MSD/Electrical issue?

[Grimace5.0]

Need some help guys.

When driving the car occasionally the tach would jump to 7,000ish, the shift lights would light and the car would kinda miss for a second. So, in my infinite wisdom I tore into it the other night thinking it was a simple loose wire or something like that. Last night I went over the tach power wire and fixed it. The prev owner used a wire tap into another wire...half assed. I soldered it directly to the power wire. That should be good to go. Today was nice so I figured I'd drive the mustang. I got about a block and the problem is worse! I didn't recall it being RPM related but in testing tonight at about 3,000RPM in 1st gear it goes nuts. So I checked every wire the MSD box connects to, everyone was connected with a crimp stlye connector. I cut all that out and soldered the wires and insulated the joints. I still think it's wiring related though. At ~3,000RPM the car lifts the front (90/10's) pretty well and is shaking/vibrating a bit. The engine has a torque link from the drivers side frame rail to the drivers side head and solid motor mounts so the engine isn't rocking. One of the coil wires was pretty weak at the ring connector so I also replaced that. On a MSD the orange wire goes to the + side and the black goes to the - side. Mine were reversed, I wired them per MSD's instructions with orande to the + side of the coil.

I don't know what else to check/do. Any ideas?

MSD digi6 plus
MSD probillet distributor w/ fairly new cap & rotor
AutoMeter pro comp recall tach


And if anyone could tell me what the following wires connect to I'd appreciate it:
Light blue
Pink
Green

None of those 3 are connected to anything on mine......

[Paul408Notch]

Well first... the 3 wires you're asking about on the MSD box are for the additional features the box has (2-step, etc...) They're not effecting this.

Do you have a stock distributor you can throw in there for a bit? I kind of have a feeling that may clean it up.

[Grimace5.0]

No, I don't have stock anything.

Thanks for the info on the wires...

[Paul408Notch]

I can't remember what your combo is. Are you running EFI, or is it carbed or what?

[Grimace5.0]

BG 650 carb, stealth intake, canfield heads, DSS pro bullet short block, etc etc etc

[Paul408Notch]

Ahhh... I thought it was EFI. It should be pretty easy to troubleshoot without the computer getting in the way. Is there a chance the ignition switch is going bad?

[Black Horse]

Check to make sure there are no other wires running along with the MSD trigger wires, etc. High draw circuits (electric fan, coil, starter, alternator) play havoc on the waveform of the digital boxes.

[Grimace5.0]

Ahhh... I thought it was EFI. It should be pretty easy to troubleshoot without the computer getting in the way. Is there a chance the ignition switch is going bad?

Nothing has indicated a problem with it.

I'm going to track the wire that goes to "key on" and see where it goes and if it's FUBAR. I "fixed" the box end of that wire last night by eliminating the crimp connector and soldering the wires so that end should be fine. Man, I really didn't want to take the dash apart........again.

[Grimace5.0]

Check to make sure there are no other wires running along with the MSD trigger wires, etc. High draw circuits (electric fan, coil, starter, alternator) play havoc on the waveform of the digital boxes.

The wires that go to the distributor are pretty much by themselves. the fan and water pump wires are routed more along the front of the engine bay and the Alt is on the other side of the engine.

I'll update later on with what I find.

Thanks guys.

[Grimace5.0]

Alright here is what I found. I traced the "key on" wire from the box to the wires the prev owner hooked them to. They both go to the IGN switch. One is pink/green stripe the other is black/purple stripe. I don't understand why he had them going to both IGN switch wires. So I hooked it to just one, no power to the box. I then hooked it to the other, no power to the box. Hooked it back to both and have power to the box. That IGN switch is a PITA to fix if I recall, aren't they riveted in or something? Is there another place I could wire the "key on" power wire for the box?

Thanks

[Grimace5.0]

I just thought of this, I have a relay for the fuel pump with a open plug on it. Can I hook this wire to it?

[Paul408Notch]

I just thought of this, I have a relay for the fuel pump with a open plug on it. Can I hook this wire to it?

As long as the wire is still +12V when the key is in both start and run.

[Grimace5.0]

I tried it and it didn't work :confused: I hooked it back up the way it was. It's still fugged up though. Now I have the engine bay a mess and the dash tore apart....

Do you think the IGN switch could be the problem? The car runs/starts/shuts off fine aside from the aforementioned issue. The wires for "switched 12/ign key" on the MSD box are going directly to the IGN switch though......

Man, that switch looks like a PITA to remove all riveted on and stuff...

Any help?

[Timido]

The ignition switch comes off easy. Should be 2 Saftey Torx bits I think they are #27 The ignition switchs are junk on these cars. If you suspect any problems with it I would replace the switch and make sure the connecter is not burnt.

[Timido]

MSD has all there instrustions online very helpfull. I dont know if you have the wiring diagram or not

http://www.msdignition.com/pdf/frm23775_6520.pdf

[Grimace5.0]

I replaced the ignition switch, that wasn't the problem. Still working on it.

How do I tell if the:
coil is bad?
MSD box is bad?

[Timido]

http://www.msdignition.com/coil_blaster_1_8200_8202_8223.htm

You can check the primary and secondary resistance through the coil.

The Ign Box you would need an ignition tester or send it to MSD. They have a MSD tech forum.

[Timido]

http://www.msdignition.com/forum/showthread.php?t=8785

Sounds like your problem. Try changing the dial for the cylinder select and then put it back to V8.

Where is your MSD box mounted?

[mustang8998]

Jay, the only wire you didn't mention, was the ground. Double check it, as well.

I think (maybe wrong), that you have to send the box, to MSD for testing.

[Grimace5.0]

http://www.msdignition.com/coil_blaster_1_8200_8202_8223.htm

You can check the primary and secondary resistance through the coil.

The Ign Box you would need an ignition tester or send it to MSD. They have a MSD tech forum.


As per MSD's troubleshooting page I tested the box with a jumper wire, I got spark. So I guess the next thing is the coil. How exactly do I check the resistance? I didn't check your link yet..


Thanks

[Timido]

It sounds like the box is jumping from thinking it is a V8 to a 4 cly . It is doubling the tach signal and the miss you are experiencing is probably the around 7000 top rpm limit

[Grimace5.0]

The box is mounted in the front drivers side corner of the engine bay, right behind the headlights (where it's been since who knows how long). I'll try the dial and see what happens.

I didn't mention it but I also pulled the ground wire, put on a new connector, sanded the attatchemnt point and reconnected it to the car.

Thank all!

[Timido]

Mount the Box inside the car on rubber isolaters. Les vibration mud snow water and other junk.

[Grimace5.0]

I just tried to turn the dial to the 4cyl setting. Same thing happening. I then returned it to the 8cyl setting and the problem is still there.

[Grimace5.0]

Mount the Box inside the car on rubber isolaters. Les vibration mud snow water and other junk.

If I were the one who installed it I would have put it inside. This is a prev owner deal and I'm honestly, tired of jerking with this car. I have it sold and just need to fix this problem :D

[Grimace5.0]

I misread on MSD's site, it says if there is NO spark check the coil. Back to square one......

[Paul408Notch]

The problem isn't the coil if the tach jumps too.

I've never in my life seen an MSD box work intermittently. They either work or they don't.

So the problem is either the ignition switch, or the distributor. Have you opened up the distributor to make sure there's nothing loose inside?

[Grimace5.0]

I took the cap & rotor off and had a look around. Didn't see anything that immediatly looked f'd up. Anything I should look for?

[Black Horse]

You aren't by chance running a crank trigger set-up are you? If you are - lessen the gap.

[Grimace5.0]

No, just a regular old style distributor. The car has ran previously with these same componants. It just started to act goofy like this. I talked to MSD's tech line today. The guy there said he thinks it's a "noise" issue. Not a coil, box or distributor problem. The only thing that I can think of it would be getting interference from is the fuel pump...or the fan..I forget what wire it is. Any way, when I wired it I needed a "key on" source and wired it to a wire on the IGN switch, well it turns out thats the same wire the msd box is wired to for "key on power". So now I need to locate another wire that has power with the key on only. Any idea's which ones? Car is a 85GT with a carb.

[Grimace5.0]

It runs again.......

I routed the fuel pump wire to another "key on" wire and tried it. Still acting goofy on the tach. I unhooked the tach and reved it up....no miss. Took the car down the block for a few WOT blasts and it didn't miss. Preliminary diagnosis is the tach is FUBAR.


Thanks everyone for the suggestions!