Jds8086

My name is Jake this is my first thread here. I recently purchased a 1994 90cs with the 2.8 12v. Bought as a project, has no spark. Previous owner went crazy and started replacing everything (ignitior, coil pack, wires, plugs, alternator, battery, etc.. you get the point). So I started with hooking my scope up to the cam sensor, it has three wires, a power, a ground, and signal. I'm getting good power and ground but the signal wire has me concerned. Do these have a bias voltage? If I unplug the sensor I get about 6th on the signal wire, plug the sensor back in, same reading, put a price of metal in between the sensor and the magnet and the voltage drops maybe 300mv at the most which I know isn't right but mainly what I am trying to figure out is if the sensor is supposed to pull the signal wire up to 12v or down to ground? I just want to make sure I don't have a wiring issue before replacing the sensor. Thanks in advance for any help.

Rusty Spokes

Can
you check for error codes? The camshaft sensor is cheap $16 ..I used one with no issues from Hans:078905161C $16 VW Audi Camshaft Position Sensor 80/90 100 A4 A6/S6 Cabriolet V6

Jds8086

Well i think i got it figured out. The signal wire is evidently supposed to have the 6v on it i was seeing, and the cam sensor is supposed to pull it down to ground. I hooked my scope up to the ignitor (guy returned the coil pack when it didn't fix his problem so the car didn't come with one), then i cranked it while manually pulling the signal wire to ground with a test light and i did see activity from the ignitor. So it does look like all it needs is a cam sensor (and coil pack of course). I ordered them and i will post my results when i get them installed.

On a side note, i know nothing about these cars, this is my first audi, is there any good references for general knowledge and known common issues out there to get my feet wet with?

Thank You

Jds8086

Here is a follow up for anyone that may come across this thread in the future. The old cam sensor was most definelty bad, the way the signal circuit should work is the voltage should be 0 with the cam sensor plugged in and nothing in the way, i had 6 volts. Also as said before when i did put something in the way of the sensor i actually had a drop in voltage not a rise. With the new cam sensor i now have 0 volts with it plugged in, and when you place something between the sensor and the magnet it goes to ~5v. I installed it and hooked up my scope to all three outputs of the ignitor and the picture attached shoes what i got. Before there was no activity when cranking from the ignitor. Looking good, now i just have to wait for the coil pack to come in.

Jds8086

So I got the coil pack today and installed it. It will start for about half a second and die. I get injector pulse while cranking and for the short time it is running but the injector pulse stops shortly after it starts. If i Unplug either the engine speed sensor or timing sensor(?) It cranks but does not fire at all which I am assuming means they are doing something. I will put my scope on them later and see how they look. Fuel pressure is good. Any direction on this I would appreciate.

Rusty Spokes

The usual suspects are the camshaft sensor, camshaft sensor and ignition switch..kinda sounds like your ignition switch.."50" is the starter circuit and "15" is the ignition on running position..some things power up off of "50" and once running switch over to "15" ..if the switch starts failing..all kind of weird problems can happen. They crack at the top. Get an OEM switch if you find yours is defective..lots of junk out there.

Jds8086

Thank you, I will check the ign sw as well. I thought I had ruled that out by holding it in crank to see if it would stay running (yes I know not a good idea but it only fires a few times it doesn't gain much rpm). It still died while trying that but I suppose they could have been creative and made it so it wouldn't function that way.

Rusty Spokes

I think the 1994 models had an OBD-2 and if so see if someone has a Ross Tech license nearby and can run the codes. If you have the 2x2 data link..somewhere in the search you can find the blink codes to help find the problem using a paper clip.

Here is a link:12v Pages - Maintenance

I have several Audi cars and just bought the license and the USB connector from Ross Tech..a worthwhile investment.

CRAZY_RUSSIAN

he is still obd-1, obd-2 was installed in 96+.
so blink the codes and let us know btw, awesome diag tool i've bean wanting to get an oscilloscope for a while now