false tps readings causing lean codes? '06 4.0 v6

Hey there,
I'm new to the forum. I have an 06 with the 4.0 v6 manual and have pesky ;ean codes and hesitation lack of power issues.
i have replace the pcv valve, fuel pump and throttle body.
I noticed before and after i installed the throttle body I was still getting 16% at idle and 80% WOT and the issues were still there. the pump i replaced with a cheapo off rock auto.
i just ordered a pressure test kit for the funky fuel connector stuff toyota uses on the fuel lines so if pressure is good (50psi) what else could i be looking at? i didnt notice the gasket on the top of the fuel tank for the new fuel pump until the tank was up and installed but the gasket that was there never came off so at least it has one. also cleaned maf and had good readings (i believe)
this is everything i can think of. any advice appreciated
-D

 

Well, you mey need to understand something fundamental. All EFI engines operate based on:

• Metered air, so the ECU knows how much (volume of) air is coming into the system, so it understands how much fuel to spray - this is typically accomplished using a MAF/Mass Air Flow sensor.
• A constant pressure of fuel, typically above 38-42psi (wild baseline avg, may vary between engines/models), which depends on a functional pump, return, unclogged fuel filter (your truck doesn't have one), and functioning pressure regulator/damper
• Properly timed spark/hot enough spark/i.e. timing is good, coil packs are good, and spark plugs are correct model and good

If the engine manages to ignite based on the three above, the engine uses the upstream O2 sensor, just past the manifold, also known as "air/fuel ratio sensor", to 'read' the combustion output (exhaust) and scan it to determine: Is there too much fuel? Is there too much air? etc. It uses that information to decide whether the amount of fuel it's spraying is adequate, and adjust accordingly. I mention this last bit because we have a lot of ignorant people on this planet, who mistakenly think that "O2 sensors are just emissions crap". The number of people who believe this stupidity is alarming to me, but that's another topic entirely. If your O2 upstream sensor is reporting bad numbers to the ECU, saying there's too much unburnt fuel in your exhaust passing thru the manifold, guess what it's gonna do? Dump less fuel!! i.e. you'd end up lean. Of course, in many cases you're going to have a check engine light to warn you if the upstream

This is oversimplifying a bit, to get your brain functioning. There's obviously more to the equation, like whether the throttle position is accurately relayed, if the MAF is giving the ECU correct air volume measurements. Or ... the big one ... VACUUM.

Vacuum could easily be your problem. A vacuum leak our excess vacuum could lead to the ECU trimming the fuel it's spraying. You can actually us that info as a diagnostics tool, if you have a scanner that supports monitoring your fuel trims, so you can see what the ECU is doing? You'd want to monitor in realtime, with the engine at operating temp, and running. These three videos may help understand the what/how. I'm posting three because they all deliver info in different ways, Car Care Nut (I think) in the 3rd video explains how to detect vacuum leaks better. And many different cheap scanner units will give you realtime fuel trim info.

https://www.youtube.com/watch?v=pIJdCZgEiys

https://www.youtube.com/watch?v=ILm8sJrL2R0

https://www.youtube.com/watch?v=fDwq4OR6FT8
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yes i know how fuel systems work i have been a mechanic for years. I was hoping there would be someone with a story of a similar problem and come in with a crazy answer i wasnt thinking of..
i also checked for vacuum leaks and replaced my gas cap as well. i never mentioned the oxygen sensors are faulty, they are doing their job. yes i have been monitoring live data and all of it looks to be within spec.

 

Ok, sorry, I'm sure you'll figure it out.

 

Mind being a little more specific and list the codes. Were they in both banks ?

Are you able to view live data and if so, what were LTFT reading at Idle and WOT, given improvement from Idle to WOT would indicate one thing and no change in those operating ranges would indicate something else..

As for MAF, the specs for a 1GR are 2.0 to 3.9 g/s: Idling....is that what you got ?

 

hey there thanks for the helpful reply.
I will take a snapshot of the codes (po171 and po174) when i get home later. as for the oxygen sensors they seem to be operating both banks at almost identical parameters.
Update:
live Data
Maf at idle is reading 4.8 g/s
LTFT is hovering around 0-10 at idle or leaning out after any sort of throttle input. under load its +29-39 and a 3% difference between bank 1 and bank 2 but about 4.7 on both banks under load WOT

freeze frame data:
load 77.2
temp 190
stft b1 2.3
ltft b1 26.5
stft b2 4.6
ltft b2 28.9
rpm 2650
Maf 40g/sec
tps 28.6
02 sensor 2 bank 1 .64
02 sensor 2 bank 2 .60

 

just checked fuel pressure and its at a perfect 50 psi. it has to be some sort of vacuum leak but i sprayed starter fluid in every nook and cranny and couldnt get it to change in rpm. coukd the pcv i replaced be crap?

 

Don't forget, other things/places draw vacuum.

Power steering air control valve and brake booster being two big ones, at least with V8 on the PS-ACV, I'll assume for a sec V6 is the same.

Either can be blocked off (at the manifold/intake, ideally) temporarily to test. Booster is far enough away that if the plastic check valve where the hose meets booster can wouldn't be impacted by spraying stuff, same with the PS-ACV, it's practically sitting on top of the power steering pump with two smaller rubber hoses coming into its rabbit ears.

 

I had a TPS doing something funky one time on a vehicle i was working on, i literally replaced everything before finally replacing the TPS and resolving the issue.

So long story time:
Got a vehicle, had all sorts of weird misses and CELs. TPS low voltage, misfire, ect ect. You would be driving along at a set speed just like holding 35mph and the vehicle would stumble, act like its misfiring, sometimes backfire, sometimes continue for a minute or two, sometimes only for a few seconds then clear up. It seemed better when the engine was cold, first crank up you might run it 10-20 minutes without any issue, then it would randomly start hiccuping, lunging, losing power.

Found some corrosion inside the wires going to the coils, cut bad wires out and ran new wires, no change. Bought repair harnesses for coils, soldered them in, no change. Replaced throttlebody, no real measurable change. Did adjustment and reset on TPS, no real change. Checked fuel pressure and it was pretty whacky, changed fuel pressure regulator minimal change. Replaced whole engine harness cause i found more corrosion in the harness, no real change. Replaced throttlebody back to OEM, no real change. Drained fuel system to check for water, no real change. Replaced injectors, no change. Finally one day i had diagnostics up on screen and was driving along watching the TPS and sure as shit while holding steady at 9% throttle, the TPS went to 0%, then jumped to 129% and then bounced back and forth from 15-25% even though my foot never moved from the 8-9% i was holding. I did another TPS adjustment, reset, relearn, no change. Finally ordered a TPS and put in it and it went back to running like new. Only cost me about $3000 in parts and 30ish hours in labor to finally figure out something was wrong with the TPS.

PS, replacing a whole harness is a pain in the ass, do not recommend....

 

Also to add, when i was driving holding 9% throttle, and the TPS magically went to 0%, i was allowing in xxx% of air but the ECU now instantly sees 0% throttle and cuts the fuel delivery, hence why you would certainly get a lean condition. You are allowing more air into the engine than it thinks its getting. With the amount of fuel its metering (what it assumes will be idle conditions at 0% throttle) would certainly cause the AFR to go much higher than the 14.7 it thinks it needs at idle and 0% throttle.

 

Im thinking of replacing the fuel pressure regulator as a lean issue with a strong fuel pump points to something after or a vacuum leak, which ill go deeper, but don't think thats the issue. the header gaskets appear to be in good shape and dont hear and exhaust leaks. is there a better way to check around the headers for exhaust leaks in case im missing something? also thinking the sensor for my pedal poaition sensor isnt right. tps is on new throttle body.

i also think the accelerator pedal position sensor may be out of range as it operates between 16%-80% and on the scan tools absolute input from 0%-63%. they are expensive. is there a way to recalibrate them? ive tried disconnecting power for periods of time etc.

 

power steering doesnt have a vacuum line going to it.

my 02 sensors are reading about 2% different than each other on LTFT and at idle it seems one is 1.5+ and the other 1.5- which is kind of odd..

 

I have the 2UZ-FE, which is VVTi but clearly not the same as yours.

I typically read ~2% different between B1 and B2, with B1 being a little hotter.

I would need to read through the FSM to see if/why you don't have the power steering air control valve, or if you do. The vacuum lines don't go directly to the pump on my 2UZ. But I'm not super familiar with your VVTi V6.

 

it seems to be throttle position dependent on getting the weird hesitation loss of power thing. getti g wierd live data readings for ltft at+6 at WOT but going up to +30 at about 30% throttle. could there be an evap leak?