High RPM Misfire -- SOLVED!
#15704
07/06/05 08:32 PM
07/06/05 08:32 PM
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440Jim
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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.
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Re: High RPM Misfire -- SOLVED!
[Re: 440Jim]
#15705
07/06/05 08:42 PM
07/06/05 08:42 PM
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440Jim
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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:
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Re: High RPM Misfire -- SOLVED!
[Re: 440Jim]
#15706
07/06/05 08:49 PM
07/06/05 08:49 PM
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Joined: Aug 2003
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Runner
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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!
Last edited by Runner; 07/06/05 08:51 PM.
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Re: High RPM Misfire -- SOLVED!
[Re: StrokerPost]
#15708
07/06/05 09:00 PM
07/06/05 09:00 PM
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Joined: Jan 2003
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AdamR
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Quote:
Now get hold of MIKESDUSTER and help him out.
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Re: High RPM Misfire -- SOLVED!
[Re: Runner]
#15709
07/06/05 09:00 PM
07/06/05 09:00 PM
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440Jim
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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.
Last edited by 440Jim; 07/06/05 09:03 PM.
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Re: High RPM Misfire -- SOLVED!
[Re: 440Jim]
#15711
07/06/05 09:02 PM
07/06/05 09:02 PM
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Anonymous
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Anonymous
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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
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Re: High RPM Misfire -- SOLVED!
[Re: VanishPt]
#15713
07/06/05 09:07 PM
07/06/05 09:07 PM
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440Jim
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Quote:
did you solder the wires in the dist?
Yes, they are soldered and sealed with heat shrink tubing.
69_SM_Cuda, Vic at MSD said the Delco 1-wire alternators are the big problem. And together with the "antenna" Chysler magnetic pickup and the big block distributor right next to my alternator... everything was working against me. I ran it since 2002 with the 63 amp Delco, but I had almost no load on it (no electric fan, no electric water pump), until this year. I was trying to "upgrade" and I caused myself a lot of headache. But it did teach me some lessons!
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Re: High RPM Misfire -- SOLVED!
[Re: 440Jim]
#15714
07/06/05 10:25 PM
07/06/05 10:25 PM
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Anonymous
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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!
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Re: High RPM Misfire -- SOLVED!
#15715
07/06/05 10:39 PM
07/06/05 10:39 PM
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440Jim
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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.
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Re: High RPM Misfire -- SOLVED!
[Re: 440Jim]
#15717
07/06/05 11:35 PM
07/06/05 11:35 PM
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Bill_LBSR
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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.
LBSR
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Re: High RPM Misfire -- SOLVED!
[Re: Bill_LBSR]
#15718
07/07/05 12:06 AM
07/07/05 12:06 AM
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440Jim
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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.
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Re: High RPM Misfire -- SOLVED!
[Re: 440Jim]
#15719
07/07/05 12:15 AM
07/07/05 12:15 AM
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Bill_LBSR
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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........
LBSR
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Re: High RPM Misfire -- SOLVED!
[Re: 440Jim]
#15721
07/07/05 12:42 AM
07/07/05 12:42 AM
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Bill_LBSR
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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.
LBSR
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Re: High RPM Misfire -- SOLVED!
[Re: 440Jim]
#15723
07/07/05 06:54 AM
07/07/05 06:54 AM
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NewMemberAgain
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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
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Re: High RPM Misfire -- SOLVED!
[Re: 340RICK]
#15727
07/07/05 12:08 PM
07/07/05 12:08 PM
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TonyS451
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Good work Jim. Electrical gremlins can be a real PITA.
2 kids and a dog
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Re: High RPM Misfire -- SOLVED!
[Re: NewMemberAgain]
#15728
07/07/05 12:47 PM
07/07/05 12:47 PM
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440Jim
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Quote:
I thought that it was a no no to run solid core spark plug wires with an MSD ignition?
NewMemberAgain (BP), Those are MSD Heli-core suppression wires. The label on the wires uses the word "solid suppression" but that is misleading. The wire is wound around a core to give noise suppression. They are approved for the MSD ignitions. From the instructions, "A good quality, helically wound wire and proper routing are required to get the best performance from your ignition, such as the MSD Heli-Core or ..."
jamesc, I asked the MSD rep about the MSD noise capacitor for the power leads on the box. He said that was to stop the MSD from interfering with other equipment. Not my problem. But I agree with you it might be good insurance and can't hurt.
moper, A shielded cable has an electrically conductive material covering the insulated wires inside. This material is grounded at one end of the cable. This shields the inner wires from electromagnetic fields outside the cable.
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'Solid Core Wires'
[Re: 440Jim]
#15733
07/07/05 10:29 PM
07/07/05 10:29 PM
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NewMemberAgain
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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
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Re: 'Solid Core Wires'
[Re: NewMemberAgain]
#15734
07/07/05 10:54 PM
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440Jim
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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...
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Re: High RPM Misfire -- SOLVED!
[Re: B1Ken]
#15736
07/09/05 10:14 PM
07/09/05 10:14 PM
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Bill_LBSR
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B1Ken, are you running a Digital MSD (Digital 6,7)or are you running an Analog box (7AL2,3)?
LBSR
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Re: High RPM Misfire -- SOLVED!
[Re: B1Ken]
#15737
07/10/05 10:49 AM
07/10/05 10:49 AM
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440Jim
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Quote:
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.
Ken, Do you have the shielded cable to the distributor? I tried two different magnetic pickups in my distributor during the trouble shooting, and they acted the same. I guess if one is deteriorating and the signal is not as strong, the signal to noise ratio would get worse and might reach the MSD interference limit.
I was running for years also. It started with the addition of 15 amps more alternator load and I am thinking that more alternator output made more noise and reached the threshold. Also I noticed the Delco alternator would be better when cold, and after heat soaking and round robin, it got worse (interference).
After trying all those things and each time the car misfired, then doing this cable mod and having it work perfect, I felt so relieved. I am going to mod my spare distributor the same way. Maybe I should log off this computer and go to the shop and do it, now!
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Re: High RPM Misfire -- SOLVED!
[Re: Bill_LBSR]
#15740
07/11/05 04:27 PM
07/11/05 04:27 PM
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B1Ken
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Quote:
B1Ken, are you running a Digital MSD (Digital 6,7)or are you running an Analog box (7AL2,3)?
Bill: I'm using a 7AL2 (analog) Jim: I was talking to my son last night about the problem and I remembered that I had the alternator repaired midway through the season last year. The repair definitely increased the output of the alternator. The signal cable from the distributor runs within 3" of the alternator and is not shielded. I think I'll try your recommendation. Actually, though, I'd like to hook up the crank trigger again. My Chevy buddy, who used to break starters like me, said that the new style MSD spark retard, works great for him. I just ordered one. One way or another, I have to get this fixed. I have a points race at Delmar this week and the Sports Nationals at Columbus at the end of the month. It ain't easy dialing this thing with it running like crap on the top end.
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Re: High RPM Misfire -- SOLVED!
[Re: wildcargo]
#15743
07/12/05 10:29 AM
07/12/05 10:29 AM
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B1Ken
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Quote:
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 can't see what this would accomplish, since the alternator is bolted directly to the engine. If the alternator wasn't grounded already, it wouldn't put out any current.
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Re: High RPM Misfire -- SOLVED!
[Re: 440Jim]
#15744
07/12/05 01:10 PM
07/12/05 01:10 PM
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fast68plymouth
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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.
68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123 Dealer for Comp Cams/Indy Heads
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Re: High RPM Misfire -- SOLVED!
[Re: 440Jim]
#15747
07/13/05 06:52 AM
07/13/05 06:52 AM
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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.
In theory, there is no difference between theory and practice. In practice, there is.
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