Vanos Rebuild Start Hesitation

[sapote]

Did you replace the pre cat O2 sensors?

[jamesfoley]

Another not so interesting update. I cleaned the ICV today just to see if I’d get lucky there, but from what I can tell it hasn’t made any difference. It was definitely very dirty, and not as free moving compared to after I cleaned it. Throttle response from idle is a litre snappier now if anything, and it bogs down less when pulling away. Unsure if adaptations need clearing?

At least it was an easy exercise to understand how much of a pain in the arse the plenum hose clamps are. I know they’re not technically reusable, but got away with reusing 3. The others were fused together and I had to break them to free them. Some generic jubilee clips work for now, I just made sure they didn’t interfere with the throttle. Will most likely replace these when the plenum comes off again…

[jamesfoley]

Checking the sensor is easy with a DVM, but monitoring with engine running must be done with a scope. Are you thinking the sensor is intermittently bad? I don't believe it because the fuel status is good at idle, and went bad during driving -- so why the sensor gone bad during driving and not idle, consistently as shown in the log files?

• Long crank
• Hard rough start
• Instantly stalling after starting
• Almost stalling when coming to a stop

All the above make me believe that I have a soft failing intake camshaft sensor, or perhaps someone has fitted an eBay sensor before my ownership. Almost as if the sensor is too weak to read the trigger wheel sometimes.

The shop that did the VANOS and fuel pressure regulator did say it sounds like a fuel delivery issue, but more along the lines of a blocked line. I figured if I had a blocked fuel line I’d have starting issues all the time, and misfires especially at WOT.

[sapote]

Sorry to bring this thread up again, but just wanted to ask if anyone knows if a drop in either exhaust or intake camshaft position signals would result in a fuel system state change?

Also wanted to ask if there was a way to monitor the intake cam position sensor without using an oscilloscope? Unless graphing the VANOS intake position like I was before in TestO is the way?

Checking the sensor is easy with a DVM, but monitoring with engine running must be done with a scope. Are you thinking the sensor is intermittently bad? I don't believe it because the fuel status is good at idle, and went bad during driving -- so why the sensor gone bad during driving and not idle, consistently as shown in the log files?

[jamesfoley]

Sorry to bring this thread up again, but just wanted to ask if anyone knows if a drop in either exhaust or intake camshaft position signals would result in a fuel system state change?

Also wanted to ask if there was a way to monitor the intake cam position sensor without using an oscilloscope? Unless graphing the VANOS intake position like I was before in TestO is the way?

[sapote]

I'm not totally blaming the LTFT for the hard start, but it is and the fuel status 8 are the good target to shoot them down, then hopefully the hard start might go away.

[jamesfoley]

Yes and no. There is enough data from the log to show pre cat sensor1 is slow to react, and also during the SAP running period, the extra oxygen should cause the precat sensor signals to be below 0.1v, but they are not. These are the symptom of old and slow sensors.
If the pre cat sensors are bad and can mess up the fuel trim -- and let's assume they caused the rich fuel trim with -7 LTFT before engine shut off, then when engine started again, DME will use the last LTFT of -7 during cranking, and it might affect how the engine starts.

I don't know what will impact the hard starting, but I would try to fix the high negative fuel trim and fuel status 8 first.

Might explain the random lean code I got not too long ago, but still weird that none of the codes or behaviour is consistent. Would have thought if the LTFTs were enough for it to be too lean at crank it would happen all the time 🤔 I thought +/- 5 was considered okay?

On that logic then the car should start without any hesitation if the fuel adaptations are reset right? Though I think resetting those also reset ignition and vanos adaptations as well which might make things unhappy, so might not be a good test

[sapote]

I will do eventually, though from what I understand the car doesn't use these initially and is open loop until they warm up, so it wouldn't be the cause of the start hesitation.

I'd really like to get to the bottom of the start issue first, and then I have brakes to sort 😑

Yes and no. There is enough data from the log to show pre cat sensor1 is slow to react, and also during the SAP running period, the extra oxygen should cause the precat sensor signals to be below 0.1v, but they are not. These are the symptom of old and slow sensors.
If the pre cat sensors are bad and can mess up the fuel trim -- and let's assume they caused the rich fuel trim with -7 LTFT before engine shut off, then when engine started again, DME will use the last LTFT of -7 during cranking, and it might affect how the engine starts.

I don't know what will impact the hard starting, but I would try to fix the high negative fuel trim and fuel status 8 first.

[jamesfoley]

Are you going to change the pre cat O2 sensors?

I will do eventually, though from what I understand the car doesn't use these initially and is open loop until they warm up, so it wouldn't be the cause of the start hesitation.

I'd really like to get to the bottom of the start issue first, and then I have brakes to sort 😑

[sapote]

Are you going to change the pre cat O2 sensors?

[jamesfoley]

If you look at the air charge table in this post,

https://nam3forum.com/forums/forum/special-interests/coding-tuning/211453-s54-airbox-288-280-schrick-on-csl-software-tune

@ idle (0% throttle area, 870rpm) an air charge of 18.8% is listed.
Engine displacement = 3246cc = 541cc/cyl with a density of 1.204 kg/m3 it equals as 100% = 651.38 mg/stroke
18.8% would mean (@870rpm) -> 122.46 mg/stroke = 17.2 kg/h = 4.776 g/s
You measure 5 g/s which is 4.69% off. I wouldn't expect to much from this.

From experience 15-20kg/h I have seen and should be OK for this engine.

Ah sweet, okay. Looking at the log that seems to be where the numbers are sitting so at least I can cross that off the list.

I've picked up a fuel pump connector with wires attached that I'm going to put between the connector in the car and fuel pump so I can tap the power without butchering the harness in the car. I'm not entirely convinced its a wiring issue as I can hear the pump prime the same every time, and it sounds the same both for when it starts normally and when it hesitates.

The only other things left on the fuel delivery side are the physical lines or the injectors

[Tomba]

If you look at the air charge table in this post,

https://nam3forum.com/forums/forum/special-interests/coding-tuning/211453-s54-airbox-288-280-schrick-on-csl-software-tune

@ idle (0% throttle area, 870rpm) an air charge of 18.8% is listed.
Engine displacement = 3246cc = 541cc/cyl with a density of 1.204 kg/m3 it equals as 100% = 651.38 mg/stroke
18.8% would mean (@870rpm) -> 122.46 mg/stroke = 17.2 kg/h = 4.776 g/s
You measure 5 g/s which is 4.69% off. I wouldn't expect to much from this.

From experience 15-20kg/h I have seen and should be OK for this engine.

[jamesfoley]

sapote I have this log with a big chunk of idle, and the MAF rate is still as high as the old MAF I had fitted: https://datazap.me/u/jamesfoley/e46-...0&data=1-14-17

That being said I don't really know for sure what a normal value here should be.

[sapote]

How would I go about this without tapping the wires? Not sure I trust myself removing the pump and probing wires that way

With negative fuel trims I'm a little confused how it could be a pressure problem. Negative trims suggest too much fuel / high pressure right? If the pressure was too low with either the pump failing or potential kinked line with low pressure, wouldn't I see high positive trims / lean engine issues?

I'm wondering if perhaps I have an issue with the fuel return line, but then I guess fuel pressure would read too high...

I don't know the best way to measure the pump voltage w/o cut off the wire insulation; you could measure the the trunk relay pin that connect to the pump.
Yes, negative fuel trim means mixture was too rich, but since your mechanic said the fuel pressure was low and so we suggested to check the pump voltage as it's a new pump. checking the pump voltage is easy so you should get this out of the question.

[jamesfoley]

Yes.

How would I go about this without tapping the wires? Not sure I trust myself removing the pump and probing wires that way

With negative fuel trims I'm a little confused how it could be a pressure problem. Negative trims suggest too much fuel / high pressure right? If the pressure was too low with either the pump failing or potential kinked line with low pressure, wouldn't I see high positive trims / lean engine issues?

I'm wondering if perhaps I have an issue with the fuel return line, but then I guess fuel pressure would read too high...