2004 5.4 misfire causes?
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2004 5.4 misfire causes?
My 2004 f350 5.4l has a constant miss on # 8, I've switched the cop, plug and injector to # 5 and the miss stayed with # 8. So I figured bad connector or bad wire. Hooked noid light to fuel injector plug and got a steady flash, and voltage tester to cop plug and got 14+ volts on one terminal and pulse on the other. I am thinking burnt valve? A compression test will be my next try. Does anyone have any other things I could try? The truck has 240000 miles so it might be time for a remanufactured engine, any suggestions for where to buy a long block at a good price/quality? Thanks
Fleet Mechanic
Joined: Feb 2011
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From: Thousand Oaks, CA
My 2004 f350 5.4l has a constant miss on # 8, I've switched the cop, plug and injector to # 5 and the miss stayed with # 8. So I figured bad connector or bad wire. Hooked noid light to fuel injector plug and got a steady flash, and voltage tester to cop plug and got 14+ volts on one terminal and pulse on the other. I am thinking burnt valve? A compression test will be my next try. Does anyone have any other things I could try? The truck has 240000 miles so it might be time for a remanufactured engine, any suggestions for where to buy a long block at a good price/quality? Thanks
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compression test result
ran a compression test when I got home today. I did #5 first to have a comparison 140# first try 145# second try then #8, 138# first try 143# second try. I must be overlooking something? I read somewhere on this site a guy whose truck didn't miss the first few seconds after a cold startup and then started to miss, he checked it with a noid light and it flashed at first but stopped when it started missing. when I checked mine with a noid light it flashed so I figured it was okay and stopped but maybe I should run it longer?
on the COP connector the red wire is supposed to be hot all the time and the other should pulse correct? what voltage should the other wire be when it pulses? i am stumped and bummed out, this truck is how i make a living.
on the COP connector the red wire is supposed to be hot all the time and the other should pulse correct? what voltage should the other wire be when it pulses? i am stumped and bummed out, this truck is how i make a living.
Fleet Mechanic
Joined: Feb 2011
Posts: 1,812
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From: Thousand Oaks, CA
The 12v goes thru the COP coil and on to the PCM with probably a WH/RD wire for #8.
The PCM will control connecting the WH/RD to ground to open/close the circuit at the appropriate times.
The "other wire" should have 12v on it at all times, too.
You could check for 12v on the WH/RD wire at the PCM connector to be sure the circuit is complete to the PCM.
A COP is just a transformer.
When the PCM connects COP wires to ground a current will flow thru the COP primary coil creating a magnetic field.
When the ground is removed the magnetic field in the primary coil collapses creating a pulse in the secondary coil of 15KV that arcs across the spark plug gap to ground.
Fleet Mechanic
Joined: Feb 2011
Posts: 1,812
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From: Thousand Oaks, CA
I know I said "Hot at all times", but it's actually "Hot in Run and Start".
The RD/LG comes from the CJB and goes to the rear of the engine where it splits to go to each bank of COPS.
First try to see if there is 12v right where the RD/LG wires comes out of the harness for #8.
You may just have a broken wire at the connector.
Replacement connectors are available on ebay - 8 for under $10.
Search for "coil connector 5.4L".
Also, you could tap off the RD/LG wire on an adjacent cylinder.
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fuel injector signal
Well I did the noid test on the #8 fuel injector again it does flash for about 5 seconds then stops flashing, that explains why when first started it sounds like it's not missing. Apparently I wasn't running around to look fast enough before.
So, what does it mean when it flashes for only 5 seconds or so?
So, what does it mean when it flashes for only 5 seconds or so?
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