2UZ-FE High Long Term Fuel Trims (1 Viewer)

[Rednexus]

I normally post in the GX470 forum, but this one seems to get a bit more traffic for the engines.

I have an '07 GX470 with the 2UZ-FE and 138k on it. I installed a aFe cold air intake around a month ago and started getting PO101 codes for the MAF. I replaced the MAF (new Hitachi) and also found a few small vacuum leaks at the connection between the CAI and the throttle body that I fixed. My long term fuel trims (LTFTs) were really high before fixing the vacuum leaks (~20 at idle and ~20-23 cruising around) when monitored via Torque.

After fixing the leaks, I'm down to LTFTs of 12-14 at idle but still get up to 20-22 when driving the truck around. I did a complete vacuum leak test using carb cleaner and watching the STFT for spikes. I could not find any vacuum leaks - no negative spikes in the STFT when I hit all of the vacuum lines/connections/intake gaskets with carb clearer (it was clearly spiking negative when I used this method to find the leak at the CAI/TB coupling). I also tried pinching off vacuum lines to the power steering pump, fuel pressure regulator, etc and saw no changes to the STFT. So I'm 99% sure that I don't have any vacuum leaks. I also reset the ECU by unplugging the battery after fixing the vacuum leaks.

The Lexus runs great but the LTFTs are concerning and indicates something is wrong. I have no idea if they were this high pre-CAI because I was not monitoring them. Tomorrow I'm checking the fuel pressure and putting in a new OEM PCV valve. If that is inconclusive I'll put the stock CAI back on and see if things improve.

Anyone have any other ideas on why this 2UZ is running so lean? It does have the cracked exhaust manifolds (slight tick on both sides) that are getting replaced with headers soon, but I can't see a tiny leak affecting the U/S O2 sensors that badly. I'm not getting any other codes and all other sensor values seem reasonable.

 

[white_lx]

Unlike the name suggest, the MAF does not measure mass air flow. It measures air velocity and by knowing the area of the intake tube and flow conditions the ECM calculates the mass air flow. If your new intake air tube has a different diameter the calculated mass flow will be off. Did you compare the tube size of both intakes?

The idle mass flow of the 2UZ-FE is around 4.8 - 5.7 gm/sec at idle. What kind of numbers are you seeing at idle (warm engine)?

As your LTFT's increase from 12-14 at idle to 20-22 while driving, the FT's are not caused by a vacuum leak (FT would decrease with increasing RPM).

Any chance the wires/connector of the MAF got damaged during the install of the air intake?

Since your problems started with the AM air intake, I would re-install the OEM air intake and MAF first and go from there.

 

[Rednexus]

Unlike the name suggest, the MAF does not measure mass air flow. It measures air velocity and by knowing the area of the intake tube and flow conditions the ECM calculates the mass air flow. If your new intake air tube has a different diameter the calculated mass flow will be off. Did you compare the tube size of both intakes?

The idle mass flow of the 2UZ-FE is around 4.8 - 5.7 gm/sec at idle. What kind of numbers are you seeing at idle (warm engine)?

As your LTFT's increase from 12-14 at idle to 20-22 while driving, the FT's are not caused by a vacuum leak (FT would decrease with increasing RPM).

Any chance the wires/connector of the MAF got damaged during the install of the air intake?

Since your problems started with the AM air intake, I would re-install the OEM air intake and MAF first and go from there.

Thanks for the reply. I'm consistently at 5.8 g/s at warm idle, drive and park. So just outside of the range. It's also been 15-20 deg outside if that matters.

I've rechecked the MAF connector and put dielectric grease on it. The truck does have a SAIS bypass where I spliced into one of the MAF wires, but I've checked and even redone the connections and nothing changed. I did the SAIS bypass prior to the CAI.

I'll try the fuel pressure test and CAI swap over the weekend and see what happens.

 

[ttahara]

Do the fuel trims go back to normal if you put the OEM air filter assembly back in?

 

[KFunk740]

Yeah, check your fuel pressure if you can. If you didn’t have the means to do that, I would’ve at least changed the fuel filter for fun. Not a vacuum leak. My vote is for those exhaust manifold leaks. I think some oxygen there would easily make it go up myself.

 

[Eicca]

If your fuel trims are equally wonky on both sides that usually indicates the problem lies in a singular variable somewhere before the cylinders.

My vote is on that aftermarket air assembly. If the housing surrounding the MAF isn't precisely sized it'll throw things off. The 1UZ GS/LS guys go through this all the time.

 

[04UZJ100]

Get rid of the junk AFE filter and go back to OEM. Hitachi is not OEM, either. Denso is.

 

[CorporalClegg]

These numbers are positive correct? Indicating lean condition. The maf measuring volume at approximately 5.5grams/s indicates nothing abnormal. You can take a recording of air flow, o2 upstream, iat, and map and input those values into a program (assuming you havea tool that you can data log with ) that will calculate the readings and compare them to the maf readings and determine if they're accurate. Make sure you aren't over oiling the filter, reset all adaptations and give it another go.

 

[Rednexus]

Do the fuel trims go back to normal if you put the OEM air filter assembly back in?

I'll throw the OEM filter assembly in tomorrow and see what happens. I never bothered to check the fuel trims before I put in the CAI and performance/gas mileage remained the same/slightly better after the CAI so it's plausible that this was a pre-existing condition However the CAI itself has not yet been ruled out.

Yeah, check your fuel pressure if you can. If you didn’t have the means to do that, I would’ve at least changed the fuel filter for fun. Not a vacuum leak. My vote is for those exhaust manifold leaks. I think some oxygen there would easily make it go up myself.

I have a pressure gauge, just waiting on a banjo bolt with a 1/8 NPT tap to arrive tomorrow so I can check it.

Get rid of the junk AFE filter and go back to OEM. Hitachi is not OEM, either. Denso is.

The MAF that was in the OEM CAI was marked both "TOYOTA" and "HITACHI". As far as I can tell Denso does not make a MAF for the VVTI 2UZ-FE. The new Hitachi sensor I replaced it with was 100% identical to the OEM. It ran better with the new MAF than the old one, which I think I damaged by dropping 6" during the CAI install.

 

[Rednexus]

So with it being 6 degrees outside and my shop being unheated, I decided to wrench via Excel today. I made a full-throttle run with a warm engine and looked at the MAF readings vs. theoretical, volumetric efficiency, and fuel trims, as attached. Coincidentally, I threw another PO101 code while driving around to warm up the GX.

My volumetric efficiency (actual MAF reading / theoretical MAF reading) is around 70-80% at full-throttle and more like 15-30% at part throttle. This leads me to believe the MAF is under-reporting flow to the engine, potentially due to the CAI tubing not being sized properly as several posters had indicated, and causing the lean condition and the high LTFTs (~+20 for both for both banks of cylinders).

Still waiting on the banjo fitting for fuel pressure testing and a new OEM PCV valve to arrive so I can rule out those low-hanging fruit items. If the fuel pressure is in spec and the new PCV changes nothing it seems I'm left with the CAI itself or the MAF wiring, as I'm not sure an exhaust leak could cause the volumetric efficiency issue. If it is indeed the CAI I'll request a refund from aFe, as the CAI cost $350 and I've spent hours now messing with it and trying to troubleshoot these issues.

 

[flintknapper]

Fuel Pressure Gauge 12mm Banjo Bolt to 1/8npt Adapter - GS-FA-BANJO-Honda

 

[jerryb]

I thought about this effect when I slipped in a 3.5" or 4" aluminum pipe instead of the stock air train. (kept the stock filter housing)
I can't remember the size, It's same as OE ID 3.5 or 4 I'm guessing.

The ID of the pipe matched whatever size aluminum pipe I had at the moment.

I already had installed a new fuel pump and pcv. My trims were not out of bounds and not noticeably different than with the stock air train.
I also have the SAI bypass hardwired.
Stock MAF.
I had originally changed my fuel pump due to hard hot starts and possible fuel boiling, which was true. It can be said that if you don't know the age of your fuel pump on the SAI equipped trucks it's beneficial to replace it.

Be aware fuel is going to leak out (99%) any NPT threaded add on. Teflon or yellow Teflon might stop it momentarily but I've never been a fan of tape on a fitting on a fuel rail. AS in, I wouldn't go full throttle logging with it.
As a tool in the driveway while logging a tiny leak is fine.

I guess what I'm getting at is that matching the ID of the stock pipe to whatever pipe you're going to replace it with worked fine for me.
my trims are pretty normal, at least normal for me without cats, new manifolds and o2 calibrator.
I wanted a pipe so I could see the engine and work on it- do whatever, watch the belt, pulleys etc.
Toyota spec is plus or minus 35 combined before a CEL will be lighted on the trim.

putting that graph up makes me want to do the same when I get home. It's like getting extra work.
Read forum = go out side and do stuff that normal people never even care about. haha

 

[CorporalClegg]

So with it being 6 degrees outside and my shop being unheated, I decided to wrench via Excel today. I made a full-throttle run with a warm engine and looked at the MAF readings vs. theoretical, volumetric efficiency, and fuel trims, as attached. Coincidentally, I threw another PO101 code while driving around to warm up the GX.

My volumetric efficiency (actual MAF reading / theoretical MAF reading) is around 70-80% at full-throttle and more like 15-30% at part throttle. This leads me to believe the MAF is under-reporting flow to the engine, potentially due to the CAI tubing not being sized properly as several posters had indicated, and causing the lean condition and the high LTFTs (~+20 for both for both banks of cylinders).

Still waiting on the banjo fitting for fuel pressure testing and a new OEM PCV valve to arrive so I can rule out those low-hanging fruit items. If the fuel pressure is in spec and the new PCV changes nothing it seems I'm left with the CAI itself or the MAF wiring, as I'm not sure an exhaust leak could cause the volumetric efficiency issue. If it is indeed the CAI I'll request a refund from aFe, as the CAI cost $350 and I've spent hours now messing with it and trying to troubleshoot these issues.

View attachment 2584020

Nice, it's odd the dtc sets when you're not running abnormal efficiency (outside the acceptable range generally 80% ), bank 2 long term is interesting at around 43 seconds do you remember what was happening there? Fuel pressure readings can get you in trouble as I'm sure you know.. a fuel volume tester will definitively rule out the pump. I've also never seen an exhaust leak set a 101, a 171/4 sure, but you know what they say about hindsight. What's the code set criteria?

 

[Rednexus]

Nice, it's odd the dtc sets when you're not running abnormal efficiency (outside the acceptable range generally 80% ), bank 2 long term is interesting at around 43 seconds do you remember what was happening there? Fuel pressure readings can get you in trouble as I'm sure you know.. a fuel volume tester will definitively rule out the pump. I've also never seen an exhaust leak set a 101, a 171/4 sure, but you know what they say about hindsight. What's the code set criteria?

43 seconds was the start of a very short WOT run when the off-ramp straightened out, but I had to slow down for a stoplight. So the trims dropped to 0 as I presumably went into open-loop. The P0101 code only comes on a very light to 1/3 throttle and does not come on under any other conditions.

The banjo fitting arrived and I was able brave the Arctic temps to check the fuel pressure. 44 psi at idle with some leakage at the 1/8 NPT fitting, so I stopped the test. The spec is 38-44 psi so it passes with an A+ (and saves me from having to drop the tank or slide a bigger hole in the floor - which the 120 had the larger fuel pump cutout the 100-series has). This seems to rule out any fuel issues, leaving me with the PCV valve (which USPS must have decided to hold on to until Tuesday....) or the CAI/MAF wiring. I'm betting the CAI at this point.

The thing is the GX runs great with the CAI - I got 21.0 mpg on a 20-mile trip today, with the temp between 10-15 degrees and going 55 mph. Plenty of power, even running it on 87 octane. I never got more than 19 mpg before the CAI, even running 91 octane.

I've reached out to aFe and am awaiting their tech support. The aFe intakes do have a great reputation in the GX/V8 4Runner crowd, maybe I got a bad one. Other than this MAF issue it seemed to give me slightly more power and around 0.5-2.0 mpg extra, in addition to an awesome throaty rumble (which me and my kids love, but the wife hates).

 

[Eicca]

FWIW the MAF wiring is a possibility. My 1UZ does the same as yours but on the opposite side of the graph. Runs double digits in the negative trims until I floor it. At WOT it drops to about -5%. Whenever I monkey with the MAF plug the short term trim will immediately start to balance out the long term but after a few hours a driving it all settles rich again.

Try this: Before you go swapping the intake, unplug and re-plug your MAF ten times. Then start it and watch what the short term trims do. If they start trying to balance out your long term, i.e. LT still reads +15 or whatever but ST starts going to -15ish, that could indicate bad connection at the MAF plug.

 

[bigredmachine]

I made a full-throttle run with a warm engine and looked at the MAF readings vs. theoretical,

not really sure what a theoretical maf reading is but if its something like the calculated load on the engine your calculated load and actual load will never match up. i wouldnt necessarily look at the theoretical and actual maf reading discrepancy as an issue.

if you can stop the leak at the fuel pressure gauge check your bleed down pressure while its hooked up, you shouldnt see a 5-10 psi pressure drop over 10 min

 

[Rednexus]

FWIW the MAF wiring is a possibility. My 1UZ does the same as yours but on the opposite side of the graph. Runs double digits in the negative trims until I floor it. At WOT it drops to about -5%. Whenever I monkey with the MAF plug the short term trim will immediately start to balance out the long term but after a few hours a driving it all settles rich again.

Try this: Before you go swapping the intake, unplug and re-plug your MAF ten times. Then start it and watch what the short term trims do. If they start trying to balance out your long term, i.e. LT still reads +15 or whatever but ST starts going to -15ish, that could indicate bad connection at the MAF plug.

Great idea, I'll check that tomorrow. It's possible I disturbed the MAF plug when installing the CAI and then by replacing the MAF. I had a Subaru prior to the GX that threw PO420 codes for a decade and PO301 codes for 2 years before i realized the U/S O2 sensor connector was bad. Hard-wiring it fixed both issues.

not really sure what a theoretical maf reading is but if its something like the calculated load on the engine your calculated load and actual load will never match up. i wouldnt necessarily look at the theoretical and actual maf reading discrepancy as an issue.

if you can stop the leak at the fuel pressure gauge check your bleed down pressure while its hooked up, you shouldnt see a 5-10 psi pressure drop over 10 min

Theoretical MAF flow is the calculated airflow the the 4,663 cc engine should be moving, based on actual RPM and actual intake air temperature. Volumetric efficiency is theoretical MAF flow divided by actual measures and should be between 75 and 90%. So it's close but just a bit low.

I'll try stopping the leak with some teflon tape and check the bleed down tomorrow.

 

[bigredmachine]

I'll try stopping the leak with some teflon tape and check the bleed down tomorrow

fuel may eat away at the teflon tape, check the o-rings first before trying the tape

 

[Rednexus]

This morning I redid the 10-ga ground wire that comes from the MAF harness (moving it back to the inner fender by extending it, instead of the fender well location I had moved it to per the aFe install instructions) and tried unplugging/plugging in the MAF 10 times, after slathering the connector in dielectric grease.

As soon as I started up the GX the STFTs for both banks went way negative (15 or so) and slowly increased back to zero. It's ~6 degrees again, so presumably STFTs would go positive if the engine was functioning normally to richen the mixture in this very cold/dense air. I tried this a few more times and got similar results - highly negative STFTs that went back to zero in a few minutes. When I left the connector alone and re-started the GX the STFTs stayed around zero. LTFTs remained 20-ish for both banks during this test, but I only ran the engine for a few minutes.

So this is pointing to the MAF connector on the harness being damaged. I'm just going to order a new one and splice it in. I also checked the diameter of the aFe CAI at the MAF and it is exactly the same as OEM (3.5 inches). aFe has had this intake out for quite a while so it seems odd that it would be mis-sized or that it would have other design issues (unless I just got a bad one....). I also triple-checked the SAIS bypass wiring and found no issues.

I didn't get to the fuel bleed-down test today due to my toes losing feeling in the cold, but i'll check that next week after the PCV comes in. FYI, I'm only using the tapped banjo bolt for the test and put the OEM banjo bolt back in yesterday after I did the test.

 

[Eicca]

Definitely sounds like the connection is ok after first plugging in and then looses some continuity after a few minutes. The short terms will try to cancel out the long terms until the grody connection settles back to what the computer has adapted to. Could be weak pins, corrosion, etc. New MAF connectors are cheap enough it's worth a go.

Just some evidence for the jury—a Subaru forum where they had similar issues, but with mixtures reading rich (like what mine is currently doing) until the plug was fiddled with:

https://legacygt.com/forums/showthread.php/faulty-maf-sensor-connectori-255914.html?s=0b2d95f954b8053c0e73d4186c35f19c&

When installing the new plug I personally wouldn't use dielectric grease of any sort. Bare clean metal is the best for these highly-sensitive contacts. Some Deoxit D5 is the most I'd put on something like that.