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Gary
Gary, GMC Technician
Category: GM
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Experience:  15 years gm master tech/15 years ASE master tech
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I have a 87 chevy K20 pickup 350. I have replaced fuel pump,

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I have a 87 chevy K20 pickup 350. I have replaced fuel pump, fuel pump relay, ecm. I can add 12volts to fuel pump test terminal at relay and pump comes on. I can ground the injectors and they will spray. I can dump gas into the intake and it will start and run a few seconds and die. the ses light will not come on when key is turned on, jumped a-b on the aldl connector no ses light, hooked up a code reader and with key on it still says turn key on or cable not connected. On one plug to computer there is two hot wires, on the other there is one hot wire. I have unbolted all the ground connections i can find under the hood cleaned and reconnected. So where is the computer ground? or what should I do next to make the truck run? it cranks fine 12.8 volts at battery
is this a single tank truck?
Customer: replied 6 years ago.

No it is a dual tank truck, how ever I do have good fuel pressure at the TBI unit , all I have to do is crack the line a little and it sprays every where. I don't have a fuel pressure tester to see if it is at the 13 - 17 pounds pressure, but it sprays hard. It concerns me that it seems the computer is not operating. Because there is not check engine light when i turn the key on. And when I hook up my scout code scanner and turn key on it cant read codes it still says turn key on or cable not plugged in.

so at this point you do have the fuel pressure just no injector pulse spraying fuel in.do you have good spark at the wires where they connect to the spark plugs?
Customer: replied 6 years ago.

correct , and yes it does have good spark at the wires, If I dump a little gas in at the TBI unit it will start right up run a few seconds and die.

 

ok ecm and gage fuse are good?12 volts each side with the key on with the fuses in place?
Customer: replied 6 years ago.
yes, and at the computer one plug has two hot wires with key on , one plug has one hot wire with key on computer disconnected
ok with the computer connectors un plugged you need to check for 12 volts at C16(orange wire) and B1(orange wire) and A6(pink/black wire)

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with the key on all 3 of those terminal on the connectors should have 12 volts.
Customer: replied 6 years ago.
ok no power at c16 and B1, I have power at A6
ok this truck either had a fusible link OR an ECM B fuse that powers BOTH those terminals with 12 volts.now get to the starter and off the big post on the starter there should be a few smaller red wires can you see if any of them are broken.pull lightly and see if any separate.now if they look good at the back on the firewall there should be a power junction block with some red wires going into it.see if there is 12 volts to and from that junction box.also can you see if in that area there possibly would be a small fuse holder.can you also check and see if there is a fuse in the fuse box called ECM B ?
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Customer: replied 6 years ago.
ok I do have a ECM B fuse, it has power, checked it with test light while still plugged in. wires at starter are good, 12 volts across junction block on fire wall, there is a fuse link wire leading off, I checked both sides of black plastic tube in wire has 12 volts, i probed the wires also at junction block just to make sure the connections aare good
Customer: replied 6 years ago.
hey your right if i wiggle the ecm B fuse and pust on it just right I can hear the pump come on and a relay cllick and I can start the truck, I have a bad junction box You are the man! Thanks!
Customer: replied 6 years ago.
So now I gotta figure how to fix that

is it the fuse in the fuse box?or junction block at the firewall?

Customer: replied 6 years ago.
The pins holding the fuse in were dirty and the bolt holding the inside block and outside block together was loose.
ok good job im glad its running now for you!! great job!
Customer: replied 6 years ago.

Thanks, XXXXX XXXXX has been kickin my butt for a week off an on. I never new just replacing a rusty leaking fuel tank could cause so many problems lol.

yes those side mount tanks were a tight fit

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