# VRT Running Very Lean



## apollovr6 (Oct 16, 2013)

Hey guys, I'm having a lot of trouble with my newly built VRT running lean. Just need an outsiders perspective to help figure out something I might've missed.

Heres the setup:
Mk4 12V Vr6 Rebuilt with new bearings, rings and timing chain kit.
9:1 Headspacer and ARP Head studs
C2 Stage 2 Tune, 440cc Injectors, 4" MAF, Walbro 255 Inline Pump
Turbo, Intercooler, Rerouted DV
Short runner intake manifold
Home built 3" Exhaust with O2 sensors below the shift tower
functioning wideband, boost and fuel pressure gauges
I also rewired the harness a bit to clean things up.
All SAI components are currently wired in but relocated out of the engine bay.

When I cold start the car and its in warm-up enrichment/open loop it runs steady at 14.7AFR. But after 30-60 seconds, the AFR steadily climbs to 17.2 over 15 or so seconds. It stays there as the oxygen sensor warms up. Once the O2 sensor gets a good reading (~1.2V), the idle fuel trim maxes out at 25%. When this happens, AFR's drop to 15 or so for a couple seconds then climb right back up to 17.2.

Fuel pressure is steady at 43 psi at all times. Injectors have been tested to be good. Fuel filter was replaced a week ago. Resistance tests show ECT sensor, MAF sensor, and throttle body to be in good working order. I believe the tune is okay as I had the car running okay last year.

VCDS shows MAF readings to be between 5-10 g/sec air flow. (is that low?) I've cleaned and switched out 3 MAFs with no change. 
Some other values I recorded: Ignition ATDC: 12.8* Injection Timing: 3.69ms. NO FAULT CODES.
Vacuum only reads about 10inHg but jumps to 20 if I tap the throttle.

I've tested for boost leaks and corrected them. Checked for fuel leaks. The only other idea I have is that the MAF isn't getting an accurate reading because the filter is connected directly to the MAF housing causing low-pressure/slow air flow through the housing. What do you guys think? Thanks in advance.:thumbup:


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## apollovr6 (Oct 16, 2013)

something else I forgot to mention: when I rewired the injector harness, injectors 3&4 had the same color signal wire so I could've got them mixed up. But I think this would've presented in a more severe way.


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## vr6milz (Mar 29, 2011)

Fix the injector harness


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## apollovr6 (Oct 16, 2013)

well I just realized the car runs fine in first 30 secs or so, so I don't think that's the issue. Do you think I'm getting bad airflow through the MAF? Maybe I should try a straightener


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## vr6milz (Mar 29, 2011)

That's true. but running lean means that ur not getting enough gas and getting to much air. So if I'm thinking like this I'm thinking u don't have an airflow problem but a gas problem. After the first thirty seconds something is causing ur car not to have enough gas, what about ur fuel pump not ur inline is it in good shape ?


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## vr6milz (Mar 29, 2011)

Then again I could have no idea what I'm talking about


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## apollovr6 (Oct 16, 2013)

No I appreciate your ideas. Good thoughts but I've already gone down that road. Fuel pumps are functioning correctly and maintaining correct pressure. When the car makes the switch from open to closed loop, it starts to run bad. This leads me to believe it's the MAF, O2 or CTS. I'm gonna start inspecting my sensors and wiring


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## vr6milz (Mar 29, 2011)

I'm curious to hear what the problem is, post here when u find the issue


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## apollovr6 (Oct 16, 2013)

Yeah it blows my mind that the ecu is adding 25% extra fuel (maximum) to compensate and its having no effect.


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## apollovr6 (Oct 16, 2013)

Well here's an update. I moved the MAF away from the air filter. Now it's about half way between the turbo and filter. I also added the flow straightener that came in the stock air box. The change was dramatic. It started out running full rich, wideband pegged at 10:1. But as fuel control took over it made its way to 14.7. So it is running stoich. Unfortunately, the idle fuel trim is bouncing between -20 to -25%.

So to sum it up, the motor went from adding 25% fuel to now cutting about 22% fuel. I'm going to try swapping out my MAFs and see how it's affected.


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## vr6milz (Mar 29, 2011)

Good news man, u went with ur gut and look what happened


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## apollovr6 (Oct 16, 2013)

Well sorta. I definitely confirmed most of the problem is the MAF but I still need to getting it running between -5 to 5% fuel adaptation. Sometimes I worry the only way to get it running right is a standalone.


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## vr6milz (Mar 29, 2011)

Trust man when I had my mk3 Vrt the c2 software ran great, what software you running ?


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## apollovr6 (Oct 16, 2013)

Additional update. I'm also getting a fault code. P1388 "Control module malfunction: DBW throttle monitoring." I've fought with this is the past and ended up fixing it with a new throttle body. Just a couple days ago I cleaned up the outside of the TB with brake cleaner, and might have got some inside. So I'm assuming it's screwing with the throttle position sensor and throwing this code. Consequently, an incorrect throttle value is probably contributing to the overly rich position. So my next two steps are MAF and TB.


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## apollovr6 (Oct 16, 2013)

C2 Stage 2. Purchased two years ago


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## vr6milz (Mar 29, 2011)

apollovr6 said:


> Additional update. I'm also getting a fault code. P1388 "Control module malfunction: DBW throttle monitoring." I've fought with this is the past and ended up fixing it with a new throttle body. Just a couple days ago I cleaned up the outside of the TB with brake cleaner, and might have got some inside. So I'm assuming it's screwing with the throttle position sensor and throwing this code. Consequently, an incorrect throttle value is probably contributing to the overly rich position. So my next two steps are MAF and TB.


Good call


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## apollovr6 (Oct 16, 2013)

Thanks I'll keep you updated.


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## apollovr6 (Oct 16, 2013)

Well I replaced the CTS and no effect. Car is bouncing between 14.8-15.2 at idle and group 33 (lambda control b1s1) is at ~--23%. Group 32 (idle adaptation b1s1) is at -3% and idle is bouncing back and forth. Just can't get this thing right and I definitely don't feel comfortable driving it yet.


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## vr6milz (Mar 29, 2011)

When u accelerate what happens? I remember my idle being arounf there at some point I think  but when I accelerated it dropped down to about 11-12


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## apollovr6 (Oct 16, 2013)

Took it out again. Cruising AFR is 14.7, in boost its now holding at 11.7. The only issue is idle where AFR and rpm are hunting.


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## vr6milz (Mar 29, 2011)

That's okay then man I wouldn't worry about it to much, if it was leaning at wot I would worry but it sounds normal now


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## apollovr6 (Oct 16, 2013)

It sometimes stalls when I get into boost or rev at a stop.


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## vr6milz (Mar 29, 2011)

Jeez


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## ROBS32 (Sep 1, 2013)

Sounds like crank position sensor to me. Probably worn out.


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## apollovr6 (Oct 16, 2013)

CPS was replaced a year ago. And the car has had less then 1000 miles on it since. Now the car is breaking up in boost (probably over 4000rpm or 5psi). Started happening last night when it was kind of cold outside. During the day ambient temp was in the mid 70s and it didn't really break up, but randomly gets lean in boost. This thing is killing me


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## R32Smoker (Oct 21, 2010)

What spark plugs and gap are you running? How old are your coilpack and wires? I'd also suggest buying some maf cleaner to clean the sensor. Better yet, buy a new one so you can at least have a back up if it doesn't change anything. These tunes super finicky with maf sensors, the car will run like **** as they go bad/get dirty.


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## apollovr6 (Oct 16, 2013)

Thanks for replying. I'm really losing confidence. I've got brand new BKR7Es gapped st .020 and new performance wires. Mustang coil pack is about a year old. (Maybe not strong enough?) I've also repeatedly cleaned and switched between 3 MAFs with no change. (Never had a new one though) Cleaned my TB several times with no resulting change. I've also fixed all charge piping leaks and added the factory flow straightener before my MAF. 

Next I'm sealing all the pinhole leaks in my exhaust and changing my MAF/ intake configuration. 

Fuel pressure at idle is about 3-5 psi low so perhaps my in tank pump is weak. Another strange thing I noticed is o2 aging inactivity. I tested o2 aging and got a fail (dynamic factor .797) and "TEST OFF". I replaced the sensor with a new one and got the same result. It should've read "TEST ON" or "B1S1-OK" and Dynamic Factor around 1.99, but I see no response. Not sure if that's programmed in the tune or an ecu error.


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## apollovr6 (Oct 16, 2013)

Edit* posted multiples


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## apollovr6 (Oct 16, 2013)

Edit*


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## R32Smoker (Oct 21, 2010)

I feel your pain man! I replaced my in tank pump (which was getting weak causing me to go lean under boost) with a DW65v. This fixed that problem for me.


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## .LSinLV. (Nov 13, 2009)

honestly, get rid of that C2 ecu....I had one and the car never ran right....always ran lean.

got a UM 440 ECU, zero issues. :thumbup:


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## maxvw15 (Aug 28, 2009)

sounds to me that you probably have a bad 02 sensor. I have a vr5 turbo and they only way I can run it without the ecu triming my fuel is to run no 02 sensor. basically does this when i start it:

10-1 rich for a few seconds and then proceeds to get leaner until its running about 17-1 then it heads back to my standard idle of about 11-1 the car also drives poorly for the first 30 seconds or so during warmup. once its past that its all good 14.5 ish AFR and about 11-1 under boost


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