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Old 11/10/19, 02:26 PM   #1
Joined: Oct 11
Posts: 6
76' 302 failing....

I've got a 76' with automatic and a 302. It intermittently acted like it was dropping a cylinder previously but only lasted a minute or two. Now it is continously acting as if it is running off 6 cylinders. I thought it was a lifter clogged and therefore a cylinder was being dropped but an oil change and some "valve medic" cleaner didnt correct the issue.
I'm looking at getting another 302 to drop in its place while I rebuild or trash this one. Are there any concerns with heads, cam, accessory swapping etc that I would need to be aware of? What would be the latest 302 you would consider easily interchangeable with me putting my carbeurated intake and oil pan/ pump on?
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Old 11/10/19, 03:42 PM   #2
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Joined: Nov 03
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Sometimes it takes a few hundred, to a few thousand miles for the cleaners to work their magic. But if the lifters are not making noise then they're likely not sticking. I guess they could stick in a pumped-up position, not letting the valves close, but I think that would be unusual.

Have you given it a tune-up lately? What about a compression check?
Does it smoke or use oil?

When mine would run on 7 cylinders it was hardly noticeable other than a rough idle. When it ran on 6 though, it was pretty rough.

Could be so many things at this point.
The inter-compatibility is extensive. Mostly you just need to watch out for, and avoid completely the oddball V8's that were around sometime in the late seventies or early eighties I think, that were smaller than a 302 and had different components. (others here will know the details)
Otherwise you can use a 302 from '69 to '01 and have good luck doing all that.
The advantage to the '97 to '01 models is that they came in Explorers only, and had that great front accessory serpentine drive that everybody is scouring the junkyards for. The later blocks after a certain year ('89 or '91 maybe?) were roller cam equipped and had the more desirable "E7..." heads. The most desirable of all are the GT40 and GT40P heads from the Explorers.
The GT40P's were the pinnacle, but with their slightly odd spark plug angle are not considered to be quite as desirable for Bronco owners with headers not specifically clearanced for the P head plugs. But will accept carb intake manifolds I'm pretty sure.

There are certainly minor variations over the years, but I'm pretty sure there were only a very few that get in the way of you using a carburetor.
One consistent stumbling block though, is if you want to retain your mechanical fuel pump and if you have a manual trans.
The fuel pumps all went electric after a certain year and the front cover had no more place for a pump to mount. But if that's important then your old stuff will bolt right to the front. Even though they had like 30 different designs at one point, they ALL still bolt to the front of the engine block.
The later blocks were missing the one hole for the clutch linkage Z-bar setup. But that's easily overcome so most of us don't consider that an issue.

Good luck. Lots of good info around here. Lots of the members have detailed knowledge of doing just what you're doing.


'71 Wagon, 3.5" WH, F150 disc brakes and steering, 4.11 33x11.50 Thornbirds, Kayline soft top, Hanson bumpers. "Built, not bought"

'68 LUBR, 2.5 + 1 WH, 31x10.50, 4.56, Explorer and 4R70w by EFI Guy, WH disc brakes, Hanson front bumper, Warn winch. "Bought, not built"
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Old 11/10/19, 03:44 PM   #3
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Long Island, NY
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Hi, I would do a compression check and run it with a vacuum gauge to learn the condition of the engine. If the compression readings are good you may have a simple problem. If the compression is bad, you may just need a valve job. Good luck
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Old 11/11/19, 10:40 AM   #4
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I'd start out by isolating the dud cylinders by pulling the plug wires one at a time from the distributor with the engine idling. There are special pliers made for this, to help keep you from getting shocked.

Once you find the bad cylinder, you should compare the plug wire's resistance with a good one. The resistance should be close to the same.

Next, pull the spark plug to check the condition and gap.

Another cause for a dud cylinder can be a split and leaking intake manifold gasket. It will cause a low vacuum in that cylinder as well as oil consumption.
I actually started an overhaul once thinking an engine was worn out, only to find a split intake gasket at the intake runner.

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Old 11/11/19, 01:23 PM   #5
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I'd start with the easy stuff first . Have you checked the integrity of the spark plug wires ?All insulation in tact and No exposed wires and good internal connections. - how about the plugs themselves ? Did you check the distributor cap to see if it's cracked or some of the contacts broken .
Have you checked the coil and the resistor wire that's in the run circuit ?
a few easy things to do before diving into compression tests and etc.
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