Best guess for these LTFT readings (fuel trims)

[Drcoffee]

I am working on my new to me 07 T4R Sport. Initial thought was a head gasket but the HG radiator test did not turn the blue fluid yellow, so Im not really sure. No codes, smooth idle. So Im wondering if I have a clogged fuel injector. With the truck warmed up and driven for 20 minutes my LTFT on bank 1 is normal (near sero) while driving, but bank 2 is looking lean +7.8%. So here is what is odd to me. In park idling the numbers flip. Bank 1 is lean and bank 2 is normal.

Im mostly concerned about bank 2 and if the reading is normal at idle, but lean while under load, I assume its not a vacuum leak. Would I be off target by thinking its a bad fuel injector on #2,4,6 cyl? What else could cause this issue?

Screen shots of fuel trims at idle and and with foot on gas while parked.

 

[81runner]

Those numbers don't look bad at all. Ideally, you'd want the trims to zero out when the pedal is applied, but anything under a 10 plus or minus is usually ok. Don't think you have anything to worry about. Is fuel economy ok?

 

[Drcoffee]

Those numbers don't look bad at all. Ideally, you'd want the trims to zero out when the pedal is applied, but anything under a 10 plus or minus is usually ok. Don't think you have anything to worry about. Is fuel economy ok?

About 19 mpg but I dont drive it enough to get a solid average.

On my older lexus is300, when the LTFT went lopsided, it turned out that 3 spark plugs went bad. The pucks on the grounds were missing which increased the gap. And that was only a 6% LTFT. Id like to find the cause of this. The plugs on this truck were just change, so that rules them out. No change from old plugs to new plugs.

 

[Warwicke36]

Screen shots of fuel trims at idle and and with foot on gas while parked.

Generally speaking as long as LTFT is below 10%+/- from 0 you are OK

STFT within 25%+/- from 0


If your numbers are outside of those parameters you could consider cleaning your mass airflow sensor, looking for vacuum leaks, or checking to make sure your upstream O2 sensors are working properly.

 

[Drcoffee]

I get what you are saying. And the MAF would effect both banks. This is asymmetrical. Something is causing this. Id like to find why before it worsens.

 

[Warwicke36]

I get what you are saying. And the MAF would effect both banks. This is asymmetrical. Something is causing this. Id like to find why before it worsens.

If you're that worried about an already well running vehicle pull the plugs and put in iridiums change your air filter and inspect the things I mentioned above. Not to sound like a prick but why go looking for trouble? It runs fine per your comments. Save your worries for something else. Just my $.02

 

[81runner]

There will almost always be slight variations in the way each bank runs. The valves could cause it, the size and intensity of spark could cause it, the size of the burst from the injector could cause it. No engine is going to be exactly perfect between the two banks, that's why you are afforded tolerances on both. As long as you are within tolerance and your fuel economy is good, rejoice!

 

[Drcoffee]

Im not super concerned about it. But its more of curiosity for me. I like working on the truck and this obviously has a cause. All my other toyotas/lexus vehicles run spot on.

As the air volume increases, the lean condition also increases. Possible issues are a bad O2 sensor upstream, bad fuel injector, ... any other suggestions?

Im not that guy who believes in waiting for something to fail. The cost is usually 10x at that point when you consider the tow back home.

 

[81runner]

I'd check the vacuum lines, pcv, intake manifold(gaskets and actual manifold since it's plastic), anything that either runs on vacuum or is past the maf on the intake. If it's segregated to a particular head, check the injector seals. Could still be the intake gasket if it's one head, since you could technically still have one side of the gasket blown. That's about all I can come up with off the top of my head. And ya, I get it, I wrench for therapy as well....

 

[Drcoffee]

I'd check the vacuum lines, pcv, intake manifold(gaskets and actual manifold since it's plastic), anything that either runs on vacuum or is past the maf on the intake. If it's segregated to a particular head, check the injector seals. Could still be the intake gasket if it's one head, since you could technically still have one side of the gasket blown. That's about all I can come up with off the top of my head. And ya, I get it, I wrench for therapy as well....

Thanks. All good things to check. There are no misfires but the fact the LTFT worsens under load, makes me think fuel injector not spraying correctly. But since I need to remove the intake to get to the injectors on bank 2, I plan to replace the plenum gaskets, TB gasket and all 3 injectors and. Valve cover gaskets all at the same time.

Im also fighting. P0456 small evap leak. Just changed the fuel cap which felt loose, and replaced the evap purge valve up by the intake.

 

[Warwicke36]

Thanks. All good things to check. There are no misfires but the fact the LTFT worsens under load, makes me think fuel injector not spraying correctly. But since I need to remove the intake to get to the injectors on bank 2, I plan to replace the plenum gaskets, TB gasket and all 3 injectors and. Valve cover gaskets all at the same time.

Im also fighting. P0456 small evap leak. Just changed the fuel cap which felt loose, and replaced the evap purge valve up by the intake.

If you're sucking unmetered air and fuel vapor in through a leaky purge valve that will affect AFR. Was it leaking, did you try blowing through it?

 

[Drcoffee]

If you're sucking unmetered air and fuel vapor in through a leaky purge valve that will affect AFR. Was it leaking, did you try blowing through it?

I did try to blow thru it and it held. Could it hold vacuum, I didnt test for that. I did check for codes and p0456 did not come back. Will check over the next few days. .

If the purge valve was leaking, it would impact both banks.

 

[Drcoffee]

You mentioned mpg. I get 17 mpg mostly highway at 75 mph. Is that about average for this truck?

 

[81runner]

You mentioned mpg. I get 17 mpg mostly highway at 75 mph. Is that about average for this truck?

That's pretty normal fuel economy

 

[Drcoffee]

After watching this Scotty video, I am leaning towards bad fuel injectors myself. Much of the data he sees, I see as well.

Here's Why This Air Filter Can Destroy Your Car's Engine - YouTube

 

[Drcoffee]

Update:

I had some time this weekend and dove into the fuel injector project. At the same time decided to replace the valve cover gaskets as well. As I started removing the intake plenum, I found some oil build up on the lower intake and fuel injectors and my best guess is the oil is coming from between the plastic intake plenum and lower intake. You can see in this picture all the oil outside the gasket area on the plenum. The gasket was hard and compressed and probably the source of the air leak I could hear.

As for the bank 2 LTFT being lean under load, the number 6 injector (far left) looks clogged. Also the lower injector gaskets were hard and loose and gave no resistance to being removed. There’s no way to know for sure if they were clogged, but I replaced all 3 on the drivers side just so I wont have to go back in this deep again. Im waiting for the valve covers to dry from a quick paint job in black and then I can put it all back together and see what, if any impact all this work has had. More to come.

 

[Drcoffee]

I made some progress. Put it all back together, reset the ecm, took it for a test drive. The LTFT is now 3.21 to 3.91 on bank2 which is good.
Now I think I can look at the MAF or bank2 upstream O2 sensor to get better results. The O2 sensor is responding quickly, so MAF will be next. Any thoughts?

 

[Drcoffee]

Update. After replacing all six injectors and the MAF the LTFTs were still unbalanced. So I replaced the fuel pump. Finally the fuel trims are balanced and within a reasonable limit. Im sure the O2 sensors are most likely original with 223,000 miles. It runs fine so I dont plan to change them until it throws a code. At $120 each, I can wait.

This was driving on the highway at 70mph. Routinely adding just 5% under load but balance left and right

 

[waypoint]

Nice methodical approach. I was going to suggest running a bottle of Red Line SI fuel injector cleaner as I've had good results correcting LTFT imbalances on other vehicles (I run this before most every oil change as preventive maint).

Did you take a fuel pressure measurement before replacing the fuel pump? That would be good data, although your replacement definitely seems to have corrected the remaining issue.

It's my experience that as delivery pressure decreases, discharge volume increases (PV=nRT) and I've seen cases where low pressure caused negative LTFTs albeit on both banks. One was a bad pump, the other two were bad fuel pressure regulators with likely worn-out springs.

 

[Drcoffee]

Nice methodical approach. I was going to suggest running a bottle of Red Line SI fuel injector cleaner as I've had good results correcting LTFT imbalances on other vehicles (I run this before most every oil change as preventive maint).

Did you take a fuel pressure measurement before replacing the fuel pump? That would be good data, although your replacement definitely seems to have corrected the remaining issue.

It's my experience that as delivery pressure decreases, discharge volume increases (PV=nRT) and I've seen cases where low pressure caused negative LTFTs albeit on both banks. One was a bad pump, the other two were bad fuel pressure regulators with likely worn-out springs.

I didnt test the fuel pressure because its a toyota and nobody carries the correct adapter to plug into the fuel line, and a new kit was too expensive $300-$400 IIRC. So for $100 I bought a new denso pump and diy’d it. My thought was under load I had a lean condition and the ecu was adding fuel to compensate. With low fuel line pressure, the bank 1 injectors were not getting the same volume /pressure as bank 2 and hence, the imbalance. Just a theory.

The fuel dampers are cheap. I may just replace it for giggles.