Tried Everything but the fault won't go.......... Help Please

Adam P

Adam P

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Right as the title says I'm nearly at the end of my patience with this fault on my 8l s3 now. As some of you will know i put a rod through the block last year on my old engine, i sourced a second hand engine, took it apart rebuilt with IE rods, added a few mods and Bill @ badger 5 mapped it in October and it has been great.

A couple of months passed with me enjoying the car thoroughly. Then just before Christmas the car started to struggle to start, then when eventually it did after 4-5 tries and feathering the accelerator i got a fault light. Plugged in the v-gate scanner and a mates vagcom and i has the cam position sensor fault. So i sourced a new genuine cam position sensor, installed it, whilst i was at it i changed the fuel pump for a new one as that was tired too and made sense to do them at the same time. No change, still struggles to start. So i have had the timing checked as we did a cam belt change during the rebuild. It was fine. It also had new spark plugs, 2.0 tfsi coil packs and a new crank position sensor as i read this can trigger the fault too. I must admit when the car is running and taken for a drive, its drives perfectly with a good idle, pulls strongly through all gears with no hesitation. Im stumped!!!! the last thing i can check is the cam chain and the spacing between which i am going to do this weekend. If i was to go and start the car now it would turn over and pop and bang out of the exhaust, then about the 4th time would splutter into life. Fuel filter has been changed recently too.

I thought i would post this up as the forum has always been a great place and helped me out a lot and is worth a shot just in case someone else has by any chance had the same issue.

Thanks in advance.
Adam P
 
Is the car giving cam fault after changing it?

Check the iat sensor to make sure it's sensible.. S3s can suffer from cold start issues (oem map) due and with the recent cold weather could be that.. Have you removed the sai etc?
 
just out of interest have you done a compression test? if your still gettin the cam sensor fault after replacing it, then maybe try looking at the loom that lead to the sensor, broken wires can be a right arsh.
 
Check the maf is clean, ait sensor as mentioned and coolant temp sensor.
 
Thanks for the replies guys. After writing this post i went outside to start her. 11 times it took then she eventually started. But this time for once, no fault light or codes. Had a chat with another forum member and were thinking it could potentially be a fuelling issue. Going to check the fuel lines, fuel rail, fpr and get the injectors cleaned and tested.

Beach buggy where is this sensor located? is that intake air temperature? please can you confirm what you mean by sai? I'm still learning all the terms so sorry.

I haven't done a compression test yet, parts of the loom were rewired/soldered properly, i took the loom apart last weekend to double check my joints and the route back to the ecu and the cable is good condition. I would agree with you partially that it could be electrical as it has deteriorated over time then just stopped.

More investigation over the weekend.
 
SAI = secondary air intake system. Mine doesn't have one as its a BAM engine so not sure if yours has one or not.

Defo check the fueling as when it runs if its all ok it has to be something to do with the start up procedure so do the basic checks and make sure its getting fuel to all the right places and holding pressure too.

You will defo get it sorted mate its gotta be something simple just have to find it :)
 
Yes air intake temp sensor, in the inlet plenum next to the throttle body with multi plug on it
 
Check the fuel pressure regulator, may be allowing too much fuel through if the diaphragm is split, or even leaking fuel into the vacuum pipe, flooding the engine on start up.
 
Thanks again for the responses guys, appreciate it.
Will have a look at the air intake sensor, and the fueling system tomorrow if i get the time.
I do have a day off next week so might be then.
Planning on removing the fuel rail and fuel lines to check for blockages or damaged pipes as well as the FPR.
Will report back either way.
 
Ideal opportunity to check the fuel pressure regulator as its attached to the fuel rail.
 
Going to be getting to work on the car tomorrow, will be removing and looking at everything mentioned.
Superkarl, the engine had a new crank sensor just after the rebuild so i would like to think its not the culprit and its hasn't flagged up.
 
Just read implausible signal mate. I have removed the throttle body and it looks like the ait sensor is filthy, tried to remove this at lunch time at work but the bolt holding it in is nackered so will be drilling it out tonight and cleaning the sensor. If this doesn't solve the issue i will strip the fuel system down and check pipes and replace fpr, failing that I will send the injectors away to be flow tested and see where we are after that. I love my s3, when it ****** works!
 
Right got the ait sensor out, looks pretty coke'd up. Not sure whether to clean or just buy a new one. Any thoughts?

 
That's defo dirty dude so give it a clean but be careful as they can be damaged during cleaning. But I am pretty sure the car should still start ok even with that sensor unplugged so I don't think its the issue your looking for.

I would wonder why it was that dirty though as its not been long since you did your engine rebuild

Also out of interest how much fuel is in the tank at the mo?
 
Yeah I was going to also mention the fuel quantity as vrbob has had trouble with this in the past. Did you ever get it resolved vrbob?
 
s3mad_dude said:
Yeah I was going to also mention the fuel quantity as vrbob has had trouble with this in the past. Did you ever get it resolved vrbob?
Click to expand...

Yes mate mine runs perfectly now and will start first turn of the key even when basically running on fumes.

I took the fuel system apart and had the injectors serviced. Made sure it was all nice and clean and that the FPR was in good condition (o rings) I also replaced the fuel lines in and out of the fuel rail too. As a precaution as was having my car stage 2 mapped I also changed my fuel pump.

i think alot of starting issues are done to the fuel rail losing pressure a bit due to leaky o rings etc and it takes a few cranks to re build the pressure
 
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maybe a bit obvious but have you cleaned the earths under the battery? mine were caked up with green oxidisation and i had half a dozen faults inc yours, gave em a good wire brushing and they all cleared up, might be an easy fix and a 10min job.
 
Got a new ait sensor on the way and a new fpr just for piece of mind. I think the coking up could have been down to running with the n75 unplugged for running in potentially.
Thats an idea, jus3in i will have a look, got Friday off to get stuck in so fingers crossed i can cure it and start driving it again.
 
Right, an update, replaced the frp and the ait sensor and the pipe between the fpr and the inlet as this looked bad and worn with some breaks.
Checked all the fuel lines in the bay and wiring and sensor connections. And it still won't start, the car turns over and i get pops and bangs out the exhaust......... then after about 5 tries it will splutter into life and runs perfect and drives with no faults. Think the two next things to try are cleaning up the earths under the battery like Jus3in suggested then if no improvement remove the injectors and send them off? Failing all this il have to call Bill and book it in.
 
Did you change the CTS for piece of mind?
It might be a good idea to log as much as possible when turning the car over on cold start, you may be able to make some more sence of what's going on and elimate things as well.
If your seeing rpms you could probably eliminate the crank sensor, unless it was an aftermarket one?
I've had cold and warm start issues and know how annoying it can be, don't give up!
 
i'd revisit the crank/ cam timing tbh . That will account for the pops n bangs etc and the implausible signal
 
Have you unplugged the maf and tried to start it?
 
Latest Update, ecu area and connections all bone dry and connected, no water ingress atall.
Went to gsf and bought a new crankshaft position sensor and installed for piece of mind.
Still have the same issue, turning over with pops and bangs. This is the fault on the scanner.



Tufty has been very helpful as well as you guys and has suggested to revisit the cam to cam timing like Broken Byzan is suggesting, so will be doing that myself next. Then if that is bob on it has to be an electrical fault somewhere and il need to get a specialist involved.
 
audi upgrades
You may have to bite the bullet and have a full diagnostics from Audi or a specialist.
 
Latest update:

I am going to check the cam to cam timing this weekend, i cannot seem to find a how to DIY check list for this anywhere??? Basically a step by step guide on how to check this.....
As all i have is a garages word that they have checked it all, so it would be great for piece of mind.

Failing that i have found a replacement loom, this is the engine sensor side, and would eliminate any of the re-solders i have done. So that's a potential option as well if the cam to cam timing is correct as i suspect it is.
 
Was gonna say I am sure I have posted on this subject before :)

<tuffty/>
 
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Sorry i have been away, so update.
The cam to cam timing is fine therefore i purchased an uncut or modified loom from ebay. Spent last weekend stripping out the old loom (engine sensor side)
Have managed to get the new loom plumbed in. Have the rear oil level sensor to reconnect and put the battery and everything else back in. Fingers crossed, then i can enjoy the car through the summer. Will report back.
 
Right the new loom is in, double checked cam to cam timing again. She fired up. Took her out for a run, parked back on the drive, came back after ten minutes and ..................... ********!!! same issue again! Wont start, turns over and back fires out the exhaust then throws up cam postilion sensor fault again. I am going to try one more thing.
When i have replaced the sensor before i have used a cheap one and a middle of the range one from GSF. I have read that sometimes a genuine sensor can sort a fault and that's what im hoping. Its near on £100 instead of £30 but if it fixes this issue its worth every penny! Fingers crossed otherwise its a long dive to see Bill @ Badger 5.
 
Only other thing I can think of is the cam position sensor wheel has moved or something

<tuffty/>
 
The starting issue that I had was a slightly leaking injector, I did have mine tested twice and they said they were fine. But when the engine was warmed up and left sitting for any more than 10min it would have an extended crank before actually firing up.
take the car for a really good drive and get it good and warm, come back and remove the rail and injectors with the pipes still connected if that's possible, turn the ignition on to prime the rail to full pressure and check the end of the injectors for any fuel leaking.
I know this sounds stupid but that's what gave me my starting problems.
Have you checked your overall timing, to the crank just to be sure?
 
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