Engine Surging at 35-40 mph under light load?
Thread Starter
|
New User
Joined: Mar 2002
Posts: 17
Likes: 0
Engine Surging at 35-40 mph under light load?
My 85 302 with EFI has had this surging problem at 35-40 mph for several years. It seems to be getting worse. It occurs on level ground, engine warmed up, and foot barely on accelerator. If I accelerate, there is no problem. If I am pulling up a slight incline where I have my foot into it a little, there is no problem. It seems like to me that the computer is leaning and then richening mixture when the engine is just loafing along. I can disconnect EGR valve and I don't have a problem, but mechanic said it would ping at higher speeds, which is not good. He thought it could be faulty POS, EGR, EGO, MAP, or dirty fuel injectors or carbon problem in manifold. He said he would try replacing EGO first. What do you think?:-(
Senior User
Joined: Apr 2001
Posts: 253
Likes: 0
Engine Surging at 35-40 mph under light load?
It could be a bad fuel filter or a bad fuel pump or debri being sucked into fuel pump sock blocking off fuel entering into it after it runs for a while.I have a 1988 caravan that runs/starts fine but after you run it for a long time it surges big time.I put a fuel pressure gauge unto fuel line,and noticed fuel pressure dropping under load.GOD BLESS
Thread Starter
|
New User
Joined: Mar 2002
Posts: 17
Likes: 0
Engine Surging at 35-40 mph under light load?
Thanks for the reply Rocky 2. Fuel system has been checked. The truck has plenty of power throughout the power band and good pickup. I think there might be a sensor that is causing the computer to lean out and in when there is no load. Nothing in the computer codes points to a problem. Starts and idles nice.
Posting Guru
Joined: Feb 2000
Posts: 1,100
Likes: 0
From: Wichita USA
Engine Surging at 35-40 mph under light load?
Here are a couple of possibilitys. EGR valve itself. It is spring loaded closed and could be weak causing it to open to much to soon. Also the EVR is spring loaded closed and if weak could cause the vacuum signal to the EGR to more than needed. Both would cause a lean mixture. I know of no way to test this theory other than replace with known good component.
Moderator
Joined: Jan 2001
Posts: 56,984
Likes: 2,738
From: Virginia
Engine Surging at 35-40 mph under light load?
I vote for the egr too, since when you disconnected it, the problem went away. The egr has a sensor on top of it, that could be wore out. It sends a voltage back to the computer to tell it how far open the egr is.
Logistics Pro
Joined: Jan 2002
Posts: 4,907
Likes: 39
From: suburban atlanta
Engine Surging at 35-40 mph under light load?
Had the same problem, but to a higher degree. Would buck intermittently at cruise. Step on gas, and go away. Disconnect the EGR and seemed fine. Bought/installed new EGR. Still have same problem! Took back EGR (Lucky ME!!!! they took it back) Looked at plug wires while running after sunset. Nice light show. Bought new plug wires, installed same, no more bucking. Hmmm. Guess I needed new plug wires. Worth a shot. Or just measure resistance of each wire-- check for Bazillion Ohms, or Open. Should get a couple K ohms for the average plug wire. Plugs work harder to fire at higher speeds than idle.
tom
tom
Thread Starter
|
New User
Joined: Mar 2002
Posts: 17
Likes: 0
Engine Surging at 35-40 mph under light load?
Thanks for reply TomW. I had first taken in and told mechanic that engine was missing and he checked plug wires by spraying water on them as I remember. No problem there he said. I wish it could be a simple answer. Anybody else have this problem?
Trending Topics
Senior User
Joined: Jan 2001
Posts: 145
Likes: 0
From: Prescott USA!
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
Thread Starter
Forum
Replies
Last Post
ethanshuler97
1987 - 1996 F150 & Larger F-Series Trucks
10
Jun 14, 2016 12:48 AM
wally32
1983 - 2012 Ranger & B-Series
44
Apr 9, 2016 03:12 PM
rbarbot2
2007 - 2014 Expedition & Navigator
10
Oct 3, 2010 03:35 PM