Praetorian27

Hi guys,

I have a 2006 Lariat 5.4 Triton that is having a problem with a misfire/stumble when I go full throttle. When I am cruising along driving normal the truck is fine. Then, if I go full throttle to pass someone, the truck starts stumbling and the check engine light flashes on and off. I will get off throttle and return to normal driving and the light will flash for about 30 seconds...then shuts off again. Twice the light has stayed on solidly after flashing. I have had the truck in to the shop three times and they can't figure it out. The check engine light that was on all the time showed a misfire in cylinder 3. I have changed the plugs recently myself. I put Autolite HT15 plugs in it. Are these alright? The shop did a fuel system service, swapped the coils around etc. Nothing has worked. Now they want to pull the valve cover off and check for a broken valve spring. This doesn't seem like the best step to me. I am up to around $1,000 in bills with this shop...and the truck STILL isn't fixed. I have searched the forums but don't seem to find any solid answers. Any ideas?

Doyle Warren

Ouch. Hope it doesn't get to bad. I jus replaced the motor in mine. Its almost better off getting a new rebuilt engine. Once those heads come off and that front cover comes off.. Dollars gobflyingbeith out **** getting done. I got a salvage engine first replaced phasers chain etc. Rain OK but threw codes for timing and VVt.. Anyways gunk got into the timing area fubar'd it. So 3400 gone down the drain. Anyways bought 2 more motors (new rebuilt) installed one and have the other on stand by or sale. It drives like new, solo damnn quite . especially with the new transmission. Your treading into dark waters when you greenlight troubleshooting these motors.

vintageman

Huh, there is nothing wrong with having to take the heads or timing cover off to fix something or do some maintenance on these motors. At 100,000 plus miles, most engines will need some maintenance, especially if they haven't been taken care of as they should be. Yes, are there some flaws to this system but if you take your time, pay attention, use good Ford Motorcraft parts then most things can be fixed. I fixed mine and replaced all timing components as well as lash adjusters and followers last summer and still runs great.

OP, you said you replaced the plugs, did you use motorcraft brand, this engine likes them the best. What you describe is a classic COP problem, try replacing the boot and spring at COP #3 first to see if that helps, use some dielectric grease for a good seal. Good luck and let us know how it goes.
Tom

Doyle Warren

I was assuming he was going to have the shop tear into it.

techrep

iTrader: (1)

It's not the best next step... have they swapped injectors and read the voltage to cylinder 3.. compression test that cylinder before you remove the cover

MGD

^^^ This.

Solid advice.

OP - Removing the cover on the passenger side bank ( where cylinder 3 is ) typically involves evacuating the A/C. Not fun, not cheap. Only do it if ye have to.

BTW - here's a good read just fer reference (what one feller discovered under the sheets): http://www.f150online.com/forums/v8-...-problems.html

Good luck!

demingrick

I'd say vintageman is correct: more than likely just a bad or loose coil on that cylinder. Easy enough to troubleshoot; swap the coil between that cylinder and one that's working. If the one you swapped it to misfires, replace the coil.

Praetorian27

Thanks for the replies guys. The shop did swap the coils around, the injectors and the plugs too. Still had a misfire on cylinder 3 no matter which coil, injector or plug was there. I guess the compression test is the smartest next step?

Praetorian27

I used Autolite HT15 plugs. Are these junk? Don't think that's the problem though since they swapped the plugs around and there is still a misfire on 3. Do you need a special compression gauge that is specific to these weird looking plugs in this engine?

jdinner

Plugged catalytic converter on the right side.

Very similar symptoms.

https://www.f150forum.com/f4/06-5-4-...-fires-291476/