low voltage

[calvin6199]

i have a 93 coupe with a 351w swap it will not start it has low volts (4.3) to the injectors and no pulse. but it will fire up on starter fluid any ideas i think ecu

[silverstangboy]

sounds like you have a ground issue with your harness, re-check all of your connections if the ECU was hindering injector pulse the car would not start at all.

this is actually how my homebrew anti theft works

Mustang FAQ - Engine Tech, Air Bag, ABS, Brake Home Page

[calvin6199]

it only starts if i spray starter fluid in the intake it has no pulse from ecu at all put does have 4.3v to the injectors

[silverstangboy]

when does it give 4.3volts? key on engine off? or when the injector pulses?
you should see a full 12v when the injector fires, but partial voltage when in normal state, as the computer monitors the condition of the injector with that voltage.

one way to see if the computer is telling the injectors to pulse is tie in a 12v light in parallel with the injector, it should light up when the injector fires.

another thing to check, is your fuel pump relay turning on?

[calvin6199]

no volts with key off. 4.3 with key on. absulutly no pulse when the key is in the start position. the fuel pump is on and will suppy as much presure as i want. it is set at 55psi right know. it has no ground any time key on, key off, or in start position. the injectors are suposed to have 12v as long as key is on and a ground on and off to pulse the injector. i have a noid light it does not flash

[silverstangboy]

ah, I see what your saying, your checking the harness to a known good ground and only getting 4.3 volts, I thought you were checking it against the injector ground which would not show a full 12V, but you are right, system is 12v hot when on and computer provides a true ground when it wants the injector to fire.

this diagram should help you with some questions, you may be right about the computer
i'll try to help you with anymore questions.. im working alot of hours right now though.







check your injector to a known ground to see if it is outputing 12V, then if not go through and check all your electrical connectors for good continuity, i'd also check pin #37 at the computer itself.