killer501872000

so i just got a 78 mark V with a 460 and it runs ruff at an idel,i changed the plugs, wires, cap, rotor,fuel filter.and it still chugs.i was thinking it was the egr valve since i can see its not working,but it smoothes right out once you go down the road. so now im not shure?anyone had this problem before with one.

Rickman48

I've worked on a couple - one had a bad carb, the other a vacuum leak.
Both got horrid mileage and performance, until fixed.

MDchanic

So afterward they got good mileage?

- Eric

m371961

I would look for a vacuum leak. Maybe at the EGR since you say it isn't working.

killer501872000

the egr is staying shut so i know its not that,and i checked for vacum leaks and fund nothing leaking.i checked the vacum advans that seems to be working fine,so im going to run a compretion test.mabey i can find something there, if not im going right for the valve train.with any luck it will be something easy like a bent push rod or just a burnt valve.

killer501872000

problem solved its a bad cam.

MDchanic

Yow!

That stinks.

Of course, while you're in there, you Might As Well...

- Eric

killer501872000

im gona get a new cam and check the heads out and make shure there are no burnt valves and call it good. i did get the egr to work lol.it worth the trouble
001-5_zps3d006ead.jpg

MDchanic

I've never been a fan of F_rds, but I've always been fond of those Marks, if only for their Shock and Awe value.

Also, that Lima 460 can really kick some butt in a heavy vehicle.

- Eric

killer501872000

i bought it for 3 reasons #1 it looks good next to my 83 98 #2 its almost mint and #3 i got it for $1400

MDchanic

DING DING DING DING DING!

We have a winner!

I don't suppose they've got any more in stock?

- Eric

killer501872000

i dont have many problems finding nice cars! just finding them when i have $$$$$ lol

ThePackRat

Those are pretty rare sans the vinyl top.

Kind of surprised it has a bad cam ... are you sure ?.

Regardless, if you do end up cracking the front of the motor open ... do your research.

Many Ford V8's of that era were rumored to have timing sets that had at least 4 degree's of timing retard built into them.

Something I would have LOVED to have known years ago when doing a timing set in a 351W Cougar I had.
(I used an off-the-shelf stock replacement at the time)

At least now ... I know why most Ford stuff was so pathetic out of the hole compared to similar sized/weight/engined Oldsmobile's of the same era.

There should also be gains to be had by going with older heads as well ... as is often the case on an Olds.

Moral of the story ...

At the very LEAST :

Do NOT use a generic parts store shelf ... replacement timing set.

Either use an aftermarket performance type set or use a set spec'd out for an early 460 like a 68-70.

And make sure you choose a cam very wisely ... if you make no other changes to bump the compression up.

killer501872000

i going with a sumit racing stock or the rv cam. its going back to stock or veary close.and i now its a bad lobe on the cam.i pulled the valve cover fired it up and the intake rocker was only moving a 1/4 of what the others where.the push rod is straight as a whip, and when i look down the hole with a light i can see the liffter working, and it dosnt rattle so i now its not colapsted.

ThePackRat

If you're not already a member of a Ford forum ... probably would'nt be a bad idea to join a few.

See if anyone has thrown a new cam into something they kept fairly stock in similar drivetrain/weight car.

I'd also talk to someone that really knows cams as well ...

Might not cost much more to go w/a custom grind better suited to what you have/will have when all is said & done vs just some generic one off the shelf.

Cam selection on a mostly stock low compression engine is very important.

It's all too easy to end up with something that has even LESS performance than factory if you aren't careful.

This member does custom grinds for Olds stuff all the time :

https://classicoldsmobile.com/forums...utlassefi.html

Maybe he would have some input on Fords as well.

killer501872000

iv been reading up on them and the stock cam and the rv cam are about the only way to go with it. as its staying stock im not going to do any hotroding with the motor.

oldsguybry

lol

killer501872000

well lets see, epa is 8 city and 11 hwy.i would have to say it cant get any worse lol

78Delta

The RV cam is not a bad choice for a modest build. The carb on it should be an autolite split float with hot idle compensator in the back and evap control rod across the top. I need to see a pic if you have one. The hot idle compensator is crap, very common for bad idle and stalls when you accelerate from a stop with a warm engine. Brake boosters also notorious for leaking as well. Also, you should have the can style converters directly attached to the exhaust manifold and prior to the y-pipe if single or the front pipes if duals. Check and see if they are plugged, very common as these were the early honeycomb style.

The floats on these cars were polymer foam, which would saturate with gas and become heavy. This makes the car run very rich and poor runner as you describe, but fine at highway speed, because you are no longer in the idle circuit and transfer circuit of the carb.

I had a 72 Monterey with a 429 and a '77 Marquis with the 460/C6 Police Engine, both land rockets when tuned properly. I will say my 77 Marquis with the 460 had constant carb problems. Usually rebuilt it every 2 yrs.

killer501872000

iv never had a 460 that didnt have a motor craft carb.and its the cam not hard to tell when number one intake rocker only moves 1/4 of what the others do and there is no noise from the lifter.i can see the lifter moving in the hole.

78Delta

Sounds like you got it figured out.

junkyardjeff

Do not use a 78 timing chain set,get one for a 69 or 70 and you will notice a improvement on how it runs. Ford retarded the cam timing for emissions which also decreased performance so a set with straight up timing will make it run much better,I have a 77 460 in my 66 F250 that I think has to have the earlier timing chain set since it ran circles around a stock 77 460 I had in another truck.

killer501872000

i havnt got into the motor yet as i got another one from a 76 that im going through.all i know is that even with the bad cam this thing gets it lol.the stock motor is going to get some good parts and some more poop.