thomas0202

Im trying to diagnose a misfire/stutter when accelerating on the highway. Almost all my driving now is on the highway between school and home and its pretty annoying to have the engine missing when I accelerate around 55-60 mph. Figured id pull the plugs just to see what I saw. I changed these plugs around 10 to 12k miles ago along with the cap, rotor, and wires and I know this isn't normal for them. The electrodes are worn way down and the plugs are crusty. I figured someone here could tell me what condition I'm looking at with these plugs. At this point I'm gonna do the plugs and just do the wires and cap and rotor while at it . Anything else I should check/test with what I'm seeing here?




1, 2, and 3 from the left





1 at the top. 6 at the bottom





4-6 from the bottom up

cruiser54

Put a set of NGKs in there.

Crazy 8s

Those plugs just look like your motor runs a bit lean. Replace them but also look into fuel delivery shortages; fuel filter, fouled injectors, maybe a tiring fuel pump.

Such can account for some misfiring, but they aren't the only culprits.

Maybe new plugs will smooth it over, but they do look a bit too beat down for being only 12k miles old.

tjwalker

Don't get tunnel vision on secondary ignition parts like plugs, cap, etc. I think it's more likely that something else going on here.....

Have you seen a check engine light? If yes you must pull codes for clues and guidance.

Otherwise, I'd start with verifying fuel pressure. For your 95, you should have 31 psi at idle. Then disconnect the vacuum line to the fuel pressure regulator and the pressure should jump to approximately 39 psi. Be sure that the vacuum line to the FPR is not wet with raw fuel, which would indicate a ruptured fuel pressure regulator diaphragm.

In all honestly, there are a lot of possibilities here. Have you been running "additives" in the fuel tank?

Finding out what it is not is a big part of finding out what it is not. It's a process of elimination.

Good luck and keep us updated!

thomas0202

It hasn't given me a check engine light but tomorrow I'll do the key trick to see if it has anything stored. When I grab a new set of plugs and all that I'll rent a pressure tester and see what the fuel pressure is running at. And as for additives, I have never used anything in the tank other than an occasional shot of seafoam and the last time I did that was a good year or more ago.

thomas0202

So I haven't gotten around to checking the fuel pressure yet but today I had a little bit of time so I pulled a plug for the heck of it and did a spark test. The spark looks to be weak. Its not a strong blue spark as it should be. Its more of a dull red and weak shot. I know I need to do the plugs anyways so I'm gonna change them out then do the test again. The jeep runs just fine with the spark the way it is. Only issue is the misfires on the highway. Any ideas as to why the spark is weak?

tjwalker

The primary suspect for "weak" spark is your ignition coil.

They can be tested for both primary and secondary resistances with a meter and a manual.