Hey guys i am posting for a friend. He has a 2000 Ford Ranger 3.0 that is giving him a rough idle. About 2 months ago he replaced the head gaskets and had the heads milled and cleaned up. Since then he has had a rough idle. To me in my experiences it sounds like a misfire. He just replaced the coils, wires, and plugs to help remedy the problem but it did nothing. I have ran multiple checks with every odb2 software i have including dash command and Scanxl pro and it does not detect a misfire. there is also no check engine light. i just went trough and pulled the wire off of the coil pack one by one to see if it made any difference to check for misfires and every wire pulled it made it run worse except for one where pulling the wire off of the coil made no difference in how it ran. he took the truck to the shop and they told him that he had a rolling misfire and they didnt know y. but i dont trust shops. Do yall have any idea what i could be. thanks guys in advance

 

When you pulled the coil wires did you get a misfire report on the scanner?

If you pulled one spark plug wire and RPM didn't change then I would inspect that cylinder more closely.
Could just be a dirty injector tip, at lower RPMs the fuel mix is lean because dripped fuel isn't mixing like sprayed fuel.

Could be intake gasket near that cylinder is not tight adding a bit of air which leans out the mix at lower RPMs, engine was just worked on, so...........retorque the intake, or spray some carb cleaner or starting fluid around that area to see if rpms change.

Swap spark plugs with another cylinder.
Swap injectors.

Swap wires on the coil, this is a waste spark system, so both spark plugs on the 1 coil fire at the same time, you can reverse the wires.
And yes, one spark port can fail even though it is one coil, it is series wiring inside on the secondary of the coil.

As far as new plugs and new coil...............or anything else that is "new".

New used to mean "it works"
Not anymore
New now means "it has never been tested"

Quality control is not part of the manufacturing end of things any more, they offer a warranty, we are the quality control department now

So a new coil has never been test, you are the first to try it out, same with spark plugs

 

My truck seems to do the same. Even though no codes show, it still feel like it runs rough. Almost like the engine vibrates bad sometimes. It could be the type of gas he is using. He needs to make sure its 87 octane, and never cheap gas, like Caseys and Murphy. Since ive switched from Murphys to Shell, my engine has been running a little better. But my case could be different than his. I also need to change the plugs soon, but thats a different story...

 

i would run 2 or 3 bottles of seafoam mixed in with the fuel tank

my used mazda b4000 idled rough when i bought it

3 bottles of seafoam mixed in with the fuel cured the rough idle , she puurs like a kitty now

could just be a couple of partially fuel injectors

BTW> any time you increase a cylinders compression ratio , you have run a slightly higher octane fuel to prevent fuel pre-ignition ( detonation )

 

I had a '90 ranger, would get this engine vibration above 2,000 RPMs and it would come and go, but only at higher RPMs.
Fan clutch.........go figure

 

ah yes he had the cylinder heads milled flat but not the block too
( anytime that you mill flat cylinder heads , the block must be milled flat too )

sounds like that cylinder is compression leaking

i would go back in and retorque the cylinder head bolts

( it is not uncommon for a spark plug to be defective from the manufacture process )

and now you must run 89 octane fuel because you now have increased the cylinders compression ratio