S15 SR20DET Running Lean

[abaron13]

I got my new swap in and running but it's running way too lean at all times. It seems like the fuel map is off or something. The maf is fine, no boost/vacuum leaks, fuel pressure is perfect and it has a brand new fuel pump. What could be the reason for it running so lean besides a bad ecu?

[pacotaco345]

Have you checked fuel pressure? If you have an exhaust leak before the o2 sensor that can cause it too

[abaron13]

Fuel pressure is good, as previously stated. No exhaust leaks either


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[ka-t]

all stock ?

[abaron13]

Other than a fmic it's all stock, yes.


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[bmxer882x]

Are u missing really bad? Like one cylinder isn't getting fuel? Or is it even like all cylinders are being starved? If it's just one check your injectors. (To test pull off a coil from each cylinder when the cylinder gets no change in idle your problem is in that one)

[abaron13]

No the car runs and idles fine, I can't figure out what's up with it.


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[bmxer882x]

If it runs and idles fine I would say u have an exhaust leak. Recheck all your fittings before your wideband. Also check it's completely screwed in and tight.

[abaron13]

I triple checked that. It smells like it's running lean, and it hesitates under certain loads while driving.

[abaron13]

It's throwing me for a loop because I've already checked every logical thing it could be, other than swapping in another ecu, mainly because I can't find one anywhere...

I posted here as a last resort to see if I missed something stupid.

[801nismo104]

do you have a wideband or are you just guessing its lean?

[abaron13]

I have an aem wideband

[bmxer882x]

Only other thing I could think of is check and make sure ur ecu doesn't have a room tune in it. Or check to see that you are getting a solid 12 volts at the injectors. Iirc mine was 12.36 volts.

[abaron13]

That was the first thing I checked when I got the swap, no rom tune. That should make it run rich instead of lean anyways, I would think. I'll look at the voltage


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[abaron13]

The ecu is throwing a code for the maf, but the maf and maf wiring is fine. I'm also getting good voltage at the ecu (1.4v at idle)


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[jaxshawn]

did you get the swap as a full set up, s13/14 sr20's use 370cc injectors but the s15 uses 434cc (400 something not sure on exact)

[abaron13]

480cc and yes I have the full swap


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[jaxshawn]

adjustable fpr or stock?

and what was youe fuel pressure at idle

[abaron13]

Stock 43psi


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[jaxshawn]

did you calibrate your wideband before installing it?

[abaron13]

Aem widebands dont require calibration. However it is on the right setting.


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[oni jake]

The MAF sensor code could mean anything involving air flow. You have a boost leak somewhere if you're absolutely sure everything else is fine.

[Tom N]

How do you know for sure the maf is good?

[bmxer882x]

Just off of memory there is two different injector sizes. The 480 in the type r and the 444 (I think). The 480 came with the db turbo where as the other was in the automatics with a t28 journal bearing. I'm not sure but there should be two different ecu's. Do some searching and make sure u have the right injector/ecu combo. Sorry for not knowing exactly just trying to point u in a direction to look.

[oni jake]

All OEM manual S15 ECUs are tuned the same way; injectors are the same across the board for every stock S15 turbo motor out there.

EDIT: When ECUs go out, they don't make A/F ratio mistakes. If something were to happen, the ECU goes into LIMP mode if possible. If not possible, the ECU will shut down all together. Your problem has nothing to do with the ECU

[abaron13]

Ok I had the injectors cleaned and flow tested. They're fine. Good fuel pressure. The entire fuel system itself is fine. I have no boost leaks. And there are also no exhaust leaks pre wideband. What else could it be other than the ecu not telling the injectors to dump enough fuel?

[Tom N]

What fuel pump? Have you checked voltage at the pump?

Are you positive you have a good working S15 maf?

[abaron13]

It's a brand new dw 220 and the voltage is good. I questioned my maf so I bought a known working maf and it did the same thing. The voltages to and from the maf are good as well.

[Tom N]

Ecu could have a non stock tune on the chips.

[abaron13]

I cracked it open as soon as I got it, there's no daughter board.

[rotation3x]

Have you checked your fuel filter?
Make sure your fuel pump is working 100%
Also check coolant temp sensor.


Im kinda having the same issue with my s14a sr20det, however

I dont have a wideband so im going by what color my plugs are. My plugs are white= lean
How did you flow test your injectors?

[abaron13]

Fuel filter is brand new and the pump is 100%. Cts is new as well. I sent my injectors to a friend that has the machine to do it.

[Fuego]

Maybe I missed it but how are you sure the MAF is working properly? Injectors clean and working, pump is new, filter is new, no exhaust leak, no vac/boost leak... there's only so many options here.

[abaron13]

Few posts up. I bought a known working maf in addition to the one I already had. And the voltages in and out are good

[Def]

Do you have the stock SMIC? The one on my redtop leaked horribly when boost testing it. They use rubber gaskets that harden up in the end tanks. I took it apart and RTV'd the end tanks to the core and it held up great after that.


I'd suggest doing a boost leak test, although that would run really rich usually as you're blowing metered air out.

[abaron13]

No, fmic. Already stated no boost/vac leaks.

[Def]

What does running lean mean. What's your AFR at cruise, 0-4 psi, full boost (which is what psi)?


You're really not giving much info to run with here.

[abaron13]

Cruise 16-off the scale
15-16 in boost
Havent taken it to wot for those reasons

[Def]

What pump do you have? At this point, I'd want to look at fuel pressure WHILE driving. A weak pump will show great fuel press at idle, but fall off once you start flowing.

What code ECU do you have? Should be WC I believe. That's what came in my S15 swap.

[abaron13]

Already mentioned brand new dw 220. And WC is an s14 sr code. QT is the spec r ecu.

[Def]

Just tossing in a pump is not proper troubleshooting. You need data like fuel pressure under load to rule that out as an issue. If you're not going to properly troubleshoot, then good luck finding the problem.

[abaron13]

I not only have proper fuel pressure at idle I have steady pressure with increased rpm and a proper 1 psi increase per 1 psi of boost. Fuel pressure is fine.