1G constant power to injectors, no pulse

[Turbogsxmitsu]

I just put a motor in my 1991 GSX, car ran previous, now we cannot get her to start, it cranks its ass off, but no sign of wanting to start, first there was no spark in the 2 and 3 cylinders, put a new crank shaft position sensor in and fixed that problem ( old one had water in it), Now i have spark and this problem arisses. We use a test light on the injectors and while we crank the car over we just get a constant power, no pulsing of the injectors !!!!!!! HELP

 

[luv2rallye]

One side of the injectors is always +12 volts and the other side goes to zero only for a few millisec through the ECM. So if you connect a test light to either side and the other test light wire to ground, it will always appear on. Even if you put it across the injector it would probably always appear off since both sides of the injector are +12v most of the time.

Using a test light with a filiment cannot react quickly enough to millisec change. It also draws significant current thereby effecting the very circuit your testing. If your injectors were truely on all the time (due to voltage - not because their broken), the ECM side would always be zero volts.

In order to detect the pulses, you would have to either use an oscilloscope, or you might try a multimeter on AC position (with one lead on the ECM side, other lead to ground), or if your lucky and can look very closely in the dark you could try hooking an led (with correct polarity and series resistor to ground) first to one side and then the other to see any brightness difference. You might also try measuring each side of the injector (to ground) with an analog voltmeter to see if any change (but with millisec you might not see any difference). All this assumes you are cranking of course.

 

[Turbogsxmitsu]

Thanks for the reply, If both sides are supposed to have power, then something is wrong because only one side gets power, the other wire going to the injector has no power at all, what the hell does that mean? I cannot get this car to even sound like it is going to start, it just cranks and cranks. Please help!!!!!!!!!

 

[luv2rallye]

I said only ONE side the injectors DO get power (each injector though a series current limiting resistor from the MFI relay which provides +12v). The other side of each injector connects to the ECU which provides the ground for a few millisec (the injector pulse width). When you say that side has no power what do you mean? It has no voltage? What are you measuring with?

If you have +12v on the resistor side of the injector and you are absolutely positive the injector is not working, then it can only be a few things: 1) the injector itself is bad, or 2) the resistor (pack) is bad (too high resistance), or 3) the ECM is either bad or one of it's sensors (that it relies on to enable MFI) is bad (eg. CAS is one).

 

[mavisky]

one wire is the constant power wire, the other is the ground wire. the ecu switches the injectors by taking away the ground at a determined time. this is why you can overheat injectors when they're running wide open for prolonged periods of time (like those of us running 19psi on the street with the 450cc's) if it was the other way around they would run cooler when operating.

 

[Turbogsxmitsu]

The way i am testing the injectors is by test light and I thought both injector wires were supposed to have power, But you guys are right only one side lights up the test light when i crank it. So if the injectors are correct What is wrong. When I crank the car, fuel is definitely getting to the cylinders, So I guess the injectors are OK then, The car gets spark, air, fuel, but still no sign of the car running!!!!!!!!!!!!!!!!!!!! What else could be wrong.