2003 E85 2.5i lean code issues and odd stall on refuel

[rgd3]

First time posting here. I have an 03 Z4 E85 2.5l that I have been battling with the lean codes on it for some time now. Both banks read as lean and I will sometimes see misfire codes for multiple cylinders. The codes for the misfires will come and go oddly enough. The Car runs fine for the most part but sometimes has a rough idle and the RPM will bounce off the 500ish range.

I have done a lot of work to the car already, replaced most of the vacuum hoses, new spark plugs and ignition boots, checked the PCV valve for issues and it seems working, clean the MAF regularly. I've checked the intake boot for cracks or leaks and have found none. I have also replaced the Charcoal canister and the leak detection pump as well as the purge valve.

The other issue that im thinking might be related is whenever I go to fill up, afterwards the car does not want to turn over and I have to try a few times where the engine turns over then dies. after a couple of tries the engine starts up fine and I have no issues starting it until I have to fill up again.

Hopefully I can find some answers here. Thanks in advance!

[patriot66]

Any MAF related codes ? I had quite a bit of bother recently with poor running, fluffed SMG down changes, lumpy/erratic idle etc. Fitted a brand new Hella MAF and all is well again

[enuff_zed]

Think I'd say the same tbh.
You say you've cleaned the MAF but if its got an internal fault that won't help.
Until you fit a new one you'll never know.

[colb]

Since you have replaced numerous parts already and are certain you have no air leaks across the entire engines vaccum system I would agree its a possiible Maf fault. Mafs are nortorious for not always setting codes, If you have diagnostics that can view live data then take a look at the Mafs data when engine running and how it reacts to throttle changes. At least you will see if its working or not, deciding if its working correctly however and reporting accurate amounts of air passing through it can involve a bit of guesswork. Comparing what a Maf on another car same as yours is performing would be a good way to compare and maybe highlight that yours is under or over reporting.
Running lean causes the engine management to demand more fuel at the injectors how it decides to do this is comparing readings from the Maf and the exhaust sensors. Using Diagnostics take a look at the fuel trims, if you find they are high its a good indication that the fault is with the Maf, Exhaust sensor(s) or a vaccum leak allowing unmetered air into the system. If it is the Maf at fault, replacing it should have an instant fix to the running problems you experience. If you do replace the Maf only use a Bosch or Siemens brand that are oem, do not go for cheap pattern parts, they rarely work or perform correctly.

[rgd3]

Ok update, I replaced the MAF sensor and the lean codes still reappeared, though they have taken longer to come back so I think the maf was part of the issue. I'm going to take the car in for a smoke test and see if there is a leak I'm missing.

[patriot66]

[Spriteracer]

As you seem to have checked just about everything else, I would also look at fuel pump, fuel filters and fuel tank feed pipes and vent. It seems odd that the non-starting issue only occurs after refuelling, i.e. after opening the fuel filler. Not on a BMW, but I've had issues in the past where a tiny leak in a fuel pipe at the tank prevented the pump from pressurising properly - the fuel ran back to the tank when the engine wasn't running. The effect was having to run the starter for ages before it would start. Fixing the leak cured it.

[colb]

Air leak still a possibility then, when its smoke tested pay particular attention to the sucking jet valve down on the side of the block near the intake to the throttle body, I found one leaking on a 2.2 as well as a leak around no4 plug well that was allowing air in because the plastic cam cover was cracked and beginning to crumble from the plastic ageing as a result of continual heat cycles. Also check out the O ring in the dipstick tube, they fail and allow air in.