check pump duty cycle, pressure readout and what are your long term trims looking like. do not assume your new pressure sensor is good especially if it's not motorcraft. likewise for a non-denso MAF or O2 sensor.

don't forget about the throttle equipment, the TPS can cause weird issues as well. look up toyota p0172, their ecms are basically the same

 

If we assume that the right bank is running OK, with all of the things that are common to both, we can eliminate those from the possible cause list. That only leaves a couple of things that will cause apparent rich running on one bank.
Leaking injector(s), ignition miss and O2 sensors would be the main culprits. Unlike most cars this one trims fuel by the cat sensor as well as the upstream one. Either with slow or incorrect response could indicate/cause rich running. If you have not checked both in the left bank it may be a place to start. Not sure if you can swap the ones from the right bank to the left and see if the rich fault follows - might be worth a try.

 

Hi
First thing we did was new injectors and o2 sensors.
They had no effect on wildly swinging trims (could bounce from -25% to + 25% and back).
Then replaced fuel rail pressure sensor.
Instantly, fuel trims stabilized.
Thought it was cured.
Didn't work - P175 came back right away.
compression check says ok.
Now, cylinders 2 and 4 are fuel-fouling the plugs! I pulled those plugs a month ago and they were clean.
Trims are stable but a bit rich.
Will see what we think of next.

 

As a matter of interest did you replace all four O2 sensors?
Unfortunately new injectors have been known to fail very quickly. Those leaking definitely could trigger the fail code. Do you still have some old ones to put back in?

 

Interesting reply, thanks.
Did replace all 4 O2 sensors, had no effect.
Originally, the bad fuel pressure sensor was causing injectors to leak, or to appear to leak.
So, all were replaced.

(Had a few small vacuum leaks which were discovered with a smoke test after all injectors and O2 sensors replaced. Oddly, fixing the vacuum leaks had no visible effect on fuel trims. Maybe I should have left them there if I new that persistent rich codes were going to be an issue!).
Indie just installed new plugs, will watch and see what happens.

Thanks.

 

Just out of curiosity, did you try removing and capping the vacuum line to the brake booster? I know you are fighting a rich condition. But when I couldn't get my fuel trims to behave (lean condition) it was a bad brake booster causing the trims to go wild. Leak was not constant and trims would be fine then lean. I carefully removed the check valve from the booster and plugged it. My trims returned to normal. Replacing the booster fixed the problem.

 

HI
Thanks for the idea. I explored vacuum leaks on my own (bought a smoker, etc) but as my condition is always a rich error, finding more vacuum leaks probably won't help as they cause a lean condition. I really worked hard with the smoker to find every leaks, and even pumped directly into the brake booster at one point. Fuel trims have stabilized after fuel rail pressure sensor replaced - now just steadily rich.
Thanks for helping.

 

Does the fuel pressure regulator have a good vacuum source? I'm assuming it operates a set psi above manifold pressure and if the vacuum source is not good fuel pressure at with closed throttle will be too high causing a rich condition.

 

Hello All
to those who offered help, finally found the problem. Issue couldn't be diagnosed due to a faulty assumption, that my brand-new injectors were....brand new.
Turns out that after replacing every component of the fuel system (even the spark plugs twice, and some of my coils) we flow tested my 'new' injectors. Not one was within factory spec.

Turns out that the number of Chinese fakes is so high that even if you buy a Bosch-boxed injector from a major chain, it probably isn't legit. We ended up ordering OEM and flow-testing them before installation, and of course all problems cleared up.

For all the work I did, I would make an unusual suggestion - before installing new injectors, have them flow-tested anyway.

Now, I need to sell my 2005 xj8 with new suspension and fuel systems if anyone wants one!

 

new = never ever works