ULTM8Z

Could someone please make a voltage check for me?

Circuit 430, ECM connector location B5, there's the purple wire with a white stripe for the distributor reference.

The ECM voltage chart that I got from an official GM Port Fuel Injection service manual indicates that I should see 2.3 volts with the engine running. I'm only seeing ~.6V. I've also looked at a couple of websites (including DIY-EFI.org) that say the same thing- 2.3V.

What would cause me to only have about .6V? I've also posted this over at thirdgen.org for other opinions. Hopefully someone can get back to me soon.

Thanks!

LS1Z28

I have 2.3 volts at 430. You may have a bad ignition module or a bad ecm. Your best bet would be to pick up a service manual of a 90-92 camaro or corvette and use the flow charts in it to find the problem. Have you checked the 4 wire connector at the distributor?

ULTM8Z

WOuldn't a bad ignition module simply cause a no-start condition?

LS1Z28

No, The car can still run it just runs like crap. No power, back firing etc..

TheGreatJ

Ckt. 430 should show about 2.3-2.5v on a digital meter. It's a 5v square-wave signal, and a digital meter will show the average voltage when used on a waveform. A labscope would be the best way to check the signal, but you work with what you have.

If you're only getting .6v I'd suspect a faulty ignition module. Try unplugging the connector from the ECM, then spin the engine over. If you still have low/no voltage, replace the ICM. If you get 2.3 with the ECM unplugged, replace the ECM.

FWIW the DRP signal is what the ECM bases it's timing control (and a bunch of other stuff) off of. If that ckt in the module is bad, it will still fire the coil, just without ECM timing control....it'll just fire at the base timing all the time. The ECM also won't know what RPM the engine is at, which will really mess with the fueling and such.

ULTM8Z

My scanner shows the correct RPM readout and that the ECM is managing timing according to what I programmed on the EPROM.

Or does one not have anything to do with the other??

ULTM8Z

Well, I made some more measurements:


- Verified that I'm only getting roughly .6V with respect to any ground (ECM, battery, chassis). I've also verified that I have less than 1 ohm from ECM ground to (-) terminal on the battery. In fact, I went ahead and verified every ground on the harness(sensor, ECM, chassis, engine, etc.) just to be safe.

- Switching the multi-meter to AC voltage, I get a value bouncing around between approx 1.3V and 1.5V. The sample rate is pretty quick on the meter, on the order of less than .25 seconds

ULTM8Z

Disconnected the ECM and still only got between .6 and 1V. Put a different ignition module in there and got the same thing.