# How do 12v vr6 obd2 turbo kids sense boost? Mafs only?



## CorradoFuhrer (Mar 21, 2002)

I've been having quirky high air to fuel ratios. I though I had solved it but just installed 42# and dropped my compression via a spacer (that install sucked) 

Got it all turn key but seeing like 13-14 afr at wot. Is the mafs the only thing that sees boost here? So if I were I unplug it the ecu wouldn't know what to do? Thanks, put in a solid 20 hours the last 48 on this; wanna feel some power!


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## PjS860ct (Dec 22, 2002)

post your setup so we can get a clue whats going on


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## CorradoFuhrer (Mar 21, 2002)

Swapped out mafs, actually ran worse. Def putting my oem Bosch back in and returning this. It's just driving me nuts why it's so lean at wot. I guess I have a leak somewhere? What's leak typically mean in these chips?


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## CorradoFuhrer (Mar 21, 2002)

Kinetic 2 Fmic 9:1 spacer, t3/t4 c2 latest 42# race , I've been having the lean issue before I thought I solved it with putting clamps on the crank case to intake there on the kinetic kit post mafs. But no it's bad 14-15 getting on boost? The Bosch mafs was 13-14 afr. So I'm just lost now.


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## PjS860ct (Dec 22, 2002)

so the crank case vent is connected again to the intake pipe of the turbo?

post a picture of the current engine bay (top view)


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## CorradoFuhrer (Mar 21, 2002)

PjS860ct said:


> post your setup so we can get a clue whats going on


What's a good place to start here? If I was leaking somewhere would it drastically alter the air to fuel to be so lean?


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## CorradoFuhrer (Mar 21, 2002)

PjS860ct said:


> so the crank case vent is connected again to the intake pipe of the turbo?
> 
> post a picture of the current engine bay (top view)


It's a standard kinetic kit. Ill try and get pics when I get back home.


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## Yareka (Mar 5, 2002)

I remember that you had a fuel pressure issue before, get that sorted? Might be a good idea to rig a fp guage up that you can watch in the car to make sure its rising with boost.

Ensure you have a good clean vacuum/boost source to the fpr, I've seen check valves on fpr lines before because they were T'd off of evap or the hvac components.


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## CorradoFuhrer (Mar 21, 2002)

Yareka said:


> I remember that you had a fuel pressure issue before, get that sorted? Might be a good idea to rig a fp guage up that you can watch in the car to make sure its rising with boost.
> 
> Ensure you have a good clean vacuum/boost source to the fpr, I've seen check valves on fpr lines before because they were T'd off of evap or the hvac components.


The issue was only a few psi's off, c2 was telling me that this wouldn't affect my afr being drastically off like that but that I would have to check it under load. I chalked it up to my gauge potentially being off a few psi, not sure if it ever got dropped or something. 

I replaced everything in the fuel system and nothing has changed - fuel pump, fpr and new fuel filter.

My manifold is stock, and the vac to the FPR is new and it adjusts on and off vac accordingly at idle. I don't have a long enough fuel line to have someone monitor it under boost, but that is something I can buy to check. I recently bought a walbro 255 inline, but that would just become needed under higher boost. The stock should be on point until 10, so I don't want to raise the stakes just yet. 

I swapped in a autozone mafs, to see if maybe that was the magic culprit, but things actually got worse off (they looked real cheap compared to the bosch). Other than that the car drives fine normally, its just the AFR that i'm reading that really makes me nervous.

No CEL's. I'm able to get into Group 22 or 23 and read timing, but i'm not sure what's the ideal or what's too far out. If someone local had a vag com that would greatly help me out.

I'm not sure about leaks, i'll have to double check the vac/intake lines post mafs, as I could see unmetered air throwing this off, but i had the nipple on my turbo open and it didn't throw off my afr's like that, just lost 20 whp or so on the dyno once it was capped.

I jabbed the fuel pump wires while it was running, showed me 17 volts.. not sure why? It read 13-14 on the battery. I may have messed up my multi meter, before I had it on the wrong settings and zapped the fuel pump fuse.

The 02 is oem and only 2 years old as well. and WOT doesn't use the 02... so basically its just something mechanical being off or the mafs in these cars?


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## CorradoFuhrer (Mar 21, 2002)

not to mention my car ran great for a full year 10 -11 psi+ on the old setup, then just started being lean. I swapped out the fuel stuff, tightened clamps, clean the mafs, then it was running good again the 12's. Threw in the spacer and green giants, now i'm back where I started. Swapped out another mafs, it got worse.

So basically the mafs at WOT is the only thing monitors boost and how much fuel to add? I unplugged it and it didn't even want to drive down the street, got some bad knock at cold.


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## TBT-Syncro (Apr 28, 2001)

most fueling is controlled by the load tables, which is driven off of rpm and throttle position.


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## CorradoFuhrer (Mar 21, 2002)

It's strange when I go into boost the a/f goes richer, so I'm assuming the mafs is the main thing telling the computer more air is being moved through the suction or the turbo.

A spark issue could cause a misfire. It seems to run fine in high rpms low throttle. I discovers a cracked boot, but its not Arcing off my boost tube (caused the crack) I could put electrical tape around but I assume if its not stuttering or missing its good. I want to fix it, but inkjet bought a new set of mk4 wires, I'm not sure if I can purchase one individual wire.

I had the situation mended before, and that involved tightening the crankcase to intake tube ends. Put in the spacer, and now I'm back at this issue. Could be a voltage issue at the pump is now what I think. The autozone mafs was makin me lose power at idle, dimming my lights here and there and it also resulted in higher rpms.

Anyone in the Lehigh valley with a vag com would be greatly appreciated for a few datalogs


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## CorradoFuhrer (Mar 21, 2002)

Do the green tops require an inline fuel pump below 10 lbs of boost?


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## CorradoFuhrer (Mar 21, 2002)

How do I rule out a bad sensor causing not enough fuel or accurate ecu and sensors and say mechanical or fuel pump not providing enough fuel?

Misfires or leaks really hurt a/f this bad?


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## CorradoFuhrer (Mar 21, 2002)

vac should be 17 hg correct at idle? Does lowering the compression effect that?


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## CorradoFuhrer (Mar 21, 2002)

Ok 2 things to report. Turned my mbc all the way down - same air to fuel Ratio's as 9-10 its reading like 4-5, not sure how that is I thought it was a 6 lb spring.

2ndly I was boosting the 9-10 and up around 5k under full load I was seeing high 13 air to fuel (just like 4-5) but the mafs said about 80 g/s I didn't wanna push it any further.

So I guess the mafs is ok? Or what should that be at 10 psi? I know it was constantly increasing. But that doesn't seem like its shot.

The same af whether 4-5 or 9-10 seems telling though

No walbro or fuel test under load yet.


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## Yareka (Mar 5, 2002)

Dropping compression will affect your vacuum, 17in sounds right for your setup.

What is your a/f showing under idle? and at cruise?

So you are only seeing 80g/s at 5k at 9-10psi? That seems really low to me even on the 4" housing but I havent logged a c2 file in a long time. You are on the right track by swapping out sensors but I'm still leaning toward a fuel pressure issue since you are leaning out even at 5psi.


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## CorradoFuhrer (Mar 21, 2002)

Yareka said:


> Dropping compression will affect your vacuum, 17in sounds right for your setup.
> 
> What is your a/f showing under idle? and at cruise?
> 
> So you are only seeing 80g/s at 5k at 9-10psi? That seems really low to me even on the 4" housing but I havent logged a c2 file in a long time. You are on the right track by swapping out sensors but I'm still leaning toward a fuel pressure issue since you are leaning out even at 5psi.


I'm not entirely sure what RPM I was at because i'm on the highway driving, but the fact that it was gradually increasing.

Air to fuel is rock solid at idle 14.7-15.3 ish cycling, cruising around they are similar off boost - under boost part throttle its a tad leaner than at wot under full boost but i'm not sure what the threshold is for that, or whats normal.


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## CorradoFuhrer (Mar 21, 2002)

Yareka said:


> Dropping compression will affect your vacuum, 17in sounds right for your setup.
> 
> What is your a/f showing under idle? and at cruise?
> 
> So you are only seeing 80g/s at 5k at 9-10psi? That seems really low to me even on the 4" housing but I havent logged a c2 file in a long time. You are on the right track by swapping out sensors but I'm still leaning toward a fuel pressure issue since you are leaning out even at 5psi.


What strikes me as odd is that it leans out the same at 4-5 psi or 9-10 psi, or pretty much anywhere in that range (I have at like 7 or so now). Same deal, under full load its about 13.3 creeping up to 14.

I imagined if it was running out of fuel it would get worse or better depending on the boost level, but it doesn't matter. Off boost and idle its going for the 14.7, so that leads me to believe everything else is ok, no codes. 

I have some time finally today i'll be able to get my gauge checked out for accuracy, and get a length of fuel hose to let a passenger monitor it while its under full load to see what it says.

right now i'm a tad low if my gauge is accurate. but I've changed out everything and its made no difference, so I assume the fuel stuff to be in order.


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## Yareka (Mar 5, 2002)

Corrado****** said:


> What strikes me as odd is that it leans out the same at 4-5 psi or 9-10 psi, or pretty much anywhere in that range (I have at like 7 or so now). Same deal, under full load its about 13.3 creeping up to 14.


Thats why I keep leaning towards fuel pressure, if your fuel pressure doesnt rise with boost via fpr you are going to lean out even at low boost if it doesnt rise 1:1. Its seems like your fpr is seeing correct vacuum since your afr seems good at idle/cruise. 

If the fp checks out, go back after the maf. If you can get some maf readings from another c2 car that would be very helpful. It really would be helpful to have a vagcom so you can watch your sensors and how they react to boost.

And although you have the base kinetic kit, still show us some pics of what you are working with.


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## TBT-Syncro (Apr 28, 2001)

Yareka said:


> Thats why I keep leaning towards fuel pressure, if your fuel pressure doesnt rise with boost via fpr you are going to lean out even at low boost if it doesnt rise 1:1. I


the extra fueling you get from this rise in boost pressure is trivial.


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## Yareka (Mar 5, 2002)

Recently had a 20v bt car in the shop that hit 17:1 under boost(obviously only one time before deep diagnosis started) 
Vacuum line popped off the fpr, replaced and left at 12:1 under the same boost.

Assuming 1bar of boost on 3bar base pressure, without the pressure you are only getting 2/3 of the fuel that the ecu is expecting.


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## CorradoFuhrer (Mar 21, 2002)

thanks all for your help. I think this has nothing do with fuel pressure but the tune. After the walbro install... same deal as prior at like the same 8 psi. 

THEN:

I turned up the boost to 15 or a tad more or so... holly molly that thing got out of its way fast and the air to fuel is like 13 or 14 until the boost comes on then rockets down to 10 ish and is around 11-12 like it supposed to. FINALLY! 

Its pretty late and I kept popping this crappy rubber boost tube connection I have. (i need a t bolt). So after a few rounds of tightening, getting on it and it blowing off (all with acceptible low AFR's before being 13-14 afr then dumping down to 10 and then low 11.

I'm not sure whats good with the tune prior, it was always running good with the stock pump at 10 lbs then was being high. I think it might have something to do with my boost controller and how the boost comes on? lost?

But with this setup I think it needs to be up in the higher boost per how its mapped out. I think my drivers side axle is about to bust. Its feeling very rickity.I grabbed it, it has very little play, but clunky and shakes on the highway on throttle. I guess im going to break something and being going back to Advance auto haha until I can get some raxles. (or its a wheel bearing)

thatnks all for your help. If I turn the boost down, it was still hanging out in the low 13's prior. But now its spot on with the higher boost?


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## CorradoFuhrer (Mar 21, 2002)

Yareka said:


> Recently had a 20v bt car in the shop that hit 17:1 under boost(obviously only one time before deep diagnosis started)
> Vacuum line popped off the fpr, replaced and left at 12:1 under the same boost.
> 
> Assuming 1bar of boost on 3bar base pressure, without the pressure you are only getting 2/3 of the fuel that the ecu is expecting.


I confirmed this by taking the vac line on and off when I did a fuel pressure test at idle. It was fluctuating, my pressure was a few psi's off (prior to the walrbo - not sure now). But I had replaced everything from new pump, new filter, different injectors, swapped out FPR's, it all showed the same stuff. I had seriously no idea wtf was going on. 

Now that its turned up, its on point. I'm really nervous though. I would have expected this thing at 5 psi to still regulate to 11.6-12.5 under wot, even 8 - got up to 15+ (I havne't laid on the boost to roll up through the rpms yet, a bit nervous)

but she dips right down to the 10s after being like 13-14 as the boost creeps on and it seems way safe the few times I had it up there.


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## TBT-Syncro (Apr 28, 2001)

Yareka said:


> Assuming 1bar of boost on 3bar base pressure, without the pressure you are only getting 2/3 of the fuel that the ecu is expecting.


no. going from 3 bar to 4 bar only adds around 7% more fuel.


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## CorradoFuhrer (Mar 21, 2002)

i dunno, but apparently this works at higher boost levels but doesn't compensate for lower boost levels. That makes no sense.

it stays around 13-14 when boost creeps on and then shoots down to 10 on my gauge, then settles 11.6-12.5 afr at like 17-18 psi but as soon as I had it turned down below 10 its like 13-14 afr.

How much boost can I actually run with this setup? Where does it start being dangerous, anything over 18? I can't get a good read on it because its too fast, and I think my drivers side axles ready to break in half.

I swapped out the 007 forge dv for the yellow spring. That says for 15-18 psi.


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## CorradoFuhrer (Mar 21, 2002)

Ok, So far i'm told that I have to watch the MAFS voltage, not the MAFS G/S. I have a handheld vagcom, not a laptop based one. I think the settings are under group number 2, but i'm not sure. I also forget what the voltage should be, I think its like 4.17 or something like that? I've pushed around 21 psi and my AFR was always under 12, but I don't think I ran it to far into the red line.

FWIW I have it turned down to 18 or so... I most likely need to find a low high boost setting but I just don't see when I would need even bigger injectors... My journal Precision T3/T4 60 trim .67 a/r probably won't max them out. 

I would just like to know that i'm still safe and be able to tweak the boost pressure.


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## VW420B (Mar 17, 2013)

I'm having the same issue as you were. Did you ever figure out the cause or did you just keep the boost up?


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## dub nutz (Dec 30, 2010)

I have had your same problem except with UM 42# software, turned up the boost and did the same as yours and got my a/f down the same same as you. I wonder if its the tune? I still have this problem at low boost(8psi) and have done 4th gear pulls with a/f at 13.8ish, no adverse affects yet. I'm running 4bar regulator too. I dont have vagcom so we cant compare but would like to figure this out. P.S. You can stop turning up the boost when you run out of fuel


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## Dave926 (Mar 30, 2005)

TBT-Syncro said:


> no. going from 3 bar to 4 bar only adds around 7% more fuel.


Re-read.

Differential pressure across the injector tip is now 2 bar, reducing fuel flow to ~350ccs, assuming this is a 440cc file.

Highly doubt older Motronic has the ability to change injector constant dependent upon manifold pressure like the returnless B6 1.8ts.


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## InlinePerformance (Oct 25, 2008)

*Hmmmm*

For ****s and giggles pull the primary o2 out of the loop (unplug it) and see if it goes rich-it should. Have had other Vr and aba setups get o2 sensors that were reading rich when they were lean and causing the long term fuel trim to pull fueling. Take a scanner and read your long term fuel trim....what is it. If negative then you have a funky o2.


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