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Old 05-03-2018, 08:24 PM   #1
kingbuzo
 
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Default 1986 4x4 TBI 2.4

new tank , new fuel pump ,good relay

i can get it running by grounding the White/red wire to engage the fuel pump relay switch....

the white/red wire doesnt complete ground to engage relay....im assuming this wire leads back to the ECU....either that wire is broken somewhere...or the ecu is not giving it the ground signal...

not sure the best way to approach it...id like to fix it to normal......

can i run this truck with the white/red to ground ? it means that while the ignition is on...the fuel pump will be continuously pumping...

does the fuel pump run all the time to maintain pressure? or does the ECU switch it on and off while running..thank you
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Old 05-03-2018, 08:30 PM   #2
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Got a copy of the FSM? That will help you trace wires.
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Old 05-03-2018, 08:32 PM   #3
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Kingbuzo...I have sent you a private message. It relates to my signature below. Not a problem...

Robert
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Old 05-04-2018, 10:48 AM   #4
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> the white/red wire doesnt complete ground to engage relay...

I'm pretty good at wiring, but I don't have colors memorized or where they go.

Could you go into some detail about where this white/red wire is? Maybe a picture to show us what you are talking about?

> does the fuel pump run all the time to maintain pressure?

Pretty much. Extra fuel is returned to the tank by the fuel pressure regulator and a return line.
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Old 05-05-2018, 03:16 PM   #5
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heres a picture....the red line is original wiring...(the White/Red wire that goes to ecu 108) with this connectted the relay does not "clik" or engage to send power to the fuel pump..

i cut this wire White/Red wire near the fuel relay and added a jumper from the relay to ground... (drawn in black line) ...when key is turned on... the relay engages and the fuel pump runs and truck starts...

this truck has been sitting for a while so i am ironing out a few wrinkles......alternator isnt charging as well...thanks gang

RED line = truck doesnt start
Black line = truck starts
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File Type: jpg highlighted relay wiring.jpg (86.4 KB, 4 views)

Last edited by kingbuzo; 05-05-2018 at 03:26 PM. Reason: make clearer
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Old 05-05-2018, 03:25 PM   #6
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heres the layout of the fuel pump control...thx


ADDED: i just checked all fusable links...all good..alternator light goes on at start then goes off after running...so bulb good...

...i may have to just got around vehicle and remove clean all ground connections to everything that touches motor and body...
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Last edited by kingbuzo; 05-05-2018 at 06:28 PM. Reason: added more vehicle checks to troubleshoot
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Old 05-05-2018, 07:21 PM   #7
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It looks like you have essentially done what the stock wiring is attempting to do, but by going through the ECU.

I'm not sure what the reasoning is of having the Fuel Pump Relay ground through the ECU, though. If you are not getting any kind of code, then the wiring you have set up seems to be identical.

Just to help anyone who is following along, this page is also in the d21_truck_1989.pdf on EC-136

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Old 05-06-2018, 06:33 AM   #8
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Looks like you need to test continuity of the W/R from the relay to pin 108. Unplug the harness from the ecm. Wiring is a pain.
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Old 05-06-2018, 01:13 PM   #9
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Quote:
Originally Posted by cadillacdude1975 View Post
Looks like you need to test continuity of the W/R from the relay to pin 108. Unplug the harness from the ecm. Wiring is a pain.

yes...i did that later in the day and forgot to update thread...sry.. its all good...im thinking its the ecu...i may take it apart and look at the underside of the circuit board...the top of the board looks great....
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