Fuel pump relay not turning on

[warthog70]

I'm getting ready to start my new efi. I have new painless wiring harness and an Al9 Ecm. I have 12vdc to the coil of the relay but when I turn on the ign it doesn't come in. I'm thinking the other side of the coil goes to ground through the ecm? Looks like it goes to the #22 pin. Shouldn't it turn on momentarily to pressurize the system?

 

[Viperwolf1]

I'm getting ready to start my new efi. I have new painless wiring harness and an Al9 Ecm. I have 12vdc to the coil of the relay but when I turn on the ign it doesn't come in. I'm thinking the other side of the coil goes to ground through the ecm? Looks like it goes to the #22 pin. Shouldn't it turn on momentarily to pressurize the system?

Yes. You might check for voltage on the fuel pump wire when the key is turned on. I don't know if the painless system uses an inertia switch but you might check it if you have one.

 

[warthog70]

I have voltage to one side of the coil. The other side that goes to #22 on the ecm goes to ground to bring in the coil right? What tells it to do that? How dose the ecm know to turn the fuel pump relay on?

 

[Viperwolf1]

I have voltage to one side of the coil. The other side that goes to #22 on the ecm goes to ground to bring in the coil right? What tells it to do that? How dose the ecm know to turn the fuel pump relay on?

Yes. The ECM is programmed to turn the pump relay on.

 

[Timmy390]

I have voltage to one side of the coil. The other side that goes to #22 on the ecm goes to ground to bring in the coil right? What tells it to do that? How dose the ecm know to turn the fuel pump relay on?

The ECM ground (pin 22) is constant it's the key on hot that closes the coil in the relay thus turning on the fuel pump.

Do you have voltage on both big end of the relay? Not the key on but the source voltage (should be fused) coming into the relay and going to pin 19 as well as running through the inertia switch (if you have one) to the fuel pump?

Have you checked the ground at the fuel pump?

This may help
http://www.veryuseful.com/mustang/tech/engine/images/91-93_5.0_EEC_Wiring_Diagram.gif

Tim

 

[bax]

First thing I thought of was bad ground. But I'm always wrong.

 

[EFI Guy]

The PCM will ground the relay via pin 22. However, the PCM only grounds it for roughly 2 seconds after switching the key to the on position to prime the system. After that it must see pip (rpm) signal from the distributor before it will ground it again. This way fuel is only being pumped while the engine is running except for the 2 second prime.

 

[warthog70]

I have no ground at #22. But the ecm is grounded on #20,40,60. I jumped a ground wire to 22 with the ign on and the fuel pump comes on. It keeps running even when I pull the jumper. Hummmm I bought the ecm on eBay ....

 

[warthog70]

So I'm ready to try and start it. But if I'm not getting my 2sec prime I'm not holding out hope it will fire. I guess I can try and see if the fuel pump turns on when I crank it over?

 

[warthog70]

I have found that my grounds @ #40, #60 go from 0 ohm to 50 ohm (to ground) when I turn on the ign. I traced out the wiring in my Painless harness and found that these grounds go to the o2 sensors. I unplugged them and now they have 5.7 ohm from 40, 60 to ground.

No I turn on the ign and the fuel pump comes on and just runs.

How can the o2 sensors be putting resistance in the circuit when the grounds that go to them are in parallel with main EEC ground and 40, 60?

 

[dbasile]

Sounds similar to a problem I had. I would also check see if you injectors are getting power. The check the harness with a noid light to see if you injectors are pulsing.

Is your computer throwing any codes?

No Codes, no flash with noid light equals bad computer....

 

[warthog70]

I'm not getting 5volt to my sensor from my pcm. And I don't have a noid light but I have one on the way. Cut the seal on the computer and found a crispy capacitor. The blue one closest to the plug. I pulled it out of the board and it seems to be building resistance fine. It looks like some traces near where it was on the board might be fried. I bought this pcm on ebay so I'm not sure if this is a result of me and my wiring or came that way. I feel like I can replace the capacitor fine but not sure if I can fix the trace. Maybe Ill just buy a new 250$ ecm.

 

[cbford]

Some things to know/test I found on several sites and on here:
The computer only switches grounds. So actuators (like injectors) have 12v on one wire and ground/resistance-reference on others. Sensors generally have 5v on one side and reference on other (like ACT sensor).
The only place to get 5v is from the computer outputs between 26 and 46. SO:
Test across Pin 26 and 46 with volt meter - Should show 4 - 6 volts with key on. If not, you don't have reference voltage and ECU is likely toast in some way.
Pins 20, 40, 60 are all ground all the time whether ECU is in or not.
Pin 46 is a filtered ground that is switched by computer, so will not show ground without computer, but should when it is installed and powered on.

Pin 37(and 57, they are tied together) should have 12 volts all the time when computer is in and key is on. This is also where all your injectors get their 12v to actuate from. So you can test all the red wires on all those too to verify harness. The other wire on injectors will switch to a ground only when ECU fires injector, thus the need for noid light.

Pin 22 is a ground that is switched by computer to close coil on fuel pump relay. It also goes to self test connector, so you can look for switched ground either place.

Rather than try to explain other stuff.. This link will help a lot.
http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif
That is the stock pin out diagram for the ECU connector. You can test from ECU plug end and sensor ends to make sure your harness is good. I have been doing this a lot lately, and ended up with a bad ECU straight out of the reman box from Autozone.

 

[ransil]

The caps are just filter caps, should run run OK without them, might just do weird shit at times.

If burnt board traces or no 5 volts then someone probably connected pin 30 wrong, could be you or the last guy that owned it

 

[warthog70]

So put new caps in and fixed the trace but still no joy. I was careful about pin 30 when I first wired it up. I don't have any voltage on pin 26, so I'm feeling like the pcm isn't turning on. It have its (2)12v wires and (3) grounds. I have another a9l on the way. I fairly confident I didn't fry this one (as confident as you can be with a none working ecm in your hand) but just thought another one would be a good idea. Anything I should look at on my wiring harness before I plug the new one in?

 

[warthog70]

So I opened the pcm again and found that the cap closest to the plug (goes to pin 57) wasn't soldered completely. So I fixed that and now I my fuel pump is priming! And I have my 5v to sensors.

I'll getting all my wiring back together and try starting it again tomorrow.

 

[warthog70]

Starts right up, thanks guys