Engine pop
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Freshman User
Joined: Apr 2012
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Engine pop
I have a 1972 Ford truck with 391 engine. It pops every 4 or 5 seconds while idling but smooths out when driving. Runs smooth until highway speed then seems to start skipping or cutting out. It has all new everything timing, ignition and fuel related. Do I have the points set wrong? I've also been told about the points "bouncing" at higher RPM. Any ideas?
Fleet Owner
Joined: Dec 2009
Posts: 20,678
Likes: 83
From: NorCal
Sounds like a points problem to me. Have you re-checked them for deep pitting or arcing?
Save your self some headaches and eplace that archaic technology with a Pertronix Ignitor (I, II, or III) ignition module.
Save your self some headaches and eplace that archaic technology with a Pertronix Ignitor (I, II, or III) ignition module.
Logistics Pro
Joined: Oct 2005
Posts: 3,785
Likes: 4
From: Mddl A MexCans
Pops through carb ? exhaust? I would check the timing and that the vac/mechanical advances are working correctly.
How old are the valve springs, if they are tired or you have worn seats you could get this issue. If you have a heavy carbon deposit on pistons it can pre ignite the fuel/air mix.
How old are the valve springs, if they are tired or you have worn seats you could get this issue. If you have a heavy carbon deposit on pistons it can pre ignite the fuel/air mix.
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Freshman User
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Alot of good ideas. I've thought about and looked at the Pertronix system, but all I find says that it is for marine applications. Anybody had experience with changing over from points to electronic type system?
Elder User
Joined: Oct 2011
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Pertronix sold at advance auto and online, got mine off ebay cheap. Easy to install and nice upgrade, engine starts easier and runs better. Plus you don't have points to replace/adjust anymore.
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Freshman User
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391 misfiring
It's been over a year since I last posted. The sputtering and cutting out has persisted, but I have tolerated it since I rarely get on the highway with this truck. When I first started posting about this problem, Pertronix systems were out there , but I couldn't find anyone who had actually tried it in a 391. H.E.I. ignition distributors were around, but way too expensive. HEI systems are now affordable, but I can't find one for a 391, only 390s which I understand has a different size intake hole and different shaft size. I know there are bushngs for the intake hole problems, but what about the shaft difference.
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Fleet Mechanic
Joined: May 2001
Posts: 1,396
Likes: 4
From: Cupertino
It looks like you have to tread carefully with 390 and 391 distributor interchanges and internals. I found this. It may help you:
Big block ford 390/391 - Hot Rod Forum : Hotrodders Bulletin Board
Big block ford 390/391 - Hot Rod Forum : Hotrodders Bulletin Board
Hotshot
Joined: Mar 2013
Posts: 14,255
Likes: 199
From: Phoenix, Az.
The 391s had an internal governor in the dizzy. If high RPMs are making it loose power it is the governor kicking in. AND there is one thing that hasn't been mentioned yet. The 330 M.D. took the same size oil pump driveshaft in between the Dizzy and the oil pump as a FE motor. The 330 H.D,361, and your 391 takes a bigger diameter oil pump driveshaft.
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