Hello folks I have a 2003 E450 Motorhome with a 6.8l V10. I have replaced the troublesome PCV hose, Have had all 10 plugs replaced and all 10 coils replaced. The Rig has 34,850 Miles on it. Since the day I got it there has been a misfire/vibration under light throttle load conditions. If the van down shifts the miss goes away. Where should I start looking.

 

When it starts to miss put it in neutral. Does the miss go away?

 

Use Mode $06 data to see which cylinder is misfiring. Without accurate fault data, you're just shooting in the dark.

Either Torque Pro or Forscan/Lite as well as better scan tools will do this.

 

Make sure the vibration is actually a "miss" before you spend any more money.

Start your engine and put the transmission in first gear. With your foot FIRMLY pressing the brake pedal, give the engine enough throttle to raise the RPM, but not so much that the drive wheels spin. If you have an engine miss your vehicle should now be vibrating. If it isn't vibrating you need to look elsewhere for the issue.

 

The check engine light is off but I have codes PO301, PO303 and PO309. Not a real scan tool just a basic code reader

 

Well, there you have it. Should have stated that in the first place...

It's completely normal for Super Duty vehicles of that era to have OBD1 calibrations which do not set the MIL for numerous possible faults. A "basic code reader" will likely be insufficient.

Time to dig deeper and get some history:

1. What were the fault codes before the parts cannot was fired?
2. What brand and part number of plugs and coils were used in the parts cannon?
3. Were the fault codes reset post parts cannon firing?
4. How long have you owned the rig and how many miles has it been drive with this condition?

 

Move coils around. See if the codes follow the coils.
if the codes don’t change
Move plugs around see if the codes follow the plugs.

new doesn’t mean good. I’ve had new coils and plugs be bad.

also make sure the connector is snapped in all the ways those connectors get brittle and the little plastic tab breaks and the connector is basically jait aittig rhere and can back out. Unusually put a tiny dab of crazy glue to hold the loose connector until I can order a new one.. Like a pin head size dab

 

Ill do best to answer
I never checked codes before the plugs where replaced. Engine blew #6 spark pug out ALL Plugs replaced and retorqued
Motorcraft spark plugs SP479 DG508 where used, Life time warranty Amazon coil set was installed.
I erased all codes then took rig on a 100+ mile road trip. Read codes when I got back. Codes for Lean Bank 1 and Bank 2 along with 3 other misfires present before reset. That made me replace the PCV vacuum hose hose elbow and PCV valve. NONE of the previous misfires where the ones it has now. Misfires seem random but PCM will not give PO300 code

I have owned the rig for about 6 months it has ALWAYS had the vibration/miss. I thought it was drivetrain at first. Had shop determine it was engine.
I've put about 5000 miles since we bought it every single with miss/vibration issue.
It only has 34K on it very low miles.
Also used Injector cleaner as part of the parts cannon.
The miss appears as a vibration under part throttle load conditions. If I apply more throttle to climb a slight incline it misses, if a make the rig down shift the miss goes away. If I drop the throttle while its missing it goes away. It seems to not like any type of lug on engine.

 

My rig runs great cruising at a constant speed at part throttle. If I need a little more power to maintain speed it misses. It also seems to Idle rough, this is my first experience with a Ford V10 so I figured the rough Idle was how it ran always been this way.

 

The mild (or not so mild) misfires under moderate load are typical for this family of engines. Usually just after it shifts into overdrive with moderate throttle. An uphill slope aggravates the issue. Usually 45-55 mph, more or less.

Almost always spark plugs and/or COPs. Don't care that they were just replaced, they're still at the top of the list of suspects.

If you bought the parts from Amazon or eBay from any seller other than an online Ford dealer, I'd be suspicious of counterfeits.

 

One other thing I believe when the #6 cylinder blew the spark plug all plugs and coils where factory original but it had the issue before the plug blew out.

 

This is a motorhome no way to quickly or easily move plugs or coils around. Just getting to a plug takes 30 minutes removing air cleaner assembly and dog house. The air cleaner needs to be put back together to drive.

 

Yeah, life is hard and it takes work.

Doesn't change the advice on how to diagnose without resorting to parts swapping.

 

Ok called my shop when the #6 plug blew I also had mis fire codes PO304,PO306 and PO310. Changed the plugs coils and repaired threads on Cyl 6. Next set of codes after 300 miles where PO171 Lean Bank 1, PO174 Lean Bank 2, PO302, PO305 and PO307, The cracked PCV vacuum line was replaced now after 150 miles PO301, PO303 and PO309. We are missing something. So now Cylinders 1,2, 3,4,5,6, 7 and 10 have thrown misfire codes, 3 different cylinders at a time. So I'm to believe 7 of 10 new plugs or coils are bad. We are missing something.

 

Has fuel pressure been tested?

Has the performance of the MAF sensor been checked?