Uglybronco

iTrader: (2)

Sorry this isn't a 3rd gen but its a pretty simular system so I figured I would see if anyone can help. (also posted on fullsizechevy.com)

I have swapped out the engine in my dad's '89 1-ton with another 454 TBI & have everything plugged back in the same as far as I can tell. The engine will turn over & fire off if I pour a little fuel in the TB. At first it had no fuel to the TB, So I hot wired the oil sender harness and it pumped away. Then I wasn't sure if the injectors were maybe gummed up so I hot wired them & they both spray strongly.

So I have worked it down to a problem with the injectors not getting signal. Has anyone run into a simular problem or have a strong idea as what I may have overlooked? I am pretty familiar with these systems from working on this truck & my Firebirds TBI but am currently stumped and am tired of messing with it. I am asking to hopefully avoid having to chase down the actual wires through the harness to the computer etc. This truck had been parked for quite a while but with the exception of poor rings (low compression & burning lotsa oil.) it ran fine.

Help help help...

RFmaster

Hey ugly - sorry, but you ask for it

TBI injectors are fired when ECM pulls one of the two wires to the ground. Which means the other side (typically red) is at +12 Volts. Get your DVM out and measure some voltages - make sure that one of the two wires is at +12 Volts (ign key in run and while cranking). Tying off injectors to fire continuously will lead to injector failure and engine 'drowning'.

Get a test light and back probe injector negative side wire - during cranking it should blink off. If you are not getting +12 volts check injector fuse.

//RF

Uglybronco

iTrader: (2)

Welllllll... 1st off thanks for the help, greatly appreciated. Actually ended up figuring out how to test that on my own before I got to read this. So that ended up testing good.

So my next thought was maybe something happened to the distributor. (I'm re-using all the previous engines components, but have most of the ones from the new engine also.) So I was about to plug in the other dizzy (I guess thats the popular term on here) & spin that one to see if I could get a signal. Well so I skipped that & just messed with the wiring harness, plugged the dizzy back in, twisted the thing (with the key on) & BAM!!! Squirt Squirt!!!!

& BTW, I never just held my "hot wire" on, I used some wires from an old battery charger with alligator clips & just scraped the wires over the battery, making them kinda/ sorta pulse...

Uglybronco

iTrader: (2)

Having a reacurring issue now... I posted this elsewhwere, then copied & pasted it here so I apologize for any redundant information. After an engine swap I had trouble getting it to fire. I checked a bunch of things and finally found it to be a problem with the computer apparently not getting signal from the distributor.
Well I finally got it running from what seemed to be some lucky wiggling of loose wires. But now I can't get it to run again. I know that with the system working properly you can twist the distributor with the key on & make the injectors pulse. It won't do that now. I checked for continuity from the four wire distributor harness back to just before the wires go through the firewall... they are all good.
I can make it start by pooring fuel in, and I can make the injectors pulse & spray fuel by hot wiring them. I have tried a pickup coil from another ditributor and plugged the wires into that other ditributor & spun that. (Yes I grounded that distibutor.)
So all I can figure is its something way too simple that I am overlooking or its some kind wiring bug that I'm missing.

rocko350

there was a post around here that mentioned the wires from the distributor to the ecm getting pulled on a little too hard and the wires inside break but the insulation doesn't. 1 wire to distributor should be 12 volts and the other is the drp signal sent back to the ecm. should be able to see it flash with an injector noid light attatched not a test light this WILL kill the ecm.