Occasionally (usually on a long highway drive) my '14 3.5 will throw a CEL and when I scan it, there are always four codes corresponding to all four O2 sensors detecting a lean condition. I doubt all four O2 sensors are going bad simultaneously, so ideas as to what's causing it? It's not frequent or predictable, only happened 2-3 times and honestly I just cleared it out and never even wrote the codes down. I would think maybe HPFP but that would throw other codes that would make it easy. No other codes apart from the four lean sensors.

Any thoughts?

Thanks,
Darel

 

Look at fuel filter pressure ( low pressure fuel sensor ) , see what is the reading at idle and at 1st and 2nd gear max-wot RPM.
Decent scanner would have this data pid.

Also look at the high pressure fuel rail pressure.

The flexible fuel hose from car chassis to fuel inlet of engine , inspect it for collapse internal.

.

 

Do you happen to know what these pressures should be? I am at 200k, and at 150 I took it to the dealer to get the fuel filter replaced and they said "oh that's not part of the scheduled service anymore, we just change them if we think they are causing a problem". Which makes sense that now, here it may be causing a problem. I am thinking about just going and changing the filter since it's only about $120 (and I have a $100 credit at FCP Euro) but I figured it'd be nice to know what sort of presure I'm looking for.

Also you are referring to the filter in the tank, right? Are there any particular lines that cause problems more often that any other? That's a lot of line to replace and no real way to actually tell that's the problem without just replacing all of it and crossing your fingers.

Thank you!

 

Concentrate on reading your fuel pressures to diagnose your lean combustions.

No need to replace many random parts until your issue is discovered.

 

Right....but I don't know what those pressures should be. 150? 7? No idea. But if I read (for example) 45psi, change the fuel filter, then come back and read 75 psi, well, that's a pretty good indicator I found the problem. If it reads the same, that wasn't it.

However if someone knows what those pressures should be, I don't have to fire the parts cannon. If I read pressures and they match what the accepted values are, no parts. But I don't know the accepted values.

 

At this age, I’d just throw a fuel filter at it. I mean, fuel filters should never stay in the car 10 years in the first place. I replace mine every 5 years, and with today’s gas that might not be often enough. “Diagnose” if that doesn’t cure it, because then you’re likely looking at fuel pumps, which are more expensive. My view is to get any filter that *could* be clogged out of the way before it overworks the pump. YMMV

maw

 

That's where my head is as well. Without knowing for certain what the pressures SHOULD be I don't really have a way to diagnose this otherwise, so at least I can compare - pressure before vs. pressure after. And I really don't think it's the HPFP because I think I'd get other codes.

Although if there were enough restriction to cause the engine to actually run lean momentarily, shouldn't I also be seeing P0087 (fuel system pressure low) in addition to the O2 sensor codes?

 

very right
Read the LTFT fuel Trims to confirm fuel status

 

OK, what exactly do fuel trims tell me? What is that value and how do I interpret what's good and what's bad?

My iCarsoft scanner could read fuel pressure at the rail 2900psi at idle and when I give it gas, did not drive with load on) but not on the supply side.

In addition I looked up pending codes (which I neglected to do before) and I got P013D "O2 Sensor Slow Response - Lean to Rich (Bank 2 Sensor 2)" although I can run this test with my scanner and it passed, I also had P2198 "O2 Sensor Signal Biased/Stuck Rich (Bank 2 Sensor 1)" and P0157 "Oxygen Sensor circuit low voltage (Bank 2, Sensor 2)".

So now I'm wondering if it's a fuel delivery issue, an O2 sensor issue, or a bit of both. In any case I still think I'll replace that fuel filter but I probably won't get around to it until close to Xmas.

 

Would be helpful to know exactly what fault codes are showing.

Also what engine it is.

 

Now we got relevant live evidence :
It's on Bank2 only - Not both banks... not fuel supply.

Based on what I read above, the engine is burning rich, I'd question Bk2 ignition & injectors rather than fuel filter.

 

The fuel filter , the only fuel filter, is very small.
Do not wait for problem from fuel filter, as you may starved the high pressure fuel pump.
Internally, high pressure fuel pump uses fuel as lubricant, externally it uses engine oil.

Go to post #12 to see my not so dirty fuel filter vs new fuel filter pressure. Mind you my car is only 36,000KM at the most back then in 2022.
https://mbworld.org/forums/e-class-w...ml#post8568085



Quick summary







The HP fuel pump pressure vs RPM vs LOAD would be like below :




Yes, the rail pressure actually decreased when RPM goes high and load goes high.



.

 

This is excellent info, thank you! Unfortunately my scanner only reads fuel rail pressure and fuel trims, so I can't read supply pressure, but at least now I can follow your graph while driving and see if it's matching my readout.

 

Ohhh, so yours is only an OBD2 reader, thus you can not access the N118 fuel computer which is the one managing low pressure fuel filter + fuel pump.
Get baby Launch MB specific. Google this W212 section.

 

It's an iCarsoft MBII, it has a ton of functionality just not that.

AT this point I'm already planning on selling the car in the next couple of months, just want it to be 100% when it goes to a new owner. I'm not buying any more scanners or software, but I will use my $150 FCPEuro credit balance for a filter and a downstream O2 sensor.

 

OK, I managed to do some live monitoring and I have some curious findings I am hoping you guys can help me interpret.

Yesterday I cleared my DTC and went for a drive that I thought would trigger another one. I was driving up a hill maybe 55 mph, the hill is about four miles long and about 60mph so a moderate load on the car. Sure enough near the top of the hill the CEL comes on. When I got home and checked, I had four codes, ALL of them were Bank 2 Sensor 2 stuck lean. I cleared them.

Today I went for a drive to watch a few parameters in real time, especially fuel pressure. Going down the hill into the valley to run a couple errands, no CEL. Fuel rail pressure at idle ~2100 psi, at anything above idle 2800-2900. I cannot read the low side pressure with my scanner.

Some notes: Fuel system 1 status constantly showed "CL_fault" (closed loop with a fault), system 2 status just showed "---". While down in the valley I had no codes, but cleared them anyway.

After clearing the nonexistent codes, Fuel system status Bank 1 changed to CL (closed loop) occasionally going blank. Fuel system 2 never showed anything other than "---" So, point 1, I think bank 2 is never going into closed loop.

I watched short term fuel trims on both banks, and while I have no idea what this actually means, I was expecting these two values to be very close to each other, but they could not have been more different. Bank 1 stayed fairly consistent, showing values in the negative, from maybe -2 to -11 or 12. (I was trying to drive and can't confirm if these were actual min/max or just representative).

On Bank 2, however, I was constantly showing POSITIVE values within the same range - so from 0.0 to +2 to +12. For example I was taking pictures of the screen and here are a few snapshots I got:
Bank 1 -6.3% 0.0% -3.9% -11.7% -0.8% -2.3% -1.6%
Bank 2 3.9% 11.7% 11.7% 0.0% 6.3% -1.6% 7.0%

So I finished my errands and cleared the phantom codes. I got on the uphill on-ramp for the highway and the CEL comes on. I pulled over BEFORE the big hill and checked the codes, I had P2198 O2 sensor signal biased / stuck rich bank 2 sensor 1. So now I'm confused. Last few days I have gotten codes relating to all four sensors, but far and away the most codes were for Bank 2 sensor 2 sticking lean. Now it's sensor 1, and it's rich. I pulled over at the bottom of the big hill to get a clean run, cleared the codes, NOW I am seeing Bank 1 fuel system in "CL" with no fault, bank 2 still blank. I drove up the hill, not babying the car at all, and no CEL.

My scanner has the capability to test the downstream O2 sensors but not the upstream (device not supported). I can test lean-to-rich response and rich-to-lean response. I've run the tests a few times over the last few days and they always pass.

So, why is the problem jumping around, why is it going rich occasionally and lean at other times, and why isn't bank 2 ever going into closed loop?

 

iCarsoft is usually not bad as far as coverage

I got lost with sensor 2: lean + sensor 1: rich.

Can you pls summarize your troubleshootings:
what is working vs. what is not working ?

 

I think my last post is about as good of a summary as I can give. Intermittent CEL, O2 sensors tripping codes but not consistent. Last week, all four sensors lean which made us think fuel filter (and see my other post for that nightmare). This week, bank 1 sensors rich. Bank 2 not going into closed loop but bank 1 is, however, bank 2 sensor 2 (which seems to be the most common fault) tests good. Best summary I can give of where it's at is in the post above.

Oh and along with the fuel filter I figured I would replace the bank 2 downstream sensor....NOPE! The god damn connector is up on top of the transmission. Can't replace the sensor without disassembling the entire car.

 

with this much random unstability something is up with your ECU module itself

The way this is acting wildly, you can pretty much rule out low fuel pressure.

 

I just went out and started the car again after letting it sit. When cold both fuel system status were "---". At about 110-120 degrees bank 1 went into CL. Bank 2 is not going into closed loop.

Recall that prior to the most recent CEL reset Bank 1 was always showing "CL-fault". Now I have a good "CL"

Now, as I was sitting there watching the numbers, they started matching up bank 1 vs bank 2. The trims were very close to one another, the voltages and currents of the o@ sensors made more sense left to right.

Thinking back, this car gets driven very rarely since my wife works from home anymore. I think the last time I put gas in it was August. My wife filled it up on Thursday.

Is it possible this is bad gas working its' way out?

I agree that while I should replace the fuel filter just for preventative measure, fuel pressure does not seem to be the problem.

I am wondering if I went and just did some good driving and maybe put some fuel injector cleaner in it tomorrow if that might at least "stabilize" my numbers a little more. They looked pretty normal just now.

However that does not explain bank 2 not going into closed loop.

 

You don't suppose this is indicative of oil in the wiring harness, do you?

 

It seems the GDI engine is more advanced than your iCarsoft scanner can handle. Other members have used it, I thought it had fair coverage.

Then I'd stick with OBDII fault codes if that all you can really count on.

Not replacing the downstream sensor is a great mode: rarely useful! Upstream yes helpful but not "downstream".

 

I assume this battery is fully charged, correct? Like, it's sitting on a battery tender all this time when it's not driven? If not you could be chasing all sorts of random computer based ghost faults that have nothing to do with anything.

Fuel filter is still a good idea at this point. But so is always storing the car with a full tank of gas. Extra room in the tank is mostly air and corrosion waiting to happen. Consider those best practices.

For your specific issue, I'd say run a full tank of gas and Chevron Techron through it and see what happens before you do anything. Maybe dump the fuel filter after the Chevron runs through.

These are old cars. My '06 sits a lot. A couple months ago it threw a CEL. I suspected coil packs just because I know they're due. One got replaced a year or so ago (less than 5k miles) and I didn't have time to do all 8, so I just did the one. Before I could get it to my guys and have them replace all the coil packs, the CEL went away. Do I know why? No. But I know the battery is full and the fuel filter is new-ish (with that new coil pack). Coil packs will wait until next spring maybe.

It's the price you pay for driving a better car with no car note. Charge it to the game.

maw

 

Yeah I'm thinking I'll go get some injector cleaner and take the car for the next two weeks and run it through a few tanks of gas, then maybe reattack from there.

 

If your engine has done 100,000 miles or more and is 10 or more years old, replace all 4 oxygen sensors.
They are consumeable parts, albeit high mileage.
Do you know how hot they get under use ? 800C or more or 1,472F or more.
They also get contaminated by burning oil and whatever minor coolant leak into combustion chamber if any.
Usually they are lazy first and then slowly become REAL bad.

Front is wide band sensor decent price, rear is narrow band very cheap.
2023 August price for my M276.820 3.0 Turbo engine
If I go MB genuine, for my country it will be 300 - 400% more money.




My front wide band is BOSCH ( LSU 4.9) and rear is NTK if from MB, as installed on the car since 2014.

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Replace all 4 first as part of your 11th year refresh program and troubleshoot further when you still have problem.