ECU not turning on my fuel pump...??

[theCRANKwalker]

1995 AWD talon...

when i turn the key on the pump does not click on for that split second and when i try to start the car same problem, no pump...

i followed the power wire all the way to the mfi/fuel pump relay relay and if i give the pump power using another battery and ground the pump goes on, so i know the power wire going through the cars frame is fine...now i tested the harness on the MFI relay and when i turn the ignition on, the black/white wire gets 12v's but the fuel pump power wire (black with blue line) does not
i then spliced into the fuel pump ground wire on that harness (white w/pink line) and i grounded it to the car then turned on the key...the pump went on and stayed on until i broke the ground connection...

so this iw where i stand...the ECU is not sending the "ground" signal to the fuel pump relay..does anyone know where i can view a schematic of the ECU? that way i can see which wires are meant for ground on the ECU and i can then test those......any other suggestions would be appreciated, i hope i made sense

 

[MikeL]

Replace the relay. ECU doesn't send a "ground signal" either your ground is bad, or the relay is bad.

 

[Tevenor]

Thread moved.

 

[theCRANKwalker]

Originally posted by MikeL
Replace the relay. ECU doesn't send a "ground signal" either your ground is bad, or the relay is bad.

when i give the relay power it clicks, when i give the ground a new source, the pump goes on....question: how does the fuel pump relay know when the key is turned on? maybe that'll help me find the problem

 

[MikeL]

Didn't alex already tell you that the key in the ON position does not turn on the pump. If you borrow his cable you can set DSMLink to turn the pump on with the key in the ON position, but otherwise it's only on when starting and running.

 

[Wizard]

It should get a 1-2 sec prime from the pump. Most FI cars do that to build up pressure and prevent long cranking starts to build up pressure.

Also.......Check your ECU. That is one of the circuits that goes bad when the caps leak. Fuel control.

Pump works, relay works, but the ECU controls the relay and it obviously isn't working.....

Pull the ECU and check it out.

Wiz

 

[theCRANKwalker]

Originally posted by MikeL
Didn't alex already tell you that the key in the ON position does not turn on the pump. If you borrow his cable you can set DSMLink to turn the pump on with the key in the ON position, but otherwise it's only on when starting and running.

yea we figured it out yesterday, the pump actually primes when your cranking the motor because i had to disconnect the starter, then turn the key with the clutch down as if i was starting the car to get the pump to go on...

 

[DSM93]

Ill side with Wizard had a friends with the same deal and the ecu would not send the signal to the fuel pump relay.Remove your ecu and pop it open you should be able to see the problem.Good Luck.

 

[markmakeitso]

Geez, twice in one night. Usually the bad caps are in 1G cars. If 2G cars do it too somebody tell me and I'll stop spreading misinformation.

 

[steve]

As theCRANKwalker discovered the ECU doesn't ground the fuel pump relay coil until the ignition is switched to start. It then watches the CAS to make sure the engine is running, if it doesn't see the engine turning it turns the fuel pump off after about 0.6 seconds. 2G's only have one coil in the fuel pump relay so the ECU controls the whole process. 1G's have two coils in the part of the MPI relay that serves as the FP relay. The starter circuit directly drives one and the ECU the other.

Contrary to what MikeL says, most of the things the ECU controls are switched by the ECU pulling the signal low (to ground) and compleating the circuit.

Steve

 

[Boosted 1.8]

check crank angle sensor

 

[theCRANKwalker]

thanks for the help guys but as stated above i already figured out the problem, the car has been running nicely for a week now, 230miles on the new motor so far