silverd2

The starter would turn with bad crank (engine speed) sensor, but fuel pump would not activate. You could have a bad switch AND a bad crank sensor...you got the code AND you have no-start when starter turns...just a theory, but possible.

The drawing below shows relays (under passengers feet, in "central electrics") on a US 97 model..not sure if yours is the same. The number stamped on the relay is just a production number, not matchable in a manual...they vary from car to car & new ones likely have different numbers. The number location on the panel is the only consistent checkpoint (small number stamped on receptacle. The numbers in the drawing (J207) are Audi's designations, not on the relay.



Your CEL (yes lightning bolt inside engine icon) should come on with the ignition before starting, then go off (if OK)with engine running. If it's not coming on with ignition switch, the bulb (changeable) could be burned out...it happens. (Drawing is from Bentley "1997 bulb designations") >>>

pocketchange

How about checking the starter voltage and the other connections (grounds too) under the car?

Follow the flow... battery, starter, switch, etc., etc..

Try to do things in (some sort of) order sos not to go nutz !!!

It's acting like you have a intermittent ground problem between the switch and starter??

Do you have a friend with a scope? It would be well worth the money to locate someone.

Case in point; A nice little Caddy (that had gone swimming with the last flood) was drug in the other day. The owner had spent lots of time, effort, money with no luck. Plugged in the scope and had it running within an hour.. (crudded up relay.)

good luck, pc

Proph3t

I agree with the fact I seem to have 2 issues. Bad ignition switch which explains to slowly increase times over the past few weeks that I've had a no crank situation, and then on 2nd or 3rd try its ok.

...then once it is cranking it wont fire now due to the crank position sensor, as shown in the error codes everytime it has cranked. Might also explain some of the odd engine response and idle issues I've had here and there, not major things, but just something I noticed.

The Central Electric Panel is the same as mine. Relays 4 and 6 have been my main focus at the moment, but I guess 1 should be active too at crank right?

In regards to the CEL, I honestly cant recall ever seeing it. Like you said might be a blown bulb, or in some strange cases I've heard some A8 didn't come with one, and just have a dummy plug inserted. I'll check the handbook and see if it references the CEL.

Really appreciate you going to the effort with the pictures, good to confirm this stuff visually.

I'll strip out the ignition switch and look for obvious wear or damage there. Once I get it cranking I'm confident the Crank Position Sensor will be the non-start cause.

Proph3t

Thanks for that

The major issue I have is that its parked on a busy street so legs-out under the car isn't really possible (unless I get some witches hats), so getting to the starter, let alone the crank position sensor or located bad earths is kind of hard, especially since its lowered haha. But dang it, I'll just go jack the damn thing and get under there from the front, neighbours can deal with it

Battery is sitting pretty at 12.5volts, new clamps and cleaned terminals.

So the connection from the switch to the starter is the "exciter wire" that I've read about? I'm assuming the starter has a fairly direct connection to the battery and this wire from the switch, via the start relay, fires the starter? Am I close?

Big question, which side is the start on? Cant see a thing from up top. Like to know before I go jacking

The fact its intermittent and slowly got worse, until it barely worked, if at all, could point to a bad earth underbody. So I'll look for that too.

Do you mean the scope that something like VAGCOM has with it? My VAGCOM is only the lite version, but its pulling codes just fine, and if the Scope side would help, I'd happily fork out for the full version.

Thanks pocketchange.

albundy3670

SilverD2 is right. same thing happened to me a few years ago. Engine speed sensor. Pretty easy fix. Tozo sent me pics in posts years ago if you want to search the posts. Was a huge help to me!
I have 2 sensors as back ups if you can't find 1.
Get the ross tech software and bentley manual for the D2 A8. Invaluable info, especially the Ross-Tech.
Best of luck with the car.

BrianC72gt

After you pull the stored error codes, you should clear them. Then see if you get any NEW codes. They could be very old and not relevant to your current problem. And it sounds like the contacts in your ignition switch are intermittent. Had a similar issue on my old miata (MX5), it would crank but power to the ecu would drop out, but only while cranking. Diabolical. If the Check Engine Light isn't lit at ALL times in the RUN and START positions, then my first suspicion would be your ignition switch.

You mentioned that you pulled your fuel pump. Even Audi Factory techs have problems re-installing it correctly. That's why it ran perfectly for a short time then died. The pump is not at the lowest point in the tank. Above roughly a half tank, the pump cup is submerged. Below that, the cup is filled by suction through a series of hoses secured to the floor of the tank. If the pump is misaligned, then the pump housing suction pickup (all the way down on the side of the housing) will not mate with the "cup" assembly inside the tank. Its like trying to do a mid-air refuelling in a hurricane, blindfolded. A mis-aligned fuel pump will NOT throw any error codes.

Simple way to check is pour in a pint of fuel. There is a corrugated hose clipped to the guts inside the tank (aka the "cup" assembly) that pours directly into the pump cup. It should start....then die within a few minutes. You could also open the hose at the fuel rail and do an output test.

Bentley offers the following to confirm the pump is properly seated: drive around with a gallon can of gas in the trunk (in case it stalls) as the factory authorized method to confirm proper fitment. Idiotic. My method to put a straight hose barb in place of the banjo bolt on the output of the fuel pump; put 6 feet or so of cheap fuel rated hose (not high pressure) onto the barb; then push the contact points closed on the fuel pump relay in the electronics box underneath the passenger's side carpet and pump out the entire tank. To close the points inside the relay, remove the relay then carefully pop the cover off. Inside you will see an electromagnet and a set of points. The ECU powers the low amperage electromagnet which pulls the points closed completing the high amperage power circuit to the fuel pump. Reinstall the relay with the cover off. Push the points closed with a screwdriver handle, or a folded up piece of rubber fuel hose etc. Switch the key to the RUN or ON position, and the pump will power up. Switch off, and the pump goes off. I've done two pumps this way. One was troublesome. Both worked perfectly after I pumped out the entire tank.

Anyway, if you throw in a pint of gas, you will prime the pump. It will run on the prime, then die because it is not picking up fuel from the bottom half of the tank.

Good luck,

Brian C.

Proph3t

Thanks Brian. I have made a habit of just keeping a simple text file on my laptop to copy and paste any codes I pull, then I always clear them. Lets me keep a record of when and where, but gets them out of the car. Now there are no codes what so ever until I get it to crank, then the crank position sensor no signal one appears.

The mobile mechanic I got out just to pull codes when my VAGCOM wasnt working said there wasnt any relevant codes (yeah right, only 15 years worth) so he cleared them all without a copy or printout. But he mentioned to my wife he didnt think the ECU was getting power.

Long story short, I'm currently waiting on my new ignition switch to arrive as I found a giant crack across the top and the spring is partial hanging out and the mechanism is off centre, pushed out, and no longer has any return action on it. You spin it, and it just stays there. Doesnt exactly feel smooth either.

If it isnt the problem, it soon would have been.

Whether this is some how effecting the crank sensor I dont know yet, but I'm guessing it will solve the cranking issue. *fingers crossed*

Proph3t

So the new switch is in and it seems to have solved the no crank issue. Engine has cranked every time and very strongly, but still no firing... I'm also NOT getting the Engine position sensor error code anymore, but not sure whether I've cranked it enough. I read somewhere it doesn't always show immediately. Sunday morning isnt the day to sit out front the unit and crank a straight-piped V8

Dunno. Time to check fuel pressure and spark. I can hear the fuel pump priming and the relay is switching etc.

Proph3t

So I tested the fuel pressure and that ECU relay was working correctly and the ECU was powering up, and I started looking around at other obvious wiring issues. While looking for the Engine Position Sensor harness I noticed a taped up connector. Upon removing the tape I found a brittle, broken connector and what looks like a real issue. I found the part number on the cable (077905381b) and found that it was actually the engine position sensor cable! Which may explain a lot. So I've order one up and install ASAP.

BrianC72gt

How'd you test fuel pressure? My hunch was that the pump was mis-seated. It is a very common problem if the bentley installation procedure isn't followed exactly and often occurs even when it is. If you have any doubt, pour in a pint of gas...it will prime the cup...and the car will start then die if the pump suction spigot is not inserted into the tank cup assembly.

Scratching head...what other no start issues won't throw a code? The ECU light stays on while in RUN and while cranking in START, yes? Assuming ignition switch already solved that one.