msd7al-3 problem

[buzzinhalfdozen]

Flash, I'm glad you found a problem, however I doubt that will be the long term fix as the magnets will not change polarity (ie North or South pole) due to being turned in an opposite direction. I'd still consider putting a new pick up on as it's been documented many times that they can actually change polarity. I'm not exactly sure how or why they do it but I've seen it quite a few times. Perhaps we have an electical engineer on here that may be able to shed some lite on that subject. All this of course is moot if you're not running the "flying magnet" wheel. Good luck Joe

[flash]

I purchased a new sensor,changed it ,and still had the problem-that's when we read a 2002 msd troubleshooting manuel and it had a full section on being sure you did not have the wheel backwards.thats when we discovered the wheel was backwards because we could see the direction arrow on the back side with a mirror and was pointing the wrong way. we reversed the wheel,put the wires "-M & +M " the correct way and it worked. really not happy with MSD tech as we talked to them 3 separate times about this and all the said was that's not possible! I got better info on classracer.com

[buzzinhalfdozen]

Flash, glad to here that, though the reasoning behind it eludes me. Thanks for the follow up sure to help someone else with a similar issue.

[OhioMafiaWireGuy]

This is becoming problem we see more and more. When a car comes into our shop, that I cant start for any reason, I tape a note to the switch panel reminding the owner they have to check the timing and then reverse the polarity and check it again.


MSD has even published an Appendix stating the same. The rule of thumb is this: Check the timing and then reverse the wires and check it again. For Analog ignition boxes you want the mag pick up wiring that gives you the most retard. For Digital boxes you want the most advance. Leave the polarity that yields one of those for that given type of box.


On a dyno, I have seen this be worth 96 Hp on my personal motor.


In regards to the 7AL3's... ensure the box is grounded directly to the battery! Ensure all the 0 chips are installed! AND...ground the unused step retards.

[colormebad]

Anyone ever find out what is causing this ??

[flash]

I figured it out what was causing the timing to retard of idle.the crank trigger wheel was installed backwards ! that reversed polarity and caused the problem. reversed the M+ & M- wires and that fixed it but I wanted to know why? kep looking and figured it out.looked in a old MSD trouble shooting book and it had a whole page on asking and telling you to make sure the wheel is on correctly.