miss fires under load
Thread Starter
|
New User
Joined: Jan 2012
Posts: 15
Likes: 0
miss fires under load
Sorry to batter you guys with my problems but this is my only vehicle besides my motorcycle and its cold out. I have a 86 f150 inline six with the feedback carb(unfortunately). The truck idles like a champ and drives fine on level ground, but once i start going up hill for a bit it miss fires pretty dang bad, i have to let off the gas to get it to stop and half the time downshift and go real slow.
I just replaced spark plugs, wires, cap, rotor, EGR valve, and rebuilt the carb. I measured the resistance to the coil it has 0.78 manual says its good from 0.6 - 1.0 base timing is set at 10 degrees and when i plug the spout back in it advances past the 14 mark, im not sure what its suppose to advance to at idle, i couldnt find that. Oh and it just passed smog today, haha.
Any help will be greatly appreciated.
I just replaced spark plugs, wires, cap, rotor, EGR valve, and rebuilt the carb. I measured the resistance to the coil it has 0.78 manual says its good from 0.6 - 1.0 base timing is set at 10 degrees and when i plug the spout back in it advances past the 14 mark, im not sure what its suppose to advance to at idle, i couldnt find that. Oh and it just passed smog today, haha.
Any help will be greatly appreciated.
Moderator
Joined: Nov 2007
Posts: 22,415
Likes: 92
From: Denver Metro Area, CO
Might ask the computer what it thinks might be happening.
Fuel Injection Technical Library » How To Run a Self-Test
Fuel Injection Technical Library » How To Run a Self-Test
Lead Driver
Joined: Jul 2009
Posts: 6,477
Likes: 19
From: Sheffield, AL
penguintits,
It sounds like you have tackled many things. Might I suggest a couple more? Have you replaced the fuel filter? Check for any cracked or loose vacuum lines. See if you can rock the air filter back and forth? If so, the carburetor is likely loose and the two nuts holding it down need tightening. They really loosen on the 4.9L due to vibration and having only 2 rather than 4.
Finally, several years ago while driving my son's 1984 [very similar system to your 1986] and going up hills or trying to pass another vehicle, it would miss badly. Like yours, it had just been tuned up so I looked elsewhere. With the engine idling [make sure your e-brake is engaged] I shook the wiring harness. As I shook the factory air filter housing, the engine stumbled. There was a single small wire [14 gauge?] which ran to the feedback carburetor [I am pretty sure if my memory is correct] and it had cracked and was grounding out when moved [due to engine torque]. I wrapped the area with electrical tape and the problem instantly and permanently went away!
It sounds like you have tackled many things. Might I suggest a couple more? Have you replaced the fuel filter? Check for any cracked or loose vacuum lines. See if you can rock the air filter back and forth? If so, the carburetor is likely loose and the two nuts holding it down need tightening. They really loosen on the 4.9L due to vibration and having only 2 rather than 4.
Finally, several years ago while driving my son's 1984 [very similar system to your 1986] and going up hills or trying to pass another vehicle, it would miss badly. Like yours, it had just been tuned up so I looked elsewhere. With the engine idling [make sure your e-brake is engaged] I shook the wiring harness. As I shook the factory air filter housing, the engine stumbled. There was a single small wire [14 gauge?] which ran to the feedback carburetor [I am pretty sure if my memory is correct] and it had cracked and was grounding out when moved [due to engine torque]. I wrapped the area with electrical tape and the problem instantly and permanently went away!
Thread Starter
|
New User
Joined: Jan 2012
Posts: 15
Likes: 0
Thanks for getting back to me so quickly guys, really appreciate it. The cat sounds like a likely culprit as i just replaced the muffler because it had a 6x6" rusted hole through it, this truck has been through Alaska so some rust comes along with that.
The carburetor is on tight i torqued it down after i rebuilt it 3 or 4 days ago. I tried going through the codes but couldn't get my code reader to work on it ill take a look at that link, thanks. I will also wiggle some wires like you said.
Also I took the feedback solenoid off the carb and plugged the hole and connected it back in with the connector still plugged in drove it, not a change in difference. Shouldn't that make the truck run like crap? Because the feedback solenoid controls the fuel mixture, correct me if I'm wrong, but im thinking about replacing that as well. Thanks for the input and I'll try to look mat it later tonight.
The carburetor is on tight i torqued it down after i rebuilt it 3 or 4 days ago. I tried going through the codes but couldn't get my code reader to work on it ill take a look at that link, thanks. I will also wiggle some wires like you said.
Also I took the feedback solenoid off the carb and plugged the hole and connected it back in with the connector still plugged in drove it, not a change in difference. Shouldn't that make the truck run like crap? Because the feedback solenoid controls the fuel mixture, correct me if I'm wrong, but im thinking about replacing that as well. Thanks for the input and I'll try to look mat it later tonight.
Moderator
Joined: Nov 2007
Posts: 22,415
Likes: 92
From: Denver Metro Area, CO
Apparently there is a device that can be inserted into the hole normally occupied by the O2 sensor, I believe it's connected to an air compressor and one measures the output at the tail pipe.
Something like that.
Something like that.
Trending Topics
Thread Starter
|
New User
Joined: Jan 2012
Posts: 15
Likes: 0
Sounds costly, ill probably just drop the exhaust and run straight headers with a test run and see if that works...unless theres a o2 behind the cat...ill have to check
FTE Stories
Ford Trucks for Ford Truck Enthusiasts
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
Thread Starter
|
New User
Joined: Jan 2012
Posts: 15
Likes: 0
Your correct fellro i just looked and i can drop the whole exhaust behind the headers, looks like a tomorrow project but and easy one, except for dealing with rusty bolts...I'll keep you guys posted.
Thread Starter
|
New User
Joined: Jan 2012
Posts: 15
Likes: 0
Well i dropped the exhaust today and it still has the same problem and its gotten worse. Im sick of it and instead of throwing more money at it ill go ahead and do a duraspark II conversion or something like that. Just passed smog so i got 2 years till I have to swap it back, worth it in my opinion. Any input on what year of trucks work as far as wiring harness and distributors?
Thread Starter
|
New User
Joined: Jan 2012
Posts: 15
Likes: 0
Well I feel kinda stupid not checking this before, but it was the fuel filter. I kept forgetting about it every time i went to napa for parts till today. Man that woulda saved me some heart ache. Also there are 2 vacuum lines that are suppose to go to some valve with an electrical connecter, which is missing, so the lines are open. I plugged those at the same time i did the filter, but im pretty sure it was the filter i could hardly blow and air through it. Thanks for the help!
Thread
Thread Starter
Forum
Replies
Last Post
gruub
1987 - 1996 F150 & Larger F-Series Trucks
6
Nov 29, 2006 07:55 AM
jpjahn
1980 - 1986 Bullnose F100, F150 & Larger F-Series Trucks
3
Oct 13, 2004 03:54 PM
85FordTruck
1980 - 1986 Bullnose F100, F150 & Larger F-Series Trucks
6
Dec 20, 2002 06:11 PM
