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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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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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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 · #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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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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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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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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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 · #21 ·
I have the original Fuel Pump, but I mean the original Fuel Regulator.

There is about a 10 psi increase with the old regulator. At full throttle (no vacuum to the regulator) I get 3.3 bar. Still not at 3.5 to 5 bar as the spec calls for.
 

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Discussion Starter · #26 ·
Yeah, I'm not sure why it's so expensive. That said, they gave me a new one to try, thank you life time warranty.

So, driving with the original regulator at first seemed like everything was fine, I went at least 25 miles on the highway with no issue. Stopped at my mom's to mow the lawn (yeah, 62 and I still mow my mom's lawn) and on the way home from her place,under 30 mph driving, the engine acted up like it has been.

It comes on so suddenly too, like a switch. If I put it into neutral and rev the engine it seems to clear up but I'm not entirely sure.

When you change parts and the problem persists it tends to indicate that the parts you're futzing with are not the issue.

That said, in the morning I'll put the newest regulator in and check pressures. If I don't see a significant change, I'll dig into the ignition system and see.

If 2 and 3 are regularly misfiring, I'll swap their coils with 1 and 4 and see if the problem follows the change.

If it doesn't, I may just bite the bullet and replace the pump and regulator with Bosh parts but I really hate guessing with $200 (more or less).

Film at 11:00
 

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Discussion Starter · #30 ·
But revving the engine demands more fuel, so it's a conundrum.

I'm sort of an shoot from the hip engineer and rocket scientist. Usually pretty good at troubleshooting, too.

I'll be digging in shortly (clearing my morning schedule). I also have a new and better designed fuel pressure testing system coming. The one I've been using works but doesn't have the correct fittings for putting the gauge at the tank or bypassing the fuel filter. It also only lists PSI not Bar. (why use Bar anyway?)

Also, I need to research what flow rate data is telling me. I'm currently using Torque to log the activities of various ECU data streams and was surprised fuel pressure wasn't available to log but flow rate was.
 

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Discussion Starter · #32 ·
Thanks, yes I know about BAR (but this car is Mexican) ;-)

Anyway, I picked up a copy of the VW Service manual for this car. (From Bentley) and it indicates a different spec.

It says

- Engine at idle 2.0 Bar (29psi) (I'm actually higher with the original regulator)
- Fuel pressure with vac hose disconnected 3.0 bar (44 psi)
- Residual pressure after 10 minutes 2.0 bar

Using these numbers, my original regulator is delivering, with maybe a little high numbers for idle.

The manual also lists a different method for testing the delivery rate that I will have to wait on my new testing gear to be able to try.

I thought I read somewhere there were separate ignition coils for each cylinder but it seems there is only the one. Maybe that's with later versions, so the only way to 'test' the coil issues would be to replace it.

Anyway I also remember NOW why I didn't get my regulator through Amazon. They won't allow the sale of this item to customers in California. (grrrrrr)

So I ordered a genuine Bosh 3 Bar off of Ebay - just because. :)
 
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