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.