inconsistant boost n' spiking

[speeddreamz]

I got a sr20det in a 92 fastback, here are my mods

z32 maf with megaflow, s-afc2, 3 inch all the back to a dual n1 (no cat), greddy rspl fmic, greddy bov, greddy profec b e-01 i think...the newest version.

Im having trouble turning up the boost

so...on the greddy it reads in percentages, i have the boost off and i boost up to about 9 psi. Now i try turning up the boost 50 percent. which means it should be at about 10.5ish pounds... and holding steady? well the damn thing starts to spike up to a whole bar(about 14.7 psi). It comes back down and goes to about 9 psi. I can't get it to hold. I tried even higher and it wanted to spike even more but i let off the gas before it went over 1 bar. My question is, can the afc settings in conjunction with the z32 maf have some effect on it not being able to hold boost? Or am i being dumb and not settting the greddy right. And btw i did not adjust the gain setting, i know gain can cause boost spike.

[rednerd]

hey speeddreamz.

I would play with your gain. Do fourth gear pulls. Start off by lowering your gain down two notches. I try to keep my spikes down to within 1psi of my desired setting. Drop your 'set gain' (start boost) way down while you are tuning. Once you have the spike down, start bringing the start boost up until your start getting a spike again.

If you are using the settings that I suggested in your last thread - Once I put my 3" exhaust on I needed to drop the start boost down by about about 20 (i think). The start boost setting can cause a spike as well. It will solve boost waivering problems, though.

According to Enjuku the profec can be tuned to perfecly hold boost, but I haven't seen it yet. As I said I try to tune for a <1psi spike. I have my boost controller mounted under my arm rest and I think the two miles of shiety vaccum hose may be expanding and giving the profec false readings.

As an FWI - APR (popular VW/Audi tuner) chips hold 1 bar on 1.8T engines but will spike to 20-22 psi.

As for you actual question, I think any change in the way your engine breaths could require you to tweak your boost controller settings somewhat. I doubt the s-afc would be the specific cause though. And I'd bet a could of hours worth of tuning and you could have the profec working sweet.

[240_keyy]

rednerd, could you please give us the settings you have on yours? I am having the same problem that speeddreamz is having, but mine is only wavering about 3psi, but I can't get it any closer :(

TIA man!:bow:

[speeddreamz]

I tried taking off the gain completely both the set gain and gain settings i set to zero, only modified the boost settings. I too think that the vacume lines will be the source of my problem. I was wondering if anyone had a quick fix...

This may or may not be related, my BOV does not blow off consistantly the sound wise I'm pretty sure it blows all the time tho. And like i mean if i do the exact same rev to a certain rpm and then let off it doesn't always sound the same. I know the amt of pressure determines the sound but i basically floor it to redline then let off sounds diff or can't hear it at all.

[rednerd]

I'll can't remember my current settings off the top of my head. I posted my old settings a while ago, but that was with stock exhaust. Going to full 3" caused a big spike and I had to retune. I'll post the current numbers tomorrow.

From everyone I have talked to EBC settings are more art than science...

[lilaznjeff]

internal wastegate will offen spike
is better to get a external wastegate

[speeddreamz]

gdi it jeff, why would i trust ur ass...u don't trust me about ur broke ass i/c...haha plus u noe i don't got the $$$ for an external wastegate


anyways... update:

I've gotten the boost almost up to 1.0 cm2/kg or whatever that **** is, one bar. Its more or less about 12 pounds.

When i do hit 1 bar, i hear this violent as heck backfire(almost like a gunshot). like when i'm absolutely positive i'm shooting fire kinda backfire. Im wondering...does that mean i'm leaning ou.... because its stopping sorta...but then again it sounds like a backfire...so too much fuel? Same thing happens when i can do 12 pounds and i turn on a fuel setting on my s-afc (a higher one) but when i turn on the higher one it happens at 1 bar too ? hmm what do you think the prob is?

[rednerd]

wow, that seems really really bad. I run over 13 psi at the track with no problems on a pretty stock red top.

BTW, on my profec-b you can change to displaying PSI by:

" At OFF mode hold down SELECT buton, and with in 2 sec. press the MODE button 2 times. "

Back firing does sound like too much fuel, but don't quote me on that. Does the s-afc tell you what the o2 voltage is at that point? Could it be somehow cutting spark, that would cause a rich condition / back fire...

[rednerd]

Sorry for the lag in reply. I finally got to go on a longish road trip with my 240.

I found something really weird that I've seen signs of before. The boost settings seem to change with the weather. On cooler almost cold (40-50F) days I get about 3psi more boost. I was thinking it was underhood temperatures causing the difference, but I just drove almost 2 hours and I had 13 psi of boost all the way back (I only wish I could have been on boost the entire way :).

Right now here are my 10psi settings:
Set: 50 hot / 56 cold
Gain: 9/8
Start boost 50

[240_keyy]

THANK YOU SO MUCH REDNERD!!!!!!! :boink:

The settings you gave me were PERFECT!!! No more spiking and bobbing, it is fantastic! I wanted to run a bit more boost so these are the settings I am using for 10psi and 14psi on my Profec B Spec II with SR20, stock turbo, Blitz FMIC, and full 3" exhaust from turbo back.

For 10 PSI:
Set: 50%
Gain: 8%
Start: 50

For 14 PSI:
Set: 60%
Gain: 10%
Start: 80

No spiking, no bobbing, just pure even boost. Ohh it is soooooo nice :) My car has NEVER ran this well, it feels soooooooo much better. I owe you one bigtime!

[rednerd]

240_keyy - A couple of questions:

Where do you have the soleniod and controller mounted?

What major mods do you have?

Did you use silcon vacuum hose?

Doesn't 14psi kick ass?

[240_keyy]

I have the solenoid mounted on the DS shock tower right by the PS resivoir. The boost controller is mounted in a cd tray thing under where the radio would be if I had one.

Major motor mods are listed in my post previous to this one, as for other mods, there is VERY little suspension stuff I don't have. Almost nothing on my car is stock.

I used the vacuum hose that came with the controller

14psi owntz mee!!1! :D

Actually I was running 14psi before, but not consistently, now it is much better.

[95240sxer]

I've been having the EXACT same problem as described about the boost spiking. I think my problem is I have the start boost at 0, I thought it was to make it spool quicker which I didnt feel I needed because my problem is a spike, so therefore I don't need it to boost quicker, I need it slower. But I'm now confident that those setting will fix my problem. Here is my setup:

1995 SE
S13 blacktop
Greddy Boost controller
Greddy BOV (typeS)
Hybrid Intercooler BIG
3in Custom Downpipe
Project Silvia Resonated test pipe
Apex Dual N1 exhaust

I finally got it to waver around 10psi. I thought the problems were being caused by my leaky o2 sensor housing gasket, although I don't see how it could be. But I guess it's just my settings.

Thanks in advance.. At work right now but i'll check it when I get home.

[rednerd]

Don't rule out a leaky turbo gasket. Your turbo spins because the exhaust gas expands rapidly as it leaves the engine and forces the turbine wheels to spin. Exhaust leaks near the turbo can make the turbo act quite weird.

Anyways, you are running a Profec B Spec-II, right?
What are your boost controller settings?
Do you hold decent vaccum at idle?

[95240sxer]

Yeah.. I've got a Profec B Spec-II, it holds about -6 to -8 at idle. I adjusted the boost and now it holds about 10-11psi, but it wavers while it's boosting. It's really odd, it'll go 10-11-10-11-10 the whole time. I thought the leak wouldnt effect it because it's leaking after the tubo, not before, so the turbo will spin with the full exhaust still, but maybe that's not the case? I now have it set at:

For 10 PSI:
Set: 45%
Gain: 8%
Start: 40

It's been cold at night lately (30-40 degrees), I have a test pipe which is leaking too (need to get ahold of some gaskets). I tried running it up to 14psi but it started backfiring. I hear that's somewhat normal but it scared me. I don't want the police seein me shooting fire. I'll change all the gaskets soon and hopefully it'll fix everything.

[andrave]

port the waste gate!

[95240sxer]

What good would that do? I'm going to the track tomorrow and i'd like to get it boosting at at least 12psi. I'm racing my friend's 88 Supercharged MR2 on slicks and 12psi on the supercharger. I wanna win by a landslide, not just win. When I try to run 14psi it sorta sputters while boosting, it's scary. I'm not sure why, any ideas?

[uiuc240]

Originally posted by 95240sxer
Yeah.. I've got a Profec B Spec-II, it holds about -6 to -8 at idle.

in-Hg?

That's not good...you should be at around 15-20 in-Hg in the vacuum side. Sounds to me like you might have a leak. Especially with the backfiring you're talking about. Time for a pressure tester...

Eric

[95240sxer]

It's -6 to -8psi, but I looked at it again and it's actually like -8 to -9
psi at idle. Is that bad? What pressure tester could I use? It does sound like there may be a boost leak. I'll verify that everything is buttoned down well.

[uiuc240]

type in "Intake Pressure Tester" in Google. voila!

As for the vacuum number...look at your gauge...the negatives are measured in inches of Mercury (in-Hg). Normal SRs pull nearly 20 in-Hg at idle. Mine's at about 16, but it's lumpier than most for some reason that I can't figure out (just at idle though). You probably have a leak somewhere that you need to find until moving along with your tuning....

Eric

[95240sxer]

I believe it was my bov causing the problem. I tightened it down and I was able to run a [email protected] @12psi

[uiuc240]

That's the problem with a maladjusted atmospheric BOV...it leaks so much air you lose vacuum...

Eric

[95240sxer]

Still trying to get it boosting correctly. I replaced every exhaust gasket that exists on the car (head to manifold, manifold to turbo, turbo to o2 housing, o2 housing to downpipe, downpipe to test pipe, and test pipe to exhaust). It does not spike nearly as bad, but it still spikes. Any ideas? The boost varies a lot. I'm at 2700ft. How will that effect how to adjust the boost?

[andrave]

port the wastegate! it spikes because the wastegate is having problems flowing the air you are asking it too... thats nearly always the cause of spiking when it occurs on an internally wastegated turbo. Take your turbo off and plug up the hole, use some chalk on the WG flange and then sit down with a dremel or compressor and die grinder and go to work on it...

[95240sxer]

I just got a HKS 02 housing too

[andrave]

thats probably not going to help, if the boost is spiking because of the wastegate. Have you checked to make sure the wastegate is functioning normally? opening all the way? if it is, and you are still having spike issues, you might want to try porting the ... waste gate....