View Full Version : Possible 7al2 Problem?
10-13-2003, 01:30 AM
Here's what I have for ignition 7AL2 box/ crank trigger/ Low profile crank trigger dist/ pro coil/ 8891 timming computer/ 3 step/ 8.5 super conductor wires.
The problem I'm having is on the dyno my engine made best power with 34* timing, now with the engine installed in the car it is hard starting (cranks for a while then starts fine) and requires much more timing, at 38* now and seems to need more. The tach is also bouncing around about +/- 250 RPM in high gear. Also has a high gear miss.
Things I have tried so far; I have unhooked the timming control and no difference. Checked the crank trigger pick up OHM's cold and was in spec. Moved the pick up cable away from all other wires.
Could the 7AL box be causing a weak spark (reason for hard starting) and a late signal (reason for requiring more timing)
10-13-2003, 10:25 AM
The box is generally either good or bad basically. If there is a problem with output the unit will normally just not fire. Here are a number of things that you can check that will cause a problem with firing. One thing if the motor was dyno'ed with out the 8981 your timing will change with the addition of the 8981. So if you are mechanically setting the timing then adjusting it to 34, it is normal to see a difference of 4-5 degrees. If the timing is showing 38 with a timing light, make sure that the light you are using is a non adjustable timing light, no dials or digital type lights. Here are several items that you can check, first the only 2 wires that should be physically touching the coil, should be the orange and small black of the MSD unit. Check voltage at higher RPM's it should maintain above 10 Volts, if voltage is falling too much this can cause a miss. The wires that go from the MSD unit to the distributor, make sure these wires are not close to any other power wires, try to isolate these wires away from any other power wire or spark plug wires. If you have already tried isolating these wires, you may want to check spark plug wires for resistance, to much resistance on a wire may cause a lot of RFI noise. When checking the resistance, shake them around and see if there is any resistance change or breaking up. If you have any electrical component like an electric fan or water pump try to shut these items down for testing purposes and see if it clears up.
10-20-2003, 08:44 PM
Still working out this issue, changed a lot of fuel system related things and have ruled out fuel. Do the wires that run from the box to the coil (orange/black) need to be issolated from all other wiring also?
One thing if the motor was dyno'ed with out the 8981 your timing will change with the addition of the 8981. So if you are mechanically setting the timing then adjusting it to 34, it is normal to see a difference of 4-5 degrees.
Can you expand on this more ie; reason why?
I have been rotating engine to 34* at balancer, then setting crank trigger pickup in center of one of the magnets in the wheel, and finaly aligning the rotor to #1 on cap with dist.
10-21-2003, 10:27 AM
As long as they are not run with the crank trigger wires that is all that matters. There is a mag compensating circuit in the timing controls to make the timing as stable through the RPM range as possible. All magnetic pick up's will retard a small amount as RPM's increase, the mag compensating circuit keeps this retard from happening. So anytime you go from one to the other you must recheck and reset your timing. The way you are setting the system up is correct but once you fire it up, check the timing and the rotor phasing while running.
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