Periodic backfire out exhaust then stall
03-24-2015, 01:26 AM
#1
Instructor
Thread Starter
Periodic backfire out exhaust then stall
Hi team,
I'm driving a 1970 454 with a Holley 830 cfm carb and MSD Digital-6 Plus ignition system with Mallory fuel pump, all installed via previous owner. Generally speaking, everything runs excellent. Very strong. I rebuilt the carb last summer; it was leaking fuel so I did a simple gasket replacement and cleaning. I didn't get into the floats and jets. The rest of the car / fuel system has low mileage (around 7k) but was restored around 12-15 years ago.
Now, every once in a while, I'll get a quick hesitation, then a backfire (one quick pop) out the exhaust. It'll then usually stall and will only crank but not start. If I sit around, it may eventually start after a few minutes. This has happened about 5 times.
I called the service department at MSD; tech support stated the unit would completely fail and would not be intermittent. I don't have experience in these matters and can't confirm.
I just replaced the cap and rotor and haven't given it a new test run. That should come tomorrow. It did start and idle as before.
Any thoughts as to fuel vs spark and how I should conduct additional testing?
Please help a rookie out,
Eugene
I'm driving a 1970 454 with a Holley 830 cfm carb and MSD Digital-6 Plus ignition system with Mallory fuel pump, all installed via previous owner. Generally speaking, everything runs excellent. Very strong. I rebuilt the carb last summer; it was leaking fuel so I did a simple gasket replacement and cleaning. I didn't get into the floats and jets. The rest of the car / fuel system has low mileage (around 7k) but was restored around 12-15 years ago.
Now, every once in a while, I'll get a quick hesitation, then a backfire (one quick pop) out the exhaust. It'll then usually stall and will only crank but not start. If I sit around, it may eventually start after a few minutes. This has happened about 5 times.
I called the service department at MSD; tech support stated the unit would completely fail and would not be intermittent. I don't have experience in these matters and can't confirm.
I just replaced the cap and rotor and haven't given it a new test run. That should come tomorrow. It did start and idle as before.
Any thoughts as to fuel vs spark and how I should conduct additional testing?
Please help a rookie out,
Eugene
03-24-2015, 12:12 PM
#3
Melting Slicks
When it will not start check for spark. If no spark then check for power to the MSD. The instruction tab of this page has a link to the installation instructions that explain how the wires to the MSD are connected.
https://www.msdignition.com/Products...n_Control.aspx
If you don't have spark and you have power to the MSD then check for power to the positive side of the coil.
If no spark and you have power to the coil then it's probably the coil but could also be a shorted condenser in the distrib if you still have points or the pickup if you no longer have points. I'm pretty sure the condenser is only there to suppress radio noise so you can disconnect it from the points to test. Of course all of this has to be done while it still won't start so it's good to make sure it still won't start if all the tests pass.
Good luck.
https://www.msdignition.com/Products...n_Control.aspx
If you don't have spark and you have power to the MSD then check for power to the positive side of the coil.
If no spark and you have power to the coil then it's probably the coil but could also be a shorted condenser in the distrib if you still have points or the pickup if you no longer have points. I'm pretty sure the condenser is only there to suppress radio noise so you can disconnect it from the points to test. Of course all of this has to be done while it still won't start so it's good to make sure it still won't start if all the tests pass.
Good luck.
03-24-2015, 12:51 PM
#4
Melting Slicks
Member Since: Jan 2014
Location: Downers Grove Illinois
Posts: 2,474
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When it will not start check for spark. If no spark then check for power to the MSD. The instruction tab of this page has a link to the installation instructions that explain how the wires to the MSD are connected.
https://www.msdignition.com/Products...n_Control.aspx
If you don't have spark and you have power to the MSD then check for power to the positive side of the coil.
If no spark and you have power to the coil then it's probably the coil but could also be a shorted condenser in the distrib if you still have points or the pickup if you no longer have points. I'm pretty sure the condenser is only there to suppress radio noise so you can disconnect it from the points to test. Of course all of this has to be done while it still won't start so it's good to make sure it still won't start if all the tests pass.
Good luck.
https://www.msdignition.com/Products...n_Control.aspx
If you don't have spark and you have power to the MSD then check for power to the positive side of the coil.
If no spark and you have power to the coil then it's probably the coil but could also be a shorted condenser in the distrib if you still have points or the pickup if you no longer have points. I'm pretty sure the condenser is only there to suppress radio noise so you can disconnect it from the points to test. Of course all of this has to be done while it still won't start so it's good to make sure it still won't start if all the tests pass.
Good luck.
03-24-2015, 03:44 PM
#5
Le Mans Master
Now, every once in a while, I'll get a quick hesitation, then a backfire (one quick pop) out the exhaust. It'll then usually stall and will only crank but not start. If I sit around, it may eventually start after a few minutes. This has happened about 5 times.
03-24-2015, 04:40 PM
#6
Instructor
Thread Starter
The MSD was installed by the PO during the restoration, probably around year 2000-2002. Points presumably removed during this time.
I'll run through the checklist during the next failure, thanks so much for the lead.
Regards,
Eugene
I'll run through the checklist during the next failure, thanks so much for the lead.
Regards,
Eugene
04-07-2015, 11:55 PM
#7
Instructor
Thread Starter
I replaced the distributor cap and rotor as part of maintenance and to start the troubleshooting process. Turns out it had a hairline crack from bottom to top. Difficult to see even. I have about three hours of driving in, everything's been great.
Thanks to everyone for the input.
Regards,
Eugene
Thanks to everyone for the input.
Regards,
Eugene