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Glendale Arizona
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Discussion Starter #1 (Edited)
At least it's puzzling the heck out of me. Motor is a 468 cu in BBF basically stock. Hydraulic flat tappet cam, roller rockers, Comp pushrods with guideplates, stock crank and rods, edelbrock Performer RPM heads with small chambers (75cc) and about 10.5:1 compression, tunnelram with two holley 750 dps.

Problem new fuel pump carbs and 4 port regulator. Fuel pressure is at 6.5 psi, idle mixture screws are 1.5 turns out and floats adjusted.

One pump on the throttle when cold and she lights right up. Idle sounds real good and no indication of any problem. When running there's a bit of a hesitation off idle then she gets up and runs pretty good (thinking this is unrelated to the problem but something else to work on).

While under way sounds like it's hitting on all 8 cylinders and I'm pulling my normal rpm at WOT and various ranges of throttle. Ran it about 4 miles just taking it easy most the way and romping on it a few times. Got to the cove and let her settle into an idle and it sounds like it's running on 7. Kinda popping and coughing. Got into the cove and let it sit for a bit. After about 10 minutes I disconnected my driveline via the jetaway and it fired right up and sounded normal again.

Later left the cove and did the same routine on the way back. Started up with a bump of the key and sounded fine at idle, cruise and everything in between, but when I got back to the ramp and let it idle it started crapping out again. After it's on the trailer for ten minutes or so, fire it back up and everything is back to normal again.

I'm thinking I've got a hydraulic lifter taking a shit one me. Can't figure out what could be changing from cruise to idle and why after sitting everythings o.k. again. Keep in mind if you just start it and let it idle without running it around, it'll idle fine as long as you care to run it. It's not until you take it out and cruise around a little that the problem arises.

Any ideas?
 

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702 Posts
Sounds heat related, ignition side maybe. I am sure you have done this....plugs....wires... ect...ect... then if u can get a heat temp gun and try to find a colder hole and work from there.
Good luck
 

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1,450 Posts
My guess is ignition. I had a circle boat that was doing the same dam thing to me and I swapped out the mag and violla! !!
 

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Glendale Arizona
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2,368 Posts
Discussion Starter #5 (Edited)
Can't rule out ignition completely, but it should be in pretty good shape. MSD 6AL and the box was tested recently on MSD fixture by a local shop, MSD pro billet dizzy, replaced cap and rotor at the end of last season and no more than a couple hours of run time on it. Relatively new MSD 8mm wires.

I've got a temp gun and I'm going to take it with next time I run it to see if I can find the cylinder that's going dead. I didn't have it on the last outing.

As for tank venting, I don't think so but I'll pull the caps next time it starts falling on it's face to see if it helps.

Is there any way to test hydraulic flat tappet lifters to see if they're bleeding down or otherwise malfunctioining? Can they even cause an intermittent problem like I'm seeing here?

Due to the nature of the problem this damned thing is almost impossible to duplicate on the trailer which makes it real tough to nail down.
 

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25,975 Posts
Oooo got u pumping down losing lift. That would suck!!!
More importantly, the further down the line in the lifter gallery you go, the less oil to the lifter.
Ford pumps are one the best pump in the industry. Titan pumps are patterned after the Ford gerotor pump. But they are the best movers low (idle) speeds.

Heavy leak combined with low volume/light hot oil can result in low flow at the end of the line.
On a Ford 460, the mains and rods are being fed by one the lifter galleries. That's a lot of oil demand dependent on the lifters sealing, not leaking to the pan at low RPM.



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More importantly, the further down the line in the lifter gallery you go, the less oil to the lifter.
Ford pumps are one the best pump in the industry. Titan pumps are patterned after the Ford gerotor pump. But they are the best movers low (idle) speeds.

Heavy leak combined with low volume/light hot oil can result in low flow at the end of the line.
On a Ford 460, the mains and rods are being fed by one the lifter galleries. That's a lot of oil demand dependent on the lifters sealing, not leaking to the pan at low RPM.
Wow yes thanks for taking me to school again!:thumb:
 

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Not saying that has to be the problem. But we are just now starting to see some decent flat tappet hyd lifters after a few years of some very questionable ones. The 385 Ford is a little unique in its oiling, and loose lifter, both internally and externally, along with a less the top condition standard volume oil pump, hot oil the stack tolerance can all add up.

If this thing didn't always have this problem, I would seriously consider if he changed oil brands/weight/type.



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A heat related fuel issue? Or a delivery issue?
If runs fine balls out, and takes a shit when he brings it to an idle afterwards, doesn't sound like a delivery problem.
He never said it takes a shit while his foot is in it. Or even off idle.
Well understood and viable but has the O.P. ever mentioned a clacking noise from the engine-or an oil pressure drop? it could be leaning a cylinder out! I would recommend next time it drops a hole, shut down and read the plugs-don;t wait for the trailer just do it on the water! If a clacking noise was heard than I would believe a lifter bleeding down but that was never mentioned? At same time I would check carb bowl for fuel level! JMO.
 
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