Vanos Rebuild Start Hesitation

[jamesfoley]

So why status 8 only happened with closed throttle -- this is the key to solve the mystery. I don't remember if you posted the MAF rate in g/sec; just want to make sure it's not related to bad MAF.

I mean I guess it’s possible the ICV isn’t letting enough air through, or too much through for what’s being commanded? Another thought is an issue with the EVAP purge valve leaking and enriching the mixture causing it to run richer than expected?

MAF is brand new from BMW and rates were fine last time they were checked.

It would be awesome if there was a way just to see what criteria the DME used to trigger a fuel status of 8.

There is always the possibility that it’s just normal fuel cut on deceleration…

[sapote]

Little bit more research and it appears the MSS54 doesn't only use the actual throttle body for engine load below 15%, so low speed, low engine load, low throttle input, the Idle Control Valve actually provides air. So I guess the 0% throttle position is actually where the ICV is providing air and the throttle bodies stay closed?

I have had the ICV out and cleaned it to free up the flap inside, but I mean it wasn't bad to begin with, and cleaning it made no difference. Hopefully its not still causing issues, from all my logs I can't find a fuel system status 8 reading where the throttle position isn't reading 0...

So why status 8 only happened with closed throttle -- this is the key to solve the mystery. I don't remember if you posted the MAF rate in g/sec; just want to make sure it's not related to bad MAF.

[jamesfoley]

From the log I see fuel status 8 happened only once in idle.
I don't see any correlation between status 8 and ignition timing, as below pic shows 24* ignition advaced. I do see all of these status 8 happened with absolute throttle = 0. Could be an intermittent faulty throttle sensor tells the DME it's closed but it's not, hence the status 8?

After a bit of research it sounds like ignition timing should drop to 0 the same way fuel is cut on deceleration / throttle close, but I thought it should be fuel status 4, not 8 with a fault.

Faulty TPS is plausible, though again from what I’ve read they always throw a fault code of some sort. Been a good few months with not a single code being thrown.

I don’t really understand the relation between throttle position reported in my log compared to the actual throttle position, as the log shows it at 0% a lot of the time. If it was always 0% the car wouldn’t be drivable…

Edit to avoid double posting:

Little bit more research and it appears the MSS54 doesn't only use the actual throttle body for engine load below 15%, so low speed, low engine load, low throttle input, the Idle Control Valve actually provides air. So I guess the 0% throttle position is actually where the ICV is providing air and the throttle bodies stay closed?

I have had the ICV out and cleaned it to free up the flap inside, but I mean it wasn't bad to begin with, and cleaning it made no difference. Hopefully its not still causing issues, from all my logs I can't find a fuel system status 8 reading where the throttle position isn't reading 0...

[sapote]

No, not tested anything related to the gear position. Both open loop faults and ignition timing drops happen at idle in neutral so I don’t think it can be gear position related.

I don’t know if I’m seeing the ignition timing drop because it’s going open loop, or if it’s going open loop because there is an issue with ignition timing.

From the log I see fuel status 8 happened only once in idle.
I don't see any correlation between status 8 and ignition timing, as below pic shows 24* ignition advaced. I do see all of these status 8 happened with absolute throttle = 0. Could be an intermittent faulty throttle sensor tells the DME it's closed but it's not, hence the status 8?

[jamesfoley]

Bentley manual says this:

Ignition timing is electronically mapped and not adjustable. The ECM uses engine load, engine speed, coolant temperature, knock detection and intake air temperature as the basic inputs for timing control. A three dimensional map similar to the one shown is digitally stored in the ECM.

So unless there is an issue with the DME I’m not sure how fuel status would change ignition timing.

Knock counters don’t report anything, and temperature sensors appear to be fine, so I’m just a little bit confused.

Also just found this in the Bentley manual:

Traction control also comes into operation during deceleration. Decelerating on snowy or icy road surfaces can lead to rear wheel slip. If a rear wheel starts to drag or lock up, the ASC system can limit the problem by adjusting throttle, fuel injection and ignition timing.

Ironically the week before I had the VANOS done one of my rear reluctor rings cracked and I lost ABS, traction, and my speedo didn't work. Ended up driving to get the VANOS done with the dash lit up like a Christmas tree and no speedo. Had a new reluctor ring fitted along with a new ABS sensor at the same time the VANOS was done, which did fix all the faults. Just sort of made me wonder if the traction system is pulling timing / cutting fuel randomly, though I don't have the dash light flash or anything so probably not related.

[jamesfoley]

No, not tested anything related to the gear position. Both open loop faults and ignition timing drops happen at idle in neutral so I don’t think it can be gear position related.

I don’t know if I’m seeing the ignition timing drop because it’s going open loop, or if it’s going open loop because there is an issue with ignition timing.

[sapote]

se
Fair enough, not even sure how I'd test either of those if I'm honest.

Did you test these parts? I think using INPA you can read the status of these components -- close/open, gear engaged/neutral

[jamesfoley]

Sorry for resurrecting this thread, but although I've sort of lived with this for a while I think I still have issues.

I have an OBD log which I included ignition timing on along side fuel system status and throttle position and can see that almost every time I have the fuel system go into open loop fault, my ignition timing drops close to 0 or sometimes negative.

https://datazap.me/u/jamesfoley/e46-m3-2?log=0&data=1-2-3-4

Is anyone able to explain what might be happening here, or if this is normal?

[jamesfoley]

Manual tranny have GPS and SMG don't (but the shift rod actuator does have the position encoder which provides the same needed information as GPS for the DME).

Fair enough, not even sure how I'd test either of those if I'm honest.

[sapote]

I've a manual car so not sure if I have a gear position sensor?.

Manual tranny have GPS and SMG don't (but the shift rod actuator does have the position encoder which provides the same needed information as GPS for the DME).

[jamesfoley]

One of the function of the clutch sw and GPS is to let the DME know when car coasting in gear and cut off injectors without causing stalled engine. If DME doesn't know it is coasting in gear with engaged clutch then it doesn't cut off injectors then this could be your fuel status 8 issue.

I've a manual car so not sure if I have a gear position sensor? Car is also Euro, so I don't need to press the clutch to start the car, unsure if this changes anything but searching about I can only find stuff that links the clutch switch with cruise control.

Some extra unfortunate news is that the car started hesitating on start again today, so I had a good 4 days after the head was rebuilt. LTFT's are 5% negative now with the same fuel system status 8 readings sprinkled about. I tried logging throttle position against it to see if it was instead throttle close that was triggering it, but I can't really see a pattern, it matches up with RPM drop more than throttle position.

I guess even though bent valves is a problem, it and the VANOS weren't the source of the starting issue.

Starting to feel more and more like its the DME tune messing with fuel delivery...

[sapote]

The GPS and clutch switch I’m not sure about, what does these actually do that would interfere with open / closed loop? I have fully working cruise control so I’d imagine they are both fine.

One of the function of the clutch sw and GPS is to let the DME know when car coasting in gear and cut off injectors without causing stalled engine. If DME doesn't know it is coasting in gear with engaged clutch then it doesn't cut off injectors then this could be your fuel status 8 issue.

[jamesfoley]

Are you saying the engine start hesitation problem was due to the bent valves?

So far every start has been perfect so it’s probably safe to assume the valve was the issue. I’m guessing it was something to do with what cylinders were trying to fire when starting based on where the engine was left when shut off. If you was trying to start on or close to cylinder 5 in the firing order then it would basically misfire due to leak.

Although saying that both the VANOS timing and valve shims were wrong which could have also been the cause. It seems to be important that this is 100% correct otherwise you're just going to have issues either with running, or bending a valve like mine did.

I would look at the the clutch switch and GPS, or tune software

The GPS and clutch switch I’m not sure about, what does these actually do that would interfere with open / closed loop? I have fully working cruise control so I’d imagine they are both fine.

Also I have no idea how I realistically check to see if my DME has a map on it that is different to factory. Maybe it’s worth putting the Evolve map on it or something?

[sapote]

Bit of an update to this. Car is back with me now after just over two months. Long story short is the VANOS job I had done resulted in both intake valves on cylinder 5 to kiss the piston and bend enough for them not to close properly. Ended up needing the seats recut as the bent valve had damaged those. Also had new guides and a set of intake valves.

Car now starts on the button every time (so far), so its probably safe to say this has been sorted.

I feel like I am clutching at straws a little bit, but is it possible I still have a fuel delivery issue? -4% long term fuel trims on both banks, open loop fault on deceleration, and the car smells noticeably rich.

Are you saying the engine start hesitation problem was due to the bent valves? I wonder why the issue was not consistence and no backfire in the intake.

-4% fuel trim is small, but since the fuel trim has been stable then the mixture should already at stoichiometric at idle and coasting.
It rings the bell in my head now, about the fuel status 8: injectors should be cut off completely during engine braking/deceleration when above certain minimum rpm but yours does not, seems to me. Maybe the DME doesn't know that the clutch and the gear are engaged -- I would look at the the clutch switch and GPS, or tune software.

[jamesfoley]

I feel like I am clutching at straws a little bit, but is it possible I still have a fuel delivery issue? -4% long term fuel trims on both banks, open loop fault on deceleration, and the car smells noticeably rich.

Is it at all possible that I have an issue with the car regulating fuel pressure when the manifold is in vacuum, and the car is getting higher fuel pressure that it expects at times? So either the air rail to FPR line having an issue, the regulator itself having an issue, or an issue related to the return line from the regulator, basically something preventing the regulation of fuel so the car is getting all the pressure all the time.

The vacuum line and FPR are new so I doubt those are the issue, however I've not touched or inspected the return line. Car has had the RACP done in the past before my ownership so everything has been apart at some point, possible that when this was put back together a line has been crushed or pinched?

I'm 99.9% sure all the fuel pressure tests at idle I've had done have been fine, would just be trying to find out if there are fuel pressure issues while driving...