A couple of weeks ago my truck started to cut out when I was going between 45 mph and 55 mph. Now it seems to do this no matter how fast I go.

The check engine light came on and I'm getting a PO306 code. My understanding is this is a misfire on the #6 cylinder. So I pulled all my plugs and they look good, and since I had the no. 6 out, I put a new one in. Didn't help. I put a new ignition coil in (I could have bought a tester but it was more than the coil), didn't help, but in the process saw the wire from the distrubuter to the coil was cracked and burnt. I thought I had found the problem, replace the wire, didn't help.

My fuel pump has been "whining" when I get below 3/8 of a tank. I didn't think it would help, but thought it might need replaced anyhow, so I put a new one in. The pump doesn't whine anymore, but it didn't help the original problem. When I reconnected the battery, the code has cleared but the truck still runs really rough and still cuts out.

So, I don't know what to do next. I am going to pick up all new wires today, but not sure it will help. From looking thru other posts - someone mentioned the catalytic converter can cause a No. 6 or 8 misfire. Is there a way to tempararily disconnect it or test it to see if it is bad?

The other thing I saw mentioned was the injector could cause this.

PLEASE HELP!!!!

Thanks

 

swap the injector to another cylinder and see if the misfire moves to that cylinder.

to test the cat you can do 2 things. first is to get under the truck when its cold and smack it with a dead blow or a rubber hammer. if the catalyst is loose then it will rattle when you hit it. the second thing you can do is get a heat gun and check the front and back of the cat when its running, if its like 500º in the front and 200º in the back then its probably plugged up. the heat gun is 20$ at advance and will come in handy for diagnostic purposes.

if the cat is plugged then you will have crappy power and won't be able to rev the engine too high. you probably have a blown plenum gasket too if your cat is plugged so look into your throttle body with the front of the truck on a slight incline to see if there is any oil in there.

if you do have to replace the cat then you may as well go with a magnaflow, it seems to be the most popular on this forum and only cost about 75$ on summitracing.com if you get the 1 in 1 out universal. the direct fit cat is about 230$.

almost forgot, when you disconnect your battery for a while the pcm sensor data gets erased so it will idle rough for a few miles while the pcm relearns the sensors. also, the cel gets erased when the pcm is reset.

 

Have your cat pressure tested to see if it's clogged. If it is, get it replaced and also replace the O2 sensors.

 

Is swapping the fuel injectors difficult? I have never done it before. Do I need any special tools? When I changed the fuel pump, I disconnected the battery, and it cleared the error code. If I swap the injectors will the error code come back on? Otherwise I won't know if the problem moved to another cylindar. I will have to run it to the autoparts store, and have them read the code again.

Regarding the catalytic converter: I was thinking about testing it and I even called a mechanic and they can test if for $20. But it seems like everytime I take something to be tested; its bad and they can fix for me for big $$$. Maybe if I let the mechanic know I am not going to pay him to replace it, and can get a honest answer.

Sheriff420: I drove it for about 5-6 miles after put the fuel pump in, is this long enough for the PCM to relearn the sensors? It did seem to idle rough as if I made the problem worse.

Tonight I will go ahead and put on the new plugs since I already have them, and I will see if I can swap the injectors. Hopefully the error code will come back on so I know if the injector is bad. I will see if I can get in to have the cat tested.

Thanks for your guys help. I will let you know how it works out.

 

i'm not sure about the injectors but it should be just lifting the fuel rail after unplugging the electrical connector and pulling it off. the injector just sits in the manifold and is held down by the fuel rail.
i think 6 miles is just short of long enough. when you reset the pcm it will idle rough and when you tap the gas the rpms will drop below 600 and jump back up because it still hasn't learned the IAC yet.
the upstream o2 sensor is also a good idea if you have more than 80k on the truck but i'm not sure if it'll give you a cylinder misfire.
have you checked your distributor cap and rotor? and are you getting a strong spark on the #6 plug? pull that plug then reattach the wire and touch it to the block and have someone bump the key to see if it has a powerful spark.
make sure they don't start it with the plug out, just bump it. i changed the plugs in my t-bird one time and forgot to plug in one plug wire and when i started it i thought the engine was going to hop outta the car.

 

Always lube the injector o-rings and do not install them dry lest they tear.

 

swapping an injector is a good and quick test. if it doesn't change anything -
do a compression check and write down the numbers.
there's a few instances of the "unspeakable" going on in recent threads.
you might be wasting time and money swapping out all these parts.

 

First off, thanks for everyones help. I figured since I was going to replace the plug wires that I might as well replace the dist. cap and rotar (too bad they couldn't have found an easier place to put the distributer. Anyhow, the distributer cap and rotar were shot. A couple of the contacts were almost completely fried. I don't know if that means I had a couple of bad wires that caused this or what.

After I put the new cap and rotar, wires, and plugs in it fired right up and ran great.

Thanks again to everyone that helped me trouble shoot the problem.

 

I should have mentioned for you to put some dielectric grease on all of the electrical connections. You can still do so when you have a free moment.

Congrats on finding the problem.