460 losing spark

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Aug 3, 2014 | 10:24 AM

Bigolferd

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460 losing spark

I need some help here guy's. Coming home the other day i noticed it wouldn't rev over about 2000 it would just fall on its face, flooring it would only cough and pop. Have a manuel so dring home uder 2000 not a problem. I tried new inline fuel filter and checked the screen on the inlet of my Edelrock carb no change. Found my vac adv diaphram was bad. Installed new,adjusted per instructions and no change. I went through the full range of adjustment on the vac adv 1/2 turn at a time and no change. Put my spark tester inline and it looks like i have a weak spark and loose it as i rev the motor. Replace magnetic p/u in Durspark dist. and install Accel coil no change. i pulled linkage off accelerator pump and pushed down too see two nice stream of fuel shoot out. The springs and centrifugal advance all look ok in the dist. Please help me out.

Aug 3, 2014 | 06:07 PM

jl429

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460 spark problem

It sounds to me that you have covered all the bases. but you have missed the most important one, the electronic ignition module. It is located on the drivers side fender well and has two quick connecter plugs. you can pick one up from your favorite auto parts store for about $30. If this does not solve the problem, check the wiring harness going to the module for a bad wire or a bad connection in the plug.

Aug 3, 2014 | 06:08 PM

blackjack33

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From: Isla de Muerta

Looks like you've tried the usual suspects, but I want to ask...

How are the plug wires, are you losing spark on each cylinder?

How's the armature inside the distributor, how's your ignition module?

Aug 3, 2014 | 06:59 PM

Bigolferd

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I have about 2500 on the motor, all new plugs,wires, cap and rotor. I have not checked each cyl. but with the lack of rev or power it seems i'm loosing all spark. I just got through removing cleaning and tweaking my carb and nothing ive done has changed a thing

. I was also thinking of the brain box on the fender I checked the plugs and all are clean. I checked resistance through harness to dist and all wire only have 3 ohms. I think i will stop by my brothers and steal his box off his Bronco to test. Thanks for help.

Aug 4, 2014 | 08:28 AM

fmc400

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From: Austin, TX

I wouldn't count on what the spark tester says as you rev the engine up; it may not be reliable or its output visually distinguishable as the frequency increases.

If you've got spark at all, call the ignition system good. For the most part, there's nothing in the electronics that will make it cut out as RPMs climb. You need to volume test the fuel pump.

Aug 10, 2014 | 05:06 PM

Bigolferd

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Thanks for the help guy's I finally was able to work on my truck again today. I borrowed my inlaws ignition module from his 75 and had to hook it up with some jumpers to color match the wires but the truck fired up and ran great. I took my old one to Napa to replace it and found out they can test them, big suprise, mine was bad. New one is in and my truck runs great.

Aug 11, 2014 | 10:05 AM

black bird

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I have an 89 Ford f-250 xlt larit two wheel drive 3/4 ton
And i want to rebuild the engine it has a 7.5 liter 460" in
It. Its efi bank fire speed density. I was wondering if i put
A 4.500" stroke crank and bore it to 4.440" bore bigger
injectors and all new sensors new egr valve, machine
the heads for bigger valves and put a compcams valvetrain
in it new pistons for 10.5:1 compression and a jet performance
computer would i have any problems? Thanks for any input
on this.