Lurching problem

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Apr 15, 2002 | 01:55 PM

herunar

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Joined: Apr 2002

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From: Tucson USA

Lurching problem

this is a problem which has been troubling me for a year and a half. I have a 1979 F350 1ton 4x4 with a 400 engine. About two years ago i put on an edelbrock performer manifold and a 600cfm 4bbl carb to match. runs great. here's the problem. if i put any kind of load on it ( usually on the highway going up a steep hill or towing a trailer) it begins to lurch A LOT. I can give it more gas but it lurches more with no acceleration. It almost acts like it is running out of gas. it even does it just running around town, but not always. I tried puting higher octane fuel in, but that doesn't help either. i am about to my wits end. does anybody have a direction i can take.

thanks

herunar

Apr 15, 2002 | 06:44 PM

shazam

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Joined: Feb 2001

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From: Porterfield

Lurching problem

Sounds to me either a vacume leak or a fuel problem.

Apr 15, 2002 | 08:40 PM

Big Blue4x4

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Joined: Nov 2001

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Lurching problem

It sounds to me like your float level on your carburetor is too low. that would account for it running out of gas going up hills and turning around. Just my 2 cents.

79 F150 4x4 410m Built Ford Tough!(9.1:1,KB pistons,custom Comp Cams X-Treme 210/218-.508/.524,roller rockers)/c6/3.5:1 gears,4.11:1 soon, Demon 4bbl, 285/75R16 BFG Mudders on alumn. mags with New Drk. Blue paint.
65 Ranchero 170-6, 3on the tree, solid mags, New Bright Yellow paint

Apr 17, 2002 | 05:24 PM

herunar

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From: Tucson USA

Lurching problem

thanks for the replys. i'll check my vacuum tubes and my floats. do you think the fuel pump might have something to do with it? regarding the floats, it also goes out on me when i am on a straight away or accelerating out of a complete stop, would the floats be a factor then?

thanks again

herunar

Apr 17, 2002 | 05:59 PM

fatdaddy

Posting Guru

Joined: Sep 2001

Posts: 1,531

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From: in the country

Lurching problem

You aren't alone with this type of problem---I just finished installing a new 400(complete rebuild) in my 77 f250 4x4 and it is exhibiting the very same symtoms as your engine----my friend the mechanic is stumped , I'm stumped and I may start drinking excessive amounts of alcohol if it will help me solve the problem---not really---I only drink on special occaisions--I have also been told that Pork Rinds----when consumed with lotsa beer will sometimes lead to creative thiMking and consequently a solution to my\our problem----Probably either vacuum or fuel----very frustrating but solvable I believe----maybe some of the really smart folks will respond here ---I hope!!!!!fd

:-X11

Apr 17, 2002 | 06:39 PM

herunar

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Joined: Apr 2002

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From: Tucson USA

Lurching problem

i hear ya, fatdaddy. i have taken it to mechanics, asked about everyone i know, troubleshot it the best i could without breaking the bank, AND I CAN"T FIGURE IT OUT!! It's a great truck and was built for towing, but i can't tow worth crap the it is. thanks for sharing my pain.

Apr 22, 2002 | 02:15 PM

brents

Senior User

Joined: Apr 2001

Posts: 321

Likes: 1

Lurching problem

Hey

Any chance you can run a vacuum gauge inside the cab when driving so you can look at what the vacuum does when it acts up?

I would look at the first look at the ported, then switch to the mainifold vacuum, and finaly the venturi vacuum behaviour for tips.

-Brents

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Apr 23, 2002 | 10:27 AM

herunar

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From: Tucson USA

Lurching problem

That is a very good thought. when the lurching starts it acts just like it is running out of fuel or not receiving enough fuel.i'll definately check into this.

thanks,

herunar

Apr 24, 2002 | 04:37 PM

#10

bigblue

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Joined: Sep 1999

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From: Minneapolis

Lurching problem

The lack of a pressure regulator won't cause the problem. What you do need is a fuel pressure gauge that you can see from with in the truck to see what it reads when it is acting up. Also do you notice if the engine temp increases when this happens. A lean engine gets hot real fast. I had the same thing happen on my car once. It was the hood insulation falling down in front of the intake. I would open the hood and it ran great. Close the hood and hit 40 mph and it would cough and studder. Just a thought. Dan

Apr 25, 2002 | 10:30 AM

#11

herunar

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From: Tucson USA

Lurching problem

thanks dan,

question: if i do install a fuel pressure gauge and i find that the pressure drops or rises, what would be the next step in fixing the problem? i haven't noticed the engine temp being a factor in this, it really only does this if i accelerate real quickly or if i am under a load(towing or climbing a hill quickly).

thanks again

herunar

Apr 25, 2002 | 01:51 PM

#12

bigblue

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Joined: Sep 1999

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From: Minneapolis

Lurching problem

If you do find that the fuel pressure drops, then you at least know what the problem is. From there it gets hard. Maybe a vapor lock. An obstruction in the fuel tank. A crushed fuel line. A pin hole in the fuel line sucking air. A bad fuel pump. A plugged fuel filter. Bad carb floats.......

I put a vaccume gauge on all of my vehicles. Cheap ones from JCWhitney are $10, and they work just fine.

Apr 25, 2002 | 06:56 PM

#13

herunar

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From: Tucson USA

Lurching problem

sounds like a good idea. is it easy to install?

herunar

Apr 28, 2002 | 11:08 AM

#14

adobbs

Junior User

Joined: May 2001

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Lurching problem

check the power valve in the carb they cause a lot of ploblems the dipharm leaks gets rich if you have ever had a back fire in the intake usely runs the power valve or they dont get vac to them or get gummed up and don't open.