I switched from a 89' v6 mpfi to a 92' 5.7L tbi. I can't get the computer to turn on unless i ground or give power to the fuel pump relay in the engine bay... and then it doesn't want to give power to the injectors if i do that.

if i manually give +12v to 1 injector, the computer turns on, and 1 injector does too... and car runs like poop. if i give +12v to both injectors manually, neither work.

can anyone help me solve my problem?

i'll go ahead and answer a few other questions to help.

whole uncut harness is correctly installed.
89 v6 --> 92 v8
no, i haven't replaced the pump
computer is from the 5.7
the 5.7 ran great before i pulled engine from donor

does anyone think that its a VATS problem? cause i'll buy the bypass box if needed... i just really do not want to throw parts at this to see what works or does not work.

thanks, scott

 

I doubt it is a VATs issue. I don't know of any 5.7l TBI engines that was in a vehicle with it.

It actually sounds as if there is a power lead to the ECM missing. On the '8746 & '7747 ECMs battery power is on pins B1 and C16 (ORN).

Switched ignition is on pin A6 (PNK/BLK).

I would verify those with a DVM. Also, at key-on, engine-off, does the SES turn on, blink off, then turn on solid?

Your giving power to an injector doesn't sound right. The injectors are given ignition switched power. The ECM then grounds the injector to pulse it. At key on, both injectors should have +12 volts to them.

RBob.

 

when i put the key into the on position, nothing turns on (comp nor pump nor injectors). when i put +12v, i meant through the fuse block (pulling a fuse and giving +12v through that)

-Scott

i'll try your ideas tomorrow when im off

 

I'm getting 2.2v at both B1 & C16 (ORN) and 2.0v at A6 (PNK/BLK). I also tested a few other lines and they were all getting voltage too. i also checked the wires that went to my internal setup (the clear one that forks off by the ecm) and it too got voltage...

any other ideas guys? im ready to start spinnin some tires lol.

 

Sounds like to me that you have a fried fusible link down by the starter.

When you pullled the injector fuses and hot-wired 12 volts to them, you shouldn't need to do that. They should already have 12 volts with the key on.

Having 2.2 V and 2.0V on B1 & C16, and A6 is incorrect (unless the battery is dead). Should be at about 12 volts.

RBob.

 

my battery has been low, i'll toss a 40 amp 12v charger on it and re-test the wires tomorrow... if same results, where would that fusible link be?

 

with +12v charger hooked up... 11.2v at b16, 11.0v at c1, -1.1v at a6

 

No ignition switched power. Key was on during testing? Bad switch, bad fuse, bad wire. Time to start at a point in the switched ignition circuit and trace it out. Can start at the battery and move toward the switch. Or start at the switch and work your way back to the battery.

Also explains why there isn't power to the injectors as they too are ignition switched.

RBob.

 

actually i forgot to take out the +12v to the injectors, so i put the fuse back in and turned key on. alright, i hooked up the +12v and got same 2.2/2.2/2.0v...

but when i grounded out the fuel pump relay, i got these:

b1: +13.1v
c16: +13.1v
a6: +12.9v

no injectors coming on though

edit:

after some more playing around... with all fuses like they are supposed to be i turned the key into the position and measured the voltage on the injectors... all 4 wires say +12v. as soon as i ground one of them out, that injector SPEWS gas... so, for some reason, my computer is not getting a ground connection, there is a relay bad, or im missing something... in one of my other threads, someone said that the 92 had a different vats setup vs the 89... and it grounds itself out at 30 cycles/sec... im trying to stay away from the vats issue and hopefully its just a wiring problem. can i get some more input please?

thanks!

-scott

 

anyone? i think its a ground for the computer