Pcm location/diagram

[90rangerext29]

Hey everyone,
Brand new member. I have a problem with my 90 ranger with 2.9l. There seems to either be a short in the ground from the eec(pcm?) or the eec is bad. I can get the the fuel pump to run from jumping the neg terminal from the battery to a bare spot on the ground wire coming from the eec. The engine will run if I spray starting fuel into the throttle body until the starting fuel is gone. But if I keep the fuel pump running via the jumper while cranking the engine doesn't run. I am wanting to check to make sure the ground wire is good but I don't know were the eec is located and which pin is the ground going to the fuel pump relay. Good advice is appreciated. Thank you

 

[RonD]

Welcome to TRS

EEC-IV info here: http://www.auto-diagnostics.info/ford_eec_iv

Reads like fuel injectors are not opening if you are getting fuel pump to run by jumping, but still have no start.

Fuel pump Ground is pin 22, should read 12volts with key on if wire to relay is good(key on of course)

EEC has 4 "main" Grounds, as seen at above site

Follow the main engine wiring harness to the EEC, could be in passenger kick panel(2.9l should be here) or in engine bay drivers side down in fender area next to firewall(4.0l was here).

Does Check engine light(CEL) come on with the key, it should, that means EEC is getting power

 

[90rangerext29]

Thanks for the quick reply, the fuel pump has 12 volts, would pin 46 signal ground (signal being on off signal)be for the fuel pump? Or does it mean signal as in turn signal ground? Found EEC was where you said would be. tracing wires tonight.

 

[RonD]

No, pin 46 isn't used for fuel pump relay

Pin 46 is the common ground for a few sensors, so the pin 46 wire runs to sensors not a cab or engine Ground point.
Most sensors use variable voltages(.1v to 4.99v) to convey information back to the computer, so a common reference 0volts is needed for the variable voltage to be accurate.

For lights and other 12volt devices, a Ground is a Ground, 0 volts, for some sensors you need more accuracy so computer supplies Positive voltage(pin 26) AND negative voltage(pin 46) so no margin for error

 

[90rangerext29]

No 12v at fuel pin 22, no cel, and no 12v at ignition pin 37. I was using a test light( I cant seem to find my meter) not sure if that is a problem. I did have power at the 30 amp fuse labeled EEC under the hood. Not sure what direction I need to go now.

 

[RonD]

EEC relay, does it "Click" closed with key on?

Simple test
pull out the EEC relay
Turn key on
Put in EEC relay
It should Click closed when inserted

If not try WOT relay or Fuel Pump relay in EEC relay holder to see if they "click" if so replace EEC relay

WOT relay is used for air conditioning so you may or may not have one

EEC relay powers EEC(computer), and spark, and fuel injectors, and fuel pump relay

 

[90rangerext29]

Relay clicks

 

[RonD]

With key on check if you have 12volts at any one of the fuel injectors, either of the two wires on any fuel injector should show 12volts, that power comes from EEC relay.
EEC relay has 1 Red, 12volt power OUT, wire that has several spliced wires, for EEC(computer), fuel injectors, spark system and fuel pump relay.

Have a look here: http://www.therangerstation.com/tech_library/EDiagrams/index.htm

Scroll down to electronic engine controls
There are 3 diagrams for the 2.9l engine
That shows power distribution and grounds for the systems, "solid state" = EEC(computer) pins

 

[90rangerext29]

With key on I have 12v to both sides of fuel injector plug

 

[RonD]

If it was plugged into the injector that would be correct.

A fuel injector is a solenoid, so electricalwise it is just a Coil of Wire inside, so 12volt IN would show 12volt OUT.

 

[90rangerext29]

I unplugged the wire and checked it that way. It need to be plugged in?

 

[RonD]

If unplugged the injector wires should only have 12volts on the Red wire, and the other wire could also read 12volts, depends on the transistor wiring in the Computer.
But you can test the non-Red wire by hooking volt meters red probe to Battery Positive, and the Black probe to the non-Red wire.
Disconnect coil for a no start
Then crank the engine, meter should pulse a voltage reading as computer Grounds that wire.

Injector wire(not the Red one)----------Volt meter(or test light)---------Battery Positive

Volt meter should show pulsed voltage, test light would flash, if computer is Grounding that wire

 

[90rangerext29]

I checked for pulsing and nothing. I think either my ecm isn't getting power or it is fried. Any thoughts?

 

[RonD]

If the CEL(check engine light) comes on with the key then PCM is getting power.

PCM injector pulse is started by the TFI(spark module), as distributor turns the TFI module sends a Pulse to the PCM so it can time the injectors to engine RPMs, whether cranking or running.
Without this pulse the PCM doesn't even know you are trying to start the engine.

TFI has 3 wires to the PCM
PIP, this is the pulse the PCM uses to time injectors
SPOUT, SPark OUT, PCM send TFI module "suggestions" for spark timing
Ground, TFI and PCM are grounded together to insure the Pulse is acurate, common reference ground

Good read here on test TFI Module: http://www.therangerstation.com/tech_library/TFI_Diagnostic.shtml

TFI can run the spark on its own, it doesn't "need" the PCM, so engine could start with starting fluid added, but if PIP wire or Ground wire had a problem then no injectors.


And yes, the PCM could be bad, it is well out of warranty, lol, so you can open it up and look at the circuit board.

Here is what it should look like: http://www.auto-diagnostics.info/ford_eec_iv

 

[90rangerext29]

There is no check engine light with key. I looked on the diagrams for what powered the pcm and did not see anything.