TBI injectors dumping fuel with key on, engine off

[Daveo91Burb]

so I’m hooking everything back up for my new 383. Today I finally got things wired up enough I could turn the key on to check for fuel pressure. Or so I thought. As soon as I turn the key to run, injectors start dumping fuel like crazy- like what you’d expect for WOT. What do think I hooked up wrong or backwards? The weirdest part is they still do it even after I unplugged fuel pump relay on firewall. Shouldn’t that disable the pump?

I bought the rebuilt 454 injectors on fleabay -maybe they’re stuck wide open?

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[Cuba]

You must have wired something wrong. They are ground side switched by ECM. What I would do is 1st make sure to unplug injectors. Red & white of the injectors should be constant hot with key on.

If that's good, use a noid light on each of the injector connectors (or an incandescent test light if no noid light) check if while cranking the light flashes or not. This will tell you if it's ECM issue or injector issue. Best to use a buddy here, so you can see clearly what the light is doing.

What you want is flashing while cranking over, some dimming is normal because of the load of the starter, but you want a definitive on/off flash while cranking. This is good. ECM is good.

If not flashing, then you have wiring issue or ECM problem

 

[Cuba]

So you can see how to hook up a test light in my drawing here. Remember, injectors unplugged. Be careful not to short the positive side (red & white wires) to ground, as you'll blow the ECM1 fuse. You can use rags or a towel to place on top off throttle body to keep from shorting anything while testing, lay the harness & test light on top. Just some tips

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[1987 GMC Jimmy]

Agreed. You can borrow the noid light kit at Autozone. Also, if you prop the light just right using the air cleaner stud, you can just watch it out the windshield. If you’re using a test lamp, though, I think you’ll definitely need a helper.

 

[JoeR Jr]

Unplug the electrical connectors to the injectors. Cycle the key. The injectors should not spray fuel. If they do, you probably rolled an o-ring when you installed them.
If they only squirt when plugged in, you need to figure out what is grounding them.
On the short list of possibilities is:
Ground wires to injectors are shorted to ground.
PCM injector drivers are failed on.
PCM is getting signal to fire injectors (eliminate this by unplugging the 4 wire connector to the distributor).

 

[Daveo91Burb]

Thanks, all. I’ll see what happens when I unplug injectors tonight.

So why does my fuel pump continue to pump with the relay unplugged?

 

[Cuba]

Thanks, all. I’ll see what happens when I unplug injectors tonight.

So why does my fuel pump continue to pump with the relay unplugged?

If your cranking, it's because it gets power through oil sender as well. GM's backup.

If key on, it should only go on for 2 seconds then cut off, as a part of ECM prime.

 

[Daveo91Burb]

Unplug the electrical connectors to the injectors. Cycle the key. The injectors should not spray fuel. If they do, you probably rolled an o-ring when you installed them.

More like didn’t install them at all. When I put the TBI together many months ago with enlarged throttle body and rebuilt injectors I think I was just test fitting everything and not doing full assembly like I was ready to run it. I knew I should have gone through everything again yesterday when installing on manifold. Problem solved, thanks much to all.

Just need to change the oil before I fire this thing - probably a half pint of fuel in the oil now.

 

[Daveo91Burb]

If your cranking, it's because it gets power through oil sender as well. GM's backup.

If key on, it should only go on for 2 seconds then cut off, as a part of ECM prime.

Yeah was not cranking at all. I think it was going thru the prime as you mention - it behaved normally once I solved my o-ring problem described above. Will it keep pumping if it’s not building pressure in the injector pod? It definitely ran the pump for longer than two seconds when it wasn’t building pressure.

 

[JoeR Jr]

Yeah was not cranking at all. I think it was going thru the prime as you mention - it behaved normally once I solved my o-ring problem described above. Will it keep pumping if it’s not building pressure in the injector pod? It definitely ran the pump for longer than two seconds when it wasn’t building pressure.

Glad you got it figured out!
The fuel pump strategy is as follows:
When you turn the key on, the PCM turn the fuel pump on for 2 seconds, then it turns it off.
As soon as the PCM sees an ignition pulse from the distributor (purple wire/white stripe) it will run the pump again. When the pulses disappear it will run 2 seconds and stop again.

As mentioned already, the oil sending unit supplies backup power for the fuel pump relay. If the relay circuit fails, the oil pressure sending unit will supply 12V to the fuel pump as long as it sees oil pressure.

If the fuel pump runs longer than the 2 second prime something is wrong. Someone has changed some wiring. If the relay was stuck the pump would run all the time. Not just when the key was on.

 

[yevgenievich]

Not sure on the two second thing, but on mine the fuel pump will prime long enough for me to get out and come to the back to listen for it. And then it will shut off. If it runs longer than 30 seconds, then I would look for issues. However, on the Trans Am, it is about two seconds, on 89 suburban it was more around 5-10 seconds.

 

[Daveo91Burb]

Thanks, guys. I think it's OK. I don't think I ever had the key on for more than 10 seconds or so, maybe only 5. And pump might have stopped in that time, I don't know since I was up front watching my throttle bores fill up with fuel. w/o those o-rings at the bottom of the injectors it's amazing how much fuel dumps out. Oil change, fill up with the rest of fluids, other misc odds and ends and hopefully will fire it first time in truck this weekend.