P0171 Camry 02, 2.4L

2002 Toyota Camry 2.4 L 4-cylinder

Ultimate goals with this diagnosis, to help a friend pass smog check, learn more, and at all costs avoid the parts canon. Thanks in advance for your time and expertise.

OBD2 shows one code only, P0171. There is an exhaust leak after the downstream O2 sensor, located in the flex pipe. I'm currently addressing that leak or have addressed it...Explanation. I removed exhaust pipe bolted to catalytic (post cat) to facilitate the removal of the flex pipe. In completing repair I attached exhaust pipe back to the catalytic, but unfortunately I need a new nut because it left a small gap between the cat and exhaust pipe. (full disclosure offers the opportunity to learn) On to the crux of this topic/question.

P0171. Last night I performed a fuel pressure test on this Camry. First thing I experienced was no priming when I had the gauge connected. It wasn't until I started the vehicle, that the needle moved. Unfortunately is one of those Harbor Freight vacuum/fuel pressure combination gauges. I had a real fuel pressure gauge but not the adapters to make it work. That being said, the reading I received was the gauge showed vacuum of 14 hgv (needle went counterclockwise). I will include a photo of that gauge from last night. Another symptom that I encountered was when at idle, I performed a blitzing (a ScannerDanner term, someone please tell me if it is an actual proper term) of the accelerator pedal. When I performed this fast snapping of the accelerator, the vehicle stumbled before it actually raised in RPM. I feel and I'm quite sure that if I had left the accelerator pedal down that it would have stumbled and died. Because of that symptom and the DTC was the reasons for my attempt at a fuel pressure test. Please let me know if I'm on the right track and any information or advice concerning any of the information up top.

Of course there are other minor symptoms and definitely other OBD2 readings that I have take a note of. So please if any other information would be helpful, please ask. I'm attempting to address the question that's plaguing my mind currently and also trying to keep this short and sweet. And of course as always thank you very much for your time and let me say that SCANNERDANNER, as many of us know, is the man!

Ultimate goals with this diagnosis, to help a friend pass smog check, learn more, and at all costs avoid the parts canon. Thanks in advance for your time and expertise.

Welcome to the forums!

Last night I performed a fuel pressure test on this Camry. First thing I experienced was no priming when I had the gauge connected. It wasn't until I started the vehicle, that the needle moved.

I don't have another '02 Camry handy to compare to. :silly: But I have found that a lack of fuel pump prime is not at all unusual for this generation of Toyota product. I wouldn't sweat this at all.

I had a real fuel pressure gauge but not the adapters to make it work. That being said, the reading I received was the gauge showed vacuum of 14 hgv (needle went counterclockwise). I will include a photo of that gauge from last night.

No offense to you or Harbor Freight, but... There's no way this is a true fuel pressure reading. :silly: If there were truly 6" Hg of vacuum in the fuel system, the engine wouldn't be starting at all, much less stumbling during a throttle snap.

Can you post a picture of your connections? For reference, I grabbed a shot of the specified fuel pressure for this Camry, and how Toyota wants you to do the test. Obviously, nobody owns SST 09268−41047. :lol: But you get the idea.

Because of that symptom and the DTC was the reasons for my attempt at a fuel pressure test. Please let me know if I'm on the right track and any information or advice concerning any of the information up top.

I don't know that fuel pressure would have been high on my list of suspects? But that doesn't mean you were wrong to test fuel pressure.

Of course there are other minor symptoms and definitely other OBD2 readings that I have take a note of. So please if any other information would be helpful, please ask.

If your scanner can show you live data, that's where I'd go next. I'd want to watch engine speed, MAF g/s, coolant temperature, short and long term fuel trims. Watch those PIDs with the engine hot (if it'll run that long and the cooling system is OK) at idle and at 2500 RPM. How the fuel trims behave will tell us what your next best move is.

Hello!

Maybe since you have access to and OBD scanner, you could maybe graph the O2
sensors?
They are after all what determines if the system is lean or rich.

Thanks for the reply, I appreciate the opportunity for learning. I success removed exhaust and welded in a replacement flex pipe. Replaced exhaust bolts allowing Mr to close that gap. Now with exhaust buttoned up I took it for a drive and got OBD2 info at Idle as well as 2500rpm. Looking forward to your thoughts.

Absolutely and I appreciate any thoughts you have for me. These were at 2500 rpm. Unfortunately something happened to the one I took at idle.

Looks like a fuel issue since fuel trims increase positive at higher RPM and MAF reads ok.

I had meant to check the fuel trims at 2500 in Park. But I didn't specify that. :blush: My mistake!

But it almost worked out better the way you took the captures. Your 2500 shot shows high positive trims, but the idle capture shows total negative trims. Definitely lack of fuel like cj1 said.

Fuel pressure is still on the table, but not my first suspect. I'd dig into the MAF or unmetered air first. A visual of the sensor itself and the intake tubing is a good place to start. Tears in the intake tube, missing resonators, loose clamps, like that. If you find a dirty sensor, carefully clean it with some MAF cleaner and a Q-tip.

Great I appreciate it, I have some direction at least to go in. Correct me if I'm wrong though, if it were unmetered air would not the fuel trims be really positive at idle and then somewhat correct themselves at higher rpms?

I've had a new development in the way of an additional DTC. P0136 Circuit Of Oxygen Sensor - Bank 1 Sensor 2

Otbrecords3 wrote:

Great I appreciate it, I have some direction at least to go in. Correct me if I'm wrong though, if it were unmetered air would not the fuel trims be really positive at idle and then somewhat correct themselves at higher rpms?

If there were a vacuum leak, absolutely, the trims would be positive at idle and correct at higher engine speeds. But it's possible to have unmetered air (air not measured by the MAF) that isn't a vacuum leak. Especially if it's a tear in the intake tube that only opens up when the engine shifts around while the engine is under load.

I've had a new development in the way of an additional DTC. P0136 Circuit Of Oxygen Sensor - Bank 1 Sensor 2

Interesting. :huh: The downstream sensor seemed to be reading rationally (.720V) during your 2500 RPM capture. Was there a Freeze Frame for P0136?

Thanks once again for your help. Tonight I hooked up a vacuum gauge at the brake booster vacuum line. It was steady at 21hg, no movement whatsoever. I snapped the throttle and as expected the engine "bogged down" before the rpms went up. The needle went close to zero before going to 24 hg and settling back down at 21 hg. I also did a smoke test. The smoke "machine" was a DIY project using tiki torch WIC wrapped with resistor wire. It works fairly well producing good smoke. I removed the upper section of the air filter box and rolled up a towel and shoved it and the smoke machine hose into the intake hose. Found two spots where smoke was escaping. See photo. I will get that Freeze Frame and post it. Also would it help to do the 2500 RPMs in park and post that as well? Appreciate all the help.