working on my cousins kids truck the last few days its a 71 f250 360 435np only modification to motor is an aluminum 4bbl intake and holley carb and the trucks motor sounds good no misses at all when its not under power, you can rev it up and it never misses a lick but once you get it out on the highway it misses and cuts out and lose's power.... we have replaced dizzy (still does it) changed carb's (still does it) changed coils (still does it) changed plugs and wires (still does it).........i have searched and searched but cannot find a single vacuum leak... i have looked in the dark for any wires grounding out or sparking and replaced all wires that could have possibly been bad from the firewall forward........ the truck smokes a bit when you take off first in the morning or if you let it set for a while (i assume valve guide seals are bad did leakdown test and compression test and all was good only one cylinder was 7 lbs less than expected)......and then he tells me he ran it out of oil 2 miles from home a couple weeks before problems started and limped it home with no oil pressure..... so am i right to assume that he might have wiped his cam lobes a little bit causing this entire fiasco? would the cam cause this effect? whats your feelings on this fellas i have troubleshooted all the other possible problems i think

 

i'm not sure how to answer the cam lobe question.

but- have you checked voltage at the coil while its running?
fuel pressure?
i'm assuming you changed the points & condenser with the new distributor.

 

Sounds like the fuel pump is not filling the bowls fast enough. Timing and spark is on so I don't know how long I would chase that dog.

They sip fuel at idle, and can rev up and down no problem. But at a sustained fuel use the pump needs to supply more fuel than the engine can handle. The float valves determines how much fuel is available, and if not set right your engine will starve for fuel. Before I bought a new fuel pump I would check float levels.

 

Off the top of the Ol' noggin:
1. Weak coil. Was the 2nd one used or new?
2. Coil being used meant to get 12v running but getting fed by resistance wire.
3. 2X above on float level and fuel pump.
4. What is the current oil pressure while idling? I think it would wipe bearings before the cam lobes. Bobby would know more about that though. Hopefully he'll chime in soon.
Have you read the plugs or put a vacuum gauge on it?

 

changed carb's, 4 bbl Holley, 4 bbl edelbrock, 2 bbl holley, and 2 bbl motorcraft so i think i can rule out the float level and i checked fuel pressure and its 6.5 at an idle......and we have adjusted and adjusted timing back and forth and can choose whether it will miss out more at higher rpm or adjust it the other way and it does it at lower rpm...... we checked different condensers and points against the new ones in the dizzy and they all respond the same..... the timing chain is less than a year old and it has all metal teeth none of that nylon coating...... that is why i have kind of am resorting to thinking it could be cam issues since he told me he ran it out of oil

 

I had an old chev years ago with 3 worn lobes on the cam . Took me a bit to find it . Ran great at idle and take off . But under load or highway .. It wouldn't pull a greased string .

 

40-45 lbs oil pressure on mechanical gauge at highway speeds goes up to 55-60.....used a brand new coil and then an older used coil and then the one off of my truck....he has drove the truck for 6 months prior to this issue with no problems and it only started doing this a couple weeks after he ran it out of oil...... and could you go a little more in depth on your number 2. JEFFFAFA

 

Well that pretty much knocks out my #3. How 'bout 1,2,and 4?

 

i'm trying to think (out loud) of what wiped cam lobes would do:

no cam lobe = valve not opening fully

at idle, when not much air is moving- everything's ok.
at speed, when you're trying to move more CFM - there's not enough airflow.
so- not enough intake charge. not enough exhaust flow.

sure seems like that could cause a stumble.
ouch.

 

If you really think the cam is wiped, pull the oil filter and cut it open at the top, remove the innards, unfold the pleats and look and the goodness inside.

 

kind of what i was thinking possibly Rustywheel68 but i wonder since it slightly changes if you adjust the timing aka you can choose whether you want it to miss more on bottom end (1000-2000 rpm) or top end (2000-3000+ rpm)....... i have drove it down the highway it was cutting out like crazy pressed the clutch in and it revs sharp and fast and never missed a single noticeable hit but the second you let the clutch back out it goes right back to singing the same ol tune

 

My idiot first wife drove a 1980 Crown Vic/302 FIFTEEN MILES with no oil pressure. Ruined the crankshaft, rod and main bearing, and cam bearings, but not the cam. I didn't have enough money for a cam anyway...

I'd check the dwell. How old are the points? If the spring is weak, it will cause the points to bounce and misfire.

 

Does his motor have the harden exh valve seat in the heads.?

What was the highest & lowest compression when you did your testing?

Was #7 some what fouled?

And what type of gas has he been using???

orich

 

When you switched carbs to eliminate them, im assuming you switched intakes as well? Figuring you used one intake for the 2bbl, one for the 4bbl, and 4 different carbs, statistically you have eliminated carbs and intake manifolds, right? How about gaskets/mating surfaces between block/manifold or heads/manifold? Warpage, porosity, its totally a guess, im way out into speculation, but no one else has asked.

 

2bbl to 4 bbl adapter plate and no switching of intakes iggybob......orich motors only change since factory was the 4bbl aluminum intake all else is original except the basics like belts and filters and such, and the truck has drove for quite some time with out this problem that is until recently he told me he has ran the tank completely dry and ran super unleaded, has ran half a dozen different combos of gas and additives with no change, all the compression readings are in a book at his house,and it was number 8 that was 7 psi lower than the next lowest on the list i remember that.....vocatexas read post 5 we replaced the points remember.....