Supercharged Lean Out Issues

I'm getting some weird behavior with my afr, at mid throttle levels I'm seeing well into the 15s, sometimes even low 16:1 range. With boost, without boost, regardless of gear, etc. I don't know what % of throttle/load I'm at, but I'd guess the 20-50% range it'll "randomly" start running lean. I'm no expert on tuning, I just know lean = BAD, so this has me worried. It's primarily when towing (~4000lbs), but I think that's only because I'm in this weird zone when towing. At full throttle it'll richen out into the 11s, so I don't think it's a fuel flow issue (TRD green injectors and Aeromotive 340 pump) but I'm not sure what else it could be. Help?

So back story, this started/I noticed this 3 weeks ago. The truck has a completely rebuilt Magnuson and also got the injectors cleaned, and then got a brand new "stage 2 built" transmission from Certified Transmissions. All that happened, and immediately I towed my utv to California (like 3 miles after getting this shit) and on the way home noticed the afr getting leaner and for longer than before, and now two more trips towing (locally) and I've noticed the same thing. I just got back from towing ~120 miles, and was getting pretty worried coming up the hill. The only thing I could think of was the ECU/TCU tune got fucked with when the tranny was replaced, so I reflashed the truck and just got back with no change in behavior.

It isn't like it runs lean for a split second as the afr is always jumping around, this is like it'll chill at 15.5:1 for multiple seconds at a time--if there's a steady grade and I'm not moving my foot, it'll just be locked at this lean ratio. This is both confirmed with my wideband and the trucks narrowband. TorquePro claims the ECU is aiming for a normal afr (like 14.7 or richer) but that's not what the actual measured afr is remotely reaching. But like I said, at full throttle it evidently is dumping plenty of fuel since it'll go full rich without issue. There's no CELs, or pending codes, or anything to indicate a misfire. I would say at idle the truck seems to hiccup occasionally, the kind where you have really be listening and feeling the truck and notice just a weird blip run through the idle and then it's fine. Could an injector be going out or getting a poor signal and it's not enough to trigger a misfire code but it's somehow enough to make the afr sensors pick it up (and not cause a code despite a seemingly large change in afr)? It seems like the only way to run lean is the injectors not working, or not enough fuel getting to the injectors, or the tune. Considering the tune is reloaded, the injectors are "cleaned", and it's pumping enough fuel to be rich at WOT, what am I missing here that's happening at mid throttle.

Totally rebuilt TRD Magnuson with URD Pulley
Aeromotive 340 Pump with cleaned/rebuilt TRD Green Injectors
OVTune

Someone tell me something obvious that solves this, or I'm being paranoid.

 

You may have a vacuum leak somewhere... you may have to grab some soapy water or smoke machine to find it

 

Hadn't thought of that, and it'd make sense since I took everything apart to pull the blower and could've messed up reinstalling/clamping all the lines. I'll definitely check that tomorrow!

 

I've got no idea, but hope you get it figured out. Keep us posted.

 

@snivilous Failing oxygen sensor(s)? They measure oxygen remaining in the exhaust gas, and provide input to ECM to set afr. Don't know year or miles on your truck, but they are a wearing part that eventually need replacement.

Each bank has a heated oxygen sensor mounted in the exhaust pipe between the two converters. See inspection procedure from 2015 SRM below:

 

@snivilous There is also an air fuel ratio sensor for each bank. They are located on the exhaust pipe directly below the manifold flanges. See below for 2015 SRM inspection procedure:

 

Huh, that's an interesting theory; truck has 242k+ so that's certainly a possibility. I went all over the vacuum lines spraying shit and didn't notice any change in idle or how the truck sounds. The brake booster line was MAYBE loose coming off the blower so I put a better hose clamp on, highly doubt it was that but it was the only hose that showed any signs like it could possibly be loose. I haven't towed anything since then or driven down the hill and up, so can't tell if I actually fixed anything. It seems weird if it was a vacuum leak that it'd only happen with the throttle in a certain position and nowhere else (like you'd think it'd also happen at either idle or WOT). And the fact I can only really replicate it climbing a hill under a lot of load doesn't make problem solving any easier.

I read around on "not safe AFRs", and essentially there's no set in stone value that's bad. Running leaner produces more power, and apparently 14.7:1 IS lean in the first place and manufacturers run around that to reduce emissions and boost power. So the engine will run hotter but some engines have been known to run at like 18:1 afr to get better gas mileage (specifically designed for that though). It sounds like it mostly comes back to knock being the issue, higher combustion temperatures, easier to knock, knock is bad. I wasn't experiencing any knock, and my timing advance seemed to be in the usual zone, so on the plus side I don't think I'm going to hurt anything running that lean for a couple seconds at a time and the engine should start pinging if it gets too bad. Not that this fixes anything, but at least I know I wasn't on the edge of the cliff by seeing leaner numbers.

 

Do these trucks have a fuel pressure regulator?

 

Yea it's off the fuel rail return iirc

Which on that note could it be a fuel filter issue? Again seems like it wouldn't be intermittent but maybe there's some weird fluid dynamics going on at a certain throttle level? Seems unlikely since it should always be flowing the same fuel out of the pump I'd think.

 

Looks like the fuel pressure regulator is controlled by a vacuum line off the resonator on the air intake pipe.

 

I know you've replaced the pump with and aeromotive, but how long ago, and what's the fuel pressure at?

 

The air box/intake hose are all new from Magnuson too. I sprayed all the fittings going into the intake pipe and they seemed sealed. Also cleaned out the MAF while I was checking stuff.

Replaced it a year and a half ago when I installed the supercharger. No idea what the fuel pressure is at, and I don't think the truck has a sensor that reads pressure? It'd be nice to actively monitor the pressure...


Dropped the truck off today for gears and lsd, so when I get it back I'll look over stuff more. The more ideas and things I can check the merrier, so keep laying it on me, I appreciate the feedback and ideas.

 

Speculation...With the S/C being rebuilt, that probably changes it's output as well possibly slightly increasing the boost at that particular load. You may need to have your tune tweaked some. You might need to with the ratio change too, shifting will probably change.

 

I had thought this too (and hope this is all it is, since it's the easiest solution), but since I reset everything I figured the ecu would see more air going in and compensate by adding more fuel. Is that not necessarily the case? Is there an injector duty cycle limit (or something) that can be reached, and despite the ecu wanting it richer there's other limits stopping it dumping more fuel even though the fuel system is more than capable?

I have two other tune files at the moment I could load in, the original TRD tune and the very first OV tune iteration I had. I thought about loading the TRD tune since it ran really rich with that tune, I don't know if I can get the same scenario to happen since the shift logic is way different but it seems like it's worth a shot. And even if I can't get the same gear/load scenario to happen due to the shift pattern of the TRD, that alone might prove it's the tune (if it's not running lean it's not running lean right?). Then I can adjust the OV tune in VFTuner and kind of merge the TRD with the OV assuming the TRD fixes it.

 

Maybe with the injector/supercharger rebuild and new transmission a tune tweak is needed? Probably no help, but power enrichment starts at 40% throttle on the TRD file I have, n/a truck is 70%. Might be just below power enrichment when it happens.

 

@snivilous need to get a fuel psi gauge installed. Having a wide band O2 is a great monitor to give a heads up when things go less than perfect.
Low fuel psi can be a silent killer on a boosted application.

 

I think that you and @Vizsla could be on the right track. It sounds to me like the rebuild and fresh intake may have altered how much air is being brought in. Having only just glanced at the maps in OVTune, I can't really say that I know anything. But I wonder if the refresh may have created a situation where you've....run off the map so to speak. The ECU can only adjust within a certain "range" and that may not be on the map. The range maybe need to be "recentered" if you will. I'm not even sure that descript is befitting how OVTune operates or makes changes....

Speaking of enrichment. When I had my 97 S/C'd Tacoma, there was always a struggle trying to tune for mid-throttle driving. Closed Loop was too lean and EGTs became too high, but in order to kick it into Open Loop and fatten it up, you'd have to use too much throttle and then back out of it. The ECU would eventually "learn" what was going on and try to lean out again, so you were always having to drive in a different part of the map via throttle to stay one step ahead of the ECU.

Anyway, when you get your truck back from the shop, you're going to have to go back to the tried and true method of change one thing, test, change, test, until you're able to figure out what's taking you in the right direction.

 

That is exactly what was happening to me. I could let off the gas and it'd be happy, or give it more gas and it'd be happy. At least someone else has experienced similar behavior, and it might not necessarily be a mechanical issue!

 

I'm sure that "enrichment" functions different in the Tundras than my Tacoma did and is manipulatable in OVTune, but I have no idea at this stage. It's possible that it's that straightforward, change enrichment to come in at a lesser throttle application and set a target A/F ratio. Again, I have no idea at this stage if that's even possible, but maybe adding the idea to your considerations will yield...something? lol

 

Not sure if you did see this or not.
https://www.tundras.com/threads/something-to-check-if-your-supercharged.62121/

 

Your also non flex fuel correct?

 

I'm pretty sure his truck is pre-FFV, 07-08 ish?

 

‘it;s been a while since I did this but WOT will give you the lowest vacuum since there’s a big Effie hole at the front of the intake. When you’re going to see intake manifold leaks is lifting off the gas with high rpm.... my old Camaro had one and it was a pain in the ass to find but got it eventually.

if you’ve checked for leaks and resealed then I’d chase fuel flow. Fuel pressure won’t mean shit if you have a clogged filter or anywhere down the line for that matter - you need the right pressure AND flow rate

 

I have not seen that! I will definitely check that. I still have my old Air Raid intake too, I was thinking I could swap that back on and see if that makes any difference too, since this is a classic case of change a bunch of shit and not sure what went wrong. Also yes, it's an 08 non-FFV.

 

So shouldn't it be easier to find a vacuum leak when it's at idle and has peak vacuum? Was there a special process you went through to find the leak in your Camaro? I sprayed carb cleaner at all the hose ends and listened/looked at the tachometer, I didn't try any other methods.

 

Vacuum is dependent upon rpm and throttle position. Closed throttle creates more vacuum, higher rpm with throttle plates closed just pumps more out creating more vacuum. So yes, idle has high vacuum but can be higher with high rpm, like downshifting into a corner for example.

What rpm range is this happening at? My Camaro would knock low down, 2-2500 rpm under load with throttle wide open until I finally tuned the fuel map correctly. If you’re towing, this could well be demanding more fuel than 6k rpm with light load

 

This. Definitely this. I’m here in Utah too so PM me if you need a good tuner. It’s definitely worth the money to have a custom tune performed.

 

It didn't seem very rpm dependent, it was mostly happening in 5th gear at ~2500rpm but if I dropped it to 4th and ~3200rpm it would still happen. And I was nowhere near full throttle, I'd guess 20-30% throttle mostly. And I could floor it and keep it locked in 5th or 4th or whatever and the afr would richen out, but just cruising and maintaining speed is where (and only time) it would lean out and not come back to normal unless I let off or gave it more gas and then it'd right itself.

Where in Utah are you? I'm near St George. I'll definitely be messing with the tune regardless if I fix the lean out being caused by something else.

 

Anything weird with your TPS? Perhaps run a load test with it to ensure you're in the parameters needed...it is weird where in the pedal position it is happening...just spitballing ideas...

 

I’m up north, but I can ask the guys I use if they have any recommendations for your area. These guys are top notch and I’d be surprised if they aren’t networked with someone down there.