Not MAF now Intake?

[jrb]

I just bought my 1st TDI a month ago. It has felt like it loses power around 3000. I installed a boost gauge about 2 weeks ago and boost shows around 14 psi up to 4500. I pulled the intake hose and there was about 1/4" of gunk before and around the EGR but I could not see any further. I bought a vag-com today. Here are some graph's of the symptoms I am having. I thought it was the MAF but am now thinking it may be a very clogged intake or plugged up exhaust. Any help would be greatly appriecated.

Thanks

John

 

[Curious Chris]

Re: MAF question

The middle graph is a telling one. Assuming you were at 100% throttle, I would guess MAF as 500 is the no MAF value so when the MAF starts to malfunction. Before you replace the MAF you do want to confirm that the snow screen is clean and your air filter is too.

Loosing power at 3000 rpm is also classic MAF as apparently no MAF provides adequate fuel to limp the car along but not to scream.

Oh what gear were you in when you logged the data? I ask this as you have to test underload. 14 psi is good to go as stock nominal is 13.5.

Plugged catylic filters are a rare item on TDI's so I would go with the MAF assuming there is not a restriction upstream.

 

[jrb]

Re: MAF question

I was in 3rd gear at 100% for all runs. I pulled the intercooler pipes this morning. It is crusty around the EGR valve. I looked in as far as I could and it is only greasy no grunge. I should have noticed where once the MAF reaches 2M mg/minute it only bounced around 5%.

 

[cage]

Re: MAF question

Hey I think you just helped me with my problem. I'm having a similar situation though not 100% of the time. I was going to replace my MAF just 'cause my heart is telling me that's where the problem lies. Now I'm going to replace it for sure. It appears that 3,000 is a magic number for the ECU/MAF at 100% throttle. Something obviously changes right there and if the ECU doesn't get the reading it wants from the MAF it cuts back on the fuel. Like I said mine will run up to 4,000 sometimes without a hiccup then other times it falls on it's face at 3,000. It also said in a service bulletin posted under another topic that the MAF must be tested at full load to ensure it's good. Again that tells me that something changes in the MAF under full load that doesn't show as a bad MAF when not under full load.
I guess it won't hurt to change my MAF anyway considering it's 7.5 years old and has 104,000mi. on it.
Thanks for this post!!!! You made my day!!!!!!! : )

 

[Curious Chris]

Re: MAF question

Good then I say MAF. I have had two "no CEL" MAF failures that I attribute to the a voltage attenuation in the MAF due to oxidation.

In a stock TDI there will always be some amount of oil film post turbo due to the CCV system. Around the EGR valve itself, some crustiness is also expected as at that point you are mixing hot exhaust gases with somewhat oily air.

Slight oscillation in the MAF is expected too as if you log the boost aka MAP at the same time you will see the boost pressure is in a feedback loop that can only hold value so close so it oscillates about the pressure target. Of course this means that the MAF will see a varying signal based on the vacuum of the turbo.

 

[nosootdzl]

Re: MAF question

Now I'm going to replace it for sure.

Why not clean the sensing and heating elements of the MAF?

 

[Curious Chris]

Re: MAF question

Oh it is a heated film sensor and they run very hot and when they become contaminated it is often an oxidized layer which is not solvent cleanable. Oh people have cleaned their MAF and it worked, I have tried it and it did not.

In the last plant I worked in we made flow sensors for ventilators and the poor flow sensors in the exhalation circuit had the highest failure rate do to contamintion that causes a local hot spot and poof there goes the film.

 

[cage]

Re: MAF question

I did clean my MAF a few weeks ago hoping it would cure it. I also re-packed the connection with dielectric but it still isn't right. Today it drove great. Not only did it run up to 4,000 but it even had it's little 3,000rpm kick back. I'm still going to replace the MAF just due to it's age.

 

[jrb]

Re: MAF question

I just got back from a little 100 mile round trip to the dealer to pick up the new MAF. I installed it in the parking lot next to a Phaeton. I on the drive home it felt no different. I did another 3rd gear pull from 20 mph and it looks the same. Is there something I need to do to get the ECU use the new MAF past 3k?

 

[cage]

Re: MAF question

Now you ruined my day!
Did you take the EGR off to check the gunk?

 

[jrb]

Re: MAF question

I did and it looked bad (1/4 inch) around the EGR and ok a little further in. I must be wrong about the further in part. I made the EGR mod and installed a Greddy oil catch can between the CCV and the intake. I am ready to clean the intake and see how it goes. My top chart shows that if the new MAF is good (it is acting the same way) that it hits a max cfm and will not flow anymore air.

 

[Curious Chris]

Re: MAF question

What is your boost doing duriing this decline in reported MAF?

Another wierd part about your data is that it hits specified MAF fairly low and then has a near linear drop to death. And then have you logged MAF unplugged again yet as that was a good indication that it was the MAF: no difference plugged in vs not plugged in says MAF failure or electrical connection issue.

 

[jrb]

Re: MAF question

My boost stays steady just shy of 1 bar. I have not tried unplugging the maf again and running it again. At lower speeds and around town the expected and actual are within a couple percent of each other. It is only at higher rpm and full throttle that the problem is occuring. I am hoping to pull and clean the intake today or this week. I see from the numbers it is hitting a wall at a certian CFM and not able to flow any higher. Up to that number the MAF responds like normal.

 

[gt]

Re: MAF question

You might try a vac. solenoid valve for the wastegate. The part# ends with 627A It is a vac. valve on firewall. It has a gray top, with black body. It will loose vac. You can also test it in Output test on vag-com. It should click, have had some that just thud. They don't work as well. I paid 39.00 for one last week. Dealer was 92.00

 

[jrb]

Re: MAF question

Just a follow up. I cleaned out the intake and cylinder head and it runs like a new car. I ran the same vag-com log and it stays even with the airflow it is supposed to have. The intake was fairly clean but the elbow in the intake was almost plugged and the intakes on the cyclinder head were clogged to the point I could barely get my pinky into the ports. I fabricated a tool to hook up to the shopvac to clean the intake ports. It did a great job but took about 30 minutes a port to make sure I didn't get anything into the engine.