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Old 4th September 2017, 09:03 PM   #1
john bach
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engine popping

i have SPF GT40 Mk2 P2116 Roush 427 MSD ignition. Motorcraft/Autolite plugs. lately engine pops intermittenly. at idle, at speed, accelerating, decellarating, not backfiring. not consistent. pressed down on plug wires at plugs and dist. all tight . car runs fine. changed plugs once. log, tedious process. #3 plug took forever. this just started. any suggestions, hints?
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Old 4th September 2017, 10:23 PM   #2
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Re: engine popping

Vacuum leak?
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Old 4th September 2017, 10:40 PM   #3
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Rod Brace
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Re: engine popping

Carbon tracking in the distributor cap? Coil going bad?
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Old 4th September 2017, 11:31 PM   #4
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Re: engine popping

Sounds like you could be pulling air from somewhere.....check intake manifold bolts, look for air leak, etc.

Also, someone mentioned the cap and rotor.....if you have the MSD distributor, check the cap and rotor for wear at the rotor spring and carbon button on the cap. They tend to erode quickly especially if the spring pressure is too high. Helps to put a little dielectric grease at this contact, but I digress.....
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Old 5th September 2017, 01:31 AM   #5
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Re: engine popping

Start it at night and in the dark and see if you are getting sparks escaping from the spark plug wires.
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Old 5th September 2017, 05:04 AM   #6
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Re: engine popping

Go NGK plugs, appropriate heat range, set gaps 45 thou.
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Old 5th September 2017, 11:37 AM   #7
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Re: engine popping

mine was popping and banging .... I refitted my silencers which was blowing crap out at the joint .
I removed them resealed them . no more popping and banging .. worth a look ....
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Old 25th September 2017, 05:48 AM   #8
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Re: engine popping

If the fault is ignition, read the MSD hints and tips. There is a reference to the very high voltage ionising air in the distributor. I changed my MSD to a compatible 'Streetfire' unit, which seemed to lower the voltage slightly, now no problems. If the popping is as you describe, it would suggest an ignition fault. Does it pop in the carbs or the exhaust ?
I also had a similar issue with the induction on overrun, caused by a fuel level in the float chambers that was lower than spec. Ian's darkness test is a good tip. If it's popping in the silencers, then it's probably unburnt fuel being ignited by the hot exhaust gases. The loose-piece gaskets under the inlet manifold can sometimes migrate, giving an induction leak. What do the spark plugs tell you ? Are they all the same tip colour ? All light chocolate coloured ? If there is a slight exhaust leak causing the popping to become audible, then sealing the leak will hide the problem.

Good luck !
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engine, fine, plug, plugs, runs

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