Hi.Some days ago I disassembled the upper intake to install a fuel pressure regulator. When I assembled it I tried to start the car but It didnt have spark. I changed the CAS sensor and the main relay but the car didnt start. I checked the pin out of the ECU with an osciloscope and It dint send signal to the coils.Any help would be appreciated.I drive 89 S4 t2.Thanks in advanced

 

Do you have an S4 or S5 T2? You said it was an 89 S4, but 89 was S5.

I would suspect the CAS. Did you ensure the CAS you installed was good? I don't believe the ECU primes the fuel pump or tells the coils to fire unless it sees engine RPM. Ie, if the ECU doesn't see RPM, no spark or fuel.

Does the tach bounce when cranking? Is the ECU getting proper voltage?

 

the signal part is, CAS-> ECU - Coils
the power is Battery -> Main Relay -> Main Fuse -> Coils

i've seen the CAS connector be a PITA before

 

Did you reconnect the flapper door air flow sensor plug? It reads airflow and then sends power to the fuel pump to prevent flooding, if that is not plugged in, it does not think the engine is running and wont give you anything.

 

Thanks for the answering. When I tried to star the car the inyectors are working. The CAS is in good condition and the ECU receives signal from this (I checked with osciloscope). I bought another ECU and Main relay to try. Thanks in avance. Sorry the car is an s4 turbo2 1987

 

Fuel injectors can click all day long, if that flapper door is unplugged, or not fully seated, it does not read air movement, send power to the fuel pump, and you will have no fuel pressure for the injectors to inject anything.

 

Fuel pump will run with the key in START, regardless of MAF input, so with the MAF unplugged it should start then stall out.

 

^ Good point.

If the injectors are clicking then you do not have an issues with your CAS.

With the key on run, meter the black check connector at the leading coil to see if you have 12v.

 

Intresting, when I wired my car for Megasquirt, the power for the fuel pump ran though the air flow meter, so it can not send any power to it until there is airflow, as there is a physical switch that closes when it it just barley opens. How is your car wired differently?

If you have any pressure to start and stall out, it is due to gas tank vapors expanding at that point

 

Wired stock . S4 FSM, 4B-76, Turbo Emissions Control, Circuit Opening Relay (same for NA as well). Ignition in START has exactly the same effect as signal from MAF, the fuel pump will run. This signal comes from the ECU, it also energizes the subzero start assist (that grounds through the oil-pan thermo switch, when cold enough).

 

 

Hi. I change the ECU and the car have spark!!!!!!Thanks everyone for the help!!!!