I have an 87 4x4 4speed 300 with good spark, and no injector pulse, fuel pumps will not turn on from the computer, it sends no ground signal to trigger the F/P relay, this is a problem that is driving me crazy! I have replaced a computer that had visable water damage and a horrid smell! checked al the grounds and all are good clean and tight! can someone here possibly help me in this major problem! the truck ran before with the F/P diagnostic plug jumped to ground, and it ran good, then a week later the truck just died! fuel pumps running, and no pulse good spark though! Blue-purple spark

 

When you turn the ignition key to On, you should hear
the EEC relay click. That applies 12 volts to the computer.

An indication the computer has power, is the Amber
Check Engine light on the dash should be on. If it is not on
you need to check the power and wires at the EEC relay.

The EEC relay circuit is protected by two fusible links.
One of the links is at the starter relay lug (positive terminal
lead from the battery). The other fusible link protects the
Red wire at the EEC relay.

The Fuel pump relay and EEC relay are located on
a bracket on the driver side plastic wheel well
housing behind a plastic cover.

Are you saying if you ground the Tan/Light Green wire at
the diagnostic plug the fuel pumps do not run?

Here's a schematic for a 88. 87 should be close.

 

yes the relay clicks when i turn on the switch, but the check engine light has not functioned since i recieved the truck, i did get a code 87 and a code 67 they were the only codes i got retrieved the codes with a test light and a jumper wire

 

Code 87 is check for 12 volts at the fuel pump relay. I guess this indicates
the computer doesn't see 12 volts at the fuel pump relay.

Take a good look at the fuel pump and EEC relay sockets. They get
corrosion around the socket pins.

You should measure 12 volts on the Yellow which is always hot.
When the fuel pump relay is energized the 12 volts from
the Yellow wire passes thru the relay contact and provides
12 volts on the Brown wire which goes to the fuel pumps.

On the Red wire there should be 12 volts when the ignition
is On.

Code 67 is the clutch pedal was not depressed during key on engine off test.

 

i guess that could be the problem, but i still have the issue of no injector pulse either, and the fuel relay works when you connect it to a good ground, at the STI connector, is it possible that the injector pulse is not getting a signal from the dizzy? like not getting a PIP signal?

 

Well the PIP sensor triggers the TFI module and the TFI provides a signal to
the computer. Do you have a tachometer and if so does it show a valid
rpm when you crank the engine?

Does the engine run if you spray some starter fluid in the throttle body?

The computer should ground the fuel pump relay for about a second
when the ignition is turned on. It should ground the fuel pump
relay as long as the engine is cranking or running.

 

it tries to run on starting fluid, and yes i have a tach, but it goes high during cranking reads around 500 to 700 rpm and is kinda bouncy,and i do not hear the fuel pump when i turn on the ignition, nor do i hear it during cranking without the test wire and yes the pumps only seem to run when i ground the test plug connector

 

Sounds like a bad computer.

 

It could also be no small black with a green stripe ground wire at the NEG (-) post of the battery.
Also maybe no power on the two power pins of the computer (1, 37 & 57).

 

there is no wire like that at the neg post on my truck, i will loof or it tomorrow and reply! thank youfor the insight!!! )

 

The symptom that the primary coil of the fuel pump relay is not
grounded by the EEC when you first turn the ignition on does point
to the computer.

When the key is turned to on, power is applied to a timer circuit
inside the computer. It turns the fuel pump relay on for one second
to prime the fuel system.

At the negative battery terminal there should be two small ground wires in
addition to the large ground wire that I believe goes to the engine block,

I think one of the smaller ground wires is for the computer. Can you
verify that wire is making a good connection?

 

there are no other wires at the neg terminal on my truck, I will look for them tomorrow and then we will be in better shape i hope

 

The other ground wire is for the ABS brake proportioning valve.
This info is for a 88 so I don't know if the 87 is the same.

*************************************************
That smell you mentioned is probably a dead mouse some where
and it probably chewed up the wiring harness.
Any signs of mouse droppings or a nest which looks like a pile
of lint?

 

Im betting on the eec relay or the connector being bad. If the eec relay dont energize the fuel pump relay,It don't energize the eec either. So if you don't have fuel pump prime when turning the key on, and no check engine light, I would check the mentioned above If they are fine then possably be needing a eec.

 

If it's never been replaced, the EEC relay should be the brown one.