Maf Issues/overboost

[juperwort]

2001 Sharan TDI AUY engine. Auto

Hey folks

 

Having loads of issues with the dreaded overboost and limp mode.

 

I have VCDS logging and want to confirm some numbers with you.

 

Firstly, turbo vanes move as should, and line to actuator holds vacuum well. ( lying under car with hose in mouth, can suck and vanes lever moves to full extent. Plug pipe with tongue holds in position) yuk.

 

Logging blocks 003 and 011 whilst on a drive around.

 

Firstly I notice that actual MAF readings are constantly higher than required by 200 to 500. This is obviously wrong. Can it re recalibrated?

 

I notice that boost required and actual follow themselves quite closely, until....the MAF actual reading hits 1249.5. After 5 seconds or so, the duty cycle of the MAP hits 92.4%, then stays there until you turn it off. Limp mode on.

The EGR duty cycle moves around a bit whilst driving, but again, hits 84.5% and stays.

 

I have followed vac lines to N75 and its mate, and have checked as many ends as i could get to.

 

I cannot afford to throw money and parts at it, and I know these conditions are notorious to pin down.

I am tempted to start with a new MAF.

Anyone agree?

 

Thanks

Edited January 23, 2011 by juperwort

[Jayton]

You read this guide? <_<

http://uk-mkivs.net/forums/t/394072.aspx

 

Hope that helps, sounds like you've not got boost leak and the vanes are OK. Do you know someone you could swap the MAF with before spending out on one and find it doesn't resolve your problem.

[juperwort]

You read this guide? :)

http://uk-mkivs.net/forums/t/394072.aspx

 

Hope that helps, sounds like you've not got boost leak and the vanes are OK. Do you know someone you could swap the MAF with before spending out on one and find it doesn't resolve your problem.

 

Thanks

 

Yeah, I've seen that one. In fact I think I have read them all, which gets me more confused. I am from air-cooled world, so no go with friend with MAF. Anyone in Nottingham with a spare I could try ?

 

It seems my readings, in plenty of graphical forms, doesn't quite match any of the symptoms explained.

 

Both MAF and boost actuals are higher than specified, MAF more so. I was going to chase the boost pipework along to check for leaks, and maybe have a peer inside EGR too see see how caked up it is.

 

Are the duty cycles realistic?

 

If I unplug N75 outlet to vanes, and/or N18 to EGR, would I be able to feel vacuum if parked up & someone on the throttle?

 

J

[FLENG]

im in nottingham

i havent got a spare but you can use mine to diagnose if you want..

[juperwort]

im in nottingham

i havent got a spare but you can use mine to diagnose if you want..

 

Bit of an update. MAF replaced, and certainly improved things like power and smoothness.

 

However, whilst checking vac hoses, I found that i could suck on the hose to EGR, and cannot create vacuum. This would point to EGR diaphragm shot, correct?

 

I tried a run with the EGR vac hose plugged, and it ran terrible, with jerky gear changes (auto) and sporadic brakes, mainly going on very violently.

 

Please correct me if I am wrong, but If I had a vac leak effectively at EGR, then would N75 be able to control turbo vanes effectively? ie, if N18 duty cycle is at highest, and boost needed to be turned down, would it happen ?

 

 

 

Could this be the source of my positive deviation ?

 

 

 

Thanks