CBEA hot start problems

[Dually]

2012 audi a3 150k miles. I've had this hot start problem for a few years that's only gotten worse.

Cold start is fine. Just a revolution or 2 and it runs fine.
Hot start is a couple revolutions, stumble and stall. Repeat that a few times and it will eventually stay running and run great.

It's been to a couple generic diesel mechanics and none see a problem. I've called specialists within a 2 hour radius and nobody wants to look at it.

Injector deviation seems fine. Never more than 0.3 hot or cold.
Regens are normal.
Pressure differential is 8 at idle.
If the specs in obd eleven are correct, everything is within spec.
Battery is new.
Starter was replaced while out of town with unknown brand

It's hard to get engine speed data on vcds when I have to turn key off and restart. By ear it's spinning slower when cold and starts fine. The odd thing about all this is after a timing belt change, it was starting fine everytime for a few days.

Darkside has a tune for this issue but before I go that route. There must be some underlying cause and tuning seems like a bandaid. I'd like to know what is actually happening to cause this and fix it correctly.

 

[Garrison]

I had the same issue - and in the same context

In my search, folks on here pointed to the timing being ever so slightly off - so the timing procedure needed to be redone. The issue got worse over time; eventually it left my wife stranded and that was the onus I needed to get off my ass and fix it.

I'm not saying this is your issue, but it sounds oddly similar. If you have VCDS you may have some stored codes you can share with us; could help point the way

 

[oilhammer]

Look at the temp sensors' data (air, fuel, coolant), and see if they all jive with what you'd expect them to be.

 

[Dually]

In my search, folks on here pointed to the timing being ever so slightly off - so the timing procedure needed to be redone.

Thanks, no codes unfortunately. It was my first belt so anything is possible. Was that a mechanical adjustment you made?

 

[Dually]

Look at the temp sensors' data (air, fuel, coolant), and see if they all jive with what you'd expect them to be.

All the temp sensors are in agreement.

 

[tjg]

I had a similar issue on my 2014 sportwagen, it almost seemed like an immobilizer issue but not throwing a code.
My problem was solved by replacing the crank position sensor.

 

[Dually]

I had a similar issue on my 2014 sportwagen, it almost seemed like an immobilizer issue but not throwing a code.
My problem was solved by replacing the crank position sensor.

The tach seems to behave normally when cranking so I didn't persue that. There may have been a time I didn't see it move.
I have a cam and crank sensor in the basement. I think I just entered the throw parts at it stage.

I've read that is a difficult sensor to reach. Was that your experience?

 

[tjg]

The problem was initially somewhat rare and got worse over the last 12 months.
I didn't have the time to troubleshoot anymore and was at my wits end, so I dropped it off at my local indy VW mechansir.
After some trial and error, checking the tune, ASV, etc, we tried the only other thing that could cause those symptoms, the crank position sensor. the issue hasn't occurred since it was replaced back in December.
Its odd, as there were no codes or other indicators that it was failing.

I think the tach needle would move as it was cranking/initially running, but I can't be totally certain.

I'll say that the sensor is not the easiest to change.

I don't want to send you on a wild goose chase, i would recommend you check more certain, measurable things before trying this.

 

[Dually]

I don't want to send you on a wild goose chase, i would recommend you check more certain, measurable things before trying this.

I appreciate the wise words.

 

[Garrison]

Thanks, no codes unfortunately. It was my first belt so anything is possible. Was that a mechanical adjustment you made?

Yeah unfortunately you have to redo the process (but it will be easier since you know what you're doing now

also, this might be helpful for you (crank position sensor), FWIW w/o crank cam correlation codes I wouldn't bother. [see my post history for examples]:

N6jJyxi hosted at ImgBB

Image N6jJyxi hosted in ImgBB

ibb.co

 

[Dually]

Yeah unfortunately you have to redo the process (but it will be easier since you know what you're doing now

also, this might be helpful for you (crank position sensor), FWIW w/o crank cam correlation codes I wouldn't bother. [see my post history for examples]:

N6jJyxi hosted at ImgBB

Image N6jJyxi hosted in ImgBB

ibb.co

Thanks again. I'll start with timing before I throw any parts. The video was a helpful refresher.

 

[Dually]

Yeah unfortunately you have to redo the process (but it will be easier since you know what you're doing now
>

Retimed and no change. I don't think it was out much if any. Tried locking crank then cam and it wouldn't go. Locked cam and pump then the crank just needed a little pressure to lock in place. Unlocked cam and pump and locked the gears back down.

Found a weeping water pump and corrosion under this flaky black stuff on the idler. To hard to tell if pump is leaking or my install was bad. Belt is dry. No puddles just some crusty. Either way it needs a whole new timing set. I don't know if keeping this car is in anyone's best interest. If I could figure out the hot start issue....

 

[super1]

Retimed and no change. I don't think it was out much if any. Tried locking crank then cam and it wouldn't go. Locked cam and pump then the crank just needed a little pressure to lock in place. Unlocked cam and pump and locked the gears back down.

Found a weeping water pump and corrosion under this flaky black stuff on the idler. To hard to tell if pump is leaking or my install was bad. Belt is dry. No puddles just some crusty. Either way it needs a whole new timing set. I don't know if keeping this car is in anyone's best interest. If I could figure out the hot start issue....

I'm thing Crank Sensor on this

 

[Dually]

I tried to compare cam and crank speeds during start up. This csv shows running, 4 failed starts then running. Took it for a rip and looked at the same data in graph form but didn't see anything unusual. I've seen the crank sensor mentioned a few times. Seems like a logical next step.

Thanks

 

[Garrison]

I tried to compare cam and crank speeds during start up. This csv shows running, 4 failed starts then running. Took it for a rip and looked at the same data in graph form but didn't see anything unusual. I've seen the crank sensor mentioned a few times. Seems like a logical next step.

Thanks

I've got a spare one sitting in the garage I can send you for free to try

 

[Dually]

I've got a spare one sitting in the garage I can send you for free to try

Thanks. I ordered one from fcp when I got the dmf. Forgot to give to the guy that installed the flywheel. So it's on my shelf. I'll try next weekend if the weather is good. In the mean time I might try Ross tech and see if they have any suggestions.

 

[Dually]

It was the starter.

Probably. There was a less than ideal ground between body and engine. That got cleaned up too.

 

[super1]

It was the starter.

Probably. There was a less than ideal ground between body and engine. That got cleaned up too.

Good work!