3B swapped US model 90 running issues

[Racerguy381]

Done all that Newsh... The ECU I have is a stage 1 chipset. But I have a stock ECU I tested and the car runs the same.

[Racerguy381]

Good news I figured out the source of the problem! It was the damn Vortech BOV and the vacuum line running to it. Soon as they undid the vacuum line the car runs perfectly fine! Anyone know why this would be or do I just need to not run the vacuum line to the top of the BOV considering it just vents to atmosphere and not back into the intake.

[andy10v]

Motronic is not designed to run an atmospheric blow off valve, it should recirculate. At idle engine vacuum pulls the diverter valve open and then the MAF is not metering the airflow into the engine and will not fuel correctly.

You can fit a stiffer spring to prevent idle pulling it open, but soft enough when you lift off boost it will open, you will still get incorrect afr when you do that as air that has been measured into the system is now lost.

I would just set it up as per OEM.

Or pressure mount the maf and live map, or switch to speed density if you really want it to go whoosh.

[Racerguy381]

Thanks for the info Andy! I was thinking of possibly running some kind of one way check valve in the vacuum line to keep it from opening under vacuum but still pressurize the BOV under boost.

[andy10v]

The vac line provides boost pressure to keep it shut, and vacuum to open it.

[Racerguy381]

Exactly but if the spring is light enough it won't need any help to open under vacuum. The Vortech valve has an adjustable spring tension on the top.

[UrS4boy]

By-pass Valve Info

Exactly but if the spring is light enough it won't need any help to open under vacuum. The Vortech valve has an adjustable spring tension on the top.

Here is how a By-pass Valve is supposed to work on a 3B/AAN/ABY/ADU:

Read this: By-pass Valve Info:

http://forums.quattroworld.com/s4s6/msgs/20994.phtml

[etsola]

Question like that, what is the stock vaccuum the diverger valve needs to open ? 1.3 bar ?

I have a dahlback racing diverter but unknown spring strenght in it. I want to test it before putting it in.

Glad you found your issue ! I have 1990 CQ swapped with a 3b

Thanks

[Racerguy381]

Now it's on to sorting the last little bit of wiring. My cooling system isn't operating correctly yet and a few gauges aren't reading properly either. Should be easy from here on out though!

[UrS4boy]

Question like that, what is the stock vaccuum the diverger valve needs to open ? 1.3 bar

You need to do some review of what vaccum means in Bars.

A strong throttle off vacuum on an AAN (for example) is around 22 inches of mercury (Hg). This is only about 0.745 Bar. The diverter valve should be open way way before that, like 5 inches of Hg or about 0.16 Bar (don't quote me on that but it will be a very small amount of vacuum).

[etsola]

Ok, what strenght should be the spring then ?

[Racerguy381]

Great info guys! Thank you so much for your help!

[UrS4boy]

Ok, what strenght should be the spring then ?

Force = Pressure x Area (e.g. lbs/sq in x sq in OR N/m^2 x m^2)

[Racerguy381]

Ok so I could use a little more of all your expertise on this. I'm down to the last few little things I need to sort out and one of them is the oil light flashing on the auto check computer. I'm pretty sure I have the pit out correct but not 100% positive since I do not have an English version of the wiring diagram for it. Blue with a black tracer is the wire I believe that needs to be in pin 24 of the yellow 26 pin connector. Or does it need to be in pin 19 of the white 26 pin connector. Either way I've tried it in both in the light still flashes in the auto check computer. Any ideas what else it could be? Or does anyone have a English pin out for the auto check?

[UrS4boy]

So you do have this?

http://www.isham-research.co.uk/quattro/wiring/TypC4/Audi_100_Auto-Check-System_Mj1997.pdf

But you don't have this: http://12v.org/urs/audi_c4_wiring_diagram.pdf ?

If you don't download and save and then go to Figure 40 on pg. 51/113, tracks 118 and 120 should be what you need. Or NOT (they are AAN-based, not 3B).