strange misfire problem
Thread Starter
|
Senior User
Joined: Apr 2011
Posts: 189
Likes: 0
strange misfire problem
i have an 2003 f150 5.4.......it has a misfire and often times it will be running fine but if i have to slow down quickly, immediatly afterwards it will misfire. Its bad eneough it feels like it MIGHT be more than one cyl. but not really sure about that. It feels like it though. I can floor it when it starts to misfire and it will run smooth again. ----to me, that is when the problem should be worse since its under a strain.
I have replaced all the plugs but the two on the left side near firewall. The ones i took off were all in good shape and all the same brand....so im guessing the other two are in the same condition. Also its not throwing any codes.No check engine light etc.
I dont really understand what it is doing, it doesnt really make sense to me and im not sure what to do next but to replace the two other plugs that i doubt is the problem.---thanks.
I have replaced all the plugs but the two on the left side near firewall. The ones i took off were all in good shape and all the same brand....so im guessing the other two are in the same condition. Also its not throwing any codes.No check engine light etc.
I dont really understand what it is doing, it doesnt really make sense to me and im not sure what to do next but to replace the two other plugs that i doubt is the problem.---thanks.
Lead Driver
Joined: Sep 2006
Posts: 7,907
Likes: 143
Well yes it makes sense when you know some additional information.
During cruise the EGR operates and causes a very lean condition requiring higher coil voltage.
When the throttle is lowered it leans even more.
Reapplying throttle to this lean condition with a 'faulty coil' on one cylinder will create a misfire.
When the throttle is used to force a downshift, the condition disappears because the fuel ratio goes back to normal and even richer to accommodate the call for power. The offending coil now can fire the richer mix.
Bottom line is you likely have one faulty coil with low voltage output due to shorted turns on it's coil winding.
This condition usually does not set a code because it's not considered a 'hard' coil fault failure to set a code because the condition comes and goes with the specific set of conditions as you see.
The best ways to find the offending cylinder is using a Scanner to look at the stored misfire counts for each cylinder and addressing that cylinder/s or use a Scanner trap setup to freeze the data when it happens.
There ya go, not so strange after all.
Good luck..
During cruise the EGR operates and causes a very lean condition requiring higher coil voltage.
When the throttle is lowered it leans even more.
Reapplying throttle to this lean condition with a 'faulty coil' on one cylinder will create a misfire.
When the throttle is used to force a downshift, the condition disappears because the fuel ratio goes back to normal and even richer to accommodate the call for power. The offending coil now can fire the richer mix.
Bottom line is you likely have one faulty coil with low voltage output due to shorted turns on it's coil winding.
This condition usually does not set a code because it's not considered a 'hard' coil fault failure to set a code because the condition comes and goes with the specific set of conditions as you see.
The best ways to find the offending cylinder is using a Scanner to look at the stored misfire counts for each cylinder and addressing that cylinder/s or use a Scanner trap setup to freeze the data when it happens.
There ya go, not so strange after all.
Good luck..
Thread Starter
|
Senior User
Joined: Apr 2011
Posts: 189
Likes: 0
well, BLUEGRASS...that does kinda makes sense. Im not sure why i didnt see it that way. I wasnt even thinking about it leaning out only thinking about the strain on the engine and how it seemed like it should be mising out more not less. This is my first automatic ive ever had and guess my brain was focused on truck being in high gear low power band etc......annnnnd give me some more time i can think of some other excuses lol........Thanks. I do appreciate it.
Postmaster
Joined: Aug 2004
Posts: 4,004
Likes: 1
From: North of Boston MA
Sounds a little bit like what mine is doing. Mine runs fine at idle and even under very gentle acceleration but more than a slight push on the accelerator and it starts to miss and buck very slightly. If I lay on it though, at about 3k RPM it will run great and all the power comes back. Guess I need a better scanner on it.
Thread Starter
|
Senior User
Joined: Apr 2011
Posts: 189
Likes: 0
NITRAMJR--That is the symptoms i would normally expect. There acting a little bit different but yeah a scanner is probably in our futures........i have never used a scanner and didnt even know it was possible to count misfires. That for sure will make things easier.--good luck.
Tuned
Joined: Feb 2013
Posts: 474
Likes: 4
From: SE Michigan
Bluegrass is correct on this,, mine did the same thing,, didn't make sense to me either.. But I did have one really bad coil one a bit bad coil that I replaced,, still have one more to find that's just barely causing a miss but will wait till it gets worst.. So far I have replaced a bad coil with a really really bad miss with a ford coil.. Then as more of them went bad a bought a pack of 8 off eBay.. Of these I only have two left.. One of these did go bad after a couple of years. So buy a pack of coils and a good scanner and plan on replacing as needed.. Or replace all at once..
Thread
Thread Starter
Forum
Replies
Last Post
msm7c
1997 - 2003 F150
2
May 7, 2005 06:11 AM
