azscottd

I mentioned this in another thread a couple years ago. It had happened to me a couple of times - that when I connected my dwell meter to check the MCS that it would stumble and die if I didn't disconnect it quickly enough. When I'd repeat the exercise later, it was fine.

We've come back full circle again. My son has to pass AZ emissions so I wanted to check everything. He said it had been idling poorly. Discovered that his TPS (second in last 3 years) was dead. Replace it and adjusted to .48v.

Connected the dwell meter and the MCS stops clicking.

I've had some anomalous and inexplicable things happen once or twice in the past and others suggested swapping ECU.

Thoughts?

Damon

I'd suspect your dwell meter. It's not supposed to provide continuity to ground when hooked up since it READS the ground on/off pulses of the ECM.

I assume you are connecting it to the green single-wire dwell meter connector sticking out of the wiring harness back near the firewall (pass side) with the other lead going to ground to perform this test. If not, that's probably your problem.

Ooh, I just had a third thought... a bad engine-to-chassis ground. That can cause all sorts of weirdness.

azscottd

I too suspected the dwell meter Damon so purchased another. Both behave the same way. My old one is 35 years old so suspected it may have failed - had hoped it would be the case but not so. I checked grounds and all looked good. Going to plug in another ECU tonight and when I do, will double-check everything. I hate gremlins. :-(

azscottd

OK - I swapped the ECU with a spare and it's better. Running much better however, when I connect either dwell meter, the MCS stops clicking. I don't know what it's position is, but it stops clicking. With this ECU, it doesn't stumble or die, just stops clicking. MCS is good - 24k ohms, neither side shorted to ground, etc. Stumped. Tempted to find myself a non-feedback carb, attach an external TPS, and throw a resistor on the MCS connector.

naf

iTrader: (7)

you may want to try back probing one of the leads to the mcs with your dwell meter.

be aware, however, that the meter will then read in reverse of true mcs dwell (reportedly). still can use it to get to 30 degrees

Damon

How about this for a solution: Stop doing that.

Just run it. Who cares about dwell readings? Worst case, get an old OBD1 scan tool (like my ancient Diacom setup) and read the dwell off of that if you just absolutely positively have to satisfy your curiosity.