e39 525i p0171 p0174 bank 1&2 running lean

[anonymous-user]

Hi guys recently picked up a e39 525i weekend.

Had engine warning light pop up, whilst waiting for the dealer to get back to me I've scanned it and got p0171 and p0174 lean on both banks.

I haven't had a play with the car yet just gathering ideas.

I will check all air pipes for vaccum leaks.

Anywhere else I should look?

Didn't realise how expensive mafs were for this car so don't want to change it on a whim, unless someone knows a test without bmw diagnostics.

Maybe unplug and clear codes and check? If lean doesn't come back then its the maf?

Maybe fuel filter? Bit out of my depth really and only just bought the car, any assistance appreciated

[helix402]

Check intake pipe to throttle valve, change all vacuum pipes for silicon. Change this too:

[Elliot2000]

Unplugging the maf won’t show it’s at fault - as above - most likely a split intake pipe - normally somewhere from airfilter box to manifold. Or a split/fallen off vac pipe somewhere.

[anonymous-user]

Thanks guys, would I have other codes if it was the disa valve/maf?

Fuel filter was changed a couple of years ago so will rule that out (for now!)

I will check the vac pipes shortly for leaks etc especially airbox to throttle bodie/ inlet manifold.

What is that bung/cap for?

[anonymous-user]

Any idea where this snapped vaccum line is supposed to go? Cheers guys

[Elliot2000]

It looks like that might be the one that goes to the valve in tail pipe. If u can find the engine side of the pipe u can just block it off and leave it disconnected

[helix402]

Re the bung. It’s a while since I had a petrol 6 but I think it goes at the back of the manifold.

[anonymous-user]

Thanks all after some heavy research this pipe goes to fuel pressure regulator inside fuel filter.

Have ordered replacement silicone hose along with F connector and air intake boot, because what the hell, that may have a tear in too

Bloody E39's, can remember one of the reasons I sold my 528 now

Will report back findings!

[anonymous-user]

For future searchers the pipe on the f connector to the maf had split and was sucking in unmetered air while running.

Replaced with new and a couple of crispy others plus the f connector and the elbow to the throttle body for good measure.

Cleared codes and drives with no engine light.

Thanks all for help

[anonymous-user]

Engine light back on

Will have another check of the vaccum lines tomorrow.

Does anyone have any other ideas??
I'm at a real loss and thought I cracked it

Cheers

[tgr]

Helix when you say replace all vauum pipes with silicone is there a standard diameter that one can buy a roll of and then cut to size, or? What is the most practical way to go about changing all these pipes?

[helix402]

I use 3 or 4mm internal diameter Ramair pipe from eBay. Just choose how long you want. If you measure the internal the diameter of your old pipe you can choose the closest, not that 1mm either way matters.


Just remove the old pipes one piece at a time at cut the new pipe to match.

[anonymous-user]

helix402 said:

I use 3 or 4mm internal diameter Ramair pipe from eBay. Just choose how long you want. If you measure the internal the diameter of your old pipe you can choose the closest, not that 1mm either way matters.


Just remove the old pipes one piece at a time at cut the new pipe to match.

Thanks, I done some research and have been using 4mm silicone to replace the 2 pipes the first time.

Only code I have now is p0171 which is lean on bank 1 so I'm assuming it will be a split vaccum on the left hand side of engine? Or is that me being stupid?

driving me nuts!

[helix402]

The 6 cyl has one bank, I think BMW call cylinders 1-3 bank one and 4-6 bank two. I don’t think it helps you trace the air leak.

[anonymous-user]

helix402 said:

The 6 cyl has one bank, I think BMW call cylinders 1-3 bank one and 4-6 bank two. I don’t think it helps you trace the air leak.

Thank you, I figured it wouldn't be that easy, Thursday night changed the upper air boot from maf, new f connector and 2x new vaccum hoses.

Reset the p0171 and p0174.

Last night I had p0171 pop up and not p0174 so assuming my fix has cured one of the codes.

I'm at a loss where to look to resolve this other code.. Must have another check for vaccum leaks I suppose!

[helix402]

This may help:

http://www.bimmerforums.co.uk/forum/f3/m54-engines...

Also if you have the aux air pump (you probably won’t) it can be binned and a blanking plate fitted where it attaches to the manifold.

[anonymous-user]

helix402 said:

This may help:

http://www.bimmerforums.co.uk/forum/f3/m54-engines...

Also if you have the aux air pump (you probably won’t) it can be binned and a blanking plate fitted where it attaches to the manifold.

Thank you will check this out tomorrow and go from there

[iSore]

I just buy the red and blue vac pipe from BMW, the stuff used on 335d's and so on. It'll outlast most E39's now.

[anonymous-user]

Update;

No vaccum leaks found anywhere, after test.

Replaced disa valve using a metal repair kit to stop rod snapping or me repairing it again, all good.

Code still on after a reset.

Looking like ccv or maf expensive

[iSore]

CCV isn't pricey and I've sold good used MAF's for 25 quid.