Misfire under light load - Ford F150 Forum - Community of Ford Truck Fans



Misfire under light load

Reply
 
 
 
Thread Tools Search this Thread
Old 07-26-2011, 02:25 PM   #1
Junior Member
Thread Starter
 
Join Date: Jul 2011
Posts: 5
Thanks: 0
Thanked 0 Times in 0 Posts
Unhappy Misfire under light load

Hi Guys Here is my Problem....I have an F-150 Lariat 4x4, 3v 5.4, 90,000 miles has a misfire between 45 and 50 miles an hour under light acceleration. Once parked the truck smells of unburnt fuel and the #2 (Left side) Cat smells hot and shows white discoloration, right side Cat is unaffected. The truck has intermittent check engine light and showed a #5 and #8 cylinder misfire. I replaced the COPs on the affected cylinders with no resolve. My question;: is there a reason a misfire would surface at 45-50 MPH and what steps could I take to further troubleshoot the misfire? (note: 3V 5.4 Triton does not have an EGR valve). I would appreciate any help on the subject. Thank You
Trav is offline   Reply With Quote
Old 07-26-2011, 02:33 PM   #2
Mark
5 Year Member
iTrader: (1)
 
techrep's Avatar
 
Join Date: Jan 2009
Location: Va. Beach, VA.
Posts: 27,512
Thanked 1,165 Times in 1,032 Posts
Default

What about the plugs for thoses 2 cylinders...90K miles it may be time for plugs.
techrep is offline   Reply With Quote
Old 07-26-2011, 02:49 PM   #3
Junior Member
Thread Starter
 
Join Date: Jul 2011
Posts: 5
Thanks: 0
Thanked 0 Times in 0 Posts
Default

I am going to change the plugs this weekend. What do you make of the misfire only occurring around 45-50mph? Is there something that the engine does at this speed that would change and cause the misfire?
Trav is offline   Reply With Quote
Old 07-26-2011, 04:17 PM   #4
Junior Member
 
Join Date: Jun 2011
Posts: 7
Thanks: 0
Thanked 0 Times in 0 Posts
Default

Quote:
Originally Posted by Trav View Post
I am going to change the plugs this weekend. What do you make of the misfire only occurring around 45-50mph? Is there something that the engine does at this speed that would change and cause the misfire?
At about that speed the engine is at a point where it kind of lugs just after it up-shifts. I suppose that's probably intended as part of the engine management (you tend to get the best gas mileage when the motor is slightly lugging). More than related to the speed itself, I think that it's just that any problems become more apparent when it's at that point.

I had the same problem in the truck that I bought and also noticed the same to varying degrees in most of those that I drove. Changed a few coils which made it a better. Changed the plugs which made it better. Changed the phasers, adjusters, etc., which made it better still. Now with the motor running as it should, I haven't had any more problems. Think that it's probably just a question of getting things right overall whatever that might be in your particular case.
Mike A. is offline   Reply With Quote
Old 07-27-2011, 08:11 AM   #5
Senior Member
 
Join Date: Oct 2010
Location: Virginia Beach, VA
Posts: 149
Thanks: 0
Thanked 0 Times in 0 Posts
Default

Your symptom coupled with your mileage are indicative of bad plugs. Change ALL the plugs and you should be fine.

I had the same exact symptom with less miles, and a plug & boot change cured it! If you are going to do it yourself, be prepared in case some break.
jetpilot2 is offline   Reply With Quote
Old 07-27-2011, 08:35 AM   #6
Member
 
Join Date: Apr 2011
Location: Lawrenceville Ga.
Posts: 33
Thanks: 0
Thanked 1 Time in 1 Post
Default

My 07 was misfiring at the same speed. Had 90 k miles at the time. New plugs and it ran like new again. Follow the TSB and get the lisle tool and you should be ok.
skc72 is offline   Reply With Quote
Old 07-27-2011, 06:00 PM   #7
Junior Member
 
cobrabrouk's Avatar
 
Join Date: Jul 2011
Location: Arnold, MO
Posts: 29
Thanks: 0
Thanked 0 Times in 0 Posts
Default

Trav man change your injectors before it's too late man.
cobrabrouk is offline   Reply With Quote
Old 07-27-2011, 06:29 PM   #8
Junior Member
Thread Starter
 
Join Date: Jul 2011
Posts: 5
Thanks: 0
Thanked 0 Times in 0 Posts
Default

I'll start with the plug change and see if new plugs fixes the miss. My Lisle tool just came in the mail today. I am going with the Champion 7989 spark plugs so I wont have to deal with extracting broken plugs again. As for the solvent to soften the carbon build up on the plugs I was going to try Aerokroil. Has anybody use this stuff to loosen there plugs? and it so how good did it work?
Trav is offline   Reply With Quote
Old 07-27-2011, 08:59 PM   #9
Junior Member
 
Join Date: Jul 2011
Location: Iuka, Mississippi 38852
Posts: 16
Thanks: 0
Thanked 0 Times in 0 Posts
Default

heres what i did for the carbon problem. took the air filter out and got a funnel with a hose on it to extend inside breather. then i took 3 bottles of the cheap STP injecter cleaner (walmart) and slowly poured them down the engine while revved to about 2000 rpm`s. next i poured a quart of transmission fluid down it. (lots of smoke) drove the truck about 10 miles before i changed the plugs and there was not even a trace of carbon. all 8 plugs came out without a hitch. this is a truck that i bought at an auto auction with 205,000 miles. i have no idea of its service record.
Richard Till is offline   Reply With Quote
Old 07-27-2011, 10:21 PM   #10
Senior Member
5 Year Member
 
Join Date: May 2009
Location: Elmhurst, IL
Posts: 730
Thanks: 0
Thanked 0 Times in 0 Posts
Default

After dumping a quart of tranny oil thru the combustion chamber you probably toasted your cats and o2 sensors. Why in the world would do that.

To the op - what year is the truck. 2005s have know injector problems. At 90k definitely time for a plug change. Use carb cleaner for soaking the plugs. Follow the tsb and you should be good.
kevhead75 is offline   Reply With Quote
 
 
Reply

Related Topics
Thread Thread Starter Forum Replies Last Post
Incredibly bright Led Mirror Puddle Lights Burke484 Lighting 16 10-19-2016 12:46 AM
Rough Idle/Misfiring - HELP! (2006 F150 5.4L v8) carp104 2004 - 2008 Ford F150 39 08-09-2016 07:32 PM
LEDs - Do Not Install Load Resistors for Hyperflashing! Dan2002 2009 - 2014 Ford F150 38 10-03-2015 12:29 AM
Southeast: Sct x3 SC_Titan 2009 - 2014 Part Sales 12 09-19-2015 09:59 PM
Southeast: Sct x3 SC_Titan General F150 Items 2 09-16-2015 10:34 PM


Tags
50 mph, acceleration, engine, misfire, troubleshoot

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -4. The time now is 10:57 PM.


Copyright 2006 - 2016 F150Forum.com