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7T8CJ7 03-17-2004 01:12 PM

AMC 360 timing issues
I have a 87 360 powered Jeep. That has been treated to an Edelbrock Cam, Carb and SP2P intake with an Edelbrock carb. I have also done the TFI upgrade and installed an MSD 6, all of the emissions stuff is gone. It runs pretty good except that I can't hook up the vac advance for the distributor because it kills the motor every time. Let me clarify, while at idle I can loosen the distributor and manually advance the timing maybe 15 or 20 degrees without problems. However if I apply vacuum to the canister (using a mity-vac) the engine dies before the timing advances to 10 degrees. I replaced the pickup coil fearing that it might be shorting out when the advance plate moves but it didn't change anything. I am at a total loss as to understanding the difference between changing the timing by turning the housing and changing the timing by applying vacuum to the canister. But here I am. I would really like to get the vac advance working properly as I would expect to improve performance and drivability both but the fact that it keeps killing the motor is bad. I am using a good dial back timing light while doing this and the amount vacuum I am applying with the mity-vac (10-12 in.)is less than the engine actually produces (16-18 in.). At present I am running with the timing advanced about 10 degrees at idle (700 RPM). I would really appreciate any input anyone has to offer.

RRich 03-17-2004 02:12 PM

Re: AMC 360 timing issues
That is a strange one for sure.

I wonder if the breaker plate - the plate the pick-up coil is mounted on - is loose? As I remember, the clearance between the PU coil's metal core and the reluctor is normally about .008".
Normally the plate rotates as the diaphram's arm moves it. Could be it's pulling the PU too far away from the reluctor?
You should see that by looking and using the Mity-Vac.
The plate's mounted on a flimsey bushing arrangement, could be worn or the clip's come off.

If not - then you might want to measure ohms from the PU as you move it like that. Could it be losing connection?

And - the ground tang - loose? The ground tang in the rubber feed through has to ground on the housing, not the plate. Or cut the black wire off and run it to a decent ground engine elsewhere.

Let us know what you find - interesting.

7T8CJ7 03-19-2004 11:08 AM

Re: AMC 360 timing issues
I replaced the pickup/plate assembly with no change in symptoms. I checked the old one out whith an Ohmmeter prior to the replacement and couldn't find any opens or shorts while moving the plate. I replaced it anyway as I couldn't think of anything else.

RRich 03-19-2004 11:52 AM

Re: AMC 360 timing issues
Really odd -
Try hooking an ohmmeter to the PU coil - engine off. Apply vacuum slowly to make sure it's not losing continuity.

Also - use a feeler gauge to see how far away the coil is from the reluctor. Then measure it with vacuum applied. Too far away it won't trigger.

You can measure the PU coil output - use an analog meter - needle type, a digital will lie) set it to low voltage AC - crank it - with and without vacuum to see if it's different or goes away - should be about the same test as the ohms test, but measuring actual output.

Test the ground wire the same way - black wire - with and without vacuu.

7T8CJ7 03-23-2004 09:10 PM

Re: AMC 360 timing issues
Ive done some more investigating and have learned the following;
After using the search function I found a TeamRush post about distributor rotor phasing and investigated. I drilled a hole in the cap in-line with the #1 plug wire. With the engine idling (not too well) and the timing set at 0 degrees I need to crank 45 degrees into my dial-back timing light to see the rotor through the hole. I have moved the distributor 1 tooth in each direction as well as moved the plug wires 1 position each way and no matter what combination of fiddling I use I still need to dial back about 45 degrees to see the rotor line up with #1. I cannot understand whats going on. Additionally, I checked a buddys properly functioning 360 to verify the reluctor positioning on the shaft from the factory. His reluctor has the roll pin just about centered between two of the relucor teeth (same as mine) so I'm thinking that that has to be pretty close to correct. I am totally flummoxed as to what I have learned regarding the 45 degree variance I'm seeing. Tha balancer marks were O.K. approximately 10K miles ago when I put in the cam and I have no reason the believe that thats the problem but something is amiss here and I just don't know which way to go.

Dex 03-23-2004 09:23 PM

Re: AMC 360 timing issues
was the cam installed straight up or advanced? was timming chain put on with marks correct position? was #1 at top dead center? and last , has the balancer slipped (bubber seal can do this) so that timming mark has moved?

just my 2 cents?? but im chevy man at heart.

RRich 03-24-2004 12:10 AM

Re: AMC 360 timing issues
Bet it's simple.

The output of the pick-up coil is actually a double spike - one up, one down as the reluctor passes.
I'll bet it's out of phase. It's triggering on the wrong slope.

Somehow the wires from the pick-up coil are reversed, maybe in the harness itself. A repair was made to the harness, or the wires slipped out of the connector, then went back in wrong? Could even be the module inside is wired wrong.

Try reversing them - orange and purple wires. Easy way would be to take them out of the connector and reverse them.

Phasing -- Normally the rotor won't point directly at the tower. Notice the tower and rotor tip are wide, not made into a point.
At low speed, like idle, the rotor will be slightly offset from the tower (but not as far as yours.) The edge of the tower still closely lines up with the edge of the rotor - barely.
As you rev it and the advance operates, the rotor will become centered with the tower. At high Revs, when it's fully advanced, it will be on the other side of the tower, the opposite edges line up.

The only time you need to worry about, or adjust the "rotor phasing" is when you are running super high R's with lots of advance.
Putting it in the center at idle makes it wrong at high R's.

For example a dragster motor may run at 10,000 RPM with 55 degrees advance. Stock the rotor would be pointing too far away - the spark would have to jump too far - if they used an advance mechanism. So you adjust the phasing. But at low end, idle, the rotor's waaay off - but it doesn't run there anyway, so who cares.
To get away from that problem those motors rarely have any advance mechanism - they are just set to the 55 or whatever works best - usually determined on an engine dyno. 55 degrees will kill the rings quickly, but life expectancy is only a few passes, if you win, who cares!
Starting is a problem - usually on those you crank it up as fast as you can - then turn on the ignition.

But on our engines we shouldn't run more than a total advance of 35 degrees, so stock phasing is fine.

7T8CJ7 03-24-2004 01:37 PM

Re: AMC 360 timing issues
Thanks RRich, your explanation of the phasing makes sense concerning the 45 degree offset I'm seeing. I will check into the wiring for the pickup but I just plugged the connector into the MSD harness adaptor so I have no splices.

7T8CJ7 03-25-2004 09:30 AM

Re: AMC 360 timing issues
Just for fun, I cut a new notch in the reluctor in-line with a tooth instead of between. Problem Solved!! I'm not sure why but all is well now. Thanks all for the input.

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