Help diagnosing a P0172 + P0175

impala454 · January 11, 2017

Yes it's showing rich. I haven't messed with the O2 sensors yet but admit that could be it (separate from the hard start problem). I'm about convinced it's an injector issue and just have been too lazy to pull them yet to inspect/clean. I will definitely update this post once I do.

Ogantone · January 11, 2017

I change plugs, wires cleaned maf, changed airfilter and cleaned throttle body.

impala454 · January 12, 2017

I've replaced the MAF and cleaned the throttle body so far.

rjgti · January 13, 2017

if ko/eo fuel pressure is bleeding down to 10 psi, you have the hard start issue

impala454 · January 27, 2017

More updates to this topic. Turns out my reading of the fuel pressure dropping to 10 psi was wrong (probably due to the really bad harbor freight gauge). I used a better gauge and what I see now is:

key on: jumps to 55 psi, then slowly bleeds down to about 40 (over a period of about 5 minutes). is that normal? it actually seems to start ok at this point

engine on: goes to about 60 psi and swings very quickly between 60 and 64 psi (you can barely see it the needle is moving so fast). is the jumping around normal (just due to the squirting?)

I also pulled the fuel rails up so I could check all the injectors at key on. Not a single drop that I could tell, so it doesn't appear to be a leaky injector. Some of them looked a tad gunky but the engine runs fine minus the rich condition. I can't imagine a clogged injector causing a rich condition.

Any other thoughts? I'm kind of at a loss here. I suppose it could be an O2 sensor but not sure how to tell and hate just replacing parts willy nilly.

khebert · February 6, 2017

i had the same problem with my 97 gmc and it turned out to be the coolant temp was to high causing the codes

check the level and condition of the coolant

impala454 · February 6, 2017

What should the coolant temperature be? My last few logs of data shows it in the 190s.

impala454 · February 20, 2017

More updates to this long running post. I've measured and see the Fuel Alcohol Composition percentage is showing 53%. This seems way wrong. Is there some sensor that could be bad? I've read in other places it could need a PCM reset. Are there any scan tools I can use to reset this alcohol percentage calculation? I have an OBDLink MX which does great for reading but doesn't write.

impala454 · February 22, 2017

Bit the bullet and took it to the dealer. Turns out it's bulletin 06162C which points to a messed up "virtual" flex fuel sensor (i.e. software problem). Description here. If you're under 8 years 80,000 miles it's a recall fix. Unfortunately I'm way over those so had to pony up $220 (ridiculous) to have the ECM re-flashed. My alcohol comp is now reading correctly and can only hope the P0172 and P0175 go away.