Car will crank but not start- ECU (or Immobilizer) issue

[marty20dev]

I'm rebuilding a B5 S4 which has been off the road 2/3 years. Engine will crank but not start. I cannot hear the fuel pump prime the system when I turn the car on. The orange Immobilizer light comes on for a couple of seconds when I turn the car on but turns off (I think the immobilizer is ok...). I dont see a CEL. Also I see no faults when I plug in the OBD scanner. I'm getting power at the ECU fuse. Any ideas? Is there anyway of checking the ECU? Does anyone have the pin out digram for the ECU (would like to check if power is reaching the ECU). Any help on this would be greatly appreciated.

[bergtho]

ECU was just posted in thread:
Thread: P1198 and P1199, But resistance readings on all O2 sensors are in spec?

[Mille Bornes]

You said you don't hear the fuel pump run when you key on. Have you checked the pump?
If a scan tool is able to establish communication with the ecu then it has power.

[VR6Bomber]

Fuel pump should be priming , I would definitely start there. These fuel pumps are not silent that's for sure.

[Tumbler510]

Check the fuse panel under the dash.

[neilthewheel]

They dont prime every time you turn the key so listen very carefully the 1st time you do.
If it was immo, it would start for a sec, then shut off. Pretty sure you get a code telling you it shut it down also.

You can run an output test on pretty much anything on the engine to fire the pump up manually.
Pretty much everything here is powered by the fuel pump relay so the fuel pump will come on with it.
Be careful though, you only get 1 shot at running through these before you have to start the car to reset it. I think you can unhook the ecu or battery to reset it manually though.

[Der Konig]

Does the CEL illuminate when you turn the key to accessory? If not, there is likely no communication to the ECU.

If you can hook up a VCDS tool to it, try to talk to the ECU module, if no response than its dead. Happened to me not long ago and had the same symptoms. If you can't talk to the ECU with VCDS, try other modules like the ABS. If that works but ECU talking doesn't then thats a dead give away.

[marty20dev]

Ok guys, Good feedback!

The fuel pump and relay are ok, I checked them, they work fine. All the fuses are fine. The CEL doesn't light up at all.... not a good sign.
When I connect the OBD2 scanner, it connects but I get no faults, even when I try to create a fault by unplugging sensors. The only thing I forgot to mention was that the key fob battery was completely dead and the ECU has been unconnected to a power source for a number of years (indoors, in a dry environment)......

[VR6Bomber]

Its gotta be either fuel, spark or a fried ecu.
Check the ecm's?
Disconnect a fuel line nearest the motor or fpr to see if fuel is flowing.
Pull a plug and crank it to check spark.

Do you have access to a spare ecu?

[marty20dev]

Hey!
The fuel lines are primed and full of fuel; only because I manually fired the relay to test it. I have no spark.
I haven't got a spare ecu to swap in (not sure if you can swap ecu's with the immobilizer)
When you say check the ecm's, what do you mean?

[VR6Bomber]

When you say check the ecm's, what do you mean?

My bad I meant ICMs, The two things on the top of your airbox, they connect to your coil packs.

[neilthewheel]

Fuse 28 or 29 is coil power so maybe take a look at it.
It is power to the ldp also so you would prob have an open/short code for that also if it were blown.
Worth a look though.

And make sure the connectors on the icms arent swapped.
Both blacks on one, both browns on the other.

[marty20dev]

Hey All,
Update:
Got a replacement ECU and fitted it - when I tried to start it, its seemed like it would go but wouldn't -intermittent spark, something was off. Still no ECL on start-up, no faults from the OBD connector.

I spent a day, rechecking all the electrical connectors and wires on the wiring harness/loom and found a partially cut wire. I re-joined the cable and the car fired up for the first time in 2/3 years!!

The last 4 weeks have been painful- hope this car is worth the effort!!! Thanks for all the replies!!