Intermitent backfiring

[BAsque1]

Last Sunday I notice an intermittent backfiring which got progressively bad after a while and almost lost power altogether.
The gaskets to the exhaust manifold and header flanges are not leaking so I ruled that out.

I changed the rotor because it did not look good, however, the cap looked ok.
I am using an MSD 6A ignition system with the corresponding MSD coil, someone suggested that I should also use the MSD cap and rotor to complement these. It is on order already.
Could it be a stuffed gas filter ?
Another possibility is that I changed the oil and I accidentally added a bit more than normal which could have fouled my plugs. I took a plug out today and it was dry. So I am stumped by thus sudden missing.
Any thoughts?
By the way it is not the alternator, it was checked and it is fine and there was no loss of amperage when the backfiring started nor the tach gave out huge fluctuations.
Help anyone please

[DanEC]

I recently suffered a clogged fuel filter on my Lightning. The symptoms were it would run OK at light throttle but as soon as I gave it any gas it would stutter and miss which went away as soon as I let up. That's with fuel injection. A carb might be a bit more tolerant and not cut out as immediately since the fuel bowl provides a little reserve.

[joyridin']

Is it backfiring up through the carb, or out through the exhaust?

[BAsque1]

exhaust, my rule of thumb is that electric missing is all the time gas caused missing is intermittent, but i could be mistaken

[Tommy]

Basque I,
I may not be able to diagnose your problem, but I might be able to help you better describe it for those who can. "Backfire" means different things to different people, so tell us this.
1. Is it popping from the exhaust, especially during deceleration?
2. Is it misfiring (hesitation like one cylinder didn't fire) during cruise, acceleration or deceleration?
3. Have you changed anything else recently, other than the oil?
4. Does the symptom only occur during certain circumstances? If so, what are they?
5. Have you checked the timing recently? If so, what is it?

[FWB]

Lou, if i remember correctly you have a 427 in that not the 429-460 right?

check the rockers you may have an adjuster backing off....

Fred

[Tedster]

I had the same intermittent backfiring problems which got worst over time... I had to change a few parts before i realized it was a bad coil..
Never suspected to be the ignition coil due to the fact it had about 1k miles of use since new with no issues.
I now have a new coil and a bunch of spare parts. I'll throw that one in the experience bag..

[RICK LAKE]

BAsque1 First name would be nice for free info. There is no 100% way to check the cap. How does the center contact look? MOst times these things burn out the carbon center with high voltage coils. You should always replace both at the same time for maintainance. Have seen a couple of caps lose their cnenter point and still fire off the plugs but run ugly.
Coil you didn't say which coil from MSD you are running, Some oil filled coils MUST be mounted vertical and not horizontal. If you can also mount it off the motor this helps. Unless it's an "E" coil, vibration and overheating 1/2 the coil windings, you can get total failure or weak spark to the plugs.
There is a basic test for the module inside the distributor. I have only seen 1 module go bad over the years.
The last thing is the 6AL module. Yes they fail. MSD will rebuild it if needed.
Start with the cap and road test. If still doing this, you choice is coil or module. If it's 1 missfire, make sure the pinwheel inside the distributor is clean, blow out with low air pressure.
If there is no change, start with pulling spark plugs and look for a problem or different color than the rest. Check the valve lash at this time for all cylinders. Write back and tell us what you have. Good luck Rick L. Ps LIke others have said with MSD buy all the parts and install in a bag in the trunk for the ignition system. Coil, msd module, spare distributor, ballist resistor, and 1 long spark plug wire. Basic tools to change out any one of these on the road. Been there done this on the track. Some of the guys use a standard black cap on there MSD system and have no or little problems. Look up old threads about running other caps on the MSD. THey have solid centers and brass contacts like the old accell caps had.

[BAsque1]

Originally Posted by Tommy

Basque I,
I may not be able to diagnose your problem, but I might be able to help you better describe it for those who can. "Backfire" means different things to different people, so tell us this.
1. Is it popping from the exhaust, especially during deceleration?
2. Is it misfiring (hesitation like one cylinder didn't fire) during cruise, acceleration or deceleration?
3. Have you changed anything else recently, other than the oil?
4. Does the symptom only occur during certain circumstances? If so, what are they?
5. Have you checked the timing recently? If so, what is it?

Tommy:
1.During acceleration
2. yes
3. Nope
4. No just normal driving
5. 8 degrees BTDC @ 750 rpms
Lou

[BAsque1]

Originally Posted by FWB

Lou, if i remember correctly you have a 427 in that not the 429-460 right?

check the rockers you may have an adjuster backing off....

Fred

Hi Fred!
yes 427 Side Oiler, when you say an adjuster are you talking about the rocker arm nuts? I have hydraulic lifters which are not adjustable????
Lou

[BAsque1]

Originally Posted by RICK LAKE

BAsque1 First name would be nice for free info. There is no 100% way to check the cap. How does the center contact look? MOst times these things burn out the carbon center with high voltage coils. You should always replace both at the same time for maintainance. Have seen a couple of caps lose their cnenter point and still fire off the plugs but run ugly.
Coil you didn't say which coil from MSD you are running, Some oil filled coils MUST be mounted vertical and not horizontal. If you can also mount it off the motor this helps. Unless it's an "E" coil, vibration and overheating 1/2 the coil windings, you can get total failure or weak spark to the plugs.
There is a basic test for the module inside the distributor. I have only seen 1 module go bad over the years.
The last thing is the 6AL module. Yes they fail. MSD will rebuild it if needed.
Start with the cap and road test. If still doing this, you choice is coil or module. If it's 1 missfire, make sure the pinwheel inside the distributor is clean, blow out with low air pressure.
If there is no change, start with pulling spark plugs and look for a problem or different color than the rest. Check the valve lash at this time for all cylinders. Write back and tell us what you have. Good luck Rick L. Ps LIke others have said with MSD buy all the parts and install in a bag in the trunk for the ignition system. Coil, msd module, spare distributor, ballist resistor, and 1 long spark plug wire. Basic tools to change out any one of these on the road. Been there done this on the track. Some of the guys use a standard black cap on there MSD system and have no or little problems. Look up old threads about running other caps on the MSD. THey have solid centers and brass contacts like the old accell caps had.

Hello Rick, Lou(Basque1):
Thanks for the detailed diagnosis.

I am now waiting for the new cap & rotor (MSD)
I do have the MSD coil mounted sideways, I know about these and on the instructions it calls for "it can be mounted sieways) If you deem appropriate I might be able to reinstall it vertically instead.
I will star testing one thing at a time and will report back. It will take more than 2 days I have contractors in my house doing some work the next two days.
Thanks so much
regards
Lou

[ERA 778]

I went through a very similar exercise recently. My 428 started missing and occasionally backfiring and I tried everything. I also have MSD ignition hardware and eventually swapped out everything before determining that it was the coil. In my case it was the epoxy filled high vibration coil, but I suspect heat to be the source of the failure. My coil is bolted to the front of the driver's side head and gets really hot. I ended up remounting the coil with a large insulator that I think will keep it a little cooler.

Never could find a temperature spec. for an MSD coil, but the new mounting dropped the coil temperature by 10-20 degrees.

Hal

[BAsque1]

Tks Hal:
I am considering relocating my coil in the vertical position, mine is on the DR side up front where it gets the benefit of good air flow from the fans, but insulation seems like a greatr idea. I will do that too.
Cheers
Lou

[Mdman352]

Lou,
I have the same setup and experienced the same situation too many times. I got tired of replacing the MSD cap, which burns out the center contact, ripped all MSD equipment out, and now run a Pertronics setup with NO issues.
I tried the MSD tech bulletin fixes, like more and better grounds and drilling holes in the cap to no avail. Been there and done that and have a drywall bucket of wires and MSD stuff for the FE if anyone wants it.
David A.

[STEVE-O]

Originally Posted by BAsque1

Hello Rick, Lou(Basque1):
Thanks for the detailed diagnosis.

I am now waiting for the new cap & rotor (MSD)
I do have the MSD coil mounted sideways, I know about these and on the instructions it calls for "it can be mounted sieways) If you deem appropriate I might be able to reinstall it vertically instead.
I will star testing one thing at a time and will report back. It will take more than 2 days I have contractors in my house doing some work the next two days.
Thanks so much
regards
Lou

If you get the MSD 8222 Blaster coil, it can be mounted in any position since it is high vibration epoxy filled.
If you are using an MSD ignition, then I believe you dont need the ballast resistor. The resistor is used with points style ignition.

[Rick Parker]

Intermitant missing is a "*itch" to track down. Knowing how the "Miss" feels is KEY. I like to desribe an electrical miss as a "Sharp" cylinder misfire heard in the exhaust, where a fuel related one is where the engine more or less noses over temporarily and then recovers; it "Sounds" different than electrical miss and it feels different too. I may be over simplifying this but if you have actually chased both and resolved them, you will know how the engine reacts to each.
Look at your wires near where they attach to the plugs, burned boots on the plugs or compromised wires near the headers, potential crossfiring (if electrical??) Be sure the center contact on the distributor cap is touching the spring contact on the rotor. Many of these parts are mixed by the manufacturers and not originally matched with each other. For example the Chevy style rotor adapted by MSD and their "Small Diameter Cap" and other applications, used in various applications. Hence the mismatch problem many of us unknowingly encounter. Also the more resistance created throughout the secondary system with resistor plugs, High Voltage Coils and resistance wires all create more heat being put into the carbon button of the distributor cap, thus affecting its life an that of the cap too.
I once was chasing an intermittant electrical miss and while actually adjusting and tuning found the plastic under the spring blade on the rotor eroded with a hole being burned, allowing the spark to jump grounding itself through to the distributor shaft.

[BAsque1]

Ok guys here it goes:
I changed the rotor and cap for original MSD-no change in the backfiring
Opened the in line gas this was clean no impurities in the wire mesh, nevertheless I blew it with compressed air just in case.
relocated the MSD coil to vertical position even though it says it does not matter, now while doing this I noted the ground cable for the coil was attached to the same bracket as the coil to the side of the fender, however, it was loose or poor ground connection. All was buttoned down nice and tight and test drove it and the backfiring appears to be gone. I am still skittish that this was sorted out but for now it looks that way. I will test drive it tomorrow again for a longer run and report back. Tks guys. Yes I do have a pointless electronic ignition I do not need the ballast resistor for this set up..
cheers
Lou

[ERA 778]

Something doesn't sound right or I am missing something. For the MSD 6 series of ignitions, there should be two wires from the box running to the coil. There should not be a ground wire at the coil. Both the orange(+) and black(-) wires should run from the coil back to the MSD box. I suppose that if the engine ran before with the coil wire grounded, then an intermittent connection could explain your problem, but I just don't know if an MSD system can run if wired the way you described.

Also, if the problem actually was with the coil, relocating a bad coil should not fix the problem.

[BAsque1]

Originally Posted by ERA 778

Something doesn't sound right or I am missing something. For the MSD 6 series of ignitions, there should be two wires from the box running to the coil. There should not be a ground wire at the coil. Both the orange(+) and black(-) wires should run from the coil back to the MSD box. I suppose that if the engine ran before with the coil wire grounded, then an intermittent connection could explain your problem, but I just don't know if an MSD system can run if wired the way you described.

Also, if the problem actually was with the coil, relocating a bad coil should not fix the problem.

The two wires are indeed connected to the coil but the ground wire that I am talking about comes from the loom from the box and it was a ground wire as per the directions. This MSD system has been in my car for over 2 years now without a hitch. I just relocated the coil in the vertical position just for peace of mind.
I will report back after my next longer test drive, but it seems that the backfiring is gone.

[ERA 778]

OK. That makes sense. A loose ground wire for the MSD box would certainly cause a problem! Mounting the coil upright is the right thing to do. Make sure you drive long enough to get everything really hot under the hood. My problem would sometimes come and go with heat under the hood.
Good luck, but I think you found your problem.