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Pete
Pete, Auto Service Technician
Category: Ford
Satisfied Customers: 29112
Experience:  Over 17 years diagnosing and repairing automobiles various makes and models with some training and certifications.
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I have 2008 f350 6.4 that is giving me a cylinder 8

Customer Question

I have 2008 f350 6.4 that is giving me a cylinder 8 misfire,How serious could this be? What's the worst case scenario? I'm running a dog delete an a sct4x runner.
JA: How many miles are on the car? Is it a steady misfire? Or random?
Customer: Dpf delete not dog delete! 211k
JA: Are you fixing your F350 yourself? What have you tried so far?
Customer: I'm just hoping it's nothing serious
JA: Anything else you want the mechanic to know before I connect you?
Customer: Keeps blowing glow plug harness off
Submitted: 2 months ago.
Category: Ford
Expert:  Pete replied 2 months ago.

Hi my name is ***** ***** I will be happy to assist with this today.In some cases I may need more info to assist better.I apologize for any delay.

In most cases it can be an injector needing replaced.In other cases you may have low compression due to a burned valve in the cylinder head or piston ring failure or even cylinder wall damage.In any of these cases though this can be serious and needs to be checked into.If a diesel is running lean on one cylinder due to an injector fault this can cause an over heat issue in that cylinder and can damage the cylinder wall and piston.

If the glow plug harness itself is coming off this can be due to poor hold downs causing this issue needing corrected but if there is actual pressure coming from around the glow plug blowing off the harness then this needs checked into further to see if the glow plug needs replaced or if there is another mechanical fault with the engine causing this fault here.

If more help is needed, use the reply tab to continue our conversation. If no further assistance is needed, kindly rate my service,your 5 star rating is appreciated ( should be a link to click on here or above).You can rate at any time and we can continue to work on your question as this will not close out your question.Keep in mind in some cases it can be difficult to fully diagnose or help repair your vehicle without seeing it and I work on delivering the best possible answer from what I see to work with.

Thanks Pete

Customer: replied 2 months ago.
What's the most common with the info that I'm giving you
Expert:  Pete replied 2 months ago.

Usually it is the injector itself needing replaced.I have seen several injector failures in the past before cause the misfire you see here.Glow plug operation is not needed once started and ran so this seems more to be a fuel injector fault.

Let me know if you need anything else and feel free to rate my help here or above ( should be a link to click on ) as this is how I receive credit for my time.Your 5 star rating is appreciated

Thanks Pete

Customer: replied 2 months ago.
Even with the glow plug harness blowing off ?
Expert:  Pete replied 2 months ago.

Now is the harness blowing off or just coming loose and is this at only the number 8 cylinder?

Customer: replied 2 months ago.
It's blowing off
Expert:  Pete replied 2 months ago.

Is it only blowing off the #8 and is the glow plug blowing out as well?

Customer: replied 2 months ago.
Just the harness
Expert:  Pete replied 2 months ago.

O.k.,if it is just the harness then it has to be a connection issue to the glow plug itself.I would check the harness for any damage to see if it needs repaired or replaced first.This needs corrected first to see if this resolves the misfire just in case the computer is only detecting the misfire on start up as this can be the cause.

In some cases this harness needs replaced if it cannot be repaired.But I would start with this first.

Let me know if you need anything else and feel free to rate my help here or above ( should be a link to click on ) as this is how I receive credit for my time.Your 5 star rating is appreciated

Thanks Pete

Customer: replied 2 months ago.
But what would cause the harness to go bad
Customer: replied 2 months ago.
Have you ever worked on a 6.4 ?
Customer: replied 2 months ago.
Not trying to be rude but I need to sure before I throw money into it.
Expert:  Pete replied 2 months ago.

It is possible the glow plug is getting to be to hot causing the connector to loosen and causing it to pop off.I have seen that occur before and had to replace the glow plug and pig tail glow plug harness.You can get the glow plug harness cheap around $50.I have found one here:

https://www.amazon.com/Ford-5C3Z-12A690-A-WIRE-ASY/dp/B000NTBRT6

It would be a good idea to replace the #8 glow plug and this harness.

I have worked on some of these before.

Let me know if you need anything else and feel free to rate my help here or above ( should be a link to click on ) as this is how I receive credit for my time.Your 5 star rating is appreciated

Thanks Pete

Customer: replied 2 months ago.
Ok but what would cause the glow plug to be to hot
Expert:  Pete replied 2 months ago.

It may have to much resistance in it and may be heating up or shorting out causing issues with heat build up.You can usually test resistance by taking a multi meter and testing resistance from the connection prong on the injector to the metal engine block with the harness unplugged from it.If the resistance of the glow plug is more then the others when they are tested ( test at least 2 others ) then the glow plug should be replaced.

Thanks Pete

Customer: replied 2 months ago.
think it's anything seriously wrong with the internals ?
Expert:  Pete replied 2 months ago.

It's hard to say for sure.It may be something as simple as a worn out connection at the #8 glow plug and all that is needed is the harness or a glow plug with high resistance or a short with both harness and plug needing replaced.

But if there is a compression fault or over fuel issue from the #8 injector this can cause some issues inside that cylinder which can lead to damaging the glow plug which may have heated the harness.

You can have that worry eliminated by having a compression test done and having the injector tested but keep in mind this can be a time consuming diagnostic procedure that a shop or dealer would usually do.

If it were me I would replace the harness and glow plug if the glow plug tested to have high resistance or when pulled and inspected it looked damaged.Then start and run it to see if anything maybe sounds odd with the way the engine is running or any running issues and if there are any then have the compression test and injector testing done.

Let me know if you need anything else and feel free to rate my help here or above ( should be a link to click on ) as this is how I receive credit for my time.Your 5 star rating is appreciated

Thanks Pete