flight_of_pain

I recently acquired a S4 n/a (86 base), and am having a bit of an issue. The ecu that came in the car had a mouse nest on it and was visibly fried. I swapped in a known good ecu, and have no spark or inj pulsing.

I have verified:
known good ecu, coils, cas
at the ecu plugs, the cas wires and coil triggers have continuity through the harness to their respective plugs
the ecu harness has 12v at the white/blue battery voltage wire, and 12v on the Black/white IGN on wire.

She cranks just fine, but no ign or fuel events. What else sends a signal to the ecu that could keep it from working?

Isaac

satch

iTrader: (1)

The B/W wire you speak of is this being measured at pin 3I which is the Main Relay pin?

Have you checked the grounds?

Does the Brown/White wire at the TPS have close to 5 volts w/key to on?

point-blank

iTrader: (9)

Have you gone through all of the checks in the fsm?
if so:
Check your Intake air temperature sensor, it is a small two wire plug on the drivers side of the dynamic chamber under the BAC valve.
I had a similar problem, and as it turns out, one of the wires on that connector (IAT) snapped off inside the plug.

hope that helps

-Miles

flight_of_pain

Yes in pin 3I, grounds were the first thing I checked, I will check the 5v vref in the morning.


I will check in the morning, thanks.

satch

iTrader: (1)

Another thing would be continuity is not always the best way to diagnose a problem as a single thread of a multi threaded wire will allow continuity to pass through such that a continuity test is better served for searching the end of a known wire. So make sure that both orange connectors (FEM-01 and FEM-02) near the ECU are a tight/snug fit.

flight_of_pain

With the ECU unplugged, and the key on, I have 12v on the brown/white Vref wire. Verified at the TPS and AFM. Pulling the EGI comp fusible link drops it to zero volts.

Since this should be 5v from the ecu and the ecu is unplugged it leads me to think there is a faulty component that is shorted inside and feeding the brw/white wire with 12v. unplugging the tps and afm have no effect. Sorry if my questions are dumb, I am a 1st gen guy

Isaac

satch

iTrader: (1)

What does the wire in question read w/the ECU not disconnected? If the plug to the ECU that houses the BR/White wire is unplugged then you are disconnecting the ground signal to the various sensors you took the voltage reading, which I believe will cause the 12 volt reading you are seeing.

flight_of_pain

12v either way.

Isaac

satch

iTrader: (1)

If you went to the fuel check connector which has two wires and checked the for voltage on the Black wire w/key to on what does it read? Should be ground voltage.

Pin 2A feeds the Variable resistor, Pressure sensor and Atmospheric sensor in addition to the TPS and AFM. Continue to disconnect these one by one and check the BR/W wire each time w/key to on. Focus on the Pressure sensor first.

57bronco

I'm having the same problem with my 86 n/a. I drove it to the parts store one day and would not start when I started home. Turns over fine. I hope what fixes yours will fix mine, or visa-verse.

flight_of_pain

A friend who was helping me decided to unplug, re-plug, and wiggle every connector in the car while I had lunch. When I went back to working on the car, it was all working the way it should, spark, fuel, AFM, all was good. A shot of starting fluid and she fired right up. I am guessing there was a bad connection in the ecu harness or the main harness plug, but I have no way to verify.

Isaac

Thank you all for the help.