Vanos Rebuild Start Hesitation

[jamesfoley]

Postcat sensors don't control DME, but they indicate the rich condition of mixture (unless they are old and bad that don't function properly). IOW, they smell too much fuel and switching as the precat instead of staying at high level most of the time.

ICV is ok.

bad purge valve should pop the error code, so I think it's fine

fuel return hose can't be blocked.

measure the fuel pressure anywhere between regulator output and fuel rail.

here is the log:


https://datazap.me/u/sapote/e46-m3?log=0&data=10

I mean, looking at that log you do have the same open loop fault readings that make me think its normal for the MSS54 to do that for some reason? Out of curiosity whats the software version on your DME?

The fuel return idea came about because a previous owner has done the RACP work, which means the fuel tank has been out before. More so wondering if the fuel return was pinched or damaged rather than physically blocked.

[sapote]

Mine also has status 8 sometimes; never see 8 on M52 or M54 engines.
It has stock Dme firmware

If fuel return hose blocked, you would run out of fuel with half capacity show on gauge due to suction pump not working to transfer left to right tank

[jamesfoley]

Mine also has status 8 sometimes; never see 8 on M52 or M54 engines.
It has stock Dme firmware

Was just wondering if its an early software version thing really. if yours was also as old as mine it might be, though if yours is more recent then its doubtful.

If fuel return hose blocked, you would run out of fuel with half capacity show on gauge due to suction pump not working to transfer left to right tank

Fair point, all return is done through the same line that the regulator bleeds through.

[jamesfoley]

Just want to get some clarification on something.

MSS54 documentation says that the throttle body TPS should be 0.5v closed and 4.5v open, with the TPS on the actuator flipped at 4.5v closed and 0.5v open.

Pulling TPS values from DIS I have 0.39v closed and 3.94v open on the throttle body, then 4.35v closed and 0.57v open on the actuator.

Actual throttle positions are going 0-100% so I'm guessing it adapts to the open and closed position values.

Is it possible that either of those are worth replacing?

[jamesfoley]

Replaced the front TPS with a Hella 6PX 008 476-271, part seems identical to the original other than the BMW logo has been removed.

New sensor gives me 0.53v closed, and 4.07v open on the DIS diag page. BMW technical documents kind of suggest both the throttle and actuator sensors should be opposite, so the throttle TPS when open should match the actuator TPS when closed, but mine don't seem to. I don't know if that suggests the throttle isn't opening as much as the DME thinks it is?

I do realise the MSS54 adapts both the closed and open points, so chances are this wouldn't change anything. Either way, new sensor is in and all adaptations cleared in DIS. Throttle position adaptations were still present after an adaptation reset in DIS though, so unsure if its just reset fuel, ignition, and VANOS adaptations, and it leaves the throttle to continue to adapt on the pre and post drive checks.

First drive made no changes to how it reports a fuel system status of 8 when off throttle, but not sure I care about this anymore as it seems to be normal: https://datazap.me/u/jamesfoley/e46-...g=0&data=1-2-3

Will just see what the starting characteristics are like over the next couple of days I guess.

[sapote]

New sensor gives me 0.53v closed, and 4.07v open on the DIS diag page. BMW technical documents kind of suggest both the throttle and actuator sensors should be opposite, so the throttle TPS when open should match the actuator TPS when closed, but mine don't seem to. I don't know if that suggests the throttle isn't opening as much as the DME thinks it is?
.

If no codes related to TPS then they are working fine.

[jamesfoley]

If no codes related to TPS then they are working fine.

I kind of guessed that would be the case, but figured a new TPS wouldn’t hurt even if it was just an experiment.

Just can’t understand what’s going on with this to be honest, the car thinks everything is fine but clearly something isn’t happy…

[sapote]

I kind of guessed that would be the case, but figured a new TPS wouldn’t hurt even if it was just an experiment.

Just can’t understand what’s going on with this to be honest, the car thinks everything is fine but clearly something isn’t happy…

Is your main concern about the status 8, or other problems? Mine also has fuel status 8 ocationally but I think my engine is normal.

[jamesfoley]

Is your main concern about the status 8, or other problems? Mine also has fuel status 8 ocationally but I think my engine is normal.

Intermittent start hesitation is my main issue really. Sometimes it doesn’t just crank and fire, it sort of stumbles into life. 60% of the time it starts normally, and there are a handful of times where it feels like it starts too fast with barely any engine rotation before it fires up.

[sapote]

Intermittent start hesitation is my main issue really. Sometimes it doesn’t just crank and fire, it sort of stumbles into life. 60% of the time it starts normally, and there are a handful of times where it feels like it starts too fast with barely any engine rotation before it fires up.

Maybe the starter is weak due to cable resistance or weak batt.
Do this: first thing in early morning, measure batt voltage with engine off. Then run car at idle, measure voltage at batt posts directly (not on cable clamps), then measure from the fender jump post to engine body and see the difference.

[jamesfoley]

Maybe the starter is weak due to cable resistance or weak batt.
Do this: first thing in early morning, measure batt voltage with engine off. Then run car at idle, measure voltage at batt posts directly (not on cable clamps), then measure from the fender jump post to engine body and see the difference.

I'm 95% sure the starter is okay, the car has never had an issue cranking, even way back when I had long cranking issues.

Can certainly check voltages though, battery neg to battery pos, and then jump post pos to engine block right? Both with engine off and then engine running?

[sapote]

Yes

[jamesfoley]

Yes

12.02v across battery terminals.
12.00v from positive jump post to block.

14.01v across battery terminals with engine running.
14.30v from positive jump post to block with engine running.

No accessories running.

[sapote]

12.02v across battery terminals.
12.00v from positive jump post to block.

14.01v across battery terminals with engine running.
14.30v from positive jump post to block with engine running.

No accessories running.

`12.02v is low for a battery. What was the ambient temperature and when it was last driven and how far?

14.01 and 14.03v shows that the big cables have good connection.

[jamesfoley]

`12.02v is low for a battery. What was the ambient temperature and when it was last driven and how far?

14.01 and 14.03v shows that the big cables have good connection.

Battery is a 6 month old Bosch S5 which I fitted as part of troubleshooting this issue. The battery it replaced was also a Bosch S5 and there wasn't a change in behaviour when I fitted the new one.

Car was sat for two days before I took those readings, averaging around 14°C ambient at a guess. I can drive the car for 2 hours, turn the car off and then try and start it again and it would still hesitate. But it will also happen first thing in the morning sometimes after being sat overnight. It's completely random.