Trouble with new 440

66HOTROD · Jun 1, 2019

I have a recently rebuilt 440 in a 1971 Charger that is giving us trouble. It starts and runs great but under load develops a real noticeable miss and loses power. We switched carbs and it does the exact same thing. Could we be having some electronic ignition conversion problems? It has all new components, distributor, wires, cam, lifters, rockers, heads, intake, carb, etc. This has us tearing the rest of our hair out. Any suggestions appreciated.

greycharger · Jun 1, 2019

Believe it or not, I have had spark plugs cause your problem.
A vacuum gauge can diagnose a lot of issues.

Ironbuilt · Jun 1, 2019

Check your timing, and not just at idle. Do you have vacuum advance? Is it working properly? Do you have adequate voltage to the coil? New components don't always mean GOOD components. A little more info will help us help you more.

Mebsuta · Jun 1, 2019

I had the wrong ignition coil one time. It would run fine at low speed, but would start missing and losing power if you tried to get on it.

Bob Sawyer · Jun 1, 2019

Does it have a manual fuel pump? How about the fuel pump push rod?

1967coronet · Jun 1, 2019

What I can add is while hunting this down just make one change at a time.
Do not shot gun it or you will never know what the problem was.

66Satellite47 · Jun 2, 2019

Mis-matched coil a possibility, in my case was inadequate fuel system, too small electric pump in the rear & too small fuel line. If you have just the mechanical pump, check the pump rod & maybe a higher volume pump.

AR67GTX · Jun 2, 2019

Can you provide more detail on the engine components and the electronic ignition. A picture of it would be good also. If you are using one of those tall MSD distributors it may be shorting to your hood when it's closed or the air cleaner base. They will blow a hole right through the distributor cap boot to a nearby piece of metal. Not familiar enough with a 71 hood and fresh air assembly if you have one but it's been driving a friend of mine nuts with his 69 Hemi RR. He's waiting on a converted Prestolite distributor not to replace the MSD one.

If running a Chrysler electronic distributor then never mind the comments on the MSD. But check your system voltage when under power as low voltage will cause modern electronic ignition boxes to act up.

PRHeads · Jun 2, 2019

Need a little more info about the symptoms.

How much load to make this problem occur? 1/2 throttle? 3/4? Almost full throttle?

Does it happen instantly when you step on it, or does it take a few seconds before it starts acting up?

Instant loss of power under load is likely electrical(ignition), a delay in the loss of power would point towards the fuel system.

miller · Jun 3, 2019

66HOTROD said:
It starts and runs great but under load develops a real noticeable miss and loses power.

Carb change made no difference...should be pretty telling.

Under load, like in gear? Go to your ignition/timing/tune. Somewhere in there, is the fault. Something I've always looked at, for overall ignition tuning, is the RPM drop. Idle RPM set, then put it into gear...if the 'tune' is even close, the most RPM drop you get is 50.

Alot of bases to touch, in the ignition, but that's where I'd look...at everything in the ignition.

Jeff Brundage · Jun 3, 2019

Had the same problem, brand new engine was on the dyno so it was easier to troubleshoot. Ended up being the brand new distributor from mopar performance. Changed to msd billet. Problem solved, idled smoother and no more breaking up under load.

biomedtechguy · Jun 3, 2019

Ignition. Wires, plugs, cap, rotor, timing.
Have you checked your timing curve, at idle, when it comes in, and the total advance at what RPM?
Good luck, let us know what you find!

gary h · Jun 26, 2019

Any Updates ? I am having some issues too.

Trouble with new 440

66HOTROD

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greycharger

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Ironbuilt

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Mebsuta

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Bob Sawyer

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1967coronet

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66Satellite47

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AR67GTX

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PRHeads

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miller

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Jeff Brundage

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biomedtechguy

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gary h

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