HELP! 2006 Toyota tundra very high fuel trims

Hi everyone, I have been experiencing very high fuel trims on bank 2. A little background about the truck. My truck is a 2006 Toyota Tundra double cab. I had bought the truck with a blown engine for a steal. I recently swap a 186k thousand mile motor in and have got it running. My CEL light keeps reappearing for code P174 and P0150. I have probably driven this truck 10 times now and the light keeps coming back everytime so something is definitely wrong. I have replaced my MAF sensor with an OEM one as well as my upstream O2 sensor with Denso ones. After replacing these, the light still comes on. I took my OBD 2 scanner and started looking at fuel trim levels. Both short term percents are reading close to 0 which is great but bank 1 long term is reading 22 while bank 2 long term is reading 44. I went and replace my fuel injector seals and cleaned my fuel injectors because hey why not it can't hurt. This actually improved my bank 1 long term reading and got them at 3 which again is great. However bank 2 fuel trim didn't move from its 44 reading. I have done a smoke test to check to see if I had a vacuum leaks and found no leaks. Really stump as to what it could be. I am newer to automotive mechanics but I try to do the best research I can to try to fix the issue. If anyone has an idea on what this could be please let me know.

 

Welcome!

What did this motor come out of?

I ask because VVT-I and non-VVT-I are not the same. You could have a mismatched ECM. Just guessing here really quick.

 

It actually came out of another 2006 Toyota tundra double cab. So I would assume there shouldn’t be any ecm issues I wouldn’t think. I was told before on the truck I bought that there was absolutely nothing wrong besides they ran the engine out of coolant and thus blew it up. No codes were on the dash even with the severe engine damage. So it kinda makes me think the new engine itself is making a lean condition somehow.

 

How is the exhaust manifold on bank 2? A small crack could skew your a/f readings. Do fuel trims change depending on the engine temperature?

 

That is the one thing I haven’t taken a deep dive into yet. I have felt around while the engine was running and could feel no apparent leaks and even tried to smoke the exhaust but don’t beileve I was able to really build pressure in the exhaust to fully check. I’m thinking I might have to take the shroud off tomorrow and check a little better. Is this a common problem with the exhaust manifold gaskets leaking on these year Toyotas? This is my first Toyota tundra.

 

Cracked exhaust manifold are a pretty common thing on the first gens. On cold start you may be able to hear a ticking noise that goes away when its warmed up

 

Yes. It's in the MEGATHREAD. It's a long read, but worth its weight in gold.

 

Ok, I’ll definitely take a better look into that and will update within a couple days. Thanks

 

More common on the 2000-2004 with the non-VVTi engines (silver intake). On the VVTi V8, they use a rubber formed gasket, so far less common.

Typically with intake gasket leaks, I expect to see one or two cylinders on a bank misfiring, which makes it really fun to differentiate between a coil pack, plug, or intake gasket. The usual defacto test to rule out an intake gasket is to use propane torch, brake cleaner, or similar flammable gassy source and spray around the base of the intake and listen for surges. Of course, proceed with caution. The test for coil pack vs. plug is to swap coil packs between cylinders, and see if the misfire moves. But you're dealing with fuel issue.

Upstream O2 sensors are responsible for telling the ECU if the fuel/air ratio is correct, by reading the exhaust. Any leak/suck of air between the head and the upstream sensor (i.e. leak at the manifold gasket, manifold, manifold-to-cat gasket) could allow extra air to escape/enter, and cause the upstream sensor to fudge the numbers handed to the ECU. That said, if the ECU is getting bad data from the MAF, telling it more/less air volume is entering the engine than reality, it may push more/less fuel to compensate. Likewise, if the engine thinks the throttle position (from the throttle assembly) is not realistically as-open as it truly is, that could influence things as well.

Lastly, you need to understand something. You know what a fuel pressure regulator (damper) looks like? Almost like a round, upside down tophat on/near the fuel rail. On the passenger side, specifically, there's a vacuum hose that comes off it, and goes to the boxy part of your intake, unless you're one of the ill-informed folks who made the mistake of installing a K&N or similar hot-air intake, then it's going to the intake tube. That vacuum line (being crack free) is important. It should be drawing vacuum on the fuel pressure regulator, and re-burning off any vapors that should pass by. I believe the vacuum on that line will cause the vacuum to open the bank 2 regulator more, so, step on the gas, more vacuum is created, the regulator opens, more fuel flows to bank 2 rail. Make sense?

There's a variety of things that could be causing your issue here. Bad upstream O2 sensor, bank 2 / sensor 1, which, surprise surprise, triggers P0150 and a few other codes, which I guess you know because you've replaced with new Denso already. but P0150 is an interesting code, because it's "circuit malfunction", not a bad heater or and over-volt/under-volt situation. So ... looking at the Factory Service Manual, or "FSM", which is readily available to download near the top of the MEGATHREAD @The Black Mamba so kindly linked you with, you'll see Toyota's take on the common sources for that code. And, well, given you've replaced the sensor, it seems like you need to be testing the upstream circuit, my friend. @BubbaW is superb with circuits and may have thoughts on that, since the '05-'06 manual, I couldn't find P0150 reference info (this is from '03 FSM):

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So I was able to to use carburetor cleaner and I sprayed the whole intake down and got zero changes in rpm. I did replace all 8 plugs when the motor was out so that has been done. I actually replaced the fuel pressure regulator and the hose that went to it to ensure that it wasn’t a leak there. I guess it’s time to look for that exhaust leak later today. Thanks for that info shifty.

 

Your search mojo has not failed you given they discontinued P0150 beginning with the 05 along with a few others, as noted in the New Features pdf. I question @sirgibs234 code reader.

 

I’m with you on that one BubbaW. I’m suspect of that code the same. My goal of replacing the 02 sensors and maf sensor with oem parts was to hopefully rule those out as possible problems. I know throwing parts at something is not how you diagnose but they weren’t crazy expensive. I cleaned my throttle body with the specific cleaner to hopefully again rule that out as a problem. Once I get off work today I’m hopefully going to be able to check that exhaust for leaks. Personally I’m leaning towards that being the issue since when my truck idles for say 3-4 minutes and Im sitting in it with the ac on, I smell a little exhaust fumes coming thru the ac vent but this is just sometimes, not all the time. My exhaust when I did the smoke test didn’t show any significant leaks so I don’t beileve it to be dumping fumes under the truck and that is what I’m smelling rather it being fumes coming up from the front of the truck.

 

With a complete motor swap, there are a large number of additional variables to consider. If this were the original motor, no significant work has been done to it type situation, O2 sensors are my first stop for fuel trim issues. You only replaced the upstream sensor, I would replace in pairs. You could try swapping downstream sensors to see if the codes resolved or moved for free. The exhaust leak due to cracked manifolds issue seems like a non-culprit to me. They leak, but they won’t be pulling fresh air in, they will be pushing exhaust out. Don’t think they will give you codes like you’re experiencing. MAF and TB issues should affect both banks, not just one. Unlikely all injectors on one side are faulty, but those could all be swapped to the opposite side to check for free as well. A timing issue would likely manifest itself differently with poor running and misfires. So I would be chasing fuel delivery and ECU / O2 sensors fuel metering.

 

I mean, it's also entirely possible the truck has a pre-2005 ECU in it also. So it would throw the code. OP didn't mention that, but ...

Only way to know would be for OP to pop out the glovebox to access the ECU and take a pic of the sticker on it to share.

 

I asked

 

That’s a good point. I’ll check that ECU number today hopefully and post a picture of it.

 

So I was able to inspect the ECU and after doing a bit of research, it is the correct one that’s supposed to be in the truck. This was a one owner truck by the way if that means anything to anybody. I just got off work so I’m going to look at the bank 2 exhaust and see if I can find anything. I would like to note something that I found out yesterday in regards to my fuel cap. I have heard that these fuel caps not being tighten down well will throw a code up. I haven’t had any evap codes pop up but I found something interesting when using the live data setting on my obd scanner. When I would crank my gas cap down at least 3-4 more clicks my fuel trims all went to a perfect zero except for bank 2 long term fuel trim. And when I did this it also went into open loop fault. When I backed it off and re-tightened it just 2 clicks all fuel trims went crazy jumping up and down like 15% in both directions. Then it went to closed loop. I found this so confusing why this was affecting it so greatly but I’m an amateur when it comes to this.

 

In general, your fuel system (and EVAP) relies on a bit of vacuum. Part of that vacuum is generated by the seal created by the gas cap.

It shouldn't be necessary to click your gas cap down 3-4 times, 1-2 clicks should be ample. The fact you're seeing this makes me think you should replace it, if for nothing else than these could be symptoms of a cap failure, or maybe the cap is non-OEM and not functioning to the degree the OEM cap expects. I've definitely had issues with Stanton brand caps (specifically) on other trucks, to the point I'll always use OEM gas caps (never purchasing them from scAmazon or fleaBay) to avoid the added headaches.

I'd be curious to see what you see after replacing the gas cap. I can't imagine it's the actual root of the problem, but I've seen stupider things I didn't think would ever be related actually fix people's issues on here, so ....

 

Gotcha, I’m gonna order up a new cap and I’ll come back and post if I had any changes. Thanks

 

I have been doing a little more research just trying to find if there is anything more I can test. I was going to run this by y'all and see what you think. So this truck sat for 2 years outside. It had about 1/4 tank of bad gas in it. I attempted to start the original blown up motor that was in the truck by turning the key over and hearing it crank. The motor started so the fuel pump was working. This I believe would have cleared the bad gas stored in the lines from the past 2 years. Then after this, I swapped the engine and did all the things to get it running. I drained practically all the old gas out and put 20 gallons of new gas with injector cleaner additives. I measured my fuel psi and I got 40 psi out of it so I thought ok, my fuel pump is good. My odb 2 scanner on live data says open line fault on both fuel systems(fuel system 1 and 2). When I first got the truck to crank and run a month ago this was in closed loop. Do y'all think I have dislodged something in my tank to clog the pump somehow or got crap in the fuel line and there is a blockage? I saw some people online that say you can have all the psi in the world but have little to zero volume of gas coming out. I took the line off yesterday and got my brother to crank it over. It has flow but to be honest I can’t tell how much it should be. Any insight is appreciated.

 

I would actually re-check every quick connect fitting on your fuel lines. We've seen, several times, where someone's quick-disconnects on the fuel lines weren't fully attached, allowing the tiniest bit of air to leak in (and typically producing a tiny occasional drip of fuel) and caused lean codes. Go to each joint, pull the lines away from each other to see if they disconnect, which they shouldn't without force and/or specialized fuel line tool, and if they don't, push them together to see if they click further into seating.

That said, someone else had a lean condition recently that tied back to one of the dampers (there's one per rail) not behaving properly. SMP, which is a pretty well respected brand and OEM for (at least) General Motors' fuel injection parts on some engines, has a replacement fuel damper ($35 here) *IF* you can't swap the ones over from your old engine to give it a shot.

 

I had the banjo fuel fitting leaking when I had first started the engine up but got that to quit. I will check that fitting that you are talking about and see if it is right. I have the old dampener so I can try that and see if it helps.

 

IIRC, there should be 1 damper/pressure regulator per side. Passenger rail should have a vacuum tee, driver side doesn't? Or maybe I'm confusing the damper and regulator.

 

It's my understanding (and I could be wrong), there is a damper on the drivers side (where the fuel line comes in), then into the driver side fuel rail, a crossover to the passenger fuel rail, then to the fuel pressure regulator (which has the vacuum line), then to the return line. I'd have to go look to be sure.

 

An exhaust leak can absolutely give you a lean condition on one bank. And swapping an engine out involves faffing around with the exhaust manifold, so it's a distinct possibility.
What does the scan tool say for the A/F reading on that bank? As you have a 2006, I believe the upstream is an Air/Fuel sensor and not an O2 sensor, so I don't think you are supposed to see the 'wave' pattern oscilating between .1V and .9V....

 

I'm thinking you're right.

 

my A/F readings on both sides are 3.9-4.2 consistently. I don't know if I mentioned it before but I also got OEM downstream 02 sensors to replace the Chinese ones that were on it. I am about to swap out the damper with my old one. About three days ago had got a new fuel cap and replaced it. I decided to "reset" the pcm by undoing the battery and left it for like 8 hours. I reinstalled the battery and put my odb 2 scanner on and started it up. To my amazement my readings for fuel trim were all zero! I drove the truck for at least 30 miles and reading were staying in there health range. I thought well it was fixed. Just drove it and it was running great then all of a sudden long term jumped up to 44.5 again. This time its bank 1 not bank 2...huh. It was bank 2 that was giving me trouble and now bank 2 reads perfectly zero on short and long term. I'm fully convinced that now it is 100% fuel related and not vacuum/gasket related since it is jumping around. I'm so confused now. I'm getting pretty defeated on this one. Again I'll go check that damper and leave an update. What do you guys think the possibility is it's the fuel pump even though pressure is good at 40psi? The truck body had 301,000 miles on it before I did the engine swap.

 

I noticed as I was looking at the live data while driving that when I let off the pedal my bank 1 long term fuel trim went to 24.5 then when I pressed the pedal again it went to 44.5. I heard that that was a sign of a vacuum leak somewhere but that means that it somehow jumped banks from bank 2 to bank 1 now???

 

I started setting up a dashboard with my OBDLink MX+ to grab some prelim fuel numbers on the VVTi engine to share 'normal' operations, at least for my engine, with ~82.5k original miles.

I grabbed a shot of some fuel trim and giming info while at idle RPM yesterday, but I totally forgot to take a screencap at cruising (~2.2k) RPMs. I also need to add RPM to the fuel dashboard for clarity, I guess.

First two images are at idle (675-720 RPM) and operating temp (i.e. not cold). Not sure it really helps you out, but maybe it's interesting to see? And also interesting my LTFT are where they are. I've been suspicious of my B1S1 sensor for a while now, my B1S2 ate shit 3 years ago and I've been procrastinating on replacing B1S1, I'm the asshole on here always telling everyone to replace in pairs, but I guess the "cobbler's children have no shoes" and all...

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It's definitely helpful to see. My data looked almost identical 3 days ago and I was so happy because I thought I fixed it. My downstream 02 sensors were reading just like yours so that is reassuring. My maf sensor is reading 7.4 at idle and I saw somewhere it should be reading like 4.7-6.0 but I heard atmospheric pressure changes this I believe. But idk, what is your opinion on taking it to a shop? I'm not a pro at automotive mechanics but really feel I have been diligent in my search for the problem. Again I'll mention I have checked twice for vacuum leaks, checked for exhaust leaks, replaced all 02 sensor with denso, new injector seals, cleaned injectors, tested fuel pressure regulator by swapping with old one, have 40 psi fuel pressure, replaced fuel dampener with the old just now, new OEM maf, new plugs, and checked all hoses. I'm just laying this out to try anything else before I probably have to take it to someone.