2015 Silverado 4.3L Rich condition

Bradley Technician Wisconsin Posted   Latest   Edited  
Resolved
Driveability
2015 Chevrolet Silverado 1500 WT 4.3L (H LV3) 6-spd (6L80)
P0172 — System Too Rich Bank 1
P0175 — System Too Rich Bank 2
Rich Condition

I've been fighting with this 2015 Silverado with a 4.3L for a few days now. It came in with rich codes, and both bank long term fuel trims at -30 or so. It also misfires at idle (computer doesn't count them but you can feel it shaking) It was due for a tune-up (119K on stock plugs) so we did that. Found fuel in the oil and suspected the high pressure fuel pump leaking into the crankcase, changed that out, no change. While we had the intake off to replace the high pressure fuel pump, we noticed the intake valves have pretty nasty carbon deposits on them. Did a BG fuel system service, no change. Tried a new MAF sensor even though the readings looked normal, no change. Compression test was good, ~225 psi across the board, plus or minus a couple psi here and there. At this point i'm running out of ideas, unless the carbon buildup on the intake valves could be causing incomplete combustion, but I would think that would show on a compression test. Anything else I can try? Pulling my hair out here. Thanks!

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Caleb Diagnostician
Indiana
Caleb
 

I do not see that you did an oil change. Need to do that an reset trims before going any further. If no change after that, can you do a VE test and report back with the results please? Also when is it rich? At idle, hot, cold, under load, all the time etc? But change oil first cause its saturated with fuel.

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Bradley Technician
Wisconsin
Bradley
 

I did change the oil, forgot to put that in the post, changed the oil immediately after doing the high pressure fuel pump. It's rich all the time, but fuel trims seem more negative at idle than anywhere else

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Bradley Technician
Wisconsin
Bradley
 

Attached the VE test results below, looks good to me, but let me know what you think

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Frank Owner/Technician
New York
Frank
 

Did you check the alcohol %? I’ve seen rich fuel trim caused by a faulty alcohol content reading.

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Bradley Technician
Wisconsin
Bradley
 

I had considered this, but the PID for alcohol % is at 1%

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Jeff Technician
South Carolina
Jeff
 

Sounds like walnut blasting is definitely in order, In cylinder pressure waveform and a first look pulse sensor on the intake will prove it if it’s an intermittent valve seating condition. First decide if it’s a real rich condition or I’d it a result of a lying input or unmetered air. If you suspect a leaking injector, crank the engine, get it to operating temperature and monitor fuel rail…

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Bradley Technician
Wisconsin
Bradley
 

Thanks, Jeff! I will give this a shot. Unfortunately I don't have a way to measure cylinder pressure, but I will try the test for a high pressure fuel leak you mentioned. I suspected leaking injectors, but since it's both banks fuel trims going negative, I'm assuming I'd have to have at least one bad injector per bank? Or can these DI Injectors leak into the crankcase? We're a relatively small…

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Jeff Technician
South Carolina
Jeff
 

Those carbon deposits on the back of the valves you see are on the injector tips too so if they get to bad it can keep the pintos from closing. If you find that’s the case, I would sell injectors and a walnut blast

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Bradley Technician
Wisconsin
Bradley
 

I got it up to operating temperature and did the test you suggested. Fuel rail pressure does indeed go up with key on engine off hot, so it would seem there aren't any leaks from the injectors. I did notice that at idle the spark advance is only about 4 degrees, and the torque management spark retard pid is showing about 21 degrees, any idea why it would be calling for torque management at idle…

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Jeff Technician
South Carolina
Jeff
 

Couldn’t answer that without looking at the tune file but they have been progressively pulling timing as a early protection measure for cheaper hard parts for years. how high did the pressure rise? Should have been a considerable amount over a ten minute time frame. And if that test passes an injector balance test is redundant at that point. So the fuel trims are still high negative? And is that…

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Steve Diagnostician
Florida
Steve
 

So a few things on this case, what is the pulse width average and what is the engine vacuum at idle. what are the O2’s doing particularly the rear ones. It almost sounds like the cats might be getting clogged. Pay close attention to engine vacuum. some thoughts

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Bradley Technician
Wisconsin
Bradley
 

Pulse width average is right around 1.1 ms average for both banks. Measured 18-19 inches of vacuum at idle. Both upstream o2 sensors are switching normally, and both downstream sensors are sitting right around 750mv, oscillating ever so slightly but mostly just staying between 740-750mv.

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Matt Technician
Saskatchewan
Matt
 

Perform an Injector Flow Test if possible. This should help verify equal amount of fuel being delivered from each injector. Reset alcohol content. Change engine oil. I’ve also seen purge solenoids not fully close, whether that would cause -30 trims or not, I doubt it, but check it.

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Philip Educator
California
Philip
 

I'd go with what Frank said, Bradley. Any chance you can do a recording and send me the data? I doubt very much that the carbon deposits have anything at all to do with the rich condition. I'm thinking you need to reset the alcohol content. I don't understand how it goes screwy, but it does sometimes.

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Jeff Technician
South Carolina
Jeff
   

I have seen that myself Philip but not with fuel contaminated oil, is it possible for a skewed fuel composition to cause that?

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Mark Engineer
Colorado
Mark
 

Philip You typed: "thinking you need to reset the alcohol content. I don't understand how it goes screwy, but it does sometimes" The most common "root cause" I see for alcohol content "shifting" is drivers leave the engine running or the key "ON" when fueling their GM vehicle. The PCM "calibration" looks for a "KEY OFF" condition to determine if it is necessary to recalculate "inferred" alcohol…

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Jeff Technician
South Carolina
Jeff
 

Great info about fuel composition strategy Mark I did not know that about filling up with engine running. But if the purge valve was stuck open wouldn’t that create a vacuum leak driving the fuel trims positive at idle? Unless of course they kept on pumping after the pump shut itself off filling the canister with liquid fuel?

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Philip Educator
California
Philip
 

Good to know. Happens all the time in cold country. I don't see it in California. Typically the purge valve will only affect it at idle until the canister is free of fuel vapor. At higher rpm usually it doesn't have enough volume to cause the problem. Freeze frame data would indeed be helpful. I'd love to have the SCM of PIDS file from a Snap On tool to examine. I'm assuming he did an oil…

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Bradley Technician
Wisconsin
Bradley
 

I did do an oil change, I apologize, I forgot to put that in the original post. Unfortunately I don't have the original freeze frame data, the codes have since been cleared. I'm using an Autel Maxisys scan tool

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Marcos Diagnostician
Arizona
Marcos
 

I had a similar situation on a 2015 silverado but it was a 5.3L. The truck did not like aftermarket bosch 02 sensors... Ac Delco upstream sensors fixed the truck.

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Bradley Technician
Wisconsin
Bradley
 

Looks like the factory o2 sensors are still installed

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Damon Technician
Florida
Damon
 

The only problem I have seen on GM engines with excess carbon buildup, is a misfire, mostly when the engine is cold. I have never seen carbon cause a rich condition. I agree with others that said you should do an injector flow test. You could have a leaking injector, but since both banks are rich I would think it would have to be more than one injector.

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Bradley Technician
Wisconsin
Bradley
   

injector pressure drop test through my scan tool shows 45-49 psi drop across all cylinders, is this the test that you meant? Or did you mean remove the injectors and flow test them on a bench? Unfortunately I don't have the equipment to do that

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Damon Technician
Florida
Damon
 

That is what I was talking about and that looks good that they are all even. I believe I read above that you had fuel in the oil? I found a bulletin for a possible leaking high pressure fuel pump, which would explain the fuel in the oil. Lookup PIP5590A: DIAGNOSTIC AIDS FOR P0172 AND P0175 (JAN 22, 2019)

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Duplicate
Bradley Technician
Wisconsin
Bradley
 

I did find fuel in the oil and we did put in a new high pressure fuel pump, thought for sure that would fix the problem, haha. We also changed the oil after changing the pump

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Damon Technician
Florida
Damon
 

I read where the ethanol reading is 1%, but I would still take a fuel sample and manually check the ethanol content, and as others have said i wouldn't rule out the purge valve or a saturated charcoal canister. Try removing the line to the purge valve from the canister and see if it makes a difference.

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Geoff Diagnostician
Hawaii
Geoff
 

Did you do the Fuel Trim Reset after replacing the HP pump? Do all the O2 react instantly and fully, when adding propane, and when creating a vacuum leak? Is there a re-flash (SW Update) available?

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Caleb Diagnostician
Indiana
Caleb
 

Matt Cherry mentioned the purge valve. Have you capped it off to see if there is any change to the trims? Also can you do a VE test and post the results please?

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Bradley Technician
Wisconsin
Bradley
 

Did a VE test, attached are the results, which look fine to me. I'll check the purge valve next.

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Ray Diagnostician
Ontario
Ray
 

Go into Generic scan data and graph all four 02s, the MAF and the Calculated Load Pids. At WOT, thru the 1st to 2nd trans shifts, all 02s should show rich and the Calculated Load should be near 100%

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Caleb Diagnostician
Indiana
Caleb
 

Thanks for the VE test results. Now do what Ray asked we know the engine can breathe now.

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Caleb Diagnostician
Indiana
Caleb
 

What did you figure out?

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Bradley Technician
Wisconsin
Bradley
 

Nothing yet, the shop got really busy and this truck got put on the back burner (it's a used car for a dealership). Will update as soon as I have news, hopefully today or tomorrow!

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Thanks
Bradley Technician
Wisconsin
Bradley Update
 

UPDATE 10/15/20 We pulled the fuel injectors (direct injection) and found the tips very carboned up, so we replaced all 6 injectors with remanufactured parts. After this repair, I reset fuel trims and bank 1 stayed around -30 or so, but bank 2 came down to -5 to -10. Took the vehicle for a drive, and it set a P015B, so we replaced the bank 1 uptream o2 sensor. Reset fuel trims again, and reset…

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Jeff Technician
South Carolina
Jeff
 

What are they at idle and at 2500 rpms?

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William Technician
West Virginia
William
 

Were the injectors part #s cross-referenced as per #20-NA-098 to make sure the correct flow rates were installed?

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Helpful
Caleb Diagnostician
Indiana
Caleb
 

Thank's for the update Brad. In your original post you talk about bad carbon. It just dawned on me that these engines eat oil past the pistons with higher miles (think 100k or above). I used to work at the GM dealer and I remember guys putting pistons in 5.3 an 4.3 GDI engines for oil consumption. Maybe this is why there is fuel smell in the oil?!

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Bradley Technician
Wisconsin
Bradley Resolution
 

Thanks to everyone for the their insight, unfortunately didn't get a fix on this one. It was a used car for a dealership, and they elected to send it to the auction rather than keep spending money on the diagnosis. I don't like not getting it fixed, but it's out of my hands. Thanks again for all the help!

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Troy Owner/Technician
Nebraska
Troy
   

1st time poster here bare with me! ! Amazingly, a month ago ran into the exact problem, same 2015 4.3l. It got new hi pressure pump and injectors. Injectors were replaced do to a cold start misfire. Installed all injectors and part number on all 6 were same number. Now after seeing wills post wondering if I got the wrong ones from the gm parts guy. I was never asked the numbers off the old…

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