(seemingly) Random no-starts

B6/7 S4/RS4
#1

Hey gents, got a new question for you. During a road trip this weekend (wedding #3 of 5 for the summer, woo) Saturday morning when I went to start the car, it just cranked and cranked.

What happened:
Let it crank for about 5 seconds then turned key off. Turned key to on again, let everything prime for that 4-5 seconds, tried again. Cranked for 10-15 seconds, tried pumping the gas pedal, no dice.

Let it sit a few minutes, did the same again, it cranked for 5-10 seconds I started pumping the gas pedal again after the first few and it fired up. Drove where I was going, stopped for gas, food, etc a few times, no issues restarting.

Next morning, same thing.

What I’ve tried/checked:
I don’t have VCDS but I do have Torque. No codes found other than SAI (from exhaust upgrade). No CEL. I do hear the pump priming when I turn the key to ON (I always let it sit for that 3-5 seconds of key ON while all the hums and whirrs go on, every time I go to start it). Fuel filter isn’t too new, probably has 50k on it since I last replaced it? Last time it was bad I never had this issue, it would jut make a squealing noise, so I’m not sure it’s the filter. No misfires or idle issues, runs just fine once started. Cranks fast (battery is good). I have noticed it taking 2-3 seconds of cranking to actually fire on over the last month or two, rather than immediately starting up. Car has always taken 1-2 seconds but yeah seems like its been an extra second or so in recent months. Car just rolled over 190k.

Any ideas on where to start troubleshooting? Thanks

#2

This isnt too uncommon in the very hot months.

First off pumping the gas wont actually do anything. the fuel is set on a pre determined path during starter cranking.

The two things to check are the evap system and the fuel filter.

What can happen is that there is a pressure bleed off when it gets hot out as the head causes even more pressure to build up in the fuel system. That can cause the fuel filter to fail or the evap system to not work properly.

To check the fuel filter get a gauge on the fuel line at the rail and test duing the hotter days.

#3

It has been a bajillion degrees. That makes sense, even regarding the last couple months of slightly slower starts. Each time it was after driving during the hot day and the car had sat overnight.

And I figured pumping the gas didn’t/doesn’t do anything, but I did it instinctively so I thought I would mention it just in case.

Thanks for easing my mind a bit and giving me a couple things to check out (if I ever get a free weekend this summer!) How do I check the evap system? Would opening the gas cap first thing to let the fuel tank equalize with atmospheric pressure help? I have noticed a couple times when I go to get gas there is a small hiss of air movement when I first remove the gas cap not sure if it is sucking air in or venting it out, I will try and pay more attention next time. Is that indicative of my charcoal filter getting gunked up or some other aspect of the evap system malfunctioning?

Thanks again

#4

Ok gonna need some help.

Car refused to start today after the gym. Got 2 codes off Torque:

P0322 - Powertrain
Ignition/Distributor Engine Speed Input
Circuit No Signal

P0688 - Powertrain

Quick searching indicates the crank position sensor? Looking on ECS there are like 50 different part #s, anyone know which one? Sorry for all the questions, car is stranded and I really need to get a jump on fixing this.

Thanks guys

#5

Yikes. CPS is a well known culprit for these symptoms in the AAN 20v 5 cal engine in the C4 urS4/6. You’da thunk Hans und Franz woulda figured this out by now.

The other culprit for hot no start in those beloved relics is fuel pump.

#6

As I look further I am finding some conflicting/confusing info. Do the codes I have indicate:

Camshaft Position Sensor
P/N 06C905163-/B
https://www.ecstuning.com/Audi-B6_S4--V8/Engine/Electrical/Sensors/ES251644/

OR

Crankshaft Position Sensor
P/N 077905381F
https://www.ecstuning.com/Audi-B6_S4--V8/Engine/View_All/ES283065/

Seems like it would be the latter (Crankshaft Position Sensor) since there is a left and right of the camshaft sensor. Can anyone confirm?

#7

Here is the crank position sensor

077905381F

As for the evap you can test it with vag com and I know the TQ app can help you read codes but you might want to get with someone with a vag com. If you have a vag com I can tell you what to log and what to check. I think most people just change there evap solioniod

#8

Thanks Justin. Unfortunately I do not have vagcom. Anyone near Louisville/Cincinnati want to help? :slight_smile:

Found it much cheaper on EuropaParts than ECS:
https://www.europaparts.com/crankshaft-position-sensor-077905381f.html

Is that really most likely it? Is there anything else that could throw that code/those symptoms?

FWIW my wife drove me back to it this evening about an hour ago and it started up, so at least I’ve got it in the garage.

#9

Just found it on FCP for $43!
https://www.fcpeuro.com/products/audi-crank-position-sensor-077905381f

#10

The thing that can be so tough on our cars is that the electronic parts dont just always fail they sometimes slowly fail so they will work fine one day and others you have to wait till they feel like working.

#11

Well I got the CPS swapped. Went with the one from FCP Euro (bosch) that matched the one I pulled out.

Interesting observation; the metallic pickup on the sensor one the OLD (failing) one was flush with the sensor housing. On the new one, it actually protruded maybe 1/2mm or so. So perhaps it is not necessarily an electrical failure but mechanical wear of some sort on the sensor. I’ll try to get some pictures up soon.

So far so good! I also used to have an intermittent issue with the stability/traction control system light come one (that triangle thing you can turn on/off manually if desired). When it was on the car would like up upshift very rapidly and make it annoying to take off because it would hit 5-6th gear at the 30mph. I’ve only driven it ~50miles since I got the new sensor in last night but so far that hasn’t come back on… fingers crossed it was the culprit of that issue to!

#12

This is what I had to deal with even after removing the axle heat shield and axle. I ended up removing the trans bolt that holds that transmission electrical line bracket (barely visible, just to the right of the exhaust pipe) and completely getting it out of the way. Those black lines are the trans cooler lines and are a pile of suck:

http://audirevolution.net/addons/albums/images/899081093.jpg

If anyone is curious, this is where the sensor goes in. And what it picks up the “signal” from.

http://audirevolution.net/addons/albums/images/738887512.jpg

Here is the new sensor being installed. Couldn’t fit a socket bit so I went by hand. 5mm. I was generous with the Loctite because I really don’t want to get in there again. Photo was taken w/zoom through the wheel well… there is a lot less room there than it appears lol. This is after the trans bolt and bracket are out of the way.

http://audirevolution.net/addons/albums/images/885798042.jpg

Here is the other end, where it plugs in. It is driver’s side on the firewall. The new one is not yet plugged in in this photo.

http://audirevolution.net/addons/albums/images/886522249.jpg

And finally, here is the new sensor. Note the metal tip protrudes ever so slightly. On the old one I removed, this was completely flush. I am assuming that was the problem.

http://audirevolution.net/addons/albums/images/528573380.jpg

#13

Good for you thats a big bag of not fun. Ive been there before.

#14

Yeah next up is a small coolant leak that I’ve got very little idea how to fix… it is on one of the small rear crossover pipes going into the back of the passenger side head… Took 5 minutes just to get my mirror & light angled the right way to even see it! I need some skinnier arms ;D

#15

That pipe and the heater core connection hose can leak too. Its not a fun job but if you take off the intake manifold and work from the top its not all bad.

Or if you really wanted to make a job out of it for easy access you can pull the transmission and go from under the car.