freeway drivability help
Thread Starter
|
Laughing Gas
Joined: Feb 2014
Posts: 815
Likes: 296
From: KY
freeway drivability help
Im on a roll today with questions I recon. New to us 84 F250, 460, C6. Holley 4180. Starts fine, idles fine, seems to run fine when your on the pedal hard but crusin down the freeway I feel a constant surge,miss,hesitation kind of feeling. The P/O had a new front in tank pump with relays installed, Ive installed new plugs,cap and rotor which did nothing for it. Old plugs looked pretty much right on color wise. Throw me some ideas. I was thinking power valve but doesnt sound like this. New wires going in today if the rain stops, other that that Im stumped. I dont understand the fuel delivery system on this thing, I see two in line filters on the frame under the cab along with a rail mounted pump. If it was fuel related Id think whan you nail it it would run terrible and its fine.
Thread Starter
|
Laughing Gas
Joined: Feb 2014
Posts: 815
Likes: 296
From: KY
Timing is right at 8 degrees. Also replaced with no change, plugs, wires,cap,rotor, fuel pump, 3 new filters, timing check out, newer carb, still need to double check the float level and fuel pressure though and I keep forgetting to check the dist shaft for excessive wear or wobble. Frame rail fuel pump weak maybe??
FTE Legend
Joined: Jul 2010
Posts: 32,875
Likes: 48
From: Northeast, OK
If it runs fine at heavy throttle then it isn't a fuel pump issue. The surge is probably a lean condition and Maytag's suggestion would account for that. A cracked or broken vacuum line would do that, and these lines are OLD so crack easily.
Moderator
Joined: Jan 2001
Posts: 56,984
Likes: 2,738
From: Virginia
Timing is right at 8 degrees. Also replaced with no change, plugs, wires,cap,rotor, fuel pump, 3 new filters, timing check out, newer carb, still need to double check the float level and fuel pressure though and I keep forgetting to check the dist shaft for excessive wear or wobble. Frame rail fuel pump weak maybe??
If I am wrong, just put the vacuum line back and try something else.
FTE Legend
Joined: Jul 2010
Posts: 32,875
Likes: 48
From: Northeast, OK
Try my experiment, it will only take a few minutes and not hurt anything. I have had a lot of vehicles have a part throttle surging problem because the timing was too advanced. You never know, your harmonic balancer may have slipped throwing the marks off or someone has installed the wrong dist or the wrong vacuum advance unit sometime before.
If I am wrong, just put the vacuum line back and try something else.
If I am wrong, just put the vacuum line back and try something else.
Trending Topics
Lead Driver
Joined: Jul 2009
Posts: 6,477
Likes: 19
From: Sheffield, AL
Please make it easy on yourself and listen to the suggestions made, apache84. These men know their stuff! 
FTE Stories
Ford Trucks for Ford Truck Enthusiasts
10 Things Every Truck Owner NEEDS (2026 Edition)
Michael S. Palmer
Rezvani's Latest Post-Apocalyptic Monster Is a Ford F-150 Raptor Underneath
Verdad Gallardo
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
Thread Starter
|
Laughing Gas
Joined: Feb 2014
Posts: 815
Likes: 296
From: KY
Will do on the timing suggestion. Believe it or not at 50+ years old this makes vehicle number 200+. Most have been pretty much tired old 4x4 trucks. I like trouble shooting for some reason. I would think far to advanced timing would have this thing pinging like crazy which I dont hear and I have a multi mile long grade to go up on the freeway on the way home. Not to dispute the suggestion but if it sucessfully passed smog about 100 days ago and the docs show 8 btdc dont they take these numbers off actual timing from their machines and not physical timing light check? I did check the float level and dist shaft play which were on the money and good. I dont hear any vac leaks and it idles smooth. Even not plugging the one vac line to the air cleaner when removed makes it run rough. Be great to do a smoke check test for leaks but I haven't the equipment.
Tomorrow should be interesting as we bought the truck with a travel trailer which Im picking up tomorrow. The PO used the combo little and only locally, hope I make it home OK. Thanks all and keep ya posted.
Tomorrow should be interesting as we bought the truck with a travel trailer which Im picking up tomorrow. The PO used the combo little and only locally, hope I make it home OK. Thanks all and keep ya posted.
Logistics Pro
Joined: Jan 2005
Posts: 3,534
Likes: 85
From: penn twp.
The problem with using a smoke machine and listening for a hiss by the use of your ear is that these methods are only good for large leaks. You could have a small leak that is causing this issue. And therefore wouldn't be heard or seen with smoke.
Posting Guru
Joined: May 2013
Posts: 1,122
Likes: 0
From: Haysville, KS
I beg to differ a bit..
A smoke machine can show very small leaks. Mine has a dye you can add that will mark any leaks and can be seen with UV light.
Hearing a leak is a different matter, but I've been able to find very small leaks using a smoke machine.
A smoke machine can show very small leaks. Mine has a dye you can add that will mark any leaks and can be seen with UV light.
Hearing a leak is a different matter, but I've been able to find very small leaks using a smoke machine.
Moderator
Joined: Jan 2001
Posts: 56,984
Likes: 2,738
From: Virginia
You can have a fairly large vacuum leak, and it will not affect the engine at running speed, only at idle.
A small vacuum leak will be very large at idle, since the throttle blades are closed not letting much air into the engine. A small leak at speed will not be noticed by the engine at all, since it's so small in proportion to the large amount of air entering through the throttle blades of the carb.
When you are cruising your timing number will be the initial(8 degrees) + centrifugal(affected by rpm) + vacuum(affected by load on the engine). It's just curious to me what would happen if you took the vacuum part of it out. It may not necessarily be the problem, but if the problem goes away, it would be something to chew on for awhile. When you are troubleshooting, you can do things to the engine and it will react to these things you do, it will be almost like it's "talking" to you. When you do something and it reacts a certain way, it gives you something to think about.
A small vacuum leak will be very large at idle, since the throttle blades are closed not letting much air into the engine. A small leak at speed will not be noticed by the engine at all, since it's so small in proportion to the large amount of air entering through the throttle blades of the carb.
When you are cruising your timing number will be the initial(8 degrees) + centrifugal(affected by rpm) + vacuum(affected by load on the engine). It's just curious to me what would happen if you took the vacuum part of it out. It may not necessarily be the problem, but if the problem goes away, it would be something to chew on for awhile. When you are troubleshooting, you can do things to the engine and it will react to these things you do, it will be almost like it's "talking" to you. When you do something and it reacts a certain way, it gives you something to think about.
FTE Legend
Joined: Jul 2010
Posts: 32,875
Likes: 48
From: Northeast, OK
I agree. It does take a large vacuum leak to cause a problem at cruise, but something like the brake booster will do it. Especially if the mix is already lean.
As for the engine talking to you, that is a good analogy. Trying something, like pulling and plugging the vacuum advance, is like asking it a question. It will respond and the answer helps solve the problem - something like playing 20 Questions.
As for the engine talking to you, that is a good analogy. Trying something, like pulling and plugging the vacuum advance, is like asking it a question. It will respond and the answer helps solve the problem - something like playing 20 Questions.
Senior User
Joined: Nov 2000
Posts: 285
Likes: 1
From: sunny san diego
I highly suggest 2 items.....faulty/ leaking vacuum advance unit, easy to check AND the 3 way fuel filter next to the carb. I've mentioned this several times already, rust from the old fuel tanks will collect in it and restrict the flow resulting in the surging described, been there done that with both of these. Also vacuum leaks are suspected.
Thread Starter
|
Laughing Gas
Joined: Feb 2014
Posts: 815
Likes: 296
From: KY
I highly suggest 2 items.....faulty/ leaking vacuum advance unit, easy to check AND the 3 way fuel filter next to the carb. I've mentioned this several times already, rust from the old fuel tanks will collect in it and restrict the flow resulting in the surging described, been there done that with both of these. Also vacuum leaks are suspected.