gas mileage with your 460 cid.

[Shelly Harris]

This is the week for getting the exhaust manifold on and a dual exhaust system on the Mark IV. Also putting on a slew on new steering linkage items to see if that minimizes the little bit of shake left. No question that the rubber on those items was shot and dried out,

But here's the reason for the post. I finally got around to checking gas mileage. I was expecting something like 12....well, 207 miles used 22 gal and that comes to 9.4 WOW! I guess I can stop thinking of going on long road trips! What are you guys getting??

[Barry Wolk]

14 hwy. Don't check city. Probably what you got, or worse. I tend to do rapid starts. Blows people away to see that boat move out. The Mark II is faster, though.

[Barry Wolk]

Did you try vacuum tuning it? I worked on a friend's 430 yesterday and was able to smooth it right out.

[Shelly Harris]

Did you try vacuum tuning it? I worked on a friend's 430 yesterday and was able to smooth it right out.

I should, but I haven't. I'm taking baby steps, one thing at a time. It's starting up ok --- so I thoguht I'd leave well enough alone. For the little driving I'm doing I didn't want to touch the ignition until after I got the older timing set installed and the horrible carb replaced.

[Barry Wolk]

Same carb as I have and mine runs like a top. Actually, if it's not leaking and the accellerator pump is working the vacuum tuning will make a difference.

A simple vacuum test willl tell you if you have a vacuum leak, causing poor mileage.

[Shelly Harris]

My complaints on the carb (Motorcraft 4300) concern the problematic automatic choke. With 80K miles on it you know it's plenty dirty and I have elected to replace it instead of rebuilding. I understand that later Marks trashed it, so I will too.

[Don Henschel]

Did you check your vacuum advance diaphragm. A friend of mine figured his quadrajet on his truck needed a kit. I asked how it ran and he mentioned about the same as before but much harder on gas. I checked his advance and his diaphragm leaks not giving full advance, just a fraction of what it should.

[Shelly Harris]

Don... the carb is garbage and I'm not wasting any time with it. I'll be doing the timiing chain and carb change this fall or early winter when I won't regret it being in the garage torn down and not being able to drive it around. For the moment I'm getting the quick stuff done so I can enjoy showing it off on the week ends. I switch between the Mark II and IV every week.

[Nick DeSpirito]

I still have the 4300 in My 1976 Lipstick. The choke does act up sometimes making it hard to start. It rumbles, stalls, and gives off black smoke out of the exhaust until it warms up and smooths out. But, when this happens, I tell my L/M dealer service Tech about it when it goes in for an oil change. They either clean it and/or adjust it for me and after that, it starts on fast idle and runs fine. I think the condition is aggravated by sitting too long. Although, it had been sitting since last summer and It started up perfectly a few weeks ago.

Also, my car has factory dual exhaust. The 1974 Saddle and White I bought new back in '74 did not.

Gas mileage? This car sucks up gas like it's going to the electric chair tomorrow. :-)

[Shelly Harris]

Nick; What's your gas mileage? Any mods to your 1976 460cid?

[Nick DeSpirito]

Shelly, I never clocked the gas mileage. All I know is that it drinks gas with four straws. :D

No mods, totally stock and every part i replace is FOMOCO from the dealer including the (24F) battery.

[linmk2]

Shelly, I owned a 1977 and 78 Mark V's with 460 CID engines as new cars. Both returned about 10 MPG in town and about 16 Hwy. The Mark IV is somewhat heavier, so I would guess the mileage to be less. I still have the window sticker for my 78 Pucci and the EPA show 11 city, 17 Hwy. with a 13 combined. Test weight of 5000 lbs. and 2.75 rear end. My how things have changed. 11 MPG and a $17413 MSRP!

[Don Henschel]

Oh so you havnt done thetiming chain yet.I assumed you had and its still hard on gas.If your chain is stretched your timing on the valves and distributor will be late. First things first since you havnt changed them. Take your distributor cap off. Get a socket to fit the crankshaft bolt and a large 1/2 inch flex head bar and rock your engine crankshaft back and forth while watching your rotor and how much your engine turns each way before the rotor moves. This will tell you how bad your chain is stretched. Next check your advance diaphragm. These fail alot more often than people realize causing a fuel hog. Like Barry mentioned he has the same carb. on his Lincoln with reasonable gas milage. Last but not least yank out all of your plugs and give this thing a quick compression test making sure you have a good battery so all the cylinders crank the same

[Shelly Harris]

Thanks Don.... I get faster, better information for my Mark IV and the 460 over here then at other forums which are suppose to cover those cars (no forum names please)

[Barry Wolk]

Maybe it's because we actually own and work on these vehicles.

I find that a lot of web sites like that have a preponderance of wannabees and lurkers that don't add much to the technical data.

[Don Henschel]

Shelly, I mentioned the compression test because it gets right to the point. It tells you what you got to work with for an engine right off the bat! Leaking valves, poor compression rings, uneven compression etc. It is totally amazing how many times I have heard the carburator blamed for valve problems, ignition problems etc. By the way- if your timing is late, you will need richer choke settings. You should have that vacuum valve on your thermostat housing?? I think that vintage would still have it. Its purpose is to give straight manifold vacuum to your distributor when the engine is cold. Over advancing the timing on a cold engine makes them run much better. When the thermostat opens, the valve closes only allowing vacuum from the off idle port of the carb. I wonder how stretched your chain is. Maby it has been changed already.

[Shelly Harris]

Good advice which I will follow.

The engine has 80K on it. I'm still figuring out how much oil it burns in relation to miles... haven't driven it far enough to know anything that way. Changed out the plugs and 6 of them were nicely tan and two were black/greasy. I'm certain the timing chain is original. I'll do a compression check this weekend. The greasy plug cylinders will probably be weak. I wouldn't be surprised if it needs rings and valves. I bought the car because the body, paint, bright work, upholstery/interior, trim are beautifull and everything except the gas tank sender worked perfectly. So I was willing to accept whatever surprises the engine and suspension might bring. Taking one step at a time. Looking forward to driving with the new exhaust and steering parts. Thanks for the tips

[Barry Wolk]

My '68 460 had two wet cylinders. No damage, just a buildup of carbon. I suspect a lifter was adjusted too tight and not letting the exhaust valve close all the way. A Valve adjustment might have taken care of it without pulling the head.

[Shelly Harris]

Even if it has hydraulic lifters ????

[Don Henschel]

Yes. The valves could be ok but the valve guide seals may have failed. Two fowled plugs cold cause this thing to guzzle fuel. Try a running test by shorting out each cylinder, one at a time and see if you have any weak cylinders + do a compression test. I use a test light with a long sharp skinny probe (grounded of course) and carefully slip the probe in between the boot and wire to short it out so you dont damage the ignition wire. I dont like to pull the wires while its running as this sometimes can be hard on solid state ignition. You cold also use an ohm meter and test your wires. Usually a weak ignition wire will act up while you accelerate and run fine at an idle.