02 Toyota Sequoia - Lean codes!

Hi group! My 02 Toyota Sequoia has been running with lean codes (P0171, P0174) for a few months now. When starting hot or cold it usually needs a few seconds to turn over, rest for a second, then it fires up on the second turn. Also, low power under load. It won't go over 80Km/h up a little hill. I'm down to 40Km/h on the big climbs with an empty trailer.

I have replaced the fuel pump, fuel filter, injectors (12 hole upgrade), fuel pressure regulator, MAF sensor, O2 sensors, and spark plugs. There are no vaccum leaks. Fuel pressure at the rail is within spec. I've done full resets after replacing each item. I'm at a loss. No other codes.

I have attached some data from the bluedriver. You can see from the MAF and %Load that I was at idle until the mid point, revved it to 2500 for a few seconds at the mid point, then started driving at the very end. I don't know what to make of it other than my fuel trims are through the roof and it seems like an oxygen sensor may be acting up? I wouldn't rule out that a new part may be faulty, but that just makes it more difficult for me to figure out. Any input is much appreciated! Any critical questions to guide me in the right direction?

Thanks,
James

Your description "low power under load" fits perfectly into Paul's Low Power complaint check from his book.
Have you checked for a plugged exhaust on this vehicle?

Thanks for the reply Bills! I don't know what a proper check would include, but I did feel pressure with a rag at idle out of the tail pipe and checked for leaks in the exhaust while plugging the tail pipe. Pressure seems good. I had a P0420 code that would come and go for years. My Dad found a pin hole exhaust leak around one of the O2 sensors. I haven't seen the code since replacing them all. Would a plugged cat cause this without a more specific code?

Graph your 2 upstream sensors only, and do a wide open throttle check, ie. gas pedal to the floor briefly and somewhere safe. your 2 upstream sensors should go over 800 millivolts at wide open throttle. if this test is good, I would remove one of the upstream sensors ,find a hill and see if performance improves with the forward O2 sensor out. Make sure to check your pcv hoses, valve, etc.

Thanks for the suggestion! I just watched one of Danner's videos where he diagnosed a bad MAF and some vaccum leaks by doing this. Good call on removing an O2 sensor to check for improvement. Those converters are original and could very well be getting plugged up. I will report back with results.

also you might want to check Danners interior leak check vac from oil dip stick. and fuel oil now that you had that problem for awhile good luck

I'd also be interested to see a WOT pull from a stop through second gear, like bills4065 suggested. Add Calculated Load, MAF, IAT and engine speed to your capture. With those, an air measurement or breathing issue will stand out.

Well, wide open throttle test showed O2 sensor voltages tanking to 0 very quickly. They stayed there until I let off the gas. I had power though since I wasn't towing the trailer. Seemed to run decent actually. Little shaky at idle after. RPM's would dip low and stutter before coming back up for a couple of minutes. I attached the data of WOT test here (circled test area in white). I'm guessing this indicates that my problem isn't the converters being plugged? I noticed my MAF sensor didn't read anything different during the test.... Could that be my issue? It was reading accurately the last time I tested with normal driving.

Thanks for the tip Lupe! I've never heard of doing this before.

The maf reading not changing is definitely a problem! The test confirmed you have a fuel delivery problem. The maf sensor could be dirty, or sensor no good. I would back probe maf sensor checking power and ground with key on engine off. Did you happen to graph the maf gm/ sec readings during your test? And it is looking like plugged exhaust is not your problem.As @Tyler suggested graph all he said and I would do the wide open throttle again as per his suggestion .

Thanks for joining in Tyler. I added air temp today and noticed the reading way way off. Not sure what that means, but it said air temp was 30 degrees when it should have been about 5 or 6. I swapped my fuel cap today, checked plugs, swapped for old MAF sensor, and re-checked fuel pressure at the rail. Old MAF seems to be working great, unlike the replacement I likely didnt need. Same issue. Starting was difficult. Took a 5 second cranking, release, and a second go to get it firing up. WOT test again shows O2 sensors drop to 0V instantly. So this is a fuel delivery issue even though I have good pressure at the rail? It is possible that I should be looking into the EVAP system? I'm just feeling so lost with this....  Thanks again for all the feedback!

At this point, it seems down to inlet air temp sensor or wiring.O2 sensors should never drop to 0 at wide open throttle, if they do it indicates fuel pressure/volume issue. I know you said you replaced fuel pump, injectors, and O2 sensors. I would now try adding propane with engine idling and try driving the 2 upstream sensors full rich and go from there. See what other forum members think for next steps.Possible some of parts replaced no good. 

Nice capture, James. Both upstreams going lean at WOT definitely suggests a lack of fuel delivery. It also suggests both cats are good. If one was plugged, you'd have one bank going rich, and one lean.

The MAF PID not changing is weird. But your Calculated Load max of 98% suggests that not only was the sensor working, but that the engine is breathing well. And the air mass is likely being measured correctly. If your BlueDriver will allow you to look at MAF sensor voltage in OEM data, you could use that as a check against the MAF g/s PID.

I'm not really worried about the IAT at the moment. The IAT doesn't have that much weight in the fuel delivery calculation, in my experience. Plus, the IAT is always going to read higher than ambient temperature due to being located under the hood. If you looked at IAT after a WOT run (underhood temps are high), that'd explain the large difference.

What were you saying about the fuel injectors? 12 hole upgrade? I'm not familiar with that. Were the injectors replaced in response to the lean condition, or some other reason?

EDIT: I wouldn't sweat the EVAP system, either. Block off/plug/pinch the vapor hose going to the purge valve if you want to prove it.

Thanks again Tyler! I will dig a bit deeper into fuel supply here. I found out I can check fuel pressure at "full load" by taking the vaccum line off of the regulator. Maybe the system is failing there only.

That would make sense for the intake temp. I didn't think of the temps rising that quick under the hood. I will check the scanner as soon as I start up from cold here this morning out of curiosity. Glad to know it isn't a likely cause though!

Yes, new fuel injectors were to hopefully resolve this lean issue. I figured even if they weren't the problem, they would be a good upgrade. The toyota OEM injectors have 4 holes that squirt fuel in, but the 12 hole upgraded injectors offer a more even misting. Everyone who does the swap seems to agree that performance and mileage improves noticably.

I am definitely starting to think there is a wiring issue or bad "new" part...

I've never used the propane trick. I will try that! Is it to confirm that the O2 sensors are working correctly and will read full rich?

The two upstream sensors should go full rich adding propane at air intake box, add the propane long enough to make sure you get a response. I would graph their response as well. Let us know how this goes.

I found out I can check fuel pressure at "full load" by taking the vaccum line off of the regulator. Maybe the system is failing there only.

I was thinking about a weak fuel pump or falling rail pressure. But, you'd measured fuel pressure with the engine idling and found it to be in spec. If the fuel pressure is correct, but you were showing total trims of +40-50% in your first captures, then I tend to think fuel pressure isn't the problem.

If you wanted a more stressful fuel pump test, you can power brake the engine with the gauge installed and visible. Pressure shouldn't drop out of spec under load.

What was your fuel pressure reading, exactly? My service info shows spec of 38-44 PSI.

Final thought on this one for today. The reaction of both upstream O2 sensors at wide open throttle goes so against how they should have reacted has me thinking it is possible you were sold the wrong sensors for this vehicle. My thinking only, your mileage may vary.

JamesNWT, are you still working on this one? Not nagging, just following up.

Sorry for the late reply! Little cold snap here and the shop isn't well insulated, so I took a couple of days off.

I managed to do another fuel pressure test last night and it was only holding 20PSI at idle! I had managed to get 35-38PSI before, mind you the issue was not nearly as bad then. Thanks for suggesting a second check!

This is where it gets interesting. I had 20PSI at idle. Pressure dropped within 5 seconds of shutting off the engine. I pinched off the return line on the regulator to see if that is where it was going, and then I only got 15PSI, but it held pressure perfectly. I was expecting it to reach the pump's full potential without the return line dumping fuel through.

So, it seems the regulator is failing. Why would I not be able to pressure up the system with the return line pinched off though? Does that mean the pump is also weak? My smoke tester is arriving shortly, so I will be doing a check from exhaust and intake for any leaks as well. Rregulator is on the way, but trying to figure out how to isolate the pump and determine whether it is also failing.