Daniel Landrith

last month my 1999 f150 5.4 started misfiring, and after having the code checked it came up DPFE sensor and a cylinder 8 misfire, we concluded it was the coil pack. i bought both but didn't change neither at first. after 2 days the misfire went away and very seldom returned and when it did it didn't last but a few seconds, and about 3 weeks later I changed the DPFE thus resulting in the check engine light going off. and as recent the misfire has returned for the past 2-3 weeks and hasn't went away at all. I do plan to change the coil pack tomorrow. but it's worrying me to death, I've only had this truck 2 months and dont want to have to spend a large amount of money in repairing it. should that fix the problem? I just don't understand why the light went off after repairing just 1/2 of the codes.

mbb

The light comes on when it fails a misfire test in obdii. Which is basically misfiring about 2% of times during test. Mode 06 stores raw test data and can show misfires as little as 1 in 1e09 revolutions. Some limited small amount is ok and normal, it when it exceeds test limit a code is thrown.

When it passes, it goes off
Code doesnt go away by itself unless it passes a bunch of times

Conditions have to be right for the misfire test to run too. If fuel level is less than certain amount it may not run. It may not run without completing a drive cycle. You can search for your year ford obdii guide for details . In other words, you can misfire and not get code for it at all under right conditions.

Replace the coil and plug, thats common. That might not be problem though, but its a good place to start.

R&TBabich

You may just have two separate problems.
Try swapping the COP on #8 with #7 and see if the misfire moves.
Is there any moisture under the #8 boot?
I had a firewall pad leak on our Exped and water would drip onto #6 & #7 causing misfires.
Would go away after a day or two and living in Socal it doesn't rain much here so it was very intermittent.
Codes were not set most of the time, but I could feel it misfire at idle.
I used a garden hose to flood the windshield and found the leak.
How many miles on the COPs?
The boots may be degraded from age.
You can change just the boots, Denso 671-0001, are less than $5/ea on ebay.

mbb

Also if you cleared the codes when replaced DPFE, (or disconnect battery) it may go thru another drive cycle before it tests again.

Daniel Landrith

crazy to say, but the first time the misfire came was after a carwash. and also we've had a lot of rain here recently, and it just recently came back. you think water could be getting in there?

R&TBabich

Try running water on the windshield with a hose and see if any is getting to the engine.
If the misfire was on the passenger side #3 or #4 I would look for a crack in the heater control valve or a crimped hose fitting which are plastic.
Your misfire is #8 so you might have a leak on the driver's side if there's water under the spark plug boot.
Even if it is dry when inspected if the spring is rusty there was moisture there.
On our 2003 Exped the pad on the firewall was misaligned when installed and got under the plastic panel holding the hood seal.
This allowed a trickle of water to flow down between the pad and firewall and drip onto #6 & #7 causing misfires when they got wet.
Eventually it destroyed the cat which I had to replace.
I trimmed the pad and used black silicone along the entire trim panel and no longer have a leak.

carriec

Had our first problem with the 3.5 EB 37233 miles. Just completed a 2800SM trip hauling a TT at our limits with no problems other than worse than usual mileage for the trip. Two days after our return coming up to speed in the acceleration lane onto I64 it stumbled and started shaking and losing power. Check engine light came on and I started to pull over as I got off the throttle it started smoothing out and after about a minute the CEL went out and engine started running better. Went home scheduled appointment with dealer. Code P0306 Told me coil pack on #6 was bad and replaced both it and the plug which was fouled. No follow up yet as we just came home and there was no freeway driving/acceleration involved. Searched for similar problems from others but didn't see any. Surprised at the amount of discussion on plug change schedule and wonder if I should pull all of mine and have a look.

FL_F150

Been having coil pack issues lately, misfiring on startup... at first turn of the key it starts right up and hits about 1,500 rpm, after about 20 seconds it starts to idle down. That's when it starts the misfire.
I changed out 4 and 6 (tester says d and f) along with the plugs (gapped)...twice.... I also have put dilectric grease in both the spring and connector.
I still get code and misfiring when temps are below 45 degrees.
So, i'm watching this post to see what everyone has done.
If I keep the rpm above 2,000 for about 5 minutes, the misfire disappears and the truck runs fine.

carriec

These coils aren't inexpensive and it seems that failure rate is a bit high. The "known problem syndrome" is no comfort at all. All the modern technological wizardry aside, I do miss working on my own vehicles with a tool box and not a computer.

R&TBabich

[QUOTE=carriec;5125222]These coils aren't inexpensive and it seems that failure rate is a bit high......QUOTE]

I have not had a coil go bad, yet.
The COP assembly has 3 parts - coil,boot,spring.
I have had boots degraded and rusty springs.
Most misfires are caused by moisture or degraded boots.
I've read Denso is the OEM supplier for Ford and are available on ebay:
Denso 671-0001 boots/springs are around $30/pack of 10
Denso 673-6000 COP assembly $27/ea
I currently am running NAPA Beldon 702418 boots/springs that were $5/ea.
I change plugs/boots/springs at 50k and haven't had any more issues.
I have had to replace 2 coils - one when a plug blew out breaking off the hold down tab, the second had the connector boss break at the coil housing when trying to remove the connector.