Should fuel be at both injectors or just one until more fuel is needed.

On an 1988 D150, w/3.9, auto,smec. The truck seems to not have enough fuel. No fault codes except 12 and I noticed only one injector seems to put out fuel. Now if I switch the injector wires then the other one
works.Should fuel be at both injectors or just one until more fuel is needed? 12 is the one that tells you your battery have been disconected correct.
Thanks in advance
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They should both squirt. When you switch wires does the other one quit? Sounds like a bad connection, broken wire or a bad computer.
Al
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When you switch wires does the other one quit? Yes it does. I've had the harneses out before. Is that the only reason one wouldn't squirt. Because I beleave I had the same voltage at both sides, but I'll have to check again.
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The computer or SMEC (single module engine controller) has two outputs for the injectors. One (wire 18 WT) is pin 2-9 at the computer, the other (wire 18 TN) is 2-10. The color stays the same all the way to the injector plug. On the injector plug, the outside wires are the grounds, both 16 gauge black wires. The center two are the drive signals. There is a connector (right fender) that they pass thru. Use a test lamp. Don't use a digital meter to troubleshoot this or you will get lots of confusing readings. 18 TN is an 18 gauge tan wire, the other is 18 gauge white. Just look at the colors at the injector plug to be sure.
BTW: I do not have a wiring diagram for an 88, this info is from an 89 manual. I believe they are the same. If the signal is at the computer terminals, and you can't find the break in the wiring, just "jump" the wire from the computer to the injector connector. In a pinch, you could disconnect the dead wire and jump the good wire to both injectors. My 89 manual says the SMEC is in the center of the dash panel.
Hope this helps, good luck,
Al
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On that engine, you get 12v supply to both injectors from the autoshutdown relay. First make sure you have 12v to both injectors via the Dk GN/ BK tracer when you turn the key on. You'll have voltage for about three seconds when you firest turn the key or when cranking the engine over. The smec fires the injectors by grounding the white and tan wires. You can check continuity from the white wire on #1 injector to the 14 pin connector at the smec position #9. The tan wire goes to position #10 in the connector. If you have voltage to the injectors and continuity from the injectors to the 14 way connector you probably have a bad smec.
Denny
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