Breaking up over 3500rpm

[Lostneye]

Runs decent below 3500rpm most of the time. Then most of the time it will break up over 3500. Occasionally will run to redline with no issues. No codes. Fuel pump?

 

[08T1]

Change fuel filter

 

[Transporter]

What do you mean by "Breaks Up"? Are you talking an missing/knocks?

Need more info: How many miles on vehicle? When and at what mileage was your last tune up?

The issue could be the fuel filter, a bad tank of fuel, COPs and Plugs. If you change the fuel filter and its No Joy, then when it starts to knock, keep the vehicle at that load and RPM to attempt to get it to throw a code or see the CES light flash or stay on.

 

[Lostneye]

Fuel filter isnt that old but its cheap enough to try. 70k miles original plugs. It doesn't knock but will missed and stumble. Rarely it will flash check engine light when in overdrive up a grade but will not stay lit.

 

[2004XLT]

I would replace plugs and coil packs..it's good preventative maintenance either way.

 

[Transporter]

Fuel filter isnt that old but its cheap enough to try. 70k miles original plugs. It doesn't knock but will missed and stumble. Rarely it will flash check engine light when in overdrive up a grade but will not stay lit.

That sounds EXACTLY like a bad COP! The engine is under load when going up a hill. And if the CES light flashes, it is knocking/missing on one or more cylinders.

Go for a drive and find a nice steady steep hill and when it starts to miss behave, keep the RPMs in that range so it keeps missing and you get a solid CES light. Do you have a way to check to see if you already have a Code? Sometimes if it has missed fired enough, it will throw a code without a solid steady CES light. But if you can get a steady CES light, you have a Code for sure.

 

[jdecker]

Find a scanner that will show pending codes to determine which cylinder is mis-firing. If the service engine light is flashing you have a mis-fire, it is intermittent enough to not trip a full warning, but it will show under pending codes.

 

[docraymund]

Check fuel pressure.

 

[Red92lx]

I'm going with cops needing replacement. Check your stored codes, you probolby got one that say misfire on cylinder __