Unknown boost issues

[Coolbluelights]

ok where to start , when you floor it the boost cuts in and out making driving very difficult, I have noticed that after a while of driving it works absolutely fine although it will hunt on idle. When the engine is cold it struggles to start runs very lumpy and stalls sometimes, the only code I get and keep coming back is p0340 which I read was related to the cam sensor, so far I have put new can sensor, maf sensor, bv, and the solenoid for the turbo waste gate, I have even installed a new turbo hoping this might rectify it, there are no boost leaks that I can find either

I don’t know where else to look

 

[Stuart B]

have you done a smoke test? (it sounds like a leak - under the inlet manifold or under the cross member)
is it mapped?
if you electronically disconnect the N75 and drive it around does it still cause an issue (it will only be about 6/7psi boost)

it sounds like you have spent an awful lot of cash on this before approaching a forum, there are some real experts here. I am only a beginner.

 

[Coolbluelights]

No I haven’t done a smoke test mainly because I don’t own one, it’s on a standard map and I’ve swapped out the n75 valve for a new one with no change in Results

 

[Stuart B]

yeah unplug it - it'll help determine whether the issue is to do with boost pressure or not. without the electronic control it will be about 6/7 PSI connected ~ 12PSI (It'll feel like the handbrake is on) but if it is smooth then highlights the boost pressure issues.

what type of scan tool have you used VCDS or a third party device.

there's quite a lot of vacuum pipework which can cause issues with running.

I had a split pipe on the side of the manifold and under the cross member, along with breather leaks etc - and even the Turbo Intake Pipe can split causing issues with MAF readings where unmetered air is drawn in from other holes.

 

[Coolbluelights]

Ok so I unplugged that sensor and it didn’t come in and out of boost like it has been doing which is good but there was also no difference in power it felt just as quick as it always has

 

[Coolbluelights]

I just went back out in the car with the N75 unplugged and it started doing what it did before, coming in and out of boost, flat spots around 3k, it like it cant decided whether it wants to boost or not

 

[<tuffty/>]

Get a smoke test done as it sounds like a leak... any fault codes?

<tuffty/>

 

[Coolbluelights]

Get a smoke test done as it sounds like a leak... any fault codes?

<tuffty/>

the only code i get is p0340 or p0430 i cant remeber but it points toward the camshaft sensor, but i have already replaced it with a new one

 

[<tuffty/>]

If the cam sensor fault is coming back then the ECU is clearly not happy with the situation...

Cam position is pretty important for the engine to run properly... if the ECU is still having issues and reporting a fault then its never going to run correctly

<tuffty/>

 

[<tuffty/>]

I don't think you have a boost issue... I'd say its related to the cam position fault...

Have you had any work done on the head?

<tuffty/>

 

[Coolbluelights]

I don't think you have a boost issue... I'd say its related to the cam position fault...

Have you had any work done on the head?

<tuffty/>

No work has been carried out on the head as far as I’m aware

 

[Stuart B]

Are you sure its not misfiring?

What have you scanned it with? Android torque? Snap on?, elm327 , vcdslite?

 

[Coolbluelights]

it is miss firing on idle, and I scanned it with that cheap eurocarparts scanner

 

[<tuffty/>]

needs scanning with VCDS mate... cheaper scanners miss some of the more useful codes... ideally needs logging on the road or preferably a dyno to see whats actually going on

<tuffty/>

 

[Coolbluelights]

i just had a look at vcds and they are expensive :0, is there another alternative?

 

[<tuffty/>]

Info in this thread from the FAQs

https://www.audi-sport.net/xf/threa...lp-please-read-before-posting-updated.168407/

<tuffty/>

 

[Stuart B]

i just had a look at vcds and they are expensive :0, is there another alternative?

As I am sure tuffty has pointed you to the FAQs to read about free vcdslite and a cheap blue KKL lead from eBay for a fiver or so. That's all you need. Its probably a faulty coil or spark plugs. These Audi's are sometimes a nightmare to get a misfire reading logged, you might be able to get a log if you disconnect the N75 and just keep your foot flat when it starts shaking, until the eml light starts flashing (N75 disconnected to avoid damage due to boost spikes) but vcdslite should show up the faults.

 

[Coolbluelights]

It would appear that I don’t actually have a engine light

 

[Coolbluelights]

Well would you look at that lol

 

[<tuffty/>]

Shocking but not unsurprising... seems to be the norm for people selling these with issues... as most people don't take a scanner to see a car sadly...

<tuffty/>

 

[Coolbluelights]

Erm big problem, it’s now misfiring badly, won’t rev past 3k and has a very loud knock from the top of the engine

 

[Coolbluelights]

And now it won’t start at all

 

[antwan64og]

vcds is the first port of call, to see if it gives you a big clue whats up?

what engine/ecu is it?

 

[Coolbluelights]

All I know is that it’s a aum engine

 

[Stuart B]

As others said get vcdslite downloaded and use a kkl lead to get the fault codes. I wouldn't keep trying, its misfiring and you can't fix it by just running it. You need to find the cylinder move the coil see it the fault moves, and also change the spark plugs even of the coil is clearly the issue.

 

[<tuffty/>]

if its knocking from the engine I wouldn't be running it tbh... need to take the cam cover off and check things out

<tuffty/>

 

[Coolbluelights]

Well unfortunately my a3 has gone to car heaven, something when catastrophically wrong and there’s no compression on any of the cylinders even with all the valves shut, I imaging valves have come in contact with pistons somewhere along the lines and killed it, thanks for all your help though

 

[<tuffty/>]

belt jumped a tooth or something I suspect... also plausible that the cam pully keyway has broken... any of those would potentially cause the issues you experienced...

Sad times but 1.8t engines are pretty cheap these days

<tuffty/>

 

[Coolbluelights]

Ok I’m back, I decided to fix her, new head etc, she now runs perfectly however on the test drive to get some water for it , I noticed after the half mile drive that the cam belt has worn away in the centre so much so that the cords are on display, it’s as if something has been rubbing up against it while running however I couldn’t find any foreign objects and the belt seems very loose so before it snaps I’ve left it , not sure what I should do because I don’t want to put another belt on for it to be useless after a mile of driving

 

[hydro s3]

I think I read on here of someone's belt rubbing and they where told to check the cover because if that's not on right can rub on the belt.

 

[Stuart B]

He said the belt is loose. Did you pull the grenade pin from the new damper after you replace the head etc?

 

[Coolbluelights]

Have a look at this

 

[<tuffty/>]

Would imagine thats contributing to your knocking noise... plausible the tensioner is damaged and the belt has slipped..

<tuffty/>

 

[Coolbluelights]

Would imagine thats contributing to your knocking noise... plausible the tensioner is damaged and the belt has slipped..

<tuffty/>

This is after I replaced the head a couple days ago, new belt and tensioner there

 

[superkarl]

This is after I replaced the head a couple days ago, new belt and tensioner there

and pulley?

 

[Stuart B]

saw one similar on TT forum where two of the engine mount bolts had snapped and they belt was rubbing on it near the water pump.

(caused be re-using and then overtightening the main engine mount bolts from mount to head.)

 

[<tuffty/>]

This is after I replaced the head a couple days ago, new belt and tensioner there

Unfortunately this suggests that you may not have fitted it correctly... could be something has come loose or been dropped down in the belt area causing the damage...

Easy enough to do... I managed to tweak the lower metal cover when I did mine a fair few years back causing it to take the outside edge of the belt out... had to take it all apart and replace the belt

I would suggest you check the timing top to bottom... physical TDC off cyl 1 and check the exhaust cam is at TDC too (cam cover off and check timing mark on the chain end of the cam)

Either way you will need to replace the belt so should be obvious while doing that whats caused the damage

<tuffty/>

 

[badger5]

an errant bolt or nut sat in the lower cover I imagine from that damage