¿Ford with Misfire on #7?

Elisha Technician Odessa, Texas Posted   Latest   Edited  
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Driveability
1997 Ford F-150 4.6L (6) 5-spd (M50D)
Misfire

Hello to everyone. I am wondering if maybe someone can help me out. I have this customers truck that came in with a misfire no DTC'S registered in PCM. It needed plugs and wires so we replaced them. Still had a misfire on cylinder #7. I switched Coil packs and still the same. I went around unplugging Injectors and found #7 was the only one that had no change. Tested circuitry with my Power Probe 4. Good power and ground. Checked Injector pulse with PP4 and found that injectors on B2 were opened 1 second longer. I did notice that my LTFTB2 was 12%+ on my PID. I replaced Injector #7 and still the same thing. Started to look for vacuum leaks around the intake manifold thinking maybe something is cracked or worn out, but to no avail. If it was a fuel related issue it would probably affect other cylinders as well i reckon. I did a compression test and all cylinders were within specs. Took off valve cover for B2, but found no evidence of mechanical issue's with Cam. I have a Scope but not to familiar with it yet or else i'd use it. I am stumped by this at the moment. Any suggestions would be greatly appreciated. Thank you.

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Chris Technical Support Specialist
Commack, New York
Chris Default
 

Do you have FFD for the misfire? Does it occur at Idle? Under load? Typically an ignition issue is less prominent at idle and worse under load. Fuel and mechanical issues may be worse at idle and seem to be less severe at higher RPM's. The longer injector pulse width is likely from the false lean condition from the misfiring cylinder (not burning the fuel does not use the oxygen and skews the…

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Elisha Technician
Odessa, Texas
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Thank you Chris for your input. I do not have any FFD for it since it is not registering on the PCM. I forgot to add that info into the question. I doe's it at idle and don't notice it a higher RPM'S. I have replaced injectors 2X. Thinking it could be a defective fuel injector. I have had bad parts before and replaced them 3 times before things worked. And no i do not have a pressure transducer…

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Chris Technical Support Specialist
Commack, New York
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Experiences like that (3 time replacements) are what makes me look to move parts on the car. If we know the other cylinders are working, swapping with a known good is a great way to isolate. Especially since on this vehicle, the fuel rail only has two bolts and is easily accessible.

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Ramon Diagnostician
San Leandro, California
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Hi Elisha, Eric O. from South main Auto post a video with similar issue "Jeep Commander: Dead Misfire / No Parts Needed" I hope this help watch the video from the link attached youtube​.​com/watch?v=qzusEs…

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Elisha Technician
Odessa, Texas
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Well my question is that this truck is an late 90's model. Did older vehicles have similar MDS technology like this 08 Jeep? Not to advance i think?

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Ramon Diagnostician
San Leandro, California
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You are right sorry I was just trying to give my input but if you had control going to injector you ok there Does LTFTB2 on Graphing PID improve when you have higher RPM signal, have you pressurize the coolant system and check with borescope inside the cylinder (I ran with an issue like this before and was a coolant leak going to the cylinder)

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Andrew Technician
Midland, Texas
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I'm very near you I might be able to give you a hand elisha if you still need help?

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Elisha Technician
Odessa, Texas
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Well your help is greatly appreciated Andrew. I would have taken up your offer, but the customer did not want to spend more money on it. He is going to get another vehicle. It's good to know that there are other Tech's nearby that use the Diagnostic Network.

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Elisha Technician
Odessa, Texas
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Well it actually got worse when you would rev it up. You'd think it would improve. I did not pressurize the cooling system. I did Borescope the cylinder but found no coolant.

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Elisha Technician
Odessa, Texas
Elisha Update
 

Thanks to Chris, Ramon and Andrew for your insight on this problem of mine. The customer decided not to invest more into this money pit. Getting another vehicle. Thank you very much. I hope to help you out Lord willing someday.

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