08 8p intermittent not start

[connor steers]

Hi guy,

I’ve tried the search function and found similar problems to this and done the suggested but the issues still happening wondering if anyone else has any ideas…

my 08 170tdi is having an intermittent starting issue, there’s no pattern to it. Can happen on cold start, when warm but is yet to stall whilst driving. It normally starts after 10 mins or cycling the key. When it starts it drives spot on, no lack of power or dodgey idol, no smoke and it hasn’t once given a fault code or light on the dash.
So far I’ve changed the usual relay, egr and asv which were both well due a change and it’s had a full service. Car was fine for a few days but yesterday played up again. The only thing I can put it down to now is tank fuel pump as that’s the last thing I can think of that would cause a problem without throwing a code.
Has anyone else had this problem? Or anyone else got any ideas?
A mechanics looked it over and suggested the parts I’ve changed and now thinks pump too but I’d rather get the fix right this time!
Cheers

 

[LEE69]

Is it turning over fast enough?

 

[connor steers]

Is it turning over fast enough?

Yeah, cranks as it should every time and then randomly just won’t catch. Leave it 10 mins and I’ve found cycling the key helps and it fires up as normal and drives fine. Not had any stalling issues whilst driving either. I put a new battery on it about 2/3 months ago so don’t think that could be an issue

 

[LEE69]

Could possibly the coolant sensor, not telling the ecu the correct temperature.
Is the temp gauge on the dash sitting and holding 90 deg?

 

[connor steers]

Could possibly the coolant sensor, not telling the ecu the correct temperature.
Is the temp gauge on the dash sitting and holding 90 deg?

Yeah sitting and holding at 90 when warmed up, I did think of that but it wouldn’t explain why it doesn’t want to start at any temp to me. Also i would assume that would give a code/ light?

 

[LEE69]

Yeah it's one of those lol
They are split into two, one side goes to the ecu and one goes the dash (or that used to be the case)
Just thinking out ideas lol

 

[connor steers]

Yeah it's one of those lol
They are split into two, one side goes to the ecu and one goes the dash (or that used to be the case)
Just thinking out ideas lol

Yeah it’s proper frustrating lol.
I’ll have a look, but I’ve been playing with it this morning and the dpf lights just come on, since I changed the egr and asv last week I’m hoping it was just a hiccup and a bit of carbon was lodged somewhere and has now traveled down so gunna take it for a blast and hope it doesn’t break down might still do fuel pump just incase and look at the coolant sensors and I was profanely thinking ams too…

 

[Davill9]

Surely cycling the key would point to glow plug?
I know they are quick start same as Passat sport170 and work continuously in running to help with clean burn but I have had them not thrown faults in past until a while after they had started to break down on the tips
just a thought.
But also had same intermittent issue with tdi’s I worked on and was fuel pump once and crankshaft position sensor twice. The latter is not a nice job in car. A vice, mallet and long Allen key basically but vwag do a special tool I saw the other day

 

[Davill9]

Yeah it's one of those lol
They are split into two, one side goes to the ecu and one goes the dash (or that used to be the case)
Just thinking out ideas lol

Vagcom
Engine
MVB 002 coolant temp

I’m almost sure this shows the ecu temp readings that the ecu would be reading and dash shows the dash

also thinking more now that it sounds like an intermittent crankshaft position sensor is faulty… these never throw a fault either on any that I have ever changed but does exactly this

but you could vagcom the fuel pressure still on diesel to see if correct from tank, and HP side I think somewhere in engine? Long time since I did that on diesels now

 

[connor steers]

So it drove to work and back fine today then suddenly didn’t want to start this evening. Mechanic came and had a look and after cycling the key it fired and he’s suggesting fuel pump still on the thought it’s not building enough pressure on initial turn. Going to give that a go first as glow plugs recently done. Now to find somewhere with one in stock!

 

[Davill9]

So it drove to work and back fine today then suddenly didn’t want to start this evening. Mechanic came and had a look and after cycling the key it fired and he’s suggesting fuel pump still on the thought it’s not building enough pressure on initial turn. Going to give that a go first as glow plugs recently done. Now to find somewhere with one in stock!

Could you not use vcds or even OBDeleven etc and check low pressure side from lp pump before buying just to be sure

 

[connor steers]

Hi again,

so I changed then fuel pump and all was good for a week then suddenly the problem was back.
So as advised above I got the temp sensor and crank sensor and managed to change the temp sensor in the side of the block today, starts fine and drives fine. A judder started on idol after the pump was done but now the temp sensors done it seems to have gone…
Put it on a diagnostic and the revs are reading as they should so surely this eliminates the crank sensor?
I’m going to change it as it was only £20 and peace of mind but I need some help locating it!
I’ve checked the belt side over and over and can’t find anything there and the only one I can see that could be the sensor is behind the oil filter. Is this the right place before I start dismantling more I don’t need to? My mechanic also isn’t sure where it is on that car and you can only just see the connector so isn’t sure it’s there but he’s not Audi trained.
As above it’s the 2.0 8P 170 variant.
Any help would be greatly appreciated!!

 

[Davill9]

Hi again,

so I changed then fuel pump and all was good for a week then suddenly the problem was back.
So as advised above I got the temp sensor and crank sensor and managed to change the temp sensor in the side of the block today, starts fine and drives fine. A judder started on idol after the pump was done but now the temp sensors done it seems to have gone…
Put it on a diagnostic and the revs are reading as they should so surely this eliminates the crank sensor?
I’m going to change it as it was only £20 and peace of mind but I need some help locating it!
I’ve checked the belt side over and over and can’t find anything there and the only one I can see that could be the sensor is behind the oil filter. Is this the right place before I start dismantling more I don’t need to? My mechanic also isn’t sure where it is on that car and you can only just see the connector so isn’t sure it’s there but he’s not Audi trained.
As above it’s the 2.0 8P 170 variant.
Any help would be greatly appreciated!!

I think on these they go through a tiny hole in gearbox/block at 90 degrees with an Alan key that needs to be flexible almost and banana’d and is attached to the rear main seal, well just behind it
I’ll look at the manual in a bit to make sure as it’s been quite a while since I have done a 170 diesel crank position sensor now


Sent from my iPhone using Tapatalk

 

[connor steers]

I think on these they go through a tiny hole in gearbox/block at 90 degrees with an Alan key that needs to be flexible almost and banana’d and is attached to the rear main seal, well just behind it
I’ll look at the manual in a bit to make sure as it’s been quite a while since I have done a 170 diesel crank position sensor now


Sent from my iPhone using Tapatal

 

[connor steers]

I think on these they go through a tiny hole in gearbox/block at 90 degrees with an Alan key that needs to be flexible almost and banana’d and is attached to the rear main seal, well just behind it
I’ll look at the manual in a bit to make sure as it’s been quite a while since I have done a 170 diesel crank position sensor now


Sent from my iPhone using Tapatalk

Would be appreciated if you could as the only place I can find it to be is behind the oil filter housing want to be sure before I start ripping it off

 

[connor steers]

Thought I’d post an update to this incase anyone else has this issue as when I trawled the forum I found a lot of questions but no solution's!

the problem ended up being that timing sensor wasn’t reading the timing properly on occasion. This gave no codes at all 99% of the time and took me leaving the car with a garage to replicate the problem once over a week for it to show. so new belt pump and sensor and car is right as rain. Apparently this is a common problem but I looked for weeks and never came to this answer so hope this helps!
Would have saved me changing egr, throttle body, plugs, fuel pump, loads of relays and other sensors, inlet manifold and more I’ve probably forgotten haha.

 

[Davill9]

Thought I’d post an update to this incase anyone else has this issue as when I trawled the forum I found a lot of questions but no solution's!

the problem ended up being that timing sensor wasn’t reading the timing properly on occasion. This gave no codes at all 99% of the time and took me leaving the car with a garage to replicate the problem once over a week for it to show. so new belt pump and sensor and car is right as rain. Apparently this is a common problem but I looked for weeks and never came to this answer so hope this helps!
Would have saved me changing egr, throttle body, plugs, fuel pump, loads of relays and other sensors, inlet manifold and more I’ve probably forgotten haha.

Hi mate,
Was it camshaft or crankshaft sensor in the end ?
camshaft one yeah ?