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DIY Turbo Discussion greddy on a 1.8? homebrew kit?

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Old 04-30-2011, 06:31 PM   #1
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Default driveability after IC

Did the intercooler a couple months back and ever since then my part throttle inputs have really suffered.

The first thing I noticed was when approaching 0 vac/boost onset, my wb would read 10:1. The second and I believe related thing is, let's say I'm on the freeway and I punch it in 5th gear, car goes into boost, hits 10 psi and if I gently back off the gas I get a horrible stutter. I end up having to take my foot completely off the pedal to avoid this stuttering.

The rich condition is right at 4k rpm, 25-30%tps signal. I have tried unsuccessfully to tune out of it but it makes no difference. I even pulled 40% from my airflow map on the emb right at that cell and it made no difference whatsoever. I have the greddy sensor installed and on that map, I am adding 0 fuel in those cells. I have 305cc injectors installed.

Besides this issue, the car runs great. I have really had to change my driving style do to this. I am used to smooth throttle inputs, now it's more or less wot, off, wot, off.

Help!

Last edited by flounder; 05-01-2011 at 01:56 PM.
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Old 04-30-2011, 06:37 PM   #2
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I highly doubt it has anything with you adding an fmic. Sounds more like a tuning issue and bov setting too stiff.
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Old 04-30-2011, 06:42 PM   #3
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Ya think? I was going to try removing the bov vac line and plugging the mani to see if it made any difference.

If I understand this correctly, the bov should be held pretty tightly shut at zero vacuum, why would that cause a 10-1 afr?
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Old 04-30-2011, 06:47 PM   #4
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I dunno much about the emb, but on ms there are "overrun fuel cut" settings which cut fuel as soon as you let off the throttle and dip into vacuum. As for the surging, what bov do you have? Is it adjustable?
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Old 04-30-2011, 06:55 PM   #5
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Just a cheap ebay one, it has washers for adjustment. I had to cut a lot of the spring to get rid of comp surge already. Come to think of it, I still hear a very slight fluttering when shifting below like 3k. Maybe you're on to something?

Again, why do you think too stiff of a spring would cause me to run rich entering boost? I could see if it was too loose a spring and I was sucking in unmetered air.
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Old 04-30-2011, 07:07 PM   #6
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I think the two problems are independent of one another. You're still running the maf? Is the bov recirculated?
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Old 04-30-2011, 07:14 PM   #7
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Yes on the maf, I was thinking about that too. I already had issues with that originally because it was to close to the compressor and I was having droopy idle problems. I extended the intake pipe by about a foot and that problem went away completely. Maybe with the compressor spooling up, the maf is still picking up airflow from that and going rich?

The bov is vta right now, which I know is not the best idea on a maf car, but when I had my bpv with a check valve installed I had the same issue.
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Old 04-30-2011, 10:10 PM   #8
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Well for one, I wouldn't use the airflow adjustment map. Use the injector map and the timing maps, that's all you really need. The airflow adjustment map will **** with timing, FYI. Injector map won't. Sounds like you need to spend time tuning.
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Old 04-30-2011, 10:20 PM   #9
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I only tried using the airflow map today to lean it out around the problem area. Normally I use just the injector and ignition maps with the greddy sensor.

It was weird because regardless of how much I attempted to remove fuel with the airflow map, I still saw 10.1 on my wideband at between 25-30%throttle at 4k.
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Old 05-01-2011, 01:17 AM   #10
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There's a possibility of your bov to be partially open in that range, or at least leaking due to low pressure on the diaphragm and bleeding off some metered air.
Sounds like it anyway
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Old 05-01-2011, 12:13 PM   #11
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sounds like you have a boost leak, take a pvc end cap and drill n tap it for a compressor fitting, hook it to a compressor turn the pressure down to about 15 psi and start spraying all the joints with soapy water, spray the bov too, im sure you will ifnd alot of leaks. the computer is putting in ful for the measured amount of air, when some gets out its still putting in fuel for the amount of air that went through the maf, so it feeds it fuel for air that isnt there.
i just saw that you cut ur bov spring, what that has done is allowed the car to push air out of the bov when entering boost, as the boost level raises the pressure on the back of the diaphragm starts helping out and it stays closed. Put a tial q on there and never worry about it again.
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Old 05-01-2011, 01:26 PM   #12
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Quote:
Originally Posted by 1slowna View Post
sounds like you have a boost leak, take a pvc end cap and drill n tap it for a compressor fitting, hook it to a compressor turn the pressure down to about 15 psi and start spraying all the joints with soapy water, spray the bov too, im sure you will ifnd alot of leaks. the computer is putting in ful for the measured amount of air, when some gets out its still putting in fuel for the amount of air that went through the maf, so it feeds it fuel for air that isnt there.
i just saw that you cut ur bov spring, what that has done is allowed the car to push air out of the bov when entering boost, as the boost level raises the pressure on the back of the diaphragm starts helping out and it stays closed. Put a tial q on there and never worry about it again.
I just went out and added two washers to the bov for a stronger spring. While it did increase fluttering in low boost shifting, it did nothing for my rich condition.

From what I understand about bov's, vacuum is what tries to open it. If it stays closed at idle, why would it want to open approaching 0 vac?

I've been paying more attention to my boost gauge and does flutter a bit under boost. That would indicate a leak right? My mbc is sourced from the cold side of the IC.

Can I use the compressor wga source to do the leak test? It's capped off right now, but I still have the nipple.

Thanks for all the help!
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Old 05-01-2011, 01:42 PM   #13
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Quote:
Originally Posted by flounder View Post
From what I understand about bov's, vacuum is what tries to open it. If it stays closed at idle, why would it want to open approaching 0 vac?
The difference between manifold pressure (the post-throttle "boost" or "vacuum" we read with our gauge) and the pressure in the post-turbo intake is what opens a BOV. Therefore, high boost in the intake with 0 MAP could certainly open that valve if the spring is light. Not many of us have instrumented post-turbo/pre-throttle intake pressure, although it would be easy to do.

Honestly, I think it is time you moved on to a programmable ECU and deleted the MAF. The MAF is a restriction anyway. And the advice to look for leaks is a win no matter what else you do.
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Old 05-01-2011, 01:53 PM   #14
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If the bov leak is the cause, recirculating should solve the problem right?
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Old 05-01-2011, 03:15 PM   #15
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Quote:
Originally Posted by flounder View Post
If the bov leak is the cause, recirculating should solve the problem right?
Yes. Recirculate to post-MAF.

However, what puzzles me is that it occured in conjunction with the IC install. If it was only BOV, then I would not expect to see this connection (i.e., you should have seen the issue before). I think you should look hard for other leaks as well.
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Old 05-01-2011, 08:09 PM   #16
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Quote:
Originally Posted by hornetball View Post
Yes. Recirculate to post-MAF.

However, what puzzles me is that it occured in conjunction with the IC install. If it was only BOV, then I would not expect to see this connection (i.e., you should have seen the issue before). I think you should look hard for other leaks as well.
I was using a bypass valve before the IC. Instead of checking for leaks, I just went ahead and tightened up all my clamps went for a drive. Lol, boost went up to 13 psi without touching my mbc. I would say I had quite a leak there. But...the richness still remains. 13 psi feels great btw! I had to turn down the mbc a click to get back to 10 psi because I don't think my injectors nor clutch was up to the task. So now, it's either go stand alone or recirc my old bpv and ditch the bov.
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