Ongoing UrS4 problems...

[hunker7]

Hi guys. I am still having troubles with my UrS4, and I have ran out of ideas completely.

She's Stage 1 chipped, so she should boost to 2.5 bar, but she will only do 2.3 bar. It's not just the lack of boost. She is very sluggish and heavy, and not responsive enough. Around town it is pretty hard to drive, as I need to push pretty hard to get some momentum. Fuel economy is about 14mpg (doesn't change much if I drive her hard). Idle is perfect, smooth, no shakes or misfires.

Things that I have checked so far.

Boost test - No leaks.
MAF - New
Knock sensors - New (torqued correctly)
Exhaust - checked for blockage
Timing - Checked and correct.
TPS - Checked
Lambda - New
Filters - all new
Vacuum lines - triple checked
FPR - checked

Can't connect vagcom atm, as win10 is being a little bitch. I will try and order reader off ebay. But this problem has been going on since engine work that was done over summer, but engine has been out again since and everything is top notch.

I do want to thank John (newsh) as he's been helping me out tons, since I got my red S4. Without him I think my car would be in the local scrap yard.

John suggested possibly MAP sensor is faulty, anyone have experienced faulty MAP sensor?

Also, is anyone around Leeds and could lend me ECU to try in my car and see if that fixes the problem?

Thanks in advance.

[Dynasty]

Do you have a extra pressure gauge connected to the intake manifold (relative pressure gauge)?

[hunker7]

I don't, no.

[Dynasty]

Then you should get one (to verify that your map sensor is measuring the correct manifold pressure).

[soederblom95]

If the vacuum line to the ECU is broken then the BAR measure in the instrument cluster should show 1.0 constantly? Atleast if the hose is completly broken.

Edit: one thing that i did to my urs4 when it was struggling with the boost pressure was that i removed the exhaustpipe between the wastegate and the downpipe, then put a cap on the downpipe inlet. Then i could hear if the wastegate would open or not. If it doesnt open then it would probably only be an mechanical fault.

[hunker7]

If the vacuum line to the ECU is broken then the BAR measure in the instrument cluster should show 1.0 constantly? Atleast if the hose is completly broken.

There are no leaks from moisture trap to ECU or within the ECU.

[hunker7]

If the vacuum line to the ECU is broken then the BAR measure in the instrument cluster should show 1.0 constantly? Atleast if the hose is completly broken.

Edit: one thing that i did to my urs4 when it was struggling with the boost pressure was that i removed the exhaustpipe between the wastegate and the downpipe, then put a cap on the downpipe inlet. Then i could hear if the wastegate would open or not. If it doesnt open then it would probably only be an mechanical fault.

I'll try this when I get a spare minute

[UrS4boy]

How was the exhaust checked for blockage? Sometimes bad fuel etc clogs the matrix in the cats and this results in a very sluggish car. Test by temporarily removing the exhaust system from the downpipe back (watch where you test it though - it will be loud).

[hunker7]

How was the exhaust checked for blockage? Sometimes bad fuel etc clogs the matrix in the cats and this results in a very sluggish car. Test by temporarily removing the exhaust system from the downpipe back (watch where you test it though - it will be loud).

That's exactly what I did, removed before cats and no luck. Sound was good though.

[mike74]

Have you checked the resistance on the altitude sensor? It can affect boost as if the value is off, the car thinks you're at the top of the Alps and reduces boost.

[hunker7]

Have you checked the resistance on the altitude sensor? It can affect boost as if the value is off, the car thinks you're at the top of the Alps and reduces boost.

I haven't checked resistance, but did try and disconnect it and weirdly car still was boosting to 2.2 but with occasional misfire and was even more sluggish.

[newsh]

I'm pretty sure if you disconnect the altitude sensor the ECU is supposed to enter a figure for sea level or 200m above or something like that.

[hunker7]

I'm pretty sure if you disconnect the altitude sensor the ECU is supposed to enter a figure for sea level or 200m above or something like that.

I disconnected knock sensors, tps, altitude sensor and nothing limited boost. Disconnected TPS caused car to be jerky, knock sensors caused knock and altitude did the same.

[UrS4boy]

F96 Altitude/Barometric Pressure Sensor Information

I'm pretty sure if you disconnect the altitude sensor the ECU is supposed to enter a figure for sea level or 200m above or something like that.

Well, something like that.


F96 Altitude/Barometric Pressure Sensor Information:

http://forums.quattroworld.com/s4s6/msgs/21892.phtml

[newsh]

Ah! Charge pressure reduced to minimum!