help 94 4.0 Fuel pump power issues

[EHford]

hello everyone,
Im new to the forum and need some help.
94 4.0 5 speed 4x4 fuel pump issues
new pump(working and tested with 12v)
new filter
was driving fine but started cutting out on a hill climb, found the starter wire shorted on the exhaust manifold
getting 12v at pump with key on but wont run pump
getting good ground at pump(tested continuity and no resistance)
getting 12v at inertia switch
inertia is bypassed
changed out fuel pump relay and the diode
when i jump the relay the fuel pump runs
any ideas? thanks

 

[bobbywalter]

are you straight lining 12 v at pump? load test the 12 v you get at the pump. that isnt right but may be back feed potential.

assuming you are jumping actual fuel pump relay, and truck runs when you do this

test relay.

check for key power at what is usually a red wire which should be relay switch supply side

if that is good then manually ground switch side. if it works there is a signal issue from ign to ecm or the ecm is burned and not allowing it to ground pump relay.

cracking open the processor may show some evidence of damage.

 

[EHford]

the 12v at pump wont power a test light.
ive swapped relays
the red wire on relay which i believe is pin 86 is getting power with key on but pin 85 is also getting power with key on
key on: pin 86 11v, pin 85 11.4v pin 30 (constant power) at 11.7v.
i thought possibly bad ecm as well but i put a differnt one in from another 94 4.0 and it didnt fix, i tested the ecm in my other ranger and it ran so i believe ecm is fine.
when you say manually ground do you mean cut the wire and just splice it to the ground?

thank you

 

[bobbywalter]

how are you measuring? are you measuring across so you see potential?

or testing right from wire to ground?

test continuity from pin 22 to the relay. there should not be power on it.


when you jump 30 to 87 does the pump run?

the inertia switch is not tripped or bypassed?

 

[EHford]

i am testing from pin to ground on battery.
i tested continuity from pin 22 to pin 85 on the relay and there is continuity
yes when 30 and 87 are jumped the pump runs
inertia switch is bypassed.
just checked and i have no spark while cranking.
ive checked all fuses in fuse box and they all seem good (checked continuity between sides)

 

[bobbywalter]

the ignition module may be burned up from the short or its not getting key power not sending signal to ecm so it knows its cranking.

all fuses good?

 

[bobbywalter]

check for ignition power on the red light green stripe wire at the noise capacitor plug and ignition module

 

[EHford]

okay when you say ignition module are you refering to the icm? ignition control module on the rad support?
is there power at the icm only with key on? for the noise capacitor to check power with the key on

 

[bobbywalter]

yes

 

[EHford]

ok ill check tomorrow, i also will pull the icm from my other ranger to test in this one

 

[bobbywalter]

it gets power from the eec relay in red....from te branch that relay feeds....this could have been burned.

and it gets ignition power via the red/green strip wire on crank and run.

then there are shield grounds and ignition grounds as well.

 

[bobbywalter]

if the wire is burned changing ecm or ignition modules will not fix it.

i think pin 8 is the pump monitor and 16 is the ignition ground to the ecm.

have to look up the pinout.

but these systems are simple enough. you have the pip...spout and idm. then there is the crank sensor. if anything is toasted there it wont know its cranking and to turn on the spark and injectors and pump.

 

[EHford]

yes looking at the wiring diagram you are correct. ill check for power to the icm tomorrow and get back to you thanks