I missed where you identified this range earlier. Yes, it would appear that the pressure isn't adequate.

Wow, that's a lot of pressure for sure. Now that I've filled the tank it would be interesting to see if the pressure is greater (didn't test that).

Again, thank you - more to come.
 

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The manual states two different specs; whether the first, is running or not, is not clear:

System Pressure Specified Value: 2.5 bar. (36 psi)

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

You seemed to have passed the residual test and the 38 psi, was the engine running or turned off?

In the testing portion of the manual; the pressures show a range, I can only assume this is with the engine running and possibly under load or the engine revved up? The pressure readings are supposed to go (up); when under load or the engine is revved, if it goes (down), that would be another indicator of a weak fuel pump.

Specified value: 3.5 to 5.0 bar. (50 to 72 psi)

I would look over or print out the service manual pages and closely follow the testing procedures, to insure the accuracy of your testing process/steps. Note: deadhead and volume testing; could show a weak pump, where just a straight pressure reading and residual test, may come up inconclusive, giving you a confusing false negative reading. In my confusing Jetta 2.0L diagnosis; I just did the pressure and residual testing; seemed to come up with the psi being in the "normal" range. A new fuel pump; solved the problem, in retrospect it would have been interesting to know if the dead head or volume testing, would have indicated the weakness of the fuel pump (it was a car with over 150k and the pump was the original one).

Volkswagen Workshop Manuals > New Beetle GLS L4-2.0L (AVH) (2001) > Maintenance > Tune-up and Engine Performance Checks > Fuel Pressure > System Information > Specifications > Pressure, Vacuum and Temperature Specifications

Here are some good fuel pump testing faq's; addressing issues we have been talking about :

http://www.aa1car.com/library/Delphi_10589.pdf
 

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Discussion Starter #17
Ok so
- the 'deadhead' pressure is 92 PSI that looses less than a unit under leak down.
- the volume is greater than 1 pint in 30 seconds (I stopped when I reached a pint).
- idle with engine running is 35 PSI.
- With engine running, if I disconnect the vacuum control for the regulator then plug the vacuum port, I get and increase to 42 PSI.
- With the engine running, if I pinch off the return line after the regulator the pressure rises to 92 PSI and the engine slows a little (you can hear it)
- With the regular hooked up to a manual vacuum pump the best I can get pressure wise is 42 PSI.

So I'm thinking the problem is with the pressure regulator. I'm certainly not getting 3.5 to 5.0 bar even at idle or when there is no vacuum to it (which simulates full load)

I did replace the regulator within the last year, perhaps the new one has a problem? I guess I could spend $70 to find out.
 

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Discussion Starter #19
I actually have the original I replaced (that's how I roll) and after lunch I'm going to swap it out and see what results I get.

Stay tuned. (and thanks for being there!)
 
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