MSD 6AL green and violet wires

zje · 10:47 AM

I have an MSD 6AL model 6420 installed by the previous owner (great guy, very active on pelican). I've been reading some past posts about the MSD wiring and I have two questions:

(1) It seems that a lot of folks say you must run the green and violet wires in a separate harness. Right now, they are running into the 6pin with male quick connects. Do they need to separate all the way to the distributor or is it okay to be separate up to the old connector?

(2) I've also seen posts saying that the green and violet wires need to be reversed. Is it safe for me to test swapping them and running the engine for a bit? My current wiring is in the attached picture.

Thanks!

Walter_Middie · Walter_Middie's Garage

Violet MSD (+) wire goes to the shield of the green distributor wire.

Green MSD (-) wire goes to the center conductor of the green distributor wire

I'd check what they were connected to rather than just reversing them and doing a smoke test.

JohnJL · 07-23-2017, 01:16 PM

Is there a problem you are diagnosing?

When wiring from scratch I do run the signal wires in a shielded, grounded-shield pair. But MSD itself packages the signal harness in a twisted pair.

If you are having a misfire problem you should check this pair of wires isnt running parallel to any high-tension wires like plug wires or the coil feeds. Also the starter main cable.

Why do you ask?

zje · 07-23-2017, 10:13 PM

Yes, I am trying to diagnose a misfire that seems to appear around 3000 rpms. I was hoping it would be something as simple as two wires in the wrong place, but the connections seem to agree with what folks here are saying. Right now the wires from the MSD box are running by themselves, unshielded, to the 6pin connector. That said, since they are going into the 6pin, they run pretty close to the coil feeds as I have everything tucked under the plastic cover on the driver's side of the engine bay.

Do you think it may help to shield the wires? They are currently not even twisted...

Thanks so much!

timmy2 · timmy2's Garage

More likely the wire failure is occurring in the factory green wire, if that is even the cause of your misfire.
Is it brown and cracking at the distributor?

What rotor are you running? Resistorless is recommended for an MSD install.

3000 rpm seems to be a common point for failures in the advance mechanisms on the SC's.
Have you checked the distributor mechanical advance mechanism for lubrication and free movement and the shaft for any axial or radial play?

zje · 07-24-2017, 12:52 PM

Three days ago, I replaced the cap and rotor (the old cap had the carbon tip broken off). I was thinking of ordering a resistorless rotor, but the PO had a bosch in there for 10+ years, so I figured it wouldn't hurt to go with the factory part. I just checked the rotor and it still looks good. Went for a good 30 mile test drive after changing the cap and rotor and all seemed much improved, but still felt like it was not running great. I did not have a working tach at the time, so I could not tease out the misfire as easily. I wired up the tach correctly on Saturday, installed the front spoiler, and then had the test drive where I started questioning wiring.

The reason I am thinking wiring and possibly signal noise is the problem is very intermittent. Sometimes the car runs well, and yesterday we went for a test drive and it ran like complete crap. Lots of misfiring above 3k, tried pushing it some more to see what would happen and got a backfire at 5k. Took it back to the driveway to check timing and it ran okay sometimes (got it up to 5k rpm no problem) and misfired at other times. Timing at idle was hitting the 5DBTC mark pretty well, made a custom mark at around 25 using a paint pen and when I was able to get the car smoothly up in the rpms it seemed to hold well before that mark.

I just looked and the green wire looks good all the way from the CDI connector to the black connector at the distributor. See picture of wire and the top of the rotor below.

I plan to drain the tank and also check the screen filter, but the fuel filter and pump are new. I am running a mix of 87 and 90 E0 gas, so I am tempted to try higher octane fuel, but I can only get E10 where I am currently.

Thanks so much!

zje · 07-24-2017, 01:11 PM

Also, when it comes to play, how much is normal? I can move the rotor both up and down slightly and a little bit in the CCW direction. It holds back well if I wiggle it in the CW direction, so I'm assuming that's good.

Not sure how to check mechanical advance, I did a little searching but couldn't come up with a solid procedure.

timmy2 · timmy2's Garage

If everything else is ok and it is intermittent as you describe, it could be the MSD unit is starting to go bad. No loose coil connections or other wiring issues?
I'd go get an MSD Streetfire and swap it in to see if it is the MSD. (Or borrow one) But that is just me.

zje · 07-24-2017, 02:12 PM

The coil is a new MSD high vibration coil, replaced at the same time as the cap and rotor. The connections are tight. The wiring to the coil had some small cracks in the insulation, but looked good otherwise so I taped it up.

I've been tempted to try going back to a bosch CDI box by getting a rebuilt one, but that's a hefty price tag if it doesn't work out. I can't seem to find an MSD locally, I am currently in the Chicago area if anyone knows of a place...

Also, while I was doing my timing tests yesterday I had the car fail to start once, it cranked and sounded like it was going, but cut out after running for a split second. It pretty much died on the downstroke of the tach - instead of the rpms settling at idle the needle just kept going to zero.

Thanks!

timmy2 · timmy2's Garage

I had the main ignition wire back out of my MSD Blaster once.
The throat it goes in is a little longer than the Bosch coil.
Re seated it and it has been good for 3 years.

No local speed shops or auto parts stores near you carry the $150 Streetfire?
Amazon prime an option?

Steve@Rennsport · 07-24-2017, 05:13 PM

Before you spend ANY money:

1) Make sure you have suppression plug wires and NOT solid-core ones.

2) Put in 93 octane fuel; E10 is OK and better than the 87/90 mix you are using.

Pazuzu · 07-24-2017, 08:48 PM

If his Lambda relay was starting to go bad, it would exhibit similar symptoms, and all of the effort in the world messing with the CDI system wouldn't help...

From experience, a bad lambda relay shows VERY similar to having the green wire missing (either going bad, being affected by EMF or having the wires into the MSD swapped). Severe backfiring and coughing, *maybe* you could get the engine revved up to 3k RPM, but nothing past that, and all hell would be breaking loose at that point.

emac · emac's Garage

Zje--
Where are you located.
Ernie

zje · 07-24-2017, 10:28 PM

I have magnecor KV85 competition wires, I believe those are correct for an MSD application?

My plan is to dump this gas as I've been meaning to check the filter screen and I will replace it with 93.

Is the labmda relay the one underneath the passenger's seat? I pulled it last week and the idle definitely got much worse. I can try again tomorrow and see if it still happens (unless of course that's the wrong relay). Is there a chance the relay is still bad and would pass that test? If I start spending money, I would definitely like to start cheap!

I will mention that except for the start issue mentioned earlier when it's acting up the engine is pretty smooth up to 3k, and that's when it starts to get strange. Sometimes it's fine going higher.

Thanks all for the advice and help so far!

timmy2 · timmy2's Garage

Did a little digging of OP's past posts and I think that his car is an '83.
Really helpful for others trying to help if peeps would post up the year, model, US or other engine configuration, modifications etc.etc.etc...

zje · 07-24-2017, 10:33 PM

Ernie - I am currently visiting family in the northwest side of Chicago.

zje · 07-24-2017, 10:42 PM

Quote:

Originally Posted by timmy2

Did a little digging of OP's past posts and I think that his car is an '83.
Really helpful for others trying to help if peeps would post up the year, model, US or other engine configuration, modifications etc.etc.etc...

Sorry, thought I had that here. You are correct, 1983 911SC Targa US. I believe everything else to be stock except for the MSD which was installed 10+ years about by the PO.

Also, the scope of the topic has creeped since I asked my original questions. Would it be better to start a new topic since now we're diagnosing this issue? Or is it better to have the full history as-is for other folks reading this in the future? I have seen forums use either method and want to make sure I follow the proper etiquette.

Thanks a ton for all the help!

T77911S · 07-25-2017, 03:54 AM

Quote:

Originally Posted by Walter_Middie

Violet MSD (+) wire goes to the shield of the green distributor wire.

Green MSD (-) wire goes to the center conductor of the green distributor wire

I'd check what they were connected to rather than just reversing them and doing a smoke test.

this IS correct.
not to get too deep into it but the reason is the signal out of the dist is "upside down" for what the MD needs. its like connecting a MM to a battery. one way you read 12v and if you flip the lead you read -12v.

it wont hurt anything if you flip the leads back. If it WAS correct the car will not start. if it was NOT correct the car should start but will rev to around 2k RPM or so. the reason is the timing will be extremely advanced.
I found this all out when I put an MSD in my 930.

the wires running together will not hurt. the voltage is pretty low on the 2 wires.

T77911S · 07-25-2017, 04:29 AM

you can get a connector that will mate with the factory connector.

Pazuzu · 07-25-2017, 08:07 AM

Quote:

Originally Posted by zje

I have magnecor KV85 competition wires, I believe those are correct for an MSD application?

Those are great wires, as long as they're not worn or cracked. I started to have trouble with mine when it rained, turned out they had small cracking where two wires had been rubbing against each other, and the rain water was causing crosstalk and backfiring.

Quote:

Is the labmda relay the one underneath the passenger's seat?

YES

Quote:

I pulled it last week and the idle definitely got much worse. I can try again tomorrow and see if it still happens (unless of course that's the wrong relay). Is there a chance the relay is still bad and would pass that test? If I start spending money, I would definitely like to start cheap!

Probably not the problem then. That relay can start to intermittently go bad, it's vulnerable to water. Any basic 12V cube relay can go in it's place for the time being, it doesn't have to be a $30 metal Porsche item.