95Blackhawk

How do I check the cause of an injector not firing?

Assuming it is a ground issue (not sure) where does the PCM get its ground from?

I have 2 PCM's and neither work to fire the injectors. Using a noid light, KOEO the red connection at the injector is hot as it should be. However turning over the car, the ground is not completed as the noid light does not flash. I assume this is the same for all the injectors although I only checked #3. #3 injector is 13 ohms as it should be.

I determined I had spark at the plug by pulling #1 and seeing the spark. I have fuel pressure confirmed by a gauge.

mdenz3

Did you check the two injector fuses?

95Blackhawk

YES! Both are good.

Injuneer

And you're sure you don't have DTC 16? That will shut down the injectors. You said in the other thread you changed out the optical module in your Opti. Are you sure you hooked all the wires back up? Are you sure there isn't a damaged pin on the Opti harness connector? Did you verify the optical sensor was putting out the 0 - 5V square wave for the low resolution pulse pattern?

95Blackhawk

I didn't know DTC16 would shut down the injectors. I am not getting a code at all per Scanmaster.

I would like to confirm if I am getting a sqare wave pattern but this would mean cutting into my wiring from the opti correct? It just seems that is invasive but will do it if required to confirm a square wave. If I cut into my wires, do I use AC to check the voltage since it will be going from 0-5 or do I just use a noid light? My noid light says it is good from 6-24v so hopefully that is close enough to generate a flashing light.

On the opti, I am getting the required 12v/5v/5v/ground from the PCM. That much I know. However, I don't know what the optical encoder is doing with this information.

Injuneer

All you have to do is use the Opti harness test connector on the passenger side of the intake manifold. You can use small straight pins to probe the wires at the connector. No need to cut anything.

I though your original post asked how to test the Opti OFF THE CAR. Speedy told you to to check that the signal was varying from 0V DC to 5V DC, as you slowly turned the optical wheel. Apparently now you have the whole thing reassembled?

95Blackhawk

I never knew that about the back side of these connectors.

I did as speedy explained and have both low and high resolution from .22v to 5.01v. When I rotate the opti, the coil fires and I hear a clicking followed by a whirring sound. I assume the clicking is the injectors but no idea what the whirring sound is.

I am putting it all back together again and trying to fire it up.

The last thing left is a jumped tooth on the sprockets but no idea how that would happen. The chain is 1600 miles old and is a solid roller chain.

95Blackhawk

Confirmed with mutiple cranks that I am NOT getting any DTC's.

However, I also have determined that the computer IS giving a DC voltage to the injectors that are in line with a cranking scenario. I went back to an old DataMaster file and confirmed that this looks the same.

So, I have fuel pressure as confirmed by a gauge, I have the PCM sending a signal to fire to the injectors and I have a signal back from the opti to the PCM.

Oh, I had 6 and 8 plug wires crossed for a bit and it gave me a small backfire. Does this mean anything?

Injuneer

How did you determine "the computer IS giving a DC voltage to the injectors? The injectors are provided with a constant +12V on the pink wire at each harness connector, and the PCM supplies a ground to fire the injectors.

Guest47904

Wait just a minute. You only checked spark at 1 plug. That doesn't mean a hill of beans. Second, I told you a long time ago to squirt fuel directly in the intake while someone cranks it over. If it still doesn't start then, you have another problem OTHER than fuel. Get it? If it fires up from the fuel squirted in the intake then you might have a fuel problem.

Third, our injector clips are very difficult to keep the noid light prongs in contact with the injector clip contacts. When a poor connection occurs, it looks like the injectors are not being fired.

You are making this way too complicated then it has to be. Check at least 4 plugs for spark. One in the front and one in the back on each side. You have to understand that a SBC will not run with 3 or more plugs not firing.

You can do the fuel squirt first and if it doesn't start, then check for spark on more plugs. If it does fire with the fuel squirt, then proceed on the injector hunt.

95Blackhawk

Via Datamaster, the PCM is telling me it is sending 1.2v to each bank of injectors. Not sure what that means other than I assume it means it is trying to open up the injectors. Tell me if it is irrelevant.

ss.slp.ls1

This is a good test, I thought I had a fuel problem before, sprayed starter fluid in the engine and no start, that led me to find an ignition problem. Good luck.

Injuneer

DataMaster does not tell you what voltage the PCM is sending to the injectors. The PCM does NOT send voltage to the injectors. The injectors require 12V to fire. They are already connected to a 12V source, via the pink wires. The PCM just supplies a ground.

Is it possible you are looking at the injector pulse width (BPW mS), which is in milliseconds, or possibly the injector duty cycle [INJ DC (calc)], which is expressed in percent? In any case, if the PCM is not setting the pulse width to "0", it would appear to be trying to fire the injectors. But there is no way for the PCM to confirm they are actually firing. It does check the integrity of each injector circuit as it fires, and will set a code if it detects a problem.