Might stump ya! 08 suburban 5.3l rich and evap

[Will Parker]

Ook so 08 chevy suburban 5.3l flex (lc9 i believe)
Ggetting codes consistently for p0172 and p0175 and now a p0455 evap. First 2 are rich for each bank aas you know I am sure.
Rrun down of parts: this week: thermostat and ECT ssensor. 6 months ago 4 new o2 sensors and both ccats replaced. About a year ago: vent valve, 8 ffuel injectors, plugs, MAP sensor, updated valve ccover with new PCV valve, new TPS sensor, throttle bbody removed and cleaned, MAF sensor about 1.5 years ago and near 6 years ago the purge valve. The p0172 and p0175 codes have come on after resetting after each repair sometimes at the same time sometimes 1 before the other but always both in short order. As for replacing about 80% of those parts had to do with other codes that came up while some of it is me trying to pinpoint this extremely frustrating issue. Fuel pressure, load, air volume spark all of the usual numbers seem to be fine within norms except fuel trims as far as I can see. Short term isn’t too bad, still running negative to take away fuel but usually 1-5 for an average. LTFT though thats where I get up to 10-15 and at some points 25 negative. I have a semi advanced scan tool (launch x431-v+) but beyond maybe the purge valve going bad again or the vent canister itself i am at a loss. Any ideas!?

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[Richard Kirshy]

Might suggest you smoke the EVAP system.
I would suspect if you were to check your readiness monitors you may well fine one or more incomplete.
Had a very similar issue where I would get a EVAP code and was running rich (LTFT).
Turned out that the purge valve mounting flange had split due to rust jacking where it mounted on to the carbon canister.
Being the mounting screw was completely rusted I ended up replacing both the purge valve and canister.
Issue solved

[Will Parker]

I’ve made an appt with my local shop to do just that as I don’t have a smoke machine. On my list of never ending tools lol. Whats got me is the rich issue had come up long before the evap code. I also had gotten a misfire and that turned out to be an injector so I replaced them all. I went after market denso of course but they were custom. Instead of 4 large holes (i have the lc9 flex) it was 12 smaller holes. Meant to atomize the fuel for a more efficient burn. After the swap at first everything seemed ok for a few hundred miles, the monitors had all come back no pending codes. Then its been reading rich off n on ever since and by off and on its narrowing it down to a reading that is out of norms and replacing the part responsible (ie MAF). As for the EVAP system as I said before the vent valve was done maybe 6 months ago and I did the purge valve solenoid about 6 years ago (that 1 gave me a specific code for failure i remember) and during my troubleshooting I had thought the canister might be the issue, but not being able to test it further I went looking elsewhere and so far pretty much everything else has been replaced in the fuel system except the canister and the pump (which reads perfect down the middle for recommended PSI range). I am REALLY hoping you are right and its to do with the canister. Ive never replaced 1 myself but from what I’ve seen its not too terribly difficult. The way it goes is if I can’t figure something out (and the local shop went thru it as well for the rich codes before even after the new injectors and such and couldn’t find anything obvious as all we had were both banks rich showing) then I bring it to them for diagnosis. If I can fix it then I do. If I can’t I pay them to do it.

[Will Parker]

Oh and currently I have 2 monitors not ready EVAP and o2 (not the heated one).

[Richard Kirshy]

Let me see if I have this correct..
1 You had a miss fire, but not running rich or had a EVAP code.
2 Replaced the injectors with after market replacements and ended up running rich.
3 then you began tinkering to correct the rich fuel trims and ended up with EVAP issue.

Let me take a shot in the dark…
First question: The MAF you replaced, did you install OEM or aftermarket?
My second question: Exactly how did you determine the injector was the cause of the miss fire.
Assuming it was, due to the fact you do not state it was miss firing after replacing them.

Something is telling me you may have more than one issue happening at the same time

The rich condition may be due to the after market injectors.
You say : Then its been reading rich off n on ever since and by off and on its narrowing it down to a reading that is out of norms …
My thinking is the ECM took awhile to remap itself to the new injectors which maybe under performing, which in why you have higher trim levels.
You may well need to go and install OEM parts to solve that issue.

As to the EVAP …
It may well be causing your fuel trims to be high.
But because they are aftermarket they could also be suspect.
With my issue …
For over a year I would get varying readings on my fuel trims but never a code.
Then one day I happen to check the readiness monitors and found the EVAP was incomplete.
Looked over everything but never saw any issue, the next time I checked the monitors all were good.
Finally after last winter the EVAP monitor failed again.
After a month it never completed.
Went and got a smoke machine, couldn’t locate a leak to save my life.
Finally as I was rustproofing I happen to notice that the purge valve mounted to the carbon canister didn’t look quite right.
Got a mirror and flash light and saw it was split at the mounting flange.
There was the cause.
All the time leading up to the full time failure of the EVAP monitor was due to the purge valve somehow sealing itself.

My suggestion:
First go after the EVAP issue once repaired, see where your fuel trims settle at.

[Will Parker]

Ok gotta correct a couple things maybe I didn’t write it properly but I had some misfiring and after the shop did some checking determined that 1 injector was leaking or fails to close did a leak down test, they also checked each of them as they opened and closed and some other stuff so I replaced them all. I DID get rich codes at the time of the misfire if I didn’t say that or forgot I apologize. Now the injectors themselves are denso injectors flow matched all that but really the only thing about it being aftermarket is the screen. Instead of 4 larger holes it has 12 much smaller laser cut holes. And yes I have been inclined to think I should’ve gone with OEM ac Delco injectors from the get, but the rich was there before and after the injectors. The MAF is unfortunately aftermarket, at the time I bought it I was focused on cost, its unbranded and as far as I can tell its putting out proper readings. However in the interest of being thorough the truck goes in tomorrow its on the list to check.
Now though, throughout this entire ordeal, beyond the original misfire, and about 6 years ago the code for the purge valve which I replaced and then 6 months ago the code for the vent valve which also replaced, I’ve never had any accompa Ying codes WITH the rich codes. Leaving it as kind of a crap shoot. Ive been pretty meticulous taking care of this suburban so this has been driving me nuts. This large leak evap code is the first to pop WITH the p0172 and p0175 codes. I AM at the point that once we figure out the evap thing and get that fixed, IF that doesn’t fix the rich condition (and nothing is found wrong with the MAF) then ill go ahead and just put stock OEM injectors back in and set the fuel trims to do a relearn (I do have a launch bidirectional scan tool thats helped a lot).

[Will Parker]

Well we FINALLY seemed to.manage to dig up the culprit!! I mentioned i replaced the purge valve solenoid about 6 years back. Well over the past year I’ve taken the truck in a few different times for this rich issue and each time we found other problems like my cats were plugging up, o2 sensors going bad, leaking injectors etc which would obviously contribute to those codes but never seemed to fix the issue. Now the vent valve was done in January (had em look it up today) I said previously about 6 months ago so a bit longer. But no other evap codes til this newest p0455 large leak. So I let it sit til I brought it back in and we finally uncovered the issue. The purge valve was sticking open. Not all the time as it tested ok on previous checks but this time it had gotten bad enough to show its ugly face and they had me go into the bay to talk to the tech (he is the only 1 who works on my stuff there and he knows me and my vehicles we got a good relationship) and showed me with the smoke machine he had the rest of the evap system closed off and all that tested out just fine but this would stick open. It would close randomly when not supposed to then go back to wide open and that can easily cause a really rich running condition as the unmetered vapor flowing in is at odds with the rest of the readings and the o2 sensors are saying its too much gas. Since it technically didn’t fail it didn’t set its own code like it did before. I got about 50k miles out of it. Got to thinking that even though my LC9 is a flex engine I’ve never run e85, BUT regular gas (and I only ever use top tier rated gas) is still up to 10% ethanol. Gas dont absorb water but alcohol does. And flowing thru there as a vapor that can cause ut to gum up and cause corrosion. Jason confirmed this actually as he pointed out that over the past year he has noticed more and more of these failing on various vehicles. Ive thought about adding some water remover to my gas now n then to try and combat the issue. But gonna out the one on here in a bit and drive her around awhile see how she does. I do appreciate the input Richard it did help!

[Richard Kirshy]

Glad to hear you got it sorted out.
Hopefully this will correct your trim issue(s)

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