Can a magnetic pickup in the distributor go bad? Do they just go out, or can they slowly begin to send irratic signals?

 

They can suffer electrical failure, though it's not common, because they carry almost no voltage; usually, it'd be a pickup coil wire or lead fractured by vibration, or physical damage. An open or short failure like that would be a sudden event, usually.

The most common reason to have to replace pickups is due to the mech advance bearings wearing out, so that they don't keep proper clearance from the reluctor. That would show up as erratic behavoir, worsening over time. Wear in the dizzy bushings causes the same symptoms, and is more common.
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while i think the magnet cant go bad, everything else can. the air gap between the pickup and the trigger is important. the wires from the pickup to the ignitor are important, RFI will interfere with the signal too

 

HRM.... Cause I don't know how many people are running DF with MSD style boxes off the leading pick up, but if you look at the tach signal is's hella irratic and all over the place. I'm trying to figure out why. It did it with my MSD, Mallory, and Crane box. Hooking up a tach from the tach output, even autometer, gives a terrible signal. Jumps all over the place. When I'm on they dyno they always have a huge issue trying to get signal off the leading and usually pickup off of the trailing coil.

 

what does the timing gun on a leading plug wire look like? erratic too? check the air gap between pickup and reluctor, then separate the two wires from leading mag pickup to msd box, keep them away from all other wires. Also check your connections after mag pickup. And MSD box ground.

 

Well the timming light is firing so fast I can't tell anything. Plus the wasted spark is yet another blink, so I can't really tell anything from the light. It really starts to get crazy at 25oo RPM and above. I was wondering about seperating the + and - signal wires, but from MSD both wires are run in the same rubber shield and they are twisted together.

Going to check everything according to the FSM tonight.
http://foxed.ca/foxed/index.php?page=rx7manual#firstgen

 

Well everything checks out okay. Another thing I'm wondering is why do we even use the magnetic pick up to trigger the Box? Why not use the white wire coming from the J109 to trigger the box?
Also, could the condenser be causing an issue. I was looking at different ignition setups and for some reason the Crane instructions say to disconnect the condenser and remove it on points applications. And, in magnetic pickup connections it says, "Any condenser at the coil must be disconnected and removed." This answers the twisted cable question; "Twisted pair type cable is used on magnetic type pickups to prevent noise."

 

keep the 2 mag pickup wires from distributor to msd box away from all other wires, especially the plug wires. MSD does sell a shielded and grounded cable for this.

http://summitracing.com/parts/MSD-8862/

the + and - wires from MSD to coils, just keep them away from the mag pickup wires.

for the leading timing light, shine it on the crank pulley and see if it's erratic or skipping. or jumping to the trailing timing advance which would indicate cross-triggering. the ignitor has a dirty signal is why we feed the msd off the mag pickups directly. paul yaw found that out years ago. i don't use any condensors or resistors at the coils. originally i tried the resistors with msd blaster 2 coils but got a better spark without them. and they fall apart.

 

Added to cart...
Does the alternator emmit EMI? Because I run a FD alt and it's just so big and so close to the dizzy there's really no way to run the wires away from it.

 

it can, if the brushes are dirty/etc

 

too much dyno can ruin a magnetic pick up LOLLLLLLLLLL

 

LOL! I bet with the amount of time I've been on the dyno lately.

 

By the way, if you have an ohmmeter that reads well at the lowest scale (some dont) you can verify your pickup coil and leads by comparing the resistance of the two pickups, preferably while wiggling parts about to simulate vibration.

The only other way to check them electrically is with an oscilloscope, which most people don't have easy access to. You can examine the pulse trains coming out while the engine is running, and see if they become erratic when the problem shows up.

 

Where the hell is Jeff20B when you need him?

 

If I understand your comment you are trying to trigger the ignition box with the pulse from the pickup coil in the distributor without going through the J109. I suspect that is the problem. The ignitor acts as an amplifier to provise a good signal to the ignition box . Try using th4e output from the ignitor to trigger the box.
hope this helps

 

Common Jeff, can an ignition box be triggered by a J109 and still fire a FC coil correctly? Is there any advantage to doing it through the magnetic pick up besides the j109 having a dirty signal? I think our pckups are a pretty dirty signal in compairison. Well when you consider the issues I've had with the mag pickups.

 

Found the issue. It's the FC coil causing the weird signal. I swapped in two stock FB coils wired in parallel and no more random flashing of the shift light and no more weird interfearance like misfire from 3k-5k. I thin the coil is going bad, or just incapable of running setup like this. I'm still waiting for someone who owes me a FC coil to fu(king mail it to me. Hopefully I get it soon and I'll be able to race my car again.

 

Very weird. So you think it's a bad FC coil, and not just the act that it's an FC coil?

 

Well considering that there are a **** ton of FC and FD cars running a crane ignition I doubt the coil is bad. Only difference between their setups and mine is that I trigger the crane from the magnetic pickup and not from the stock ignitor. When I tested the FC coil it would stat at 1.5 ohms and slowly fall to 0.5 ohms. The FSM says it should be below 1 ohm and that's all it says... If I held the leads on it for a few minutes they load would start to jump around from0.5-25 ohms.

 

I am confused at this topic... but were you trying to trigger the crane box using the ignitor and sending the voltage to the 2nd gen coil?

 

What I ment was I doubt the box is bad. I'm pretty sure the coil I had has just decided to **** it's pants. What I was trying to figure out is weather a J109 could trigger a crane box directfiring a FC coil to the leading plugs. I was using the magnetic pick up to trigger the box and I thought that was the issue, so I was trying to figure out if the J109 could trigger the box. It turned out the issue I was having was caused by the coil, so I'm looking for a new one now. When you run any CDI through the cap it's being triggered by the J109, but running it right to the coil and directly to the plug might cuase different issues, so I was trying to see if anyone else had tried it that way. Right now with 2 stock diamond coils wired in parallel it's running better than it ever has. I'm concerned that the car might not like 2 coils at high rpm. When you run 2 coils you either split the voltage between the two in parallel, or double the ohm load, but you won't get all the voltage out of the crane box wired in a series. Sine normally you wouldn't be able to tel if you were having a high rpm misfire because you can't feel it. I'm hoping that I am and sorting all ignition issues out will put me over the 200whp mark. I'm considering adding 2 ignitors off the leading like DLIDFIS, but useing the ignitor to trigger indipendant crane boxes with LX92 coils. This is basically what the really high HP FC turbo guys are doing, but they're using haltech's to trigger the boxes.

 

I have never used the ignitor to trigger a MSD. I have always removed the ignitor (wired directly to the mag pickup) or used an 80 distributor that just has magnetic pickups. Never has issues

-billy