390 miss need help

Reply Subscribe

Thread Tools

Search this Thread

May 17, 2002 | 01:20 PM

bigoldblue

Thread Starter

Freshman User

Joined: Mar 2002

Posts: 47

Likes: 0

From: tucson usa

390 miss need help

Hey all,
I've got a 71 f100 4x4 390 4bbl-edelbrock 600, 4spd and i've got a miss--not much of a miss at idle-a little rough. when accelerating it misses just enough to where you can hear it and feel it, not really bad though. I went through everything i could think of, new cap rotor, plugs, wires, air filter, fuel filters, installed pertronix w/coil, did compression check 135 all even. checked for vaccum leak w/carb cleaner everywhere, vaccum isn't good, fluctuates between 7-14 rapidly, and the plugs show signs of running a little rich- not fuel fouled or anything though. the truck runs great going down the road-no miss then. any suggestions?
thanks
david

May 17, 2002 | 03:58 PM

Ratsmoker

Post Fiend

Joined: Feb 2001

Posts: 6,624

Likes: 8

From: Missouri

390 miss need help

Make sure all of your coil wires and grounds are clean and tight.

May 17, 2002 | 06:04 PM

bigoldblue

Thread Starter

Freshman User

Joined: Mar 2002

Posts: 47

Likes: 0

From: tucson usa

390 miss need help

yeah, i checked that, and also checked the timing, and firing order

May 17, 2002 | 07:13 PM

canzus

Elder User

Joined: Jan 2002

Posts: 692

Likes: 0

390 miss need help

You've either got a semi bad plug wire or plug,
or a sticky valve/bad lifter, as it's just at idle
I'm betting on the weak lifter...

Steve & the Rockette
'63 F100
'68 F100
'72 Capri 2L
'73 Capri 2.6L V6
'73 MG B GT 2.6L V6(Ford)
'98 Contour SVT 2.5L V6 (Mods)
'01 ZX2 (No Mods yet)

May 17, 2002 | 07:21 PM

Flash

Posting Guru

Joined: Jul 2001

Posts: 1,914

Likes: 1

390 miss need help

You have the indicator to look for with the bad vacuum. It can be several items from a cam going flat to a bad intake manifold. I would suggest pulling plug wires and narrowing it down to a specific cylinder. I had a 360 with a stock 4 bbl intake that had a crack between the heat for the carb and the intake runner, almost drove me nuts finding it. Also, just because you sprayed cleaner on top of the manifold doesn't mean there isn't a leak, it can leak on the inside.

May 28, 2002 | 11:31 AM

michaelws

New User

Joined: May 2002

Posts: 3

Likes: 0

390 miss need help

One possiblity that I can think of is that the valves might be too tight. What type of rockers are you using? Are they adjustable? If you do not have adjustable rockers and if the heads have been decked it you might need shorter pushrods.

May 28, 2002 | 08:36 PM

big block power

Senior User

Joined: Feb 2002

Posts: 465

Likes: 0

390 miss need help

Top 10 Most Expensive Ford Trucks Ever Sold on Bring a Trailer

Joe Kucinski

2027 Ford Super Duty Buyer's Guide (Every Model, Engine, & Package)

Brett Foote

Top 10 Ford Truck Tragedies

Joe Kucinski

AEV FXL Super Duty - the Super Duty Raptor Ford Doesn't Make

Brett Foote

Lobo Vs Lobo: Proof the F-150 Lobo Should Be Even Lower!

Michael S. Palmer

Ford's 2001 Explorer Sportsman Concept Looks For a New Home

Verdad Gallardo

10 Best Ford Truck Engines We Miss the Most!

Joe Kucinski

2026 Shelby F-150 Off-Road: Better Than a Raptor R?

Brett Foote

2027 Super Duty Carhartt Package First Look: 12 Things You NEED to Know!

Michael S. Palmer

10 Most Surprising 2026 Ford Truck Features!

Joe Kucinski

Jun 3, 2005 | 06:34 AM

William

Logistics Pro

Joined: Feb 2000

Posts: 3,565

Likes: 9

From: Sun River St. George

Try re-torquing the intake bolts! Should be 35fp with cast iron intake. Fluttering vacuum is an air leak. Do you have an EGR on this truck? Loose carb? Could be a lot of things but do the easy stuff first. My problem turned out to be the intake gasket!