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What is wrong with my 3g MAF?


jepherz Galant VR4.org Moderator
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Galant VR-4 org Post #: 1046185 posted 01/18/12 01:27 AM     Remind Me!  Send Private Message   Edit Post      
For starters, I got a brand new 3g MAF from a member here a long while back, probably 5-6 years ago. To be honest, besides burning a chip with the 3g MAF tables in it, I didn't do much tuning OR driving of the car for years. The last few years I've tracked it and had a conservative tune. It was hard not to notice, though, that there was some weird behavior on partial throttle around 2-3000 RPM. AFR's would first jump up to around 15-16 AFR and the car felt SLOW. Then, as soon as AFRs rose, they dropped off again and the car took off like a bat out of hell.

I've now installed an Evo ECU with the intent on being able to log and tune easier. To my surprise, with a few Evo maps with only injector corrections (PTE 780s) the car behaves the EXACT same. I tried to take some logs although I'm no tuner so I'm not totally sure what to look for. I logged MAF hz vs. AFR vs. RPM and it seems like the only similarities are partial throttle acceleration. Somewhere between 150--200 hz I am having issues. But the strange thing is, if I am just cruising and not under load, the AFRs seem fine at that same frequency from the MAF.

In order to narrow it down a bit, I locked the ECU into open loop and set the fuel tables to 11:1 AFR to see what would happen. Here is a log segment to show what I'm talking about:

Code:

TPS RPM AirFlow ECULoad W02
20 2187 150 58.75 11.68566
20.3 2187 150 59.375 11.86143
20.3 2218 150 59.375 11.74425
20 2250 150 59.375 11.68566
20.3 2250 150 59.375 11.74425
20.3 2250 150 58.75 11.74425
20.3 2250 156.25 59.375 11.80284
20.3 2281 156.25 59.375 11.80284
20.3 2281 156.25 59.375 11.80284
20.3 2312 156.25 59.375 11.86143
20.3 2281 156.25 59.375 11.86143
20.3 2312 156.25 59.375 11.97861
20.3 2312 156.25 58.75 11.97861
20.3 2343 156.25 60 11.97861
20.3 2343 162.5 60 12.0372
20.3 2375 162.5 58.75 12.0372
20.3 2375 162.5 59.375 12.15438
20.3 2375 162.5 59.375 12.15438
20.3 2406 162.5 60 12.27156
20.3 2437 162.5 59.375 12.15438
20.3 2437 162.5 59.375 12.21297
20.3 2437 168.75 59.375 12.21297
20.3 2437 168.75 59.375 12.27156
20.3 2468 168.75 60 12.21297
20.3 2468 168.75 59.375 12.21297
20.3 2500 168.75 59.375 12.21297
20.3 2468 168.75 59.375 12.38874
20.3 2531 168.75 59.375 12.44733
20.7 2500 175 60.625 12.38874
20.7 2562 175 59.375 12.27156
20.7 2531 168.75 59.375 12.38874
20.3 2562 175 59.375 12.6231
20.3 2562 175 60 12.6231
20.7 2593 175 59.375 12.6231
20.7 2562 175 59.375 12.79887
20.7 2593 175 59.375 12.79887
20.7 2593 181.25 60 13.209
20.7 2625 181.25 60 13.32618
20.7 2625 181.25 60 13.38477
21.1 2625 181.25 60 13.44336
20.7 2687 181.25 60 13.32618
21.1 2656 181.25 58.75 13.32618
21.1 2687 187.5 60.625 13.44336
21.1 2687 187.5 60 13.67772
21.1 2718 187.5 60 13.61913
21.1 2718 193.75 60.625 13.67772
21.1 2718 187.5 60 13.61913
21.1 2718 187.5 59.375 13.61913
21.1 2750 187.5 60 13.209
21.1 2781 187.5 59.375 13.09182
21.1 2750 187.5 59.375 12.91605
21.1 2781 187.5 58.75 12.79887
21.1 2812 187.5 58.75 12.68169
21.1 2812 193.75 58.75 12.6231
21.1 2812 193.75 59.375 12.50592
21.1 2843 193.75 59.375 12.21297


I haven't messed with the MAF tuning at all because frankly, I'm not sure I should have to. Yes, my ECU rom is set up for an Evo MAF but they flow so closely that it shouldn't be a problem. I had the actual 3g tables in my ROM on my 1g ECU and had the same problem anyways.

Anyone have any ideas? I'm tearing my hair out trying to think of what the problem is. I will buy a new 3g or Evo MAF if there is something wrong with mine, I just don't want to throw parts at the car without having a good feeling about what is wrong. Could my intake piping have anything to do with it? My BOV is recirc'd fairly close to the MAF coupler, could that matter?

Help!



-Jeff
1881/2000
50/1000


Edited by jepherz (01/18/12 02:05 AM)

Posts: 7874 | From: KC, Missouri | Member Since: 08/08/04 | IP: (184.196.109.242) | Report this post to a Moderator

Andy_S
Overcomplicated


Galant VR-4 org Post #: 1046260 posted 01/18/12 11:05 AM     Remind Me!  Send Private Message   Edit Post      
Whats your fuel pressure and injector latency?



I found v8's...

Posts: 982 | From: Shithole Wisconsin | Member Since: 01/30/07 | IP: (209.225.103.180) | Report this post to a Moderator

jepherz Galant VR4.org Moderator
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Galant VR-4 org Post #: 1046271 posted 01/18/12 11:52 AM     Remind Me!  Send Private Message   Edit Post      
Injector scaling was taken from EvoM in this thread:

</font><blockquote><font class="small">Quote:</font><hr />

PTE 780cc

Scaling: 680

Latency:
4.6875 3.624
7.03125 1.992
9.375 1.344
11.7188 0.984
14.0625 0.744
16.4062 0.576
18.6768 0.456






I will double check fuel pressure, but my intent is 36 psi (stock DSM). Not sure if that should be different since I am running an Evo tune, anybody know what base pressure is on an Evo 8?

In the end, this results in LOW and MID fuel trims within 4%.

I've read a little bit about Accel enrichment, and although that immediately sounded like it may solve my problem, my car runs lean for A WHILE before the fuel catches up. Also, I had never heard of anyone adjusting accel enrichment on DSM ECUs. I don't even remember if the tables had been found for it.



-Jeff
1881/2000
50/1000


Edited by jepherz (01/18/12 11:54 AM)

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Andy_S
Overcomplicated


Galant VR-4 org Post #: 1046276 posted 01/18/12 12:09 PM     Remind Me!  Send Private Message   Edit Post      
I think an evo is around 38-39psi. The trims are almost spot on though. You don't have a lean spot if you WOT, only at partial throttle? I'm thinking this has more to do with the physical setup instead of tuning. At partial throttle, your BOV is probably cracking open. Maybe some weird flow stuff is going on with that?



I found v8's...

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toybreaker Galant VR4.org Moderator
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Galant VR-4 org Post #: 1046280 posted 01/18/12 12:22 PM     Remind Me!  Send Private Message   Edit Post      
This car still have the egr system installed?



the bitterness of low quality remains long after the temporary joy of a low price has faded

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jepherz Galant VR4.org Moderator
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Galant VR-4 org Post #: 1046284 posted 01/18/12 12:33 PM     Remind Me!  Send Private Message   Edit Post      
Quoting Andy_S:

I think an evo is around 38-39psi. The trims are almost spot on though. You don't have a lean spot if you WOT, only at partial throttle? I'm thinking this has more to do with the physical setup instead of tuning. At partial throttle, your BOV is probably cracking open. Maybe some weird flow stuff is going on with that?




That's exactly what I was thinking. It's a factory BOV, but all custom IC piping. I can take some pictures of the actual setup and entry into the intake to see if you guys think there are any issues there. At idle, the factory valve should be open, right? Maybe at that instant when I open the throttle plate it causes some disturbance in the maf reading or something? How can I test this? Disconnect the BOV for a quick test perhaps?

Oh, and WOT will demonstrate the same problem. It's coming back from decel or idle around 20% throttle OR above at that same RPM range. Basically any time I exit a corner and start in on the gas, it has about 100 hp



-Jeff
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Edited by jepherz (01/18/12 12:37 PM)

Posts: 7874 | From: KC, Missouri | Member Since: 08/08/04 | IP: (159.140.254.96) | Report this post to a Moderator

jepherz Galant VR4.org Moderator
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Galant VR-4 org Post #: 1046285 posted 01/18/12 12:34 PM     Remind Me!  Send Private Message   Edit Post      
Quoting toybreaker:

This car still have the egr system installed?




EGR is removed and a block off plate is installed. What are your thoughts there, John?



-Jeff
1881/2000
50/1000

Posts: 7874 | From: KC, Missouri | Member Since: 08/08/04 | IP: (159.140.254.96) | Report this post to a Moderator

beaner
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Galant VR-4 org Post #: 1046331 posted 01/18/12 03:54 PM     Remind Me!  Send Private Message   Edit Post   
I'd set the base fuel pressure to what the ecu is expecting.

The BOV not staying shut seems plausible. I remember I could get my car in a weird situation, especially on the highway, where the bov wouldn't close all the way. If I blipped the throttle real fast, the bov would shut and car would take off.


Posts: 1562 | From: b'ham, mi | Member Since: 06/22/05 | IP: (99.182.1.217) | Report this post to a Moderator


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