Engine cutting out, stumbling, stuttering etc.

[Bigbang]

Hello, had a problem with my 2008 pd170 BMN audi a3.

It started 10 days ago when my engine randomly died at low revs while parking, it would not start again until after several minutes and then ran fine again. Now I got a code for the G28 speed sensor (00801) and voltage low of ref circuit a (001602). I've read that any faulty sensor on this circuit can trigger a a low voltage code such as this, so a possibility that if the g28 sensor is faulty itd also cause that code?

Anyway, since then it was absolutely fine until yesterday when it stalled/cut out while driving at around 30mph, it felt like someone killed the ignition for a second or two then put it back on (the revs fluctuated by about 400-500rpm while this was happening despite me being in gear and still rolling so impossible for them to actually fluctuate by this amount.

Since then its happened a few more times, but only lasts a second or so then the engine is completely fine again in all ways (no loss of power etc) and when it does cut off and i'm not in gear it restarts instantly again.

Now as i said i've only got the two previously mentioned codes for the 14th of this month and none for this weekend, could this be a warning of a faulty speed sensor and it didn't fail long enough for it to trigger a code? or something else? it seems easy enough to change so i was going to go to TPS tomorrow buy a new genuine one and change it myself unless anyone has anymore information and can point me in a better direction?

Thankyou for sticking with me this long!

 

[aqibi2000]

Inspect wiring as something could be momentarily shorting the 5V to ground which is shared by all the engine bay sensors - triggering the intermittent behaviour.

I would put an oscilloscope on the 5V line, then try to recreate the issue by gently moving the wires around in the engine bay until you see a dip in the 5V with the ignition on or the observe the engine hesitation with the engine running...

At least that would be my starting point

 

[Bigbang]

Inspect wiring as something could be momentarily shorting the 5V to ground which is shared by all the engine bay sensors - triggering the intermittent behaviour.

I would put an oscilloscope on the 5V line, then try to recreate the issue by gently moving the wires around in the engine bay until you see a dip in the 5V with the ignition on or the observe the engine hesitation with the engine running...

At least that would be my starting point

I couldn't actually find the sensor, does anyone know where it is exactly?

but i did give everything i could find a firm move about and pulled etc, engine ran fine. I got vcds out and removed both the ASV and EGR and did output tests on both, both seem to operate fine.

hope it throughs another code soon to confirm the sensor or anything else..

 

[aqibi2000]

Gearbox side

 

[Bigbang]

Cant seem to get it to replicate the fault again, until then i've noticed some faults, my swirl flap actuator is leaking, i have an EGR exhaust leak and a boost leak from the turbo to pipe connector, so i've got an order for everything OEM to sort this from TPS to collect tomorrow, a delete kit from ebay and a second hand BKD Manifold to remove my swirl flaps which i've just shot blasted and is looking very nice! hopefully get all this done on the weekend. Doubt any of these issues would cause what i described though?

 

[aqibi2000]

Cant seem to get it to replicate the fault again, until then i've noticed some faults, my swirl flap actuator is leaking, i have an EGR exhaust leak and a boost leak from the turbo to pipe connector, so i've got an order for everything OEM to sort this from TPS to collect tomorrow, a delete kit from ebay and a second hand BKD Manifold to remove my swirl flaps which i've just shot blasted and is looking very nice! hopefully get all this done on the weekend. Doubt any of these issues would cause what i described though?

Remember to use the metal intake gasket, and plug the hose going to the swirl flap actuator

How much was the manifold btw?

 

[Bigbang]

Remember to use the metal intake gasket, and plug the hose going to the swirl flap actuator

How much was the manifold btw?

Yeah got that on order from TPS, manifold was £30 delivered off ebay. alot on there for £50-£60. Just have to wait for one to pop up, i had to try different search terms to find this one.

Also if anyone else has issues finding the G28 speed sensor / BMN crank sensor heres a diagram i found clearly showing its location

 

[Bigbang]

ok im more thinking wiring now.. the car did it again and no codes came up, i got it to do it while running a log with VCDS, i was comparing cam sensor data vs crank speed.. the log shows the speed sensor stop working while the cam sensor still reads, so 0 on crank speed and x amount for cam.

but then it suddenly would start or anything, it then threw 3 codes, low voltage of ref circuit a, g28 crank sensor and the throttle position sensor..

then i started wiggling wires, while the engine is off but the ignition is on the EGR buzzes, while i wiggled wires i noticed the tone of buzz changed and you could hear the EGR moving as i wiggled the sensors.

im going to take the airbox etc off to have free access to that side of the engine and check the wiring more extensively. Im hoping it will be an easy find but i have a feeling this is the start of a long fix..

so tonight it went, stuttering while driving, got more frequent, then it cut out completely and would not start, then started and idled perfectly after a few mins

 

[Bigbang]

I dont have a oscillator, do you know how else i can check the 5v line? also do you know which wire it is?

 

[Bigbang]

SOLVED - anybody looking on this in the future, it turned out to be a miniscule crack in the wires that plug into the turbo actuator, causing false codes. I cleaned the area up applied some new insulation around each wire and now the problem has completely vanished.

 

[aqibi2000]

Awesome you found it.

Now let me be ironic.

Here’s a fix I did to my BMN turbo actuator position sensor wire.

 

[Bigbang]

Awesome you found it.

Now let me be ironic.

Here’s a fix I did to my BMN turbo actuator position sensor wire.

Yup it was that wire and the red one that has lost some shielding and were touching, it got a lot worse really quickly and as soon as i touched the wiring it cut out where the other day it wouldnt do it when i moved the wiring around. lucky as i was on my way to audi to pay for a new crank sensor at £120 then the pleasure of removing the oil filter housing, boost/coolant pipes etc to fit it..