Navecm

So I had a couple issues with the car (94 Z28 LT1/T56 recently)
-Hard Starting
-Low oil pressure at idle or if low enough rpm in gear (engine lugging basically) to the point where check gauges light comes on
-Had slight pop out exhaust when backing off throttle when hot (around 30mph in 3rd gear)

Now, I had it sitting for awhile and attribute some of the issues to bad gas, as it seems to start right up now with out any issue, and didn't have have any popping sound coming out of the exhaust.

With that said, thought I would test to make sure everything is within spec on the Opti test (on Shbox page - 4th Gen LT1 F-body Tech Articles).

Everything was within spec for the ICM harness.
On the Opti harness, everything was in spec except for pin D.

Where I am supposed to get ~60 ohms with key on and ~0-0.2 with key off I was getting ~295 with key on and then 1.6-2 with key off. Does anyone have any thoughts on what this really means? (Car seems to be running fine right now with the exception of low oil pressure when at low rpm).

shoebox

I wouldn't worry about it (especially with no real symptoms). Every car is going to be a little different in regards to tightness/cleanliness of grounding points and even some skew with meters and meter leads. The values are there to judge if there is something way out of the norm.

GaryDoug

It's not very helpful to make resistance measurements with power applied to a circuit. The normal current flowing will conflict with the current generated by the multimeter and the readings will be bogus.

shoebox

Gary, isn't the low reference (which the OP was mentioning testing on "D") a ground? I've been assuming it is. It has been a while, but I don't remember testing any power potential on it. I don't know why it is influenced by key ON or OFF, though. I agree that you cannot test resistance in the presence of power.

GaryDoug

Yes, it is the ground return but that carries the same current (about 0.2-0.4 ma for the sample Opti I have) as the 12v supply power wire, plus the current from the 5v pullup resistors on the low res and hi res inputs when the Opti has switched on (grounded) those outputs. That pullup resistor current varies significantly depending on the position of the timing disk. Different design Optis have different supply currents, adding another variable. Then take into account the variaion in meter stimulus current when in Ohmmeter mode and you get a very wide range of readings, which we have seen.

Navecm

Thanks for the input on this, its been awhile since I worked on that car - so checking things never hurt anything.

Time to dust off the oil pressure gauge and shake down the rest of the car.