Vanos Rebuild Start Hesitation

[jamesfoley]

The data show these issues:
Fuel system status 8 happened many times during driving, it is bad. Status 2 or 4 is ok, but not 8 or 1. This indicates engine having fuel mixture issue. This is confirmed with rich fuel trim of around -10 total (LTFT + STFT).
MAF is around 5g/s at idle which is too high. I would try to swap with a known good working unit.
pre cat bank1 O2 seems a bit lazy old. The other 3 sensors are ok.

Why hard start? The DME cut down the fuel (negative 10 fuel trim) due to the rich mixture in the last drive. When starting, the DME used the last LTFT which was around -7 and this could cause lean mixture during starting and hard start or stall. So I think good or bad start is depending on the LTFT from the last drive before parked.

Could I pull the MAF and drive about and see if the fuel status 8's go away, or check the fuel trims?

[sapote]

Could I pull the MAF and drive about and see if the fuel status 8's go away, or check the fuel trims?

Yes it's good idea, and this might help the hard start too.

[jamesfoley]

Yes it's good idea, and this might help the hard start too.

So I have two new logs, both with the MAF removed, but doesn't look like it changed much other than make the car drive horribly. Worth noting that this didn't trigger a CEL or SES light, is that normal?

https://datazap.me/u/jamesfoley/e46-...f?log=0&data=5
https://datazap.me/u/jamesfoley/e46-...f?log=0&data=5

The town driving log still have a fuel status of 8 occasionally., and it didn't make a difference to fuel trims, unless that takes a couple of trips to change? I could reset the DME adaptations to clear those trims but not sure that would help

Unless the fact the fuel status still gives me 8's without the MAF point to the MAF being bad, honestly not sure how testing this works if I'm honest.

[jamesfoley]

Sorry to double post.

Just did another drive, this time I had a EML with codes for both MAF and temp sensor which makes sense. For these runs I reset the DME adaptations before I took the car out to see if it made any change to the fueling, but now my town drive log is littered with fuel status 8 readings.

https://datazap.me/u/jamesfoley/e46-m3-town-drive-no-maf-reset-adaptations?log=0&data=5-6

https://datazap.me/u/jamesfoley/e46-m3-warm-idle-no-maf-reset-adaptations?log=0&data=5-6

With the fuel adaptations reset the car basically drives exactly the same as it does with the MAF plugged in. I did get some bucking a couple of times though, not sure if thats normal, mainly from pulling away at junctions from standstill.

Also worth noting that it still hard starts with the MAF unplugged. It's almost like nothing has changed other than I have the EML light on now.

On a positive note VANOS test now passes without an issue, results here: https://i.imgur.com/wupfK6i.jpg

[sapote]

Also worth noting that it still hard starts with the MAF unplugged. It's almost like nothing has changed other than I have the EML light on now.

So it didn't help with hard start issue. But you need to swap the bad MAF as 5g/s at idle is wrong and I don't see what else can cause this.

[jamesfoley]

So it didn't help with hard start issue. But you need to swap the bad MAF as 5g/s at idle is wrong and I don't see what else can cause this.

I'm assuming genuine BMW is the only way to go with a MAF like every other sensor? They're just pretty expensive from the dealer 😅

Also, for the fuel system status of 8, should that be happening with the MAF removed?

[ATB88]

I'm assuming genuine BMW is the only way to go with a MAF like every other sensor? They're just pretty expensive from the dealer 😅

Also, for the fuel system status of 8, should that be happening with the MAF removed?

The Bosch OEM sensor is the exact same, no need to pay for the BMW branded one. Same part.

[jamesfoley]

Jumped in the car this morning and it threw a P0174 code, lean on bank 2.

Did some graphing of the MAF, RPM, and both banks Short fuel trim and noticed the RPM fluctuates slightly, with the short trims going positive and negative constantly while idle, and the MAF sits at 5 g/s or above. I'm assuming it's upset about the fuel mixture and is constantly trying to compensate with a wrong MAF reading?

Either way I should have a new MAF here tomorrow so will do some more captures when that's installed.

[sapote]

Jumped in the car this morning and it threw a P0174 code, lean on bank 2.

Did some graphing of the MAF, RPM, and both banks Short fuel trim and noticed the RPM fluctuates slightly, with the short trims going positive and negative constantly while idle, and the MAF sits at 5 g/s or above. I'm assuming it's upset about the fuel mixture and is constantly trying to compensate with a wrong MAF reading?.

Interesting lean code in this case, as MAF=5g/s resulted rich with negative fuel trim and it should not suddenly change to lean, even if fuel trims were reset. Will be interested to see what a new MAF will do.

[jamesfoley]

Interesting lean code in this case, as MAF=5g/s resulted rich with negative fuel trim and it should not suddenly change to lean, even if fuel trims were reset. Will be interested to see what a new MAF will do.

New genuine BMW MAF installed and DME adaptations reset, gave me the following logs:

https://datazap.me/u/jamesfoley/e46-...log=0&data=2-5
https://datazap.me/u/jamesfoley/e46-...log=0&data=2-5

Unfortunately no change to the starting hesitation. With the car fully up to temp and idling, taking the key out and trying to start it a minute or two later results in it struggling to catch. It honestly sounds fuel related as if for some reason in that initial crank it doesn't quite have the fuel to start so it splutters, but the only things I've not looked into are the fuel pressure regulator and the injectors themselves.

Not 100% sure how I'd be losing _all_ fuel pressure as soon as I took the key out unless the regulator is totally shagged. If the regulator was shagged it doesn't explain how I can leave it overnight and start it without issues the next morning.

Long term fuel trims are creeping into the negatives again, and the town driving log is still full of fuel system status 8 reports, so I guess something is still wrong.

The only other small thing I've noticed is that sometimes if I'm moving forward slowly and I put the clutch in and lift off the accelerator, the RPM will drop and the car almost stalls, but it picks itself back up and recovers.

[sapote]

New genuine BMW MAF installed and DME adaptations reset, gave me the following logs:

https://datazap.me/u/jamesfoley/e46-...log=0&data=2-5
https://datazap.me/u/jamesfoley/e46-...log=0&data=2-5
.

The new MAF improves the mixture with LTFT now in the -3 instead of -7, and the pre cat o2 sensors are responding much better. Most cars should have positive LTFT as old cars trend to lean condition and not rich, but yours is the exception. There is also the fuel system status 8 during driving, happened almost every deceleration. Based on this, I would check the throttle pedal sensors.

Have you check injectors for leaking and fuel pressure?

[jamesfoley]

The new MAF improves the mixture with LTFT now in the -3 instead of -7, and the pre cat o2 sensors are responding much better. Most cars should have positive LTFT as old cars trend to lean condition and not rich, but yours is the exception. There is also the fuel system status 8 during driving, happened almost every deceleration. Based on this, I would check the throttle pedal sensors.

Have you check injectors for leaking and fuel pressure?

You mean the throttle position sensors? I know there are two on the throttle body and then the pedal right, can they be logged individually?

Would these go bad without throwing a code though, I think that's what is confusing me about everything, I have zero fault codes and its super frustrating.

Not checked injectors or fuel pressure, mainly because these are a little beyond me. Car is booked in for a new fuel regulator next week so I can get the pressure checked at the same time.

[jamesfoley]

Here is a motorway drive with a fresh tank of Shell VPower

https://datazap.me/u/jamesfoley/e46-m3-motorway-drive?log=0&data=4-5&solo=2

I've included throttle position but not sure if that really helps at all. Still seeing 8's in the fuel system status and I can't see a pattern against the throttle position really.

[sapote]

Add voltage to the log; measure the battery voltage with voltmeter and compare.

[jamesfoley]

Add voltage to the log; measure the battery voltage with voltmeter and compare.

Battery is new as of 3 months ago and has no issues cranking, so I figured it would be fine. Ironically I changed the battery thinking it was the issue in the first place

I can add voltage to the log but with all these PIDs I'm pulling its pretty slow at refreshing so not sure how accurate the data is. What am I looking for exactly with battery voltage, dips while driving?