AFRs off and small backfiring

I am hitting boost targets. I swear I think it's an intake leak as well. I've done a pressurized smoke test, and I've torn the intake down to the cylinder head to check everything. The A and C and WOT numbers come back the same no matter what I touch, about 12% off for A & C. Like you I've had a leak at the EWG line before and it smoked like crazy on the test.

My injectors are ID1000s, they are set to 655cc/min in the tune for e85. Last night I reduced the injector size 12% in the tune to 577cc/min. Went for a ride and WOT is right on target at 11.6, A & C are pulling a little less than 1% out.

Fuel pressure looks good. I pulled the FPR line and it sits right at 42.5psi. I also videotaped the boost and pressure gauge at WOT to analyze it and all looks good. For whatever reason, I'm about 12% lean everywhere, vacuum, boost, idle, cruise. With the injector size in the tune reduced 12% it's a whole different car, partial throttle is crazy responsive, boost comes on WAY faster. I would think an intake leak wouldn't be so consistent at 12% everywhere. I just don't know what it could be at this point. Really the only thing left is the ECU isn't getting the correct signal from the MAF, or it's not sending the right voltage to the injectors?

What is your fueling setup? Are you using the stock lines throughout or have you upgraded in the engine bay? Top feed or side feed?

Can you point me to a link for your mods? I know I've seen your build, but am having a brain fart right now.

Sure man.

ID1000s with topfeed conversion kit. All ID lines and rails from the FPR in.

AEM 340 pump

BNR16G

e85

ProcessWest topmount

TGVs gone

Crawford AOS

Grimmspeed 3-port BCS

Upgraded exhaust from head to tailpipe (3" after turbo, Full Race EL headers, Grimmspeed uppipe)

Perrin inlet tube (the reinforced version)

Stock intake

Stock FPR

A couple of random blind darts...

When I would boost test my car, I would plug the AOS line. Any chance one of those lines are not sealed or have a leak in them? What other lines are you blocking off?

Are you running the factory MAP sensor or an aftermarket one? What is your boost target? Do you have an analog gauge to ensure both map and analog read the same?

Engine grounds? Are they all intact? Can you throw a couple extra ones in there? I ran a 4 ga circle ground kit in my engine bay and swear it ran better.

Blind dart away!

I cleaned the 2 engine grounds on front. I had the same thoughts. Where would you add some?

I plugged the AOS line at the intake and vented the AOS to atmosphere for a test, WOT AFRs stayed exactly the same. I still can't conceptualize how crankcase air from the AOS isn't unmetered air, but I guess it's more of a pulsating suck and blow and maybe offsets itself?

If I run higher pressure into the intake I usually block the AOS line and the emissions purge line so I don't pressurize the tank or crankcase. For the smoke test I just leave them as it's only about 5psi.

I have the factory MAP sensor. Boost targets are 20.5psi. They are reading the same between my boost gauge and what Romraider shows me.

I also checked MAF voltage and g/s and it's reading right with the key off according to the service manual.

I ran one from alternator to ground, starter to ground, engine head to ground (both sides) and block to ground. Might be overkill, but dunno?

You are doing exactly what I would recommend. I never understood how the crankcase air wasn't unmetered as well? I could only come up with the same thing you did. LOL!

You are right on the edge of where I started to feel uncomfortable with the factory MAP. It's throwing parts, but if you can borrow one and rule it out it may not hurt? 12% of 20lbs is 2lbs and that can be hard to see the difference? Maybe?

I assume you have tested the fuel or tried other sources?

This is a tough one!

I have a fuel tester, but haven't tested it yet. The crappy part is I have no control on what my fuel was before even if I do measure the new.

I also have filled at least 5 tanks since the problem started, from 2 different sources. I may go seek out another station just for research purposes.

The MAP sensor is a good suggestion, it's reading lean at idle right on an ECU reset though as well. For instance, I'll reset the ECU and start it. It runs great for about 30sec while in open loop enrichment, then it switches to closed loop, nearly stumbles and then Learning A jumps to 12% almost immediately.

At least if you test now, you'll have a baseline? I started to see winter blends show up as early as September. At that point, I just switched the car back to regular fuel until the next summer.

Sounds like you've done your due diligence on the source too. Hard to say both are bad, but a third won't hurt.

The MAP sensor is a straw to grasp, otherwise, it's a wack a mole situation if you are confident there are no leaks.

So, been awhile since I posted an update. Still haven't figured it out.

But... I bumped fuel 12.5% globally and now my Learning View Fuel trims, cruise AFRs and WOT AFRs are spot on. Very weird. Since I've been through the fuel system, tune and intake, it's almost as if it's an ECU problem. I may just leave it bumped 12.5% and call it good.

I also did a compression and leakdown test, I'm at 15x,000 miles. I'm high altitude, new STIs compression test about 130psi here.

#1 125 psi, 2% leakdown

#2 130 psi, 2% leakdown

#3 125 psi, 3% leakdown

#4 119 psi, 2% leakdown

The very strange this is, when I tested at 50k, I was 116-119 psi on all cylinders, and one cylinder had 10% leakdown. I don't know how numbers can get better over time, I use different oil now. {shrug}

Are you sure it's not a tune problem?

It's a good question, but I'm positive. I've been running this exact tune for 3 years with under 3% on Learning View Fuel trims and WOT AFRs at 11.6-11.7, verified on multiple dynos. Just one day everything went lean. I've gone through the fuel system and have good pressure, I cleaned the injectors, I took the intake down to the cylinder head and also smoke pressure tested it, I had the motor health verified.

The fact that it's 12.5% lean everywhere (idle, cruise, WOT) seems way too uniform to not be an ECU problem. At this point I have to assume the ECU isn't giving the injectors the fuel it thinks it is. I suspect I could change out the ECU and the problem will go away. Not sure I want to mess with the immobilizer and such when I can just bump fuel 12.5% globally.

So I thought I would update this.

My running lean appears to have been completely a ground issue. Haven't found a broken ground, but adding a ground solved the issue. Never would have guessed that running lean was a ground issue when everything else looked ok (fuel pressure, voltage, intake leaks, etc).