Misfire under load

Bigfatts · April 26th, 2008, 07:23 PM

Two days ago my LX started misfiring. It does it when I'm accelerating, usually between 3 and 4000 rpm, or when going uphill. When I got home I changed the plugs (went with NGKs gapped at .045. The Autolites I took out of it were gapped at .040 and I thought that was kinda tight, they came in the car.) It has newer MSD 8.5 wires with an MSD Blaster EFI coil. MSD 6al with an MSD cap on a Motorcraft distributor.

After I changed the plugs I noticed it runs a little nicer. It misfires less, but it still does it occasionally. I did pretty much a whole tune up on it and cleaned and inspected the MAF and thottle body, also ran injector cleaner. Everything seems good but it still misfires occasionally. Then I thought maybe moisture in the fuel lines so topped it off and put some water remover in it.

Before this the car ran smoothly and gave me 0 problems. Could it be that I got ahold of some crappy fuel or is there something I might be overlooking?

R0B0T · April 26th, 2008, 07:52 PM

valve that needs to be adjusted
bad/weak coil

switch the coils and see if the misfire changes cylinders
main things that pop into my head

93hatch · April 26th, 2008, 07:52 PM

timing advanced? running premium if it is?

Bigfatts · April 26th, 2008, 07:57 PM

I kind of overlooked the coil because it's less than 2000 miles old. I'll have to see if I can dig up a spare and see how it runs. And I only run premium in it.

93hatch · April 26th, 2008, 08:03 PM

arent coils either good or bad with no in between?

R0B0T · April 26th, 2008, 08:07 PM

also check to make sure that the wires are seated on the spark plugs
if one of the boots isnt seated right it can cause it to misfire occasionally
i had this happen to a friends car this weekend, boot wasnt seated properly and the spark was going to the header instead of the plug haha

galzamar · April 26th, 2008, 08:28 PM

Also make sure that your 7 and 8 cyl plug wires are not next to each other they can cause a miss due to wire voltage seepage since 7 and 8 fire so close together.

nolife · April 26th, 2008, 08:32 PM

Originally Posted by galzamar

Also make sure that your 7 and 8 cyl plug wires are not next to each other they can cause a miss due to wire voltage seepage since 7 and 8 fire so close together.

I don't know about 7-8 specifically but I fixed a random misfire by organizing my plug wires.

galzamar · April 27th, 2008, 11:15 PM

I have an instructor that works at ford as a mechanic and that is what he said that if you get plug wires 7 and 8 to close it will cause a miss . . . Glad you got it fixed.

saldoggs · April 27th, 2008, 11:33 PM

check the ignition moduel i had problems like that chnged it out and it went away

April 26th, 2008, 07:23 PM	#1
Bigfatts Regular Badass Mother 3000 Twice as fast as your ass! Join Date: Apr 2008 Location: Lutz, Florida Posts: 227	Misfire under load Two days ago my LX started misfiring. It does it when I'm accelerating, usually between 3 and 4000 rpm, or when going uphill. When I got home I changed the plugs (went with NGKs gapped at .045. The Autolites I took out of it were gapped at .040 and I thought that was kinda tight, they came in the car.) It has newer MSD 8.5 wires with an MSD Blaster EFI coil. MSD 6al with an MSD cap on a Motorcraft distributor. After I changed the plugs I noticed it runs a little nicer. It misfires less, but it still does it occasionally. I did pretty much a whole tune up on it and cleaned and inspected the MAF and thottle body, also ran injector cleaner. Everything seems good but it still misfires occasionally. Then I thought maybe moisture in the fuel lines so topped it off and put some water remover in it. Before this the car ran smoothly and gave me 0 problems. Could it be that I got ahold of some crappy fuel or is there something I might be overlooking?

April 26th, 2008, 07:52 PM	#3
93hatch Hardcore Enthusiast 1993 Lx Skittle fast Join Date: Jan 2008 Location: sitting on my hand Posts: 2,867	timing advanced? running premium if it is? __________________ Greatest fail of MM's history http://www.moddedmustangs.com/forums...icer-page.html

April 26th, 2008, 08:03 PM	#5
93hatch Hardcore Enthusiast 1993 Lx Skittle fast Join Date: Jan 2008 Location: sitting on my hand Posts: 2,867	arent coils either good or bad with no in between? __________________ Greatest fail of MM's history http://www.moddedmustangs.com/forums...icer-page.html

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April 26th, 2008, 07:52 PM	#2
R0B0T Regular Join Date: Apr 2008 Posts: 118	valve that needs to be adjusted bad/weak coil switch the coils and see if the misfire changes cylinders main things that pop into my head

April 26th, 2008, 07:57 PM	#4
Bigfatts Regular Badass Mother 3000 Twice as fast as your ass! Join Date: Apr 2008 Location: Lutz, Florida Posts: 227	I kind of overlooked the coil because it's less than 2000 miles old. I'll have to see if I can dig up a spare and see how it runs. And I only run premium in it.

April 26th, 2008, 08:07 PM	#6
R0B0T Regular Join Date: Apr 2008 Posts: 118	also check to make sure that the wires are seated on the spark plugs if one of the boots isnt seated right it can cause it to misfire occasionally i had this happen to a friends car this weekend, boot wasnt seated properly and the spark was going to the header instead of the plug haha

April 26th, 2008, 08:28 PM	#7
galzamar Regular 1982 Mustang GT, SVT Swap Join Date: Mar 2008 Location: Sedalia, MO Posts: 58	Also make sure that your 7 and 8 cyl plug wires are not next to each other they can cause a miss due to wire voltage seepage since 7 and 8 fire so close together.

April 27th, 2008, 11:15 PM	#9
galzamar Regular 1982 Mustang GT, SVT Swap Join Date: Mar 2008 Location: Sedalia, MO Posts: 58	I have an instructor that works at ford as a mechanic and that is what he said that if you get plug wires 7 and 8 to close it will cause a miss . . . Glad you got it fixed.

April 27th, 2008, 11:33 PM	#10
saldoggs Regular 1993 mustang lx convertib Join Date: Jan 2008 Location: staten island nyc Posts: 140	check the ignition moduel i had problems like that chnged it out and it went away

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