Where would you start with DTC P0172

[Conor]

Howdy folks,

I've started getting P0172 on my E350, which I believe is cylinder bank 1 running too rich. I also get the same for cylinder bank 2. It sometimes disappears and comes back.

First occurrence was after I was about 3/4 tank through my first tank of Shell V-Power, i'm wondering if that is a coincidence or if the higher octane is triggering something.

Some other points to note, the air filter on the MAF was displaced a little when I previously had the engine cover off and the car is also due a B service -- with the spark plugs needing replacing as per the service schedule. I am unsure if the fuel economy has changed, but I am nearly certain that if I floor the accelerator a bit, ease of completely then tap the accelerator a bit it feels a bit jumpy and the engine bogs down a bit...I feel this is linked, based on how a rich engine acted on my model plane engines many moons ago.

From reading online and also the link below, looks like could be various sensors etc. I do recall there being a previous error code on my car relating to an upstream sensor (Nox/ 0097). Also curious about the state of injectors, but not overly concerned as both banks are erroring.

Just curious where you guys would start out with this? I am going to service next week anyway (And do the plugs).

Would a contaminated MAF have any authority on this code, as the engine bay / cover is quite oily at the moment. Will probably clean that at service time too.

Ref: Link < https://www.fixdapp.com/blog/p0172 >

Thanks in advance
Conor

 

[alexanderfoti]

Is your E350 diesel or petrol?

 

[Conor]

Is your E350 diesel or petrol?

Sorry, it's petrol (CGI).

 

[alexanderfoti]

Dodgy MAF is most likely. You need to look at fuel trims ideally, but looking at live information from the maf sensor will tell you if the values are nonsensical.

 

[Conor]

Dodgy MAF is most likely. You need to look at fuel trims ideally, but looking at live information from the maf sensor will tell you if the values are nonsensical.

Super - i'll have a look and see. I noticed before that the long term fuel trims did look a little out. Do you think the MAF filter would affect this? Worth cleaning the MAF first or just replace?

Thanks Alex.

 

[alexanderfoti]

Super - i'll have a look and see. I noticed before that the long term fuel trims did look a little out. Do you think the MAF filter would affect this? Worth cleaning the MAF first or just replace?

Thanks Alex.

Yes it would. Replace, cleaning never works.

Some versions require re adaption of new MAFS on star.

 

[Steve@Avantgarde]

I would start with a guided test on STAR...!!

Sometimes you need the correct equipment to fix the fault.

 

[alexanderfoti]

I would start with a guided test on STAR...!!

Sometimes you need the correct equipment to fix the fault.

By ar the best method

 

[Conor]

I'll keep MAF replacement on the cars as I do be believe issues with are mostly solved by just replacing..

That said... those of you with good memory might remember me asking about the gauze that sits on the MAF intake and how mine was bent out of shape.. Well, I was looking over my engine again yesterday to familiarise myself with parts for upcoming work.. and noticed the gauze had fallen down and was kind sitting right up against the actual sensor inside the housing.

May be a coincidence, but when I got back in, the engine light had disappeared. Now that said, it has disappeared before and returned, so time will tell.

 

[ajlsl600]

fickle things MAF ,good luck, dont know what happened with that so edited it think i should have gone to specsavers !!

 

[Conor]

Hi Guys,

Quick update.. The light disappeared a few weeks ago and hasn't returned. I will keep you update if it does return with this code.

I am still working on the basis that it was the higher octane Shell V-Power fuel which triggered this. In my layman opinion, it kind of makes sense, the fuel is more "dense" so the engine thinks it is running rich, based on what was historically being burnt (long term trim). But now the long term trims have been evened out, computer thinks all is fine.

Would be interesting to see if I get "lean errors" if I switched back to regular fuel.

(This could all be coincidence of course)

 

[LostKiwi]

In my layman opinion, it kind of makes sense, the fuel is more "dense"

There is no difference in fuel density - high octane fuel is just more resistant to detonation and actually burns slower than low octane fuel.
High octane fuel will only give more power if :
1. The compression ratio is high enough to detonate on regular fuel but not on high octane. High compression ratios increase volumetric efficiency of the engine.
And/or
2. The ignition timing can be sufficiently advanced to promote detonation and place ignition timing control with the knock sensor. In general the more advance an engine can run the more efficient it can become.

A car designed for 95 octane cannot advance ignition past the preprogrammed map (which is designed around 95). A car designed to run 98 will be optimised for that fuel but in the event it runs 95 knock sensing will retard the engine to suit.
To see what your engine is designed to run on refer to the handbook or look inside the fuel filler cap.