Low boost and lean

[kextyn]

I've had a CEL for a lean condition for a little while now. If I clear it sometimes I can go days without it coming back on and it went away on it's own at least once. I just got a VAG-COM and did a little bit of logging during my commute today.

The first pull was 3rd gear and the others were 4th. Would have had a nice 3rd gear pull through the whole rev range but I would have pissed off a lot of people by slowing down that much.
http://spreadsheets.google.com/pub?k...scb3YIlDKMeeIg

I have a few other short logs with 2nd gear pulls and I was hitting around 1540 and saw 1650 once (actual boost, mbar.)

What should I log to find the cause of the lean condition? Is it related to those low boost numbers or what? It's my first time logging so I don't know what a stock 2001 should be hitting for boost, but it's much lower than what the ECU is requesting.

[mike-2ptzero]

Well your requested boost is the stock and that is right around 800mbar or .8 bar (11.6psi). On your log your only hitting a max of 560mbar or .56 bar (8+psi).

Your target AFR of .891 (13:1) is way lean and your actual AFR of .899 (13.2:1) is even leaner.


You might want to log block 003 to see what type of maf readings you are getting. Also look at block 032(dont need to log) so you can see how much the ecu is trying to adjust the fuel trim. These will give you a good idea what is causing the lean and low boost issue.


My guess is that you have a maf that is near dead seeing that your load reading on block 115 wasn't even close to 100 and most people hit the max which is 191.

[kextyn]

I just realized I messed up on the adjusted boost. That's in bar, not psi.

I just modified it a bit to show psi. Am I doing some calculation wrong? You said I'm hitting a max of 8psi and I'm only seeing 4-5. I'm subtracting 1040 from the actual boost because that's ambient (what I get at idle), is that correct?

I know I've read about people cleaning the MAF, would that be a very good solution or should I just get a new one?

[kextyn]

I logged 003 on the way home, but I just realized I didn't hit redline in any of the pulls (stupid traffic.)

First one is 2nd gear and the other two are 4th.
http://spreadsheets.google.com/pub?k...scZoIbFkV7oWHw

032:
At idle additive: 3.2%
P.throttle mult.: 24.2%

[Nebone]

You are in limp mode due to a bad maf most likely and its been happening to many of us recently. Mine gave out at 125k miles. I can't check the good spreadsheets from work now, but if they are ~120 peak, then get a new MAF; cleaning it worn help.

[kextyn]

You are in limp mode due to a bad maf most likely and its been happening to many of us recently. Mine gave out at 125k miles. I can't check the good spreadsheets from work now, but if they are ~120 peak, then get a new MAF; cleaning it worn help.

I would think limp mode would feel worse than this. I need to do another run to redline to get good readings but currently I'm only seeing low 60's around 4300RPM (didn't have room to go further.) I seriously doubt I'll see more than 120 at redline though. I guess I just need to order a MAF.

[kextyn]

Who has the best prices on MAFs? ECS has the Bosch for $156.

[mike-2ptzero]

032:
At idle additive: 3.2%
P.throttle mult.: 24.2%

If those 2 numbers on 032 dont have a "-" before them your maf is toast, so your ECU is dumping as much fuel as possible to make up for the low maf readings. That or you have a huge leak between your turbo and maf.

[kextyn]

If those 2 numbers on 032 dont have a "-" before them your maf is toast, so your ECU is dumping as much fuel as possible to make up for the low maf readings. That or you have a huge leak between your turbo and maf.

No - in front. How am I supposed to mod this car when it costs so much to maintain! At least I know what the problem is.

What happens if I unplug the MAF?

[mike-2ptzero]

No - in front. How am I supposed to mod this car when it costs so much to maintain! At least I know what the problem is.

What happens if I unplug the MAF?

The ecu then just uses the Fuel maps and 02 sensor to set the fuel. It just wont run nearly as good without the maf then with a good one since it also uses the maf to adjust adv timing.

[kextyn]

So if I wanted to test it without the MAF should I clear anything in the ECU so that it doesn't keep going lean?

[mike-2ptzero]

So if I wanted to test it without the MAF should I clear anything in the ECU so that it doesn't keep going lean?

Yes.

[kextyn]

Alright, I'll try that out.

Thanks for the help guys :)

[kextyn]

Here's a 3rd gear pull with no MAF (disconnected the battery after unplugging MAF to clear everything.)

http://spreadsheets.google.com/pub?k...scbo4tnPuL62EA

I'm pretty sure there's no huge boost leak after the MAF so I'm going to be ordering a new one shortly.

[mike-2ptzero]

Here's a 3rd gear pull with no MAF (disconnected the battery after unplugging MAF to clear everything.)

http://spreadsheets.google.com/pub?k...scbo4tnPuL62EA

I'm pretty sure there's no huge boost leak after the MAF so I'm going to be ordering a new one shortly.

Well the AFR got better on that WOT pull so the maf must be causing it to stay lean when plugged in, that last run saw 12.8:1 around 4k and 11.9:1 by 5k. Even your actual AFR is right on with your target AFR on that pull while they were way off from each other on your first log.

[kextyn]

I just installed the new MAF and did a couple logs.

Block 031, 3rd gear pull, forgot that there's no engine speed on this one:
http://spreadsheets.google.com/pub?k...scZfVKBg14aKEQ

Block 115, 3 2nd gear pulls:
http://spreadsheets.google.com/pub?k...scZ7UymOMKy4NA

Is that what I should be seeing for boost on an '01? It is Virginia (hot&humid) so there was probably some heatsoak. I think it was in the mid 80's and those were all after stoplights.

How is my AFR looking now? Looks quite a bit richer than before and my CEL didn't come back on :)

[ILoveT]

You HAVE to have a boost leak.

Actually I take that back.

[kextyn]

You HAVE to have a boost leak.

Actually I take that back.

Ya, I don't think I have a boost leak. It spikes up to 9-10 when the throttle body closes.

http://spreadsheets.google.com/pub?k...scbLO9eeL3ztWg