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Old 02-09-2006, 09:03 PM   #1
tmarcel
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Default Blow thru MAF, there is HOPE!

Well well well...I just finished my MAF swap from intake pre-turbo to intake post turbo and my car is ALIVE again This really woke the car up and 100% resolved all of the bucking and stalling issues. Previously, the car would hunt for idle after you let off the gas and would buck in part throttle cruising.

After I finished with an ECU reset with UTEC on top, I let it warm up and then took it for a drive. First thing I notice though is a higher than normal idle. We're talking approximately 1250 rpms once warm and about 1500 cold. Yep, that's a bit high but better than nearly stalling at 700+ rpms

I haven't touched the maps yet as I just wanted to complete the job and see how it affected the running condition. I never got into boost as I knew that the map would need to be richened up.

Anybody have any idea about the high idle? Did I goof anything. Again, I'll take 1250rpms any day over barely able to idle. Maybe it could be the MAF placement in the 3" ID tube?? Mines not exactly on-center and actually sits a little lower than center as well.
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Old 02-09-2006, 09:59 PM   #2
AaronWRX
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I'll let you know. I'm about to place my MAF in the APS 3 inch ID tube. (two weeks)
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Old 02-10-2006, 09:29 AM   #3
ride5000
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todd, did you reset your stock ecu after the mafs move?
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Old 02-10-2006, 09:41 AM   #4
Freon
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As far as idle, what does your MAF voltage look like? AFR? Have before and after logs?
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Old 02-10-2006, 12:04 PM   #5
tmarcel
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Ken,

Yep, I did a reset as I had the battery out for about 4 hours.

Freon,

I'm just getting by right now because I need to get another laptop and my O2 sensor just took a crap about 1 week ago. Water got into the connector and kept saying "open heater" and now is just dead.

I might try another quick ECU reset (vishnu style) and see if I can't borrow my frinds laptop later today. I'm just so happy that it sounds strong at idle now. BTW, I'm also getting an immediate CEL so I need to check that out too. Maybe my wire extending wasn't on par? I used 18g wire for all five wires and did a hook and loop with a quick solder on each one. I had heard that there was a shielded wire in the harness and it's true. It's grey and then connects to pink and at the connection they used some type of rubber insulation. I wonder if anybody else has had an issue with that one?
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Old 02-10-2006, 12:24 PM   #6
ride5000
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todd, is the ID of the new maf housing similar to stock? i'm not sure what stock is.
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Old 02-10-2006, 12:43 PM   #7
tmarcel
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Quote:
Originally Posted by ride5000
todd, is the ID of the new maf housing similar to stock? i'm not sure what stock is.

I'll see if I can grab a pick for reference of the set up. Basically what I did was cut the length of piping that had the MAF housing out of my 3" SS intake tube and then measured the the same length of pipe on the IC pipe and cut that out and used couplers to tie it in. The cold side IC pipe is 2.75" and the MAF tube is 3".

I think the stock tube is maybe 2.75" IIRC. Why do you ask about that?
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Old 02-10-2006, 04:41 PM   #8
tmarcel
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Okay, here's where I am. I got another O2 sensor and at just idle the AFR is an exact 14.7 with an occasional 14.9. I reset the ECU again and now the idle has come down to just under 1k rpms. Not to bad but I'm guessing there's an issue with my wiring. The CEL comes onm immediately after the engine is started. It didn't do that before so I'll have to track that down. Does 1k rpms still sound a little high for a blow thru MAF set up with ECU plus UTEC?
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Old 02-10-2006, 05:24 PM   #9
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Todd, please please please pardon this question, but I've got to ask. How on earth did you do this? I thought our (I'm going to assume your MAF non-Subaru or something) MAF deciphered the air mass via how much voltage it took to cool the wire. Wouldn't post compressor skew that reading based on existing temp of the airflow it sees?

What pre-existing inconsistency are you trying to overcome?
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Old 02-10-2006, 05:31 PM   #10
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Ahhh. Blow-through = VAF or Karmen Vortex?
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Old 02-10-2006, 06:32 PM   #11
tmarcel
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Pat,

Nope just a OEM Subaru MAF sensor in 3" ID pipe. This isn't anything new FWIW. Going back many months ago you can search for this in the 2.5L forum and there's been several others already and successfully doing this very same thing. I just copied them

As far as the temp sensor (I've got FMIC with the MAF on the post IC side before the TB), we'll have to see how this all plays out. I feel comfortable at the moment saying that it'll work in MY car soon enough. I just need a little more time with it.

Otherwise, it runs a lot stronger/consistent at part-throttle and idle than it did before. That's what I wanted to acheive with this swap around anyway.
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Old 02-10-2006, 06:37 PM   #12
tmarcel
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Quote:
Originally Posted by tmarcel
I reset the ECU again and now the idle has come down to just under 1k rpms.
EDIT: Idle is back up again. Anybody else seen this before? I still need to pull the CEL from the ECU to know what it is.
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Old 02-10-2006, 07:24 PM   #13
gpatmac
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Post ic clears it up for me. I'm researching "big maf" and came across your post, which is pretty interesting.

Do you still have to scale it significantly?

....I will search.
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Old 02-11-2006, 06:58 PM   #14
tmarcel
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I just pulled the code that I'm getting and it's a P0102 for low input to the MAF sensor. Who want's to guess if it's in the wiring extention or maybe my sensor is actually going south.

It's worth noting that about 2 weeks ago I took the car through one of those high pressure, touch-less car washes and enough water managed to get through the space between the fender and the hood and soaked the airfilter. The car was just idling the whole time the car wash was doing it's thing and by the time it had stopped, the car was struggling to idle.

I pretty much assumed that water must have got to the intake. So it limped out of the car wash and I popped the hood to find the filter soaking wet. I limped it back home just a couple of miles and pulled the intake off. Bammm, water was all over the MAF sensor and was being drawn down the intake tube. After I finished cleaning everything out and trying to dry the filter it ran like pure crap for the last couple of weeks. That's pretty much what motivated this MAF swap around in the first place I'm happy that I did it though as it's clearly better for a big turbo such as the one I'm running.

Anyway, maybe I'll just try cleaning the sensor really well and if that doesn't work then re-wire, and if not that then replace the sensor. Obviously replacement is expensive and cleaning the sensor is the cheapest on order to track down the prob. What do you guys think???
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Old 02-11-2006, 09:54 PM   #15
mavrick
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try using some brake cleaner works well.
MAv
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Old 02-13-2006, 11:21 PM   #16
tmarcel
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Here's the deal! I cleaned the MAF and CEL comes on immediately after ECU reset. I then rewired each of the MAF wires, one at a time with a full ECU reset to no avail. Looks like it's a faulty MAF sensor after running it through the car wash. BTW, I was going to check it for voltage min as the FSM stated but I couldn't find my multimeter.
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Old 02-13-2006, 11:38 PM   #17
DonkeyPunch
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Anyway of doing this with TMIC? Or has anyone tried yet?

DP
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Old 02-14-2006, 07:37 PM   #18
PERRINJeff
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Don't forget, with the blow through, the PCV isn't sucking air after the MAF sensor anymore......... Just giving you a clue as to what your problem is.
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Old 02-14-2006, 07:43 PM   #19
Nixlimited
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Quote:
Originally Posted by PERRINJeff
Don't forget, with the blow through, the PCV isn't sucking air after the MAF sensor anymore......... Just giving you a clue as to what your problem is.
i.e. get a catch can ... maybe even a Perrin one
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Old 02-14-2006, 08:08 PM   #20
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What i said kind of sounded smart ass like. I was trying to say is that your CEL light is coming on because of the now un-metered air being sucked into the PCV.

Secondly the PCV is open sucking air around the TB cauing your higher idle. So the solution, block the PCV hole on the manifold and remove the PCV from the system.

The vents on the block will not emit much in the way of air flow so you don't have to worry about those anymore. Hope that makes sense. I hope that fixed your problem also!
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Old 02-15-2006, 08:35 AM   #21
tmarcel
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Jeff,

I'll certainly give that a try and thanks for the suggestion. However...I think that the sensor MAY actually be bad. As I stated above, when I took the car through one of those high pressure car washes part of the filter got soaked. The car was idling the whole time in the wash. When I gave it some throttle to get out of the wash it began to stumble and then stalled thereafter. I pulled the intake off and there was a trickle of water all the way down the intake. My guess is that the MAF pulled water up into it's sensor part and shorted it?? It never idled correctly after that incident either. So, I was wanting to go the blow through MAF route anyway.

I found my digital multimeter last night also and tested the connection at the original MAF sensor harness and then tested the new sensor location with the extended wiring. It tested the same voltage in both spots and seemed to be within the factory spec.

So, I will definitely give the PCV trick a try and see if that resolves it. But since the CEL comes on IMMEDIATELY after a full ECU reset I'm leaning towards the sensor being bad. Any other thoughts?
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Old 02-15-2006, 09:05 AM   #22
ride5000
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todd, do you have an intake tract pressure tester? ie, pvc pipe cap of appropriate diameter with schrader valve? i would really go over the engine with a fine toothed comb to make sure you don't have any induction leaks.

second, don't quote me on this, but i seem to remember something about the latest v5.0 firmware for the wrx utec causing a delay in the signal which it passes on to the oem ecu during bootup. on some cars it's enough to cause a cel. i know it had something to do with the mafs. i did a couple of searches but i can't find anything on nabisco. maybe a quick email/call to txs would help you out. iirc they had a beta version of the f/w that they were working on to alleviate the problem.

ken
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Old 02-15-2006, 09:14 AM   #23
tmarcel
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Ken,

Cool. I'll give TXS a ring this morning and see if they can help. I haven't heard of anything like this happening on other cars. On the tester (PVC and valve) I've actually made one of those in the past for my last FI car. I'll have to pic up the pieces from Home Depot and give it a try.
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Old 02-15-2006, 11:14 AM   #24
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tmarcel,
The car wash certainly doesn't help, but there isn't much to short in the sesnor. The only thing is water will mess up the readings until it goes away.

But now that the MAF is basically connected to the thottle body, leaks after the MAF are still bad. And for 100% the PCV is a big leak. Esspecially if you have an 02-03 WRX. The PCV hole is pretty large and would cause very high idle, and your MAF sensor to throw a code, which you have.

Imagine for your car to idle the MAF sensor flows X grams/sec. When you have a manifold leak (PCV, or poor manifold gasket seals, or hose disconnected) the MAF sensor flow is way less than X grams/sec. This large difference is what willl throw a MAF sensor low input code. The code is saying the input(air flow) is low. This is something that can happen will a BigMAF that is way to big also.
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Old 02-15-2006, 02:17 PM   #25
DISCOPOPE
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Quote:
Originally Posted by tmarcel
Jeff,

I'll certainly give that a try and thanks for the suggestion. However...I think that the sensor MAY actually be bad. As I stated above, when I took the car through one of those high pressure car washes part of the filter got soaked. The car was idling the whole time in the wash. When I gave it some throttle to get out of the wash it began to stumble and then stalled thereafter. I pulled the intake off and there was a trickle of water all the way down the intake. My guess is that the MAF pulled water up into it's sensor part and shorted it?? It never idled correctly after that incident either. So, I was wanting to go the blow through MAF route anyway.
pull the blowby return line out and use one of those expansion fittings to block the inlet hole.
start up, feel how much air is purged out of the line.

imagine that becoming unmetered air in the combustion chamber.
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