huntsman

Hey guys I get the code p0302 misfire in cylinder 2. I have new spark plugs, new wires, new injector, so im lost now. I thought it might have been the injector so i bought a new one but the code came back. I checked the spark in the spark plug and the spark is fine. So i would think the wire and distributor cap are fine, Since i do get a spark. Hmm Im thinking it could be low compression in cylinder 2 or maybe the wiring by the injectors. I looked at that and one of them seems to be pinched in. Cant tell if its cut or not. Another thing is maybe the spark plug gap is to big. Thats all I can think of, do you guys have any ideas what else it could be ? I was planning on going to UP michigan to do some off roading with a friend, hopefully i get this fixed so i can go.

tjwalker

Start by verifying gap on plug. .035 is the correct spec. Doubtful this is it, but it takes all of 5 minutes to inspect the plug and gap it. Swap it to another cylinder while you are at it to see if the code follows to that cylinder.

Compression test on all cylinders is never a bad idea. A good "snapshot in time" of the internal condition of the engine. The spec compression for the 4.0 is 120-150 psi, with no more than a 30 psi variation between cylinders.

Start there....

jhampton

what kind of plugs are you running? Run NGK V-power they are the best for chrysler. my jeep, dodge ram , and my durango will not run on anything but NGK's they misfire and and choke.

fishtaconc

Start with tjwalker's suggestions... if that checks out, you can test the injector/ wiring by swapping #2 injector with one of the other 5. If it moves its the injector, stay on cylinder 2 its something else.

tjwalker

Bosch plugs have been linked to confirmed misfires. Although some 4.0 engine can get by with them, I don't recommend them. I generally like Bosch products, but gotta go with the data here......

For 87-99, I recommend Champion copper plugs

For 00-01, I recommend NGK copper plugs (different ignition system and NGK plugs hold their gap a bit better than Champion on this distributerless ignition)

Matthew57892

check fuel pressure as well, should be 49 PSI I just chased this same problem, did plugs, cap, rotor, wires, o2 sensors, injectors o2 sensors seemed to get it

huntsman

hey thanks guys, I just put in a new distributor cap and rotor, the other one when i took it out was pretty corroded. The rotor on top was a lil corroded and kidna burnt as well. Hope fully this will fix the problem. If not il check the spark gap, fuel pressure and do a compression test.

Also since i did unplug the battery while working on the car and it resets the check engine light. So its gone for now, in this case do i have to wait until it comes back on or if i scan it itl show me right away if something is wrong ?

and actually i do believe i might have the bosch spark plugs, maybe il change them out as well to champion copper ones

tjwalker

I change my distributor cap, rotor and plug wires every 60k. Plugs every 30k.

If you still have a misfire, swap out the Bosch plugs for Champion copper plugs.

Just drive it now and see how it runs and "if" the check engine light returns. Hopefully you found it with the old cap/rotor.

huntsman

Well i changed the spark plug in cylinder 2 and either way I had champions in them previously. Just got to michigan and i remote started my car, after like 5 min of driving the check engine light came on Im thinking il switch the spark plug wires and if thats not it then what ? Guess i should check for low compression ?

tjwalker

Yes, once you've ruled out injector, spark plug, plug wire and distributor cap, that's it for peripheral things. Can't ignore a possible internal problem. Compression test is easy to perform and is a good "snapshot in time" of the internal condition of the engine.

Spec compression for the 4.0 is 120-150, with no more than a 30 psi variation between cylinders.

Good luck and keep us posted!

Matthew57892

Have you checked out the wiring to the injector as well? mostly the bundle that runs down your manifold by your fuel rail.

Begen

My 96 was throwing a #1 cylinder misfire code, and a compression test showed 45#s in it. The valve seat was bad.

huntsman

thanks guys, i have a feeling the remote starter might of messed something up. The first time i did it the engine didnt catch on. Then i just started it and after a few min the engine light came on. So i reset it and iv been driving it for a few hours and its all good. I will check tomorrow and see if it comes on. As for now im in UP michigan and if it does come on il check it out when i get home. I will probably do a compression test just to see what it reads. If it does come back on il try the spark wires and the injector wires, as well as the valve seat.

thanks for all the help guys I will report back after my short vacation lol.

Also i did check the injector wires and the one for cylinder 2, it seems like one of the wires is pinched, although its not cut. Im guessin that could be it as well. I'll know after I do some more tests.

tjwalker

A "noid light" is a nice thing to have on hand. Easy to hook up inline and it will tell you if the injector is firing or not.

I agree that is a good idea to verify that you are getting a PULSE to the injector. Swapping a new injector won't help if the injector is not receiving a pulse telling it to operate.

If no pulse in only one cylinder, suspect a wiring or connector problem specific to that injector or possibly something internal to the computer.

huntsman

ahh, Ima see how much they cost, maybe il pick one up.