Hello forum,

I bought a TPI unit and harness from an 86 F-body complete with ECM and all other sensors. Heres the problem, I have been told that the distributor sends a signal to the ECM and then the ECM sends a pulse to the injectors, well I get one without cranking. I put the light tester in, plugged the wires up and the light tester lights up.

I dont have the TPI system installed on the car, but I have it on the bench and I followed the directions from Chevy thunder as to where each of the 16pin wires go A-R, some diagnostics, some ground and some positive. I hooked all these up and the signal to the injector is full on.

Is there a way that I might have tripped a wire and the injectors got full juice? I used the pink/blk wires that come from the injectors, one for each bank and just ran them direct to the positive terminal along with a bunch of other wires that need juice when cranking or in the run position. Please help, I need to know if this TPI system is any good.

 

TTT

 

Might do better to ask this over on the DIY Prom forum since a lot of those guys have test benches. But I will say that doesn't sound right....

 

If you're testing from the injector connector to a ground, you should see 12VDC.

The injector circuit is powered full time while the ignition switch is in RUN or START. The ECM switches ground when it wants the injectors fired.

 

Figures - they do that a lot don't they? (supply power and switch the ground on - off)

I wonder why they do things that way....

 

kevinc hit the nail on the head (or is it hit the head on the nail?).

Yep, the ECM grounds the injector to turn it on for the specified PW.

 

ECM's don't like voltage spikes...

 

Okay guys, I see why that happens now, both sides of the injector wires show positive current. But when i tried to connect the Engine service soon wire to a bulb with a positive current on the other side, no juice. How can I surely make sure the SES light works so I can pull codes in the future?

Also Im just gunna fork over 50bucks and see if a HEI CC distributor can break the problem down and if the injectors will fire.

 

With the ECM powered up, but the engine not running, the ground side of the injectors may show +12v. It's just the way the injector drivers are wired, don't worry about it until you can hook it up to some type of pulse generator and see if they get the ground pulse they need.

The SES light is also ground-side controlled, which means you need to hook one side of the bulb to the ECM and the other to ignition voltage. The bulb should come on for 2-3 seconds when you first give the ECM ignition power, and it should stay on indefinitely with the ECM on and no reference pulses.

FWIW if there's a problem with the memcal, or no memcal installed, the SES light may not come on.

 

Thanks for clearing that up, what is a Memcal?

 

Thats the rectangular "chip" inside the ecm. Usually has a blue cover.

 

Is their a way to check it out? Make sure its in good condition?