P0174 Code and intermittent sputtering

Hey all. I have an issue where I’m getting a P0174 code (Bank 2 lean) and intermittent events where the engine struggles to start at crank—specifically after filling up with a tank of gas.

A little background is right now I’m clocked at 196,800 miles. So far I have replaced the MAF, all 4 O2 sensors as it concerns air/fuel. Here a few days ago, I had the timing belt, drive belt and water pump serviced. This code came maybe 3 days after the 90k service was completed at the dealer. Initially, I thought to take it back as an issue they may have created, but I remember this happened before I took it in. The difference is, I did not have a lean code at the time.

I don’t notice any impact while driving. I will say bank 2 is running quite lean. At memory, the LHFT% is about 21.1 at idle and about 13.7 at 2500 rpm. Can’t remember the SHFT. I’ll get a DTC freeze later.

As I stated above, this crank sputters only happen after filling up the gas tank (so far). The first instance I thought it was garbage gas but the same thing has happened at different stations. I have not checked the ohms on the fuel resistor, but I plan to. At inspection, I can find any vacuum leaks on any hoses. Because of this, I’m thinking the fuel pump may be taking a slow stroll to shit but I’m not sure. All the previous forum threads had both banks lean, not just one, so this is kinda unique.

Any takes?

 

While you’d think it was fuel pump, and I wouldn’t disagree if you had over 200k-300k miles, the crank position sensor wire, as we’ve covered numerous times, often gets misrouted during timing belt replacement, and it starts getting cut thru. If the ECU can’t get a signal from the crank position sensor, it kills the fuel pump power. So that is the first thing I’d be checking. There are pictures of the proper routing and damage that happens in the megathread: https://www.tundras.com/threads/so-you-wanna-buy-just-bought-a-1st-gen-tundra-eh.115928/

My initial thought is, it’s starting to get cut thru, and that’s your issue, you’re getting intermittent loss of signal or weak signal, and it’s impacting the pump. But also smell around carefully for gas in the engine bay in case a fuel line is not secured.

Search page one of that thread for the phrase “crank position”

 

I did see that in a few other threads, which lead me to believe it was a dealer mishap but the struggle to start occurred before the timing belt service—and weirdly (so far) only occurs at a gas fill up. I certainly still plan to inspect the sensor regardless. Will report back

Do you still think this is the case provided it happened before the service? That’s what led me to believe it’s the fuel pump itself.

 

The fact it happens after a change inside the tank (i.e. adding fuel) would lead me in that direction, either failed pump, rodents chewing on fittings on top of the tank, or pickup tube on the fuel pump has become loose.

The reality is reality, the things that could cause 'bank lean' on the passenger side only:

• There's a vacuum hose that goes from the boxy part of the intake tube over to the bank 2 fuel pressure regulator (metal tophat looking thing) over the passenger side head. In theory, it'll reburn vapors, but also allows vacuum on the pressure regulator to ensure pressure to the bank 2 fuel rail, and your lean code is on bank 2. I'd be carefully inspecting that hose to make sure it's intact (for one), and popping it off and squeezing the ends to inspect for signs of cracking/disintegration under pressure (for two). If found, ideally replace the hose, in a pinch, cut the last 1/8" off.
• Obviously, it doesn't happen often with the black-top intake manifolds because they use the molded rubber gaskets, but breach of the gasket could cause a lean situation, as would any problem with the bridge between the two.
• Fuel pump isn't able to create enough pressure to push fuel past bank 1 and into bank 2
• Leak/poor attachment in one of the fuel line quick-connect fittings, probably in the engine bay, less likely at the tank
• Possibly another vacuum source that's not coming to mind for me?

If this were a lean problem across both banks, I'd be wondering if the MAF was dicked up or the throttle position sensors was dicked up, and the ECU was getting bad info about how much air was coming into the engine, and under-spraying fuel bsed on that. I would also have the fuel pump as a suspect in my list with that.

If this were only bank 1 seeing lean, i.e driver's side, I'd be really stumped wtf is going on.

Given you've got ~200k miles on the truck currently, and Denso appears to be constantly running short on fuel pumps and alternators for our trucks, I think you'd be well-served to replace the fuel pump now with an authentic unit (i.e. don't buy on scAmazon/fleaBay), and enjoy another 200k miles of operation. But before I went there, I'd definitely grab a mirror and inspect the top of the tank with a bright light to ensure wiring etc. is intact.

And of course, as preventative maintenance, it's worth verifying the crank pos sensor harness is properly tucked

Let's hope it's only that rubber hose I'm talking about. But at the same time, heed the advice on the tank, and know that replacing a pump, especially when you've got about 1/8 tank or less of gas, isn't a terribly complicated job, it can just be tedious if you're doing it solo. A length of 2x4 and a floor jack and possibly a floor/furniture dolly (piece of wood with 4 wheels) is your friend. I've had to drop the tank, on the ground, in a couple of my trucks. I've also had other trucks (GM 1500s / GMT400) where it's easier just to pop the bed off. I know on my AC the pump is kinda up under the cab. Not sure on DC. But I prefer to drop the tank where I can.

 

Update:

Checked resistor. Specs call for between 0.7 and 0.76 at 68F. I clocked 0.7 at 42F. I’d imagine it’s a hundredth or two higher in warmer conditions.

Checked top of fuel tank. It was a bit difficult but I didn’t see any fraying, chewing etc on the electrical nor did I see any rodent nesting.

Checked all other vacuum hoses. Don’t see any obvious decay, though through past experiences it literally can be a pinhole or three you can’t see

Checked crank sensor. Didn’t see any compromise there. It was routed up the block, back behind the pulleys. I assume this is the correct route?

First two pics I took were of crank sensor and it’s routing from bottom and top. Third is a general pic of bank 2. The fourth is a picture where I noticed a hose from bank 2 did not have a hose clamp on it but it’s bank 1 sister did. Checked the hose and it seems ok with the exception of some very slight splitting right at its end, which I assume is just from constant expansion pressure.

 

OP, I wonder if it's just the PCV valve due to the fact that it only happens at start-up (i.e. low rpm’s)?

 

I thought about it after the fact to check the boot and valve. Usually on any vehicle you’d run lean on both bank if the PCV was a problem. I’ll give it a check later anyhow

 

I understand, because although it doesn't exhibit all the symptoms of a failed one, it checks-off enough of the boxes for me that I would consider the possibility. It is possible.

 

Hose from fuel reg to the intake is yellow arrow.
One you said was loose (I think?) is red arrow, which is PCV vent for bank 2.
Green arrow/lines are the SAI valve vacuum lines, those two brick colored plugs are the solenoids that pop open the valves for secondary air injection system. I guess check its hose going forward from the end of the loop, while you're in there.

Look at the fuel pressure regulator on the rail, where that yellow arrow'd hose terminates above the valve cover. Inspect the fuel rail, its connections. All look OK?

Do you have a bluetooth scanner or similar where you can monitor voltage on the upstream passger sensor? Have you tried unplugging/replugging that sensor, just the connector? (Since it's what tells the ECU its fuel/air mixture)

​

 

It is. When the crank hesitation started, the lean bank wasn’t there. It could have been pending but that was probably 3 weeks ago. My fear is that although a bad fuel pump can set off lean bank code(s), the two things may actually be separate

 

Yes, correlation does not equal causation. I'm only considering possibilities based on your descriptions, mileage of the truck and the fact no mention is made of replacement since owning. I typically err on the side of simple things first.

 

No sir, no hose was actually loose. However in picture 4, the hose coming from bank 2 is missing a hose clamp and is very slightly splitting at its end, unlike its sister from bank 1. I don’t think this is an issue for the situation, I could be wrong.

I do have a scanner that can monitor performance. By upstream sensor I assume you mean the AFR sensor for bank 2? If so, it’s brand new and its voltage looked good but I can take some freezes of performance and post the results

 

Question: Did they also do the cam seals, or just the timing belt?

If the timing was off by a tooth, I'd expect other oddity, like a misfire or something.

 

If you're talking about the hose i have a yellow arrow on, that's the hose giving vacuum to the fuel pressure regulator on bank 2, so it can adjust the pressure for that bank.

If the ends of it are cracked, I'd trim it back to clean, or replace. Note, you can use a zip-tie to temporarily hold hoses on if they're questionable. If you have any vacuum hose that'll fit on both bibs, I'd try replacing that hose as a sanity check "just in case", given the bank-specific symptoms.

If you're talking about the red-arrow hose, yeah, that's PCV, don't think it'd cause it, and they're often split if they're never been replaced. I don't recall if mine had a clamp or not and don't have pics on the computer to check. I replaced mine within the last year due to age/split ends.

 

Just the belts, coolant and water pump. I’d expect the same if so. The truck actually drives great. Not like you’d expect from a lean bank. Mileage is even in line for the most part.

 

But If timing were off, I would expect misfire across entire rpm range, no?

 

I’m talking about the left hand hose in this picture @shifty`

 

We've had it on here before. A VVTi truck owner who failed to use the service bolt while doing cam seals, throwing off that head's cam. He only had a single cylinder misfiring on that one head.

The thread went on for 21 pages before he figured it out, and he must've torn things apart about 6 times before he realized his fuckup. I couldn't figure it out for the life of me.

 

Right, and this sputtering/misfire only happened at low rpm and/or start up? If so, that is interesting.

 

IIRC, it started with a couple of misfires, and after adjusting the timing, he got it to only misfire on one, and only at idle.

https://www.tundras.com/threads/multiple-misfires-after-rebuild-fixed.110071/

But the thread was like 2-doz pages long and I don't want to rehash that mess

 

Update:

Fuel trim numbers for anyone who’s interested. Idle, ~1600 RPM and ~2600 RPM

 

Interesting. Because the short fuel trims are going negative, that's indicative of fuel pressure or fuel injector related.

Maybe this will help:



Edit: I didn't mention the "any" condition due to the fact that you stated the issue is on bank 2. Unless...it's IAT related

 

What procedures were performed at 90k? Based on your description in your 1st post, I believe I would go back and try to deduce from there what the possible culprit is. Not saying it is or isn't their fault, just thinking logically.

 

I wish I knew what Toyota’s tolerances are for the truck because good rule of thumb from old timers has always been anywhere between +/- 5% on either side of the range should be ok.

What’s interesting now is that now that I’ve ran some Chevron duel treatment in the tank, the long trim is actually a bit lower and P0441 and P0445 are pending. I know both have popped in the past due to the fuel cap needing to be replaced (me being lazy). But it’s interesting it’s coming back around with these events. I suppose related or not, I need to stop being lazy and spend the darn 15 bucks for a cap off principle.

 

Those pending codes make it even more interesting. I'm posting on the fly right now. You could replace the cap and see what happens. If it doesn't solve the issue, you're right back to fuel delivery, IMHO. Pump, pressure regulator, injector(s).

 

Drive belts, water pump and coolant. I double checked to make sure the crank shaft sensor wasn’t misrouted (confirmed behind the pulley). Also checked all the bank 2 hoses in case they disassembled during the repair. I couldn’t identify any issues, though PCV is on my radar after our convo.

I’m still thinking fuel pump but I’m trying rule out all other possibilities before tackling that job. At this point if it’s OWM it’s 18 years old so I guess it wouldn’t hurt anyway.

 

If they stick, I'd smoke test it, at the tank, and using the green-capped port in the engine bay. Certainly seems like you may have a leak at hand.

 

I agree with shifty. I wouldn't pull the pump until I ruled other things out 1st.

 

Update:

checked all bank 1 and 2 hoses. Sprayed starter fluid as well. Could not detect a leak. Also check hoses from fuel tank to canister. Couldn’t detect any leakage.

PCV looked fine thought I plan to replace it.

Replaced fuel cap. That seemed to take care of the evap codes like I thought. Fuel fill neck looked ok as well.


Was puzzling is even after a ECM reset via battery, the LongFT’s are still out of whack. Started all trims at zero and evaluated. Ironically the ShrtFTs are still dead on and hang around zero. It’s pretty much zero at idle. However the Longs are way up there. I reset the grind today so the attached update pic only compasses about a hour’s drive but they immediately shot from 0 to the 20-30%. Pic is at idle after driving 30 miles post-reset.

Any thoughts are appreciated

 

Keep in mind the ECM has volatile and non-volatile memory. With a battery disconnect, volatile memory is flushed and LTFT, along with other parameters, have to re-learn !
STFT is stored in non-volatile memory and remains on batt disconnect.

As an example, this is from my 04 DC LTD showing LTST reset after batt disconnect.