02 Toyota Sequoia - Lean codes!

Thanks for the reply Bills! I can double check the part numbers for the O2 sensors. I just returned a belt tensioner to Rockauto for my 99 CRV. They had the wrong part listed for it, so I guess it does happen! I'm going to head out to the shop shortly and start with the propane test you mentioned to validate the O2 sensors. My previous reply to Tyler will explain the rest of my update on fuel delivery! Thanks again for the reply. I really appreciate it.

JamesNWT wrote:

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.

Excellent! We're on the right track. 

IMO, you've got some pretty good evidence of pump and regulator failure there. There's only a couple more checks I'd recommend. One would be to do a deadhead pressure test, if possible. Engine off, pressure gauge connected to the pressure line (or fuel rail if that's not possible), return line pinched, fuel pump running. In this condition, most fuel pumps will double their specified running pressure. In your case, I'd expect 70-ish PSI.

I'd also do a loaded voltage check at the fuel pump connector with the pump running. Pump power should be within 1.0V of B+, ground should be 1.0V or less.

If the pump won't deadhead correctly, and there's no voltage drops, then it's fuel pump time.

Great advice from @Tyler here James. If you do need a fuel pump, hopefully you still have the old pump you originally replaced laying around and maybe a part number attached to it somewhere.

Thanks Tyler! I did keep the engine running for a minute with the return line pinched. I actually had less pressure than when the return line was flowing. I was expecting the pump to reach it's max as well. I will definitely check to make sure voltage is good at the pump, but it looks like it is dying as well.

Last night it ran worse than I have ever seen. I was hoping to do the propane test and smoke it, but it wouldn't even idle. No power. It just wanted to die. I tried to read data and after resetting everything multiple times there was still no O2 voltage or fuel trim data. I had everything else coming up though. Throttle position, MAF, load, and anything else. The night before I had replaced the ignition switch (it was also acting up with flashing dash lights randomly with no key in the vehicle). Not sure if that has anything to do with the new issue, but starting to think something electrical is going on as well. Checking grounds today and looking for any mice/packrat damage. This Toyota has served me well for years, but it seems we are at war now! haha

Just another update here. New regulator installed. Did not resolve any issues. I did some more testing while I wait for a fuel pump to arrive. Smoke test on exhaust and intake didn't reveal any leaks. I spent an hour looking for wiring issues and bad grounds (found one) thinking it would solve the no data for O2 sensors issue. Called my father and he informed me that they won't read anything if the engine is extremely lean. I didn't think the engine would even run if it were that lean, but I guess it does. So I moved to the propane test. Gave the intake a good shot from the tiger torch and the O2 sensors came alive! Screenshot attached.

I continued fuel pump diagnostics. Went to the relay and checked resistance. 2 of the terminals that are supposed to be dead 0 are reading 0.07ohms consistently. I then checked the fuel pump resistor. It was reading dead 0 between terminals and should be 0.7-0.76ohms. I guess that means it is shot and the pump is on high all the time? Going to drop the tank and prep for fuel pump. Dead resistor and regulator likely killed the pump this fast.

Final update here. When the shop installed the new fuel pump, they decided not to replace the 3 inch fuel line that needs to be clamped inbetween the pump and feed line. Instead, they just forced the old one (hard as a rock) over the very tip on the fuel pump outlet and called it good. So, there was pressure, but most of fuel flow was just shooting back into the tank. It explains the strange intermittent nature of this issue and why is wasn't crystal clear. Thank you all so much for teaching me to just trust the data! Everyone else I consulted kept telling me it can't be a fuel pump doing that. I guess it wasn't really the pump, but I wouldn't have dropped the tank quite yet if I hadn't checked pressure again based on the data! New WOT data attached.

Those long term trims look far better than the ones first posted when you started this thread. Well done.

Thanks for the update! Trims are looking much better.