Tune up

So I’ve began to notice a misfire here and there when I accelerate from red lights and stop signs, notice it more when I have to go up a incline. My question is should I replace both the spark plugs and coils or just the plugs?

 

just plugs unless its a specific cylinder then swap coil packs between two cylinders and see if the misfire moves to the other cylinder.

 

Don’t really know which cylinder is doing it , that’s seems to be the issue.

 

I would just change the plugs , comparing the old ones to each other. Keep track of where the old plugs lived. If you see one that looks a lot different from the others, note which cylinder it went to. Put the new, GAP CHECKED, plugs in and see how it runs. If it still misses change the coil on the offending plug. But first I would take it to an auto parts store for a free code check, to see if anything related shows up.

 

If the check engine light is not lit, there's likely no issue with the coils.

Are you sure it's a misfire and not running sluggish? You could have a fouled plug(s), a bad fuel injector(s), plugged catalytic converter, etc...

 

Hope it's not, but, head gasket?

 

Change plugs, clean throttle body and maf sensor. Also replace pcv valve. The slight stumble is contributed to a vacuum leak most likely. Check all vacuum lines as well

 

The engine light is on but it’s been on because of the catalytic converter, haven’t had it rechecked for a misfire. Gonna change the plugs this weekend and see if it helps, I’ll try spraying the maf sensor also...

 

A plugged cat can cause the symptom of a misfire, especially when you put a load on it, such as going up a hill.

And if the CEL is on, it will not know if a code came in for a bad coil unless you plug a reader and check the CEL codes.

 

Misfire usually causes a flashing CEL while its happening.

 

My cel light stays on and doesn’t flash, just started noticing the backfire in the last few days and have been noticing a decline in my fuel mileage as well.

 

Change your o2 sensors, helped me with my problems I had a bank 2 cat code replaced the upstream a/f ratio sensors and downstream o2 and light went off and runs like a champ. Also brought my mpg back to a normal

 

I always start with plugs, they have short intervals on the 4.0 and need constant replacement.

Clean MAF and Throttle body during replacement. I take off the whole air cleaner everytime I do a customers plugs just so I can clean the T/B and it makes the plugs that much easier.

 

Pull the codes and post here. If you know the cats are bad you should fix that problem before chasing others.

 

02 sensors will not cause a misfire. A vacuum leak will cause a rough running symptom at idle only. If it's misfiring under accel and load think coils and plugs

 

Thanks for all the help guys, going to start with the plugs first then see if that helps, it’s the cheapest route right now, the cats are expensive so I’m hoping that I can hold off on that for now. Is there anyway I can clean the O2 sensors?

 

O2 sensors like heat, but rarely get better over time. A hot highway jaunt is good for the catalyst, but again rarely fixes the problem, more of a preventative.

There's very few reasons to replace 02 sensors on a whim, you replace them if they are confirmed to reading improperly or if there's an issue with the heater circuit.

 

Well here’s the result, looks like to me the previous owner changed them out, but when I drove it after I put the new ones in it didn’t do anything, it ran fine, should I change out the coils just to be safe?

 

Could all that oil on the threads of the plug on the right side of the top pic be indicating a problem? Maybe me but is the insulator darker too?

 

Threads do look more oily than the others but the tips look normal. Could just be thread lube used by previous owner, or camera angle. One of mine looks shiny also; switched these out 3 week ago and all look the same but for the pic.