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Well that was a/b

a) a "lerning" experience

b) fairly expensive

Had a "no start" today with no DTCs stored. Checked the voltage to the coil and it started out at 12 then went to zero. I.e. the Automatic Shutdown Relay was turning the engine off. :/

Checked a bunch of things again... thought about the coil but then thought it should also be getting voltage so there MUST be another problem.

Frustration sets in so I have it towed to the closest Jeep dealer $89 foo.. I have it taken down.

Well, the dealer said it would probably be the next day so I'm getting ready to leave when the mechanics start gathering around the hood. Seems they found the supercharger. :) Long story short the head wrencher starts working on the ZJ. I tell him all the stuff I checked and he sets to check them again. That's when I find out if the engine doesn't successfully start in the first few revs the ASD shuts the ignition down! Well..dammit. It WAS the coil just as I thought. An Autozone $45 part.

So the dealer puts in the OEM $75 one and bills $138 for labor. (that's ok. I needed the part and the mechanic taught me a LOT about how to read a scope and diagnose spark and injectors.) I call it cheap education.

It also makes the sting hurt a bit less.

Reply to
DougW
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Reply to
L.W.(ßill) Hughes III

L.W. (ßill) Hughes III did pass the time by typing:

np, that's what the mechanic showed me. He also stated that the number of oscillations right after burn-time should be > three, anything less and the coil is starting to have internal shorts.

Also that during burn time there will be several patterns and that can tell you if there is a fouled plug, a crack, or the gap is way out. And that last dip after the oscillations is dwell. Got about two pages of notes from the tech.

Now that I understand what to look for this make more sense.

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Those were just with an old inductive pickup for my timing light hooked to my lab scope.

I should have just thrown the $39 AutoZone coil at it, but what threw me was the ASD relay was shutting the system down and that's usually associated with something being terribly wrong. Now I know better, it shuts down because it didn't sense the coil or the engine didn't fire after a couple of revs. Guess the ECU must be looking at the coil ground.

:)

Reply to
DougW

My motto is: When you're stupid you gotta be tough!

( Baptized Clemmie the other day: Had the dog harnessed in on the way for a run, no top, no doors...big downpour!)

Seahag

Reply to
Seahag

Reply to
L.W.(ßill) Hughes III

L.W. (ßill) Hughes III did pass the time by typing:

Don't think it's possible. The scope is only two channel and I've only got one clamp on pickup.

But I can store the waveforms in memory and do that on the computer. Just not real-time.

On the other hand I have seen PC based testers out there for reasonable costs. Picotech.com makes one but it doesn't look like it does multiple spark plugs like a Sun or SnapOn analizer does.

Reply to
DougW

DougW proclaimed:

There are also PC based multichannel O-scopes that work reasonably well, particularly for low frequency stuff like automobiles.

Reply to
Lon

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