aftermarket gauge questions

[Ameer Antar]

>2) What PSI would be appropriate for a fuel gauge..they are availible in
>0-15, 0-30, and 0-100 PSI. I assume the stock system on the 89 90q doesn't
>put out 100psi, but I really don't know...any help?

the max that you will ever see is 90 psi between pump and fuel dist, so 100 
psi is best. The thing is w/ CIS there's not much point in seeing the fuel 
pressure. The gauges are expensive if you get the sensor type and fuel 
leaks can cause lots of scary problems, like a burnt out Audi if you use 
the direct type [fuel line actually attached to gauge]. In CIS you need to 
monitor more than just one fuel pressure reading, but there's not much need 
to see it while driving unless there's a problem, b/c CIS is very different 
than EFI. If there's a problem, yer better off w/ a real test gauge kit 
which will more accurate and easier to read, but again really only 
important if yer having problems.

>3) In mounting an airfuel mixture gauge, I understand they use a 5 wire O2
>sensor...will it be necessary to add a second O2 port to the exhaust
>manifold, or does it replace the stock unit...I assume if it replaces the
>stock unit then the stock system is able to read off of it?

AFR gauges can work fine w/ single wire o2 sensors. Any sensor, single or 3 
wire, has only one signal out wire. The other 2 wires are for power and 
ground. If you have a single wire sensor, your job is easy. Right now the 
o2 sensor wire connects to the ecu directly. You need to change it so the 
sensor wire goes to both the gauge and the ecu. A good splice/solder and 
heat shrink will dot the trick. You may want splice the o2 sensor wire 
side, not on the wire from the ECU, so that you don't actually need to cut 
into the cars' harness. When you replace the O2 sensor you'll have to do it 
again, just splice the new o2 sensor's wire into the old sensor's wire. If 
you have a 3-wire sensor, you just need to find which one is the o2 signal. 
Using a multimeter, do not test resistance of the o2 sensor ckt, or you can 
damage the sensor. Just measure voltage and you can find the one wire which 
is 12V and ground. The other is the signal. A wiring diagram could help. 
All this will make sense when you get all the parts together.

>4) Seeing as I've already got Coolant temp, Oil Temp, Oil Pressure and a
>Voltmeter...are there any other gauges that would be particularly helpful
>in seeing more of what's going on with my car?

I think boost AFR and boost [unless it's non-turbo] would be the main ones. 
I also like seeing oil pressure, not just a warning light. I got  a goos 
deal on a 3 gauge package from R&E Racing, but there are plenty of others. 
good luck.

-ameer