YOu might also want to check your wires VERY closely. I had a problem like that and it ended up being a wire that was cracked from heat. That is why you ALWAYS keep one or two of your best wires after a tuneup. You never kinow when you might need them. THat is especially true if you have headers.

 

OK, got code P0301 this morning. Misfire on cylinder 1. So the problem didn't follow the injector swap from 6 to 2. Now I'm thinking what is common with the ignition system. I was thinking coil, plugs, CAT.

Went to the muffler man today, who happened to own a dodge also, and he told me that my cat was fine. Plenty of flow, didn't smell like rotten egg but did notice the miss. He recommended to go back to the plugs and swap the Autolite I have been running for the champions that came stock.

I pulled all the plugs (which all looked fine) and swapped them for the champions. Still runs rough.

I swapped out the coil, still runs rough.

Tested the fuel rail and have 50 PSI. Is that correct?

I also disconnected the Pre-CAT O2 sensors and went for a drive. That changed absolutely nothing.

While I had the plugs out I did a compression check on the cylinders. I got the following readings:
1- 80
2- 85
3- 97
4- 92
5- 100
6- 80
7- 100
8- 86

Interesting that after I typed that I notice that the 2 codes thrown for misfire were 1 & 6 and they have the lowest readings. Coincidence????

I'm really not sure where to go from here without just guessing. I could ohm out the wires, does anyone know what they should read? To me I keep thinking it is something common in the ignition system that is causing the misfires on different cylinders.

Any thoughts?

 

Beginning to sound more like a vac leak. Before the engine warms up completely, lightly spray some carb cleaner around the area where the intake meets the heads. If there is a leak, you'll hear your rpms increase. Also check the rubber caps over the vac tubes on the passenger side of the intake to see if one of those are cracked or split. Just more or less double check all the vac line under the hood.

 

Recheck those compression readings.. you may have more issues than you think.

disconnecting the o 2 sensor making no difference at all is another concern. it should have went closed loop and ran really rich .. which tells me the o 2 sensor is not working correctly .

 

I don't want to be like the guy who only had a hammer, so everything looked like a nail, but ....

I have a strong suspicion that it's your crank sensor. Running rough at low rpm's, smoothing at at higher rpm's, and getting codes that tell you you're misfiring ... sounds exactly like the problem I just had. Try reading the two threads "Interesting spark problem" and "5.2 stalling, stalling, stalling". Consistent misfiring on just certain cylinders is what made me really start to suspect the crank sensor (known around here as the CKPS).

A faulty CKPS isn't an all-or-nothing thing, as I now know for a fact. With my bad one in my engine wouldn't idle for crap, but it sounded great at 5,000 rpm's. Misfiring is just more noticeable at idle; simple physics. High rpm's, lots of momentum - the engine just isn't inclined to "lope" like it would at idle. I was getting erratic sparks on certain cylinders only, and sometimes no spark at all on those same cylinders, because I think the CKPS wasn't telling the PCM (computer) to tell the coil quickly enough (or at all) to start building up a sufficient charge before it fired; hence, a weak spark. And only on certain cylinders because (I think) that the failing CKPS was reading some of the cut-outs on the flywheel better/more quickly than others.

You can take the old one out and check the resistance across any of the three pins. Mine was showing infinite resistance between any two of them. If yours does the same, just replace it. I'm not even sure that's a definitive testing method, so even if it isn't showing infinite resistance, it still might be bad. NAPA has a cheap one that I got for $48 that works just fine; worst case, you'll have a spare for that trip through the Mojave Desert.

Also; it's easy enough to rule a vacuum leak in or out. If you don't have a vacuum gauge, I encourage you to buy one. They're cheap, and a necessity for anyone who works on his own vehicles.

Lastly; speaking of gauges, I think your compression gauge is shot. Those readings sound awfully low, and since they're [relatively] consistent, I think your gauge is consistently wrong (unless your engine has about 250,000 miles on it). Also, make sure your throttle plate is wide open while you're cranking the engine during the test - the cylinders need plenty of air to compress.

So I encourage you to check out those two threads and see if the symptoms sound hauntingly familiar. I've got 5 cents that says it's your crank sensor.

 

+ 1 I'd also advise on checking this out. Does it ever start to idle properly?

FWIW, if anyone knows the programming of the PCM and what goes into the calculation for doing spark advance, I'd like to see someone post the formula.

 

This damn thing is running rough as hell now at idle. Seems like it's getting worse.

Haven't had time to work on it today, but it threw a codes P0132 O2 Circuit High Voltage (Bank 1, Sensor 1) & P0152 O2 Circuit High Voltage (Bank 2, Sensor 1) this morning. Is that because I unhooked the pre-cat o2 sensors yesterday and the codes are just catching up with being disconnected?

 

As soon as you get the time, check the crank position sensor. Take it out, and do the simple resistance check on it.

And if you haven't read these two threads, I highly recommend it:

01 5.9 no signals to coil Help
Interesting spark problem

 

Do you trust your comp gauge? If so your motor needs rebuilding fsm states min 100psi to run. Double check your test numbers buy doing a comp test again.

 

Good point. If those are your real numbers, all other bets are off. Let me amend my previous post by saying that your actual job #1 is to recheck your compression with a different gauge.