Prior to tearing engine down and replacing pistons & rings there was no P0171 code. After getting the engine reassembled I get the P0171 on every second drive (service manual clearly states it's a two-drive code). What I can't figure out is why. All hoses connected. Upstream O2 sensor connected. Fittings between the MAF and throttle body have tight clamps. I captured the freeze frame data and attached them can anyone single out the issue on the freeze frame data? Thank you!
Wish it was that simple. All the hoses seem flexible and in good shape. I took off the air cleaner box and noticed that one of the clamps to the duct leading to the throttle body wasn't tight so I tightened that and thought maybe that was the fix but I drove it two more drives and the CEL reappeared
Check the hose from the PVC valve to the intake manifold. Also, check the two hoses that I wrote about in a different thread two weeks ago which I copied below.
I have ordered a new upstream O2 sensor I'm going to try that... That said all I did was disconnect those three connections down near bottom of timing of timing cover so I could sling the wiring harness up and out of the way during the engine work days. I'm 100% sure I've reconnected it correctly.
Oh yes I HATE that hose. Backstory on this car I replaced the head gasket a couple years ago and that hose split at the top so I cut it off and used a hose clamp. I did not have a P0171 CEL for doing that... Update/clarification. The hose IS connected to the top engine cover.. it's just that so little of the hose is on the nipple I thought it best to use a clamp to make sure it doesn't fall off.
I see it now.. it's the "Total FT #1" on image #2. My car doing 39% which is outside of the acceptable high of 35%... Now the question is WHY. I have new Denso Fuel injectors, new Denso coils, new NGK spark plugs, new EGR Valve, and super clean EGR heat exchanger.
And it may not be a hose, but a ruptured diaphragm - same as a disconnected hose. You need to use a vacuum pump to check them. That was week of my life that I'll never get back.
Well, if a gen3 Prius doesn't have vacuum controlled diaphragms - forget it. I'm used to working on the really old stuff that use to have those. The rubber would get old and rupture internally; so everything looks good upon visual inspection.