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Well, the "normal" spec range, seems to be + or - 10%; so, obviously, over + or - 20% is WAY out of spec. You definitely, have a MAJOR issue; that is affecting the fuel trims, more testing is required (check for: vacuum leaks, fuel pressure in spec, maf readings are in spec @ idle/WOT).

By the way, what is the small LCD OBD II scan tool; that you are viewing, live data with?
 

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2006 Cabrio, Platinum Gray, 2.5L BPS, Automatic
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So I did the brake cleaner vacuum check and that was a negative. The little guy is an Ultraguage, I keep it in my truck. Thought it might work. I think I'll go get a fuel pressure tester and check that out. I am tempted to get a smoke tester also.
 

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Can this be done at the rail? Low fuel pressure or failing pump......the car runs great on the highway and when cold/first thing. If the pump was failing would it not starve at higher demand?
 

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It is best, to follow the vw factory service manual testing procedures; you are trying to do a process of elimination. We have seen, a number of issues; that can cause fuel trim problems.

16555/P0171/000369 - Fuel Trim; Bank 1: System Too Lean
Possible Causes
  • Mass Air Flow Sensor (G70) defective
  • Intake System Leak(s)
Possible Solutions
  • Check Mass Air Flow Sensor (G70)
  • Check Fuel Pressure Regulation
  • Check Fuel Pump
  • Check Injectors
  • Check Intake System for Leaks
  • Check Exhaust System for Leaks
  • Check Secondary Air System for Leaks
  • Check Vacuum Pipes for Leaks

The way to test the fuel pressure; to shown in the service manual, you pull off the fuel line feed, to the fuel raid and install the pressure gauge connected to a "T" style adapter, then a fuel line extension. Then, the various tests, at idle, under acceleration, residual (engine off) and possibly, fuel volume.
 

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Fuel pressure specs:


testing:


Note: on many of these later model 2.5L's; that fuel pressure regulator, is included in the fuel filter assembly.

 

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2006 Cabrio, Platinum Gray, 2.5L BPS, Automatic
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Have to say I didn't see anything, also the new Bosch MAF did not make a difference. What gets me is the car runs great on the highway. At the light it has a rough idle and the exhaust smells very rich. It will throw the P0170, I clear it and there is a noticable difference in the idle. Then it goes back to idling rough. I am going to peek under the car and see if my fuel filter is the regulating type. Then I am going to order a new one. I'm sure the one installed is factory.
 

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2006 Cabrio, Platinum Gray, 2.5L BPS, Automatic
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Ok, at the rail with key on/no start it jumped to 54. I waited a few minutes and it dropped a few. I started the car and it shot to the first picture (gauge only). I let it idle for 10 minutes and took the second picture. I think the regulator is shot, do you agree? Recommendations on where to obtain an OEM filter?
 

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The fuel filter on some of these; can be tough to source; oem tends to be Mahle, Mann, etc.

You might confirm by your vin # but i believe this maybe the part# 1J0201051B:


Others, had a hard time finding it locally but were able to got it from their local vw dealer (next day special order, if not in stock) or if you are willing to wait, order it online.
 

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Yep I saw that in my Bentley. 4 bar at first then settle down to 3. So I would say the pump is just fine but way to much fuel pressure.
 

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So, what would you say; were the readings you got at idle (slightly high?) , did you check residual pressure after 10 minutes and how the psi readings change, when you rev the engine?

To view things under load, under normal driving conditions; you could tie wrap the gauge so you can see it, take a test drive (putting the car through various types if loads), if the gauge reaches that far.

Many problematic fuel pumps, can work fine; when things are cold but start malfunctioning, when the pump gets hot.

The fuel filter/regular; would be the cheaper, first thing to replace, if you believe the fuel pressure is out of spec.
 

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The first reading (picture) is first start, even then a little high but not much. The second reading (picture) is 10 minutes later. It did not drop to 3 bar as the manual said it should.
 

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Well the filter definitely took care of the fuel pressure issue and it ran great. Then after about 30 miles the CEL came back on with a P0170. I cleared the code and it ran great again. Could the EGR have anything to do with this? When first started I hear a marble in a can sound for about 15 seconds then it goes away..
 

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Ok, sounds like you are making some progress; after removing a major variable, assuming a clogged fuel filter and or a bad fuel pressure regulator. Remember, the fuel trims take time to (re)adjust; to the new fueling conditions.

What are the conditions, related to the two fuel pressure relayed photos? e.g. idle, residual, etc?

After each change you make (fuel filter); viewing live data, fuel trims in particular would, help you see the improvements made and see how the computer is adjusting to a possible ongoing lean condition. If it drops into the normal + or - 10% range, things would seem to be fixed.

However, based upon the thrown p0170 lean code; i would want to see, what the current fuel trims are. It typically, takes clearing codes, ti reset skewed fuel trims and/or a decent test drive, for the computer to get things adjusting again, to new fueling conditions.

If the fuel trims are still abnormally off, the lean code keeps coming back; you have more troubleshooting and testing to do, to find the problem.

Where is the "marble in a can", sound coming from? I have heard the sound description; being said, in relation, to a failing fuel pump or if specific to a cold start up, the secondary air injection pump, could be failed or the rubber mounts are bad, causing it to rattle when activated.

You might make a video, so we can hear the sound you are referring to and post it to youtube, link to it here.
 

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P0170 VOLKSWAGEN

Possible Causes

Intake air leaks
Faulty front heated oxygen sensor
Ignition misfiring
Faulty fuel injectors
Exhaust gas leaks
Incorrect fuel pressure
Lack of fuel
Faulty Mass Air Flow (MAF) sensor
Incorrect Positive Crankcase Ventilation (PCV) hose connection


Sent from my iPhone using Tapatalk
 
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