Last weekend, I lost in 3rd round due to an ignition misfire. This post tells the story, some background to the problem, and my initial attempts to solve it.

Another $30 win

To make this post more complete, here is the previous trouble shooting I did:

This is what I checked on Sunday:

- Spark plugs all looked good
- Spark plug wire resistance matched previous measurements in April 2005, including coil wire
I checked the plug wires as they were attached to the distributor cap
- Distributor cap looked good, inside and out, terminals good, rotor good
- All wiring connections were checked for tightness
- I did the MSD check from the instructions, removing distributor pickup wires and shorting/breaking connection.
It sparked a plug I put on the coil output during that test, so the coil apprears OK too.
- I measured the distributor (stock) magnetic pickup and it was 345 ohms, about right.
- Distributor reluctor gap was 0.006", good. There is a little play in the distributor bearings, but not much 0.002"
- The fuseblock has a separate circuit for the MSD low power (turn on) wire, and the fuse didn't seem tight when I pulled it out. I reinstalled it fully, but I don't know if it was really making a bad connection or not. The main power wires from the MSD go directly to the battery terminals.

Unless I found a loose wire, I didn't expect this to find the problem. It runs fine at low rpm, but over 4000-5000 it acts up badly. Next time I work on it, I will check more wires under the dash for chafing. I will put it back together (plugs etc) and try running the engine again. Then if it still has a problem, I will put the old alternator back in. This was a new Power Master 100 amp, 1-wire alternator I put in just before going to the track. Remember, it was running fine for 5 passes, then it started. Something must have happened, a part went bad, etc.
-----------------

On Tuesday after work, I took the MSD box (Digital 6) to Speed Unlimited (over an hour drive each way) and they tested it on their MSD display. He varied the RPM, tested the rev limiter, etc. and it worked fine. I got home and put it back in the car, installed the spark plugs etc. But it was too late in the evening to run the engine in the neighborhood with open headers, especially since I need to take it up to 5000 rpm to check things. I even took a spare distributor and pluged it in, then spun the distributor by hand, it fired the plug just fine. I am suspecting the coil is going bad, I checked the resistance (for what that is worth) and it showed 0.2 ohms and the catalog says 0.02 ohms (Blaster HVC #8252). I will try it with the old coil and the Blaster 2 (round, red) coil from the Cuda for comparison.

-------------
Today is now Wednesday. I tried the Blaster 2 coil and that didn't help. I replaced the magnetic pickup and that didn't help. I put the old Delco alternator back in (63 amp) and it now would run smoothly past 6500 rpm. This was with the fan off (see background topic). With the fan on it still misfired. At least I was back to where I was a few weeks ago, turning the fan off to run, turning it on while on the return road.

While the motor was all warmed up and running smoothly, I checked the rev limiter (MSD Digital 6) against the tach. It was real close at 5000, and 6000 rpm, but when set at 7500 it limited about 7100, and setting it at 7600 it limited at 7200. I left it there as I cross the finish line at 6900-7000.

I was feeling better, now I can race again and the Pittsburgh Mopar race is coming later this month. So, I took a break and went in the house (air conditioning) and called MSD to discuss my problems.

Vic said the Delco 1-wire alternators are the worst for interfering with the MSD box. And the Chrysler factory magnetic pickup acts like an antenna. With my big block, that alternator is right next to the distributor! He recommended the shielded pickup cable and to test by wrapping the wire with aluminum foil. I told him I already have the shielded cable, but there is about 8" of exposed wire coming out of the distributor because I have an adapter cable to go from the Chrysler connector to the MSD connector. So I will try wrapping that part.

I went out to the garage and wrapped the unshielded part of the wires and ran the engine. It didn't change, OK with fan off, not with fan on. By now I am sure it is alternator interference, and I figure the more amps the alternator is putting out (fan on), the more interference. So I tried wrapping the alternator in foil, and that was futile...

I decided to modify my distributor to get rid of the unshielded part of the cable. The MSD cable now plugs right into the distributor. The phillips screw locks the vacuum advance plate since I removed the vacuum can.

.
.
.
And now it fires perfectly even with the fan on!
Man this electrical interference thing is a pain, but it is now fixed. Here is a pic of the installation in the car:

have you tried to unplug a field wire on the alternator and then run the engine with the fan on?. could the amp dray from the fan be casuing some interferance and mabe its not the alternator at all?.

ooops i see its fixed, good deal!

Glad ya worked it out. Thats a good idea there makin it so it plugs into the dist. Now get hold of MIKESDUSTER and help him out.

Since I am using Delco 1-wire alternators, there is no field wire connectors to unplug...

I don't think it is the fan itself, since the 100 amp alternator was causing a misfire with the fan on or off. The smaller alternator must just make less interference at a given amp draw. FWIW, my fan runs off a relay. The power wire comes right off the alternator, through an in-line fuse, to the relay and to the fan. Those wires are not near anything else, they run to the passenger side of the car (where the alternator is).

That's my thinking anyway.

Is MIKESDUSTER having MSD misfire problems? I will look for his post.

now, that was worth reading. I am going to remember this one.

did you solder the wires in the dist?

Outstanding...I've been following your ignition misfire thread and I'm glad that you did a follow-up report on finding the trouble, and then correcting the issue

I'm wondering if a three wire alternator would cause the same problem ?...... and if either a 1 or 3 wire alternator was mounted lower ( not in the stock location) that the interference would not be an issue ?

I will say this, you did one heck of a job trouble shooting the issue, and I really like how you tucked the wires in the distributor.....

Nice Job!

Mike

Wow, that's some serious detective work! I'll remember that one for sure. Glad you found it.

Understood Jim,

Consider this a bump...really good info here


MODS....can we have this thread saved, so it makes it into the tech archieves

Thanks!

After all the mods I did to my factory 400 distributor, it now has some of the features of the MSD distributor! LOL
Connector plugs right into the body
No vacuum advance to bounce around
And my mechanical advance is locked out.

And you know what? I turned the start retard feature off (built-in to the Digital 6 box) for testing. And the motor starts just fine with 34º locked out ignition timing, even hot. I guess with all the duration and overlap of the MP 0.620" cam (283º at 0.050"), 106 LSA, and only 12.2 CR... it doesn't need it.

Nice solution, and great d etective work!!

440Jim, did you change anything before this problem started? I'm having the same problem with a Digital 7 box I just installed, it starts misfiring around 5000-5500. I put the 7AL-2 box back in the car and the problem goes away. I'm getting ready to send the Digital 7 box to MSD to have them take a look at it.

Bill,
IMO, the Digital MSD boxes are more sensitive to electrical interference than the analog boxes. This started when I put a 15 amp electrical fan on the car, and I couldn't make a pass unless I turned the fan OFF. The 63 amp Delco 1-wire alternator made more interference as it put out more current. Then I put a 100 amp Delco 1-wire alternator in thinking the old alternator might be overloaded. I think the 100 amp alternator made more electrical interference at lower amp draw, so the misfire occured even with the fan OFF.

So, if you have a Delco style alternator, especially with high electrical load (fans, water pumps, etc.) and an unshielded magnetic pickup distributor, you might have the same solution.

Thanks for the info 440Jim. I do have the 100 amp powermaster alt, electric waterpump, and electric fan. I don't have the shielded mag pickup wires.Maybe I'll try shielding the wires before I send the box back. I was thinking the same thing about these boxes being alot more sensative then the analog boxes. I've already replaced the cap,rotor,plugs and plug wires trying to fix this problem........

Bill,
What distributor are you running? I think a shielded cable is a good idea for a magnetic pickup. And don't run the distributor wire next to the alternator power wire or the coil primary wire (output from the MSD).

I like the charging characteristics of the Delco (GM) alternator, good low rpm output. But MSD even says in their FAQ that the Delco 1-wire alternators are big offenders.

I'm running the MSD Pro Billet.I ran the mag wires away from all the other power wires like MSD tech suggested.They didn't mention anything about the alternator or the shielded wires.

Jim, not that it would've made the difference but do you have any capacitors in the car? alternators, electric motors, primary (race ignitions run high voltage), secondary ignition circuits and solenoids all make noise than can cause problems. capacitors can help soak up some of the noise in the electrical system. even if the car seems OK i'd install one...can't hurt.

Question:

I thought that it was a no no to run solid core spark plug wires with an MSD ignition?

Or does this change when you run a digital MSD?

I have a brand new set of solid core wires like yours, but the old MSD 6al-2 and have never put them on, because of that.

Is this right or wrong, or wrong and right?

BP

JIM i may be way off here but i'll give it a go. I know on my msd stuff like 7al2 etc. it states Do Not use SOLID core spark plug wires!! I see in your pic the wires and don't they say SOLID on them? I am not sure if the digital msd can use them but it was worth a shot in saying my 2 cents

Just out of curiosity, what comprises a "sheilded" wire? Is it a special insulation? I have extended pickup wires before, I thought it was regular fine multistrand wire? Great post, BTW.

WOW Nice Job 440JIM

I have been lurking and waiting I dont think I would have ever figured that out. Nice Job sometimes its just little things that make the diff.

Good work Jim. Electrical gremlins can be a real PITA.

So how do pickup wires get classified that way? I have used plug wires (a while ago..I got them 'cause they looked cool..lol) that used a grounding strap like that, but pick-up dont. Or does the dist casing do it?

You need a special cable. They are not that way from the factory. That was why I was picking up the electrical noise from the alternator.

Ok, thanks Jim..didnt mean to sound "thick"..lol

way to go jim. i like how you fix it and not just throw a bunch of parts at it. hopeing to fix it.allso i am not trying to tell you what to do and you are a lot smarter than me.but next time try taking the wires comeing from your distributor. and twist them around each other.that way they act like a home made shielded cable.like you said two wires running right beside each other act like a little antina.thats what i had to do to a wheel speed sensor on a car when i worked at GM. i hope i said that to wear you can understand it.but any way good gob on fixing your car.mopar65

Wow!

That is great news Jim. That means for me, that i do not have to buy another set of sp wires.

Those wires as mentioned are the sames one that I have, but never used because.

I am glad that i asked, maybe it might help my msd box...

Thanks again Jim for clarifying that.


BP

Just to show I am not made of steel...
Revving the engine in the garage, in neutral to 6000 or 7000 rpm is a little un-nerving. But I did warm the engine before I did it, and that included both the water and the oil. Then I don't like "zinging" the RPM, but rather did a controlled steady increase in RPM. It started to sound a little like listening to NASCAR on TV as the engine passed 5000, 5500, 6000, 6500... After the first few times, it actually sounded nice. But a day later, thinking back, it was a little stressful! It was much worse when it would misfire at 5000 rpm, rather than the beautiful sound of the steady climb past 6000...

I'd like to drag this topic out of the archive because I'm having the same problem with my T-Bird. Last year, at the Keystone Natsionals, I noticed a misfire towards the end of the track (probably 7000-7600 rpm.). I suspected the RPM limiter might be the problem so I replaced the 8000 "chip" with an 8200 one and it seemed to fix it. This year it started to act up again, and I "fixed" the problem with a borrowed MSD box (7AL-2). I then put the original MSD box back in (was misfiring with a new box) and the problem came back. I reinstalled the borrowed box but this time it didn't help. I just bought a new pick up for the distributor (Old Chrysler Prestolite) which I hope will help. I also bought the newer type spark retard so that I can try the crank trigger again. I used to break starters with the old spark retard. This is really annoying me because I lost in the fifth round at the Div 1 race at Lebanon Valley by .002 seconds. I would have had a bye run into the final. I can't really test it without going to the track. I read your "fix" (sheilded leads) but was wondering if perhaps a weak magnet in the pick up might make the system more sensitive to noise. I also have a one wire GM alternator mounted close to the distributor, but ran this way for years without trouble. One other thing. The coil (MSD Pro Power) is mounted on the firewall. The car had a BB Chev. in it before I got it so the coil was close to the distributor. I checked the resistance of the plug wires and found that the MSD wires had about 100 ohms per foot. The coil wire was a Moroso wire which has about 1000 ohms per foot. That wire is about two feet long. I'm guessing I didn't have enough MSD wire for the coil wire so I used a wire from the Moroso set. I used to run Moroso wire all of the time and never had trouble. I did change the wire to a slightly shorter one at the track but it didn't help. Maybe I should mount the coil closer to the distributor.

B1Ken, are you running a Digital MSD (Digital 6,7)or are you running an Analog box (7AL2,3)?

Where can you get the shielded cable? Is this something MSD sells.

Summit part # MSD-8862 $18.88, got one last week ( to replace the one that I BARB- B - Q'd )

All I can say for sure, is it solved my problem. I modified my spare distributor now too. The new Power master 100 amp was worse than the old 63 amp alternator at the same amp draw.

Jim after reading this I went out and put a ground strap on the altinator. I wasen't having a problum but I guess it cant hurt. I use the pickup cable with the shield, but have a pigtail coming out of the MSD distributor old styel about 8" so maybe I will shorten that up too.
Thanks for keeping us up to dated.

excellent detective work Jim!!!

ya know, last year i installed an electric W/P drive on my motor at the beginning of the season.
about 1/2 way through the year is when i first started having the top end skip, but only with the limiter activated(if i dialed it back to "0", the skip is gone).

i feel like something is messing with the limiter in my car, and it could be a similar situation to what you had.
i'm going to get the shielded lead for the distributor, and hard wire the end onto the mag pick-up like you did.....its easy enough to do, and it cant hurt.

Jim- Where is the connector in your distributor from. Is it sold separately, and do you have a part #? Nice work.

That is the connector that comes with the MSD box. It had spade terminals on it with about 6" of wire. I cut the wires short and soldered them to the magnetic pickup wires. It is the mating connector to the MSD cable that comes with the box. Check the MSD catalog, I bet they sell it separately. I just happened to have two since I sent my box back once to be tested, and they sent me a new box with all the cables, etc.

Check #8824, and #8867

BTW, the shielded magnetic pickup cable to the box is #8862

Glad to see the problem is apparently fixed. However I am going to make few suggestions just in case.

1. Your trigger wires are too close to the coil. Move the coil.

2. The nicely bundled spark plug wires looks nice but it is asking for a crossfire problem.

3. The two primary wires from the MSD to the coil should be twisted around each other to create a "twisted pair". They will shield each other reducing interference.

4. The trigger wires,including the pigtail from the distributor should be twisted together. Looks like the trigger wires may already be twisted inside their shield so they should be alright.

5. The alternator wire, the trigger wires and the coil primary wires should all be seperated from each other.

6. Twist the fan wires.

7. Twist the fuelpump wires.

8. Twist the power wires from the battery to the MSD.

9. The distributor cap should be vented when you have a high powered multispark ignition. Keeps ozone from collecting inside and causing misfire.

I hope something here helps you and the others out.

Thanks, those are good tips for everyone. I have already tried many of them. I have moved the pickup and coil wires many times, with no change. I am using the MSD supplied cable to the coil, is it twisted inside already?

I will do more "twister" things. I have the main power wires to the MSD twisted directly to the battery. I will also vent a cap as others have recommended.