Before I look in my book, anybody know the PROPER manner in which to test my fuel injector harnesses for anomolies?

Right now with key "ON" I'm getting power to both the black, and the black/colored wires on each injector harness clip. Connecting a test light from either of those to ground gives a light ON condition. Turning the key to "OFF" kills those.

I thought one was a pulsed ground and one was a switched 12v? Hitting the service manual now.

Just changed my oil and I had a good 1+ quart of fuel in my oil. :eek: :eek:


[Modified by scorp508, 2:49 PM 10/27/2002]

 

With key ON and engine OFF I get 11.93v and 11.88v at the injector wires.

 

Sounds correct. I beleive the computer pulls the one side to ground to pulse the injector.

Chuck MacTrinder
#72 http://www.tccracing.com

 

Shouldn't one wire at the injector just be connected to NOTHING then when not running?

 

Will the car run with just one disconnected? Put your light on it then and see what it does.

 

Just did that about 20 mins ago, it pulses. Go figure. Fuel can only come from so many places, its finding out how and why. As soon as you crank the car over all you can smell is fuel, and there is fuel coming out the back.

There is continuity between the pulsed lines of the injector banks. Is this normal? Are the joined inside the ECM before the injector driver?

 

The ECM provides a ground for the injectors. I am not sure if this is a quad driver circuit of some type of NPN transistor only circuit. Never seen a schematic for the ECM. GM designed this way cause you can induce a voltage but you can't induce a ground. It's a control design feature. GM did not want stray voltage pulsing the injectors so they designed the system for the ECM to provide the ground versus the injector providing a ground and then have stray voltage fire the injector. Something like that. Those engineers worry too much. Although, some lawyer would eventually be in court saying the Bose amp caused the acceleration problem, not my client.

Now, how long the injector is held open, ie how long the computer provides the ground (pulse width) is a function of mapping tables (after evaluating sensor input), and in closed loop, the 02 sensor voltage. Remember too, unless you have changed chips/software, the computations in open loop are based on a given injector size and fuel pressure, although when in closed loop, it will simply seek stoic.

Not sure what problem you my have regarding fuel? Fuel runs out the tail pipe in closed or open loop. Idle, 2000 rpm, etc?

Hope you get your car fixed.

Keep the faith.

dlmeyers 90 coupe zf6 3 speed shocks


[Modified by dlmeyers, 5:01 PM 10/27/2002]

 

Thanks. Can anybody answer this with certainty?

With key switched on and engine not running, should there be 12v at both wires to the fuel injector. This is the condition I have at the moment. I have 12v at each wire, but if you install a test light it does pulse with engine running.

 

My '88 GM Shop Manual shows both banks connected to a "switch" within the ECM that grounds the Blk/Grn wires to fire all injectors at once.

This means that when they are not being fired but the key is On you will see +12Vdc on both the Blk and the Blk/Grn wires to any injector.

Even at idle (say 800rpm) the injectors are fired for only a few mSec at about 7Hz. So they are only On for about 3% of the time. This is likely not enough duty cycle to show up with a test light.

You "might" be able to see some indication of injector firing with a DMM set to AC Volts and connected between the BLk/Grn wire and ground, but I'm not sure. If not, set the DMM to DC Volts and look for about a .5Vdc drop at idle.

An oscilloscope is the real way to see injector firing.

 

Jim, I'm seeing the same injector driver switching them to ground, but I am not seeing where and how I will get the 12v when not switched to ground. The diagram makes the driver look like a relay that is just open or closed, not switching between sources. I'm so :confused: right now it isn't funny.

 

Scorp,

If you have the electrical supplement, head for around page 8A-20-7 Multiport Fuel Injection, Fuel Control and Delivery.

The harnes power comes out the from the fuse block, through the injector, (remember-the injector is NOT a case ground) and into the ECM. There, the power waits for the solid state ground, for the batch fire, it's ground circuit A and B, the two banks. When you are checking the harness, you have one lead to the wire (carrying 12 volts) and the other test lead is to ground. Hence, a 12 volt reading. The injector is not pulsing because the solenoid does not have a ground until the ECM decides it is time. When the ECM makes the ground, the solenoid pulses open, with pressure, fuel flows. When you hook up a noid/light, the pulsing is noted with the light flickering as the ground is applied and then removed by the ECM, pulsing the injectors. The voltage drop to zero for each injector is for another electrical theory day. Can't spell the guys name. Kirchner?. jfb will do a good job of explaining this.

Electricity sucks.

dlmeyers 90 coupe zf6 3 speed shocks


[Modified by dlmeyers, 6:01 PM 10/27/2002]

 

Been looking at that page all day. Still not sure where the 12v comes from though that is being applied to D15 and D16 (circuits 467 and 468). I've got the 12v coming into the black wires which I expect, but the black/striped wires also have 12v coming into them with key in the on position. This I did not expect. I guess I just expected to get nothing at all if the ECM was not pulsing them.

I see the ECM getting 12v from B1 and C16 which apparently goes out to A1 (fuel pump relay during start), B2 (fuel pump relay), and B6 (VATS decoder).

What confuses me is if C16 is is or not connected in some manner to D15 and D16. When the injector control is NOT switched to ground, what is it switched to? I must be reading this thing wrong.....

 

Think of each injector wired in a simple series ciruit. The power comes out of the fuse panel, through a wire, through the injector, but not to a ground. Then this single wire finds a ground and the device works.

dlmeyers

 

Looking at the Howell book the 12v comes out of the fuse panel to one side of the injector. the other side goes to the inj. driver on the ECM. With the key on you are seeing 12 volts on both wires to the injectors because it is passing through the injector to the ecm. The injectors have low resistance hence you are seeing about .15 volts drop. The do not fire because you do not have a differnce in potenial between both sides of the injector. When the ecm wants to fire the injector it grounds the one side giving you the differnce.

If you disconnect all the injectors wiring and measure the plug you should see 12v on one side and not the other..

Hope this helps/makes sense.

Chuck MacTrinder
#72 http://www.tccracing.com

 

[QUOTE]Just changed my oil and I had a good 1+ quart of fuel in my oil. :eek: :eek:


[QUOTE]

:eek: :eek: I bet that oil was like water... hope you didn't run it too long like that! :eek: :eek:

 

Scorp, the injector drivers in the ECM energize the injectors by providing a low resistance ground path which causes current to flow through the injector coils.

Of course if any injector is plugged in with the ignition On you will see +12Vdc on both wires due to feed through within the ECM.

When the ECM isn't firing an injector it is likely pulling the Blk/Grn and Blk/Pnk wires to +12Vdc, though I can't tell from the picture of the Injector Control that only says "Solid State".

So if you unplug all injectors and measure voltage on one of the injector Blk/Grn wires it may still show +12Vdc but I'm not sure. If there is an internal pull-up resistor at that "Solid State" switch it would be rather high, usually of the order of 100kOhm to 1MOhm.

If, with all injectors unplugged and the ignition On, you momentarily jumper a 10kOhm 1/4Watt resistor from the Blk wire to ground you should see no voltage drop; if you jumper the resistor across the Blk/Grn wire to ground you should see the voltage drop to nearly zero.

 

If you find your problem please keep us informed. I just posted in General(by accident) about my injector problem. Mine is a little different than yours. Right now my 1 and 6 injectors are not getting a signal to spray.