P0420 & P0430
11-01-2013, 03:34 PM
#1
Thread Starter
Join Date: Oct 2013
Location: AL
Posts: 37
P0420 & P0430
The other day I noticed a slight stumble when putting a heavy load on the engine under low rpm, going up a hill in 5th. It has gotten worse and now it does it all the time even at high rpms. Stopped by Autozone and these are the codes that came up.
The search I did came up as the cats are not working but none mentioned a stumble, any ideas?
The search I did came up as the cats are not working but none mentioned a stumble, any ideas?
11-01-2013, 04:17 PM
#2
5th Gear Member
Join Date: Jul 2012
Location: ohio
Posts: 3,628
Those codes are generic for cats not being effective , the down stream 02s are picking up high levels of co2, and NOx as well as other harmfull gasses. .
This could be related to a rich condition in the engine , such as fouling plugs leaking injectors etc etc. If you are experiencing a miss under load I would look into new plugs and wires to start.
This could be related to a rich condition in the engine , such as fouling plugs leaking injectors etc etc. If you are experiencing a miss under load I would look into new plugs and wires to start.
11-01-2013, 05:05 PM
#3
3rd Gear Member
Join Date: Nov 2012
Location: North Carolina
Posts: 574
That's not really how oxygen sensors work. They only detect oxygen not CO2 or NO.
When you have a catalyst inefficiency code it means that the downstream O2 sensors are picking up the same thing as the pre-cat sensor. That is to say that the upstream sensor should put out an oscillating signal indicating a rich, then lean, and back to rich condition where as the downstream should be a nice flat line. When the computer sees that the downstream sensor is switching it will trip a catalyst inefficiency code.
A misfire will alway trigger a lean condition because once again it doesn't know there is excess fuel, it only knows there is excess oxygen. In the event of a big enough misfire the cats won't be able to use all of the O2 in the catalyst reactions which can cause the rear sensors to switch hence the code.
I will however agree with dawson in saying that a misfire under load is usually an ignition problem. You may have a coil going bad or you are just in need of some spark plugs. If you take an OHM meter you can test the resistance of the coils. Compare your results against each other and the odd ball is probably bad.
When you have a catalyst inefficiency code it means that the downstream O2 sensors are picking up the same thing as the pre-cat sensor. That is to say that the upstream sensor should put out an oscillating signal indicating a rich, then lean, and back to rich condition where as the downstream should be a nice flat line. When the computer sees that the downstream sensor is switching it will trip a catalyst inefficiency code.
A misfire will alway trigger a lean condition because once again it doesn't know there is excess fuel, it only knows there is excess oxygen. In the event of a big enough misfire the cats won't be able to use all of the O2 in the catalyst reactions which can cause the rear sensors to switch hence the code.
I will however agree with dawson in saying that a misfire under load is usually an ignition problem. You may have a coil going bad or you are just in need of some spark plugs. If you take an OHM meter you can test the resistance of the coils. Compare your results against each other and the odd ball is probably bad.
11-01-2013, 05:14 PM
#4
Thread Starter
Join Date: Oct 2013
Location: AL
Posts: 37
Test with the coil on the spark plug or off?
Update
Just checked the coils, they ohm the same with or without being attached to the spark plug. All ohm 0.8, it was the #8 COP, the bolt holding it down had loosened and the coil wasn't seated.
Never dealt with a COP and I really could not tell if I had the plug wire on the plug or not. I pushed it down as far as the manifold would let me, still have the miss, maybe the plug went bad because of the loose coil. Going to get a new set and install tomorrow and see what happens.
Update
Just checked the coils, they ohm the same with or without being attached to the spark plug. All ohm 0.8, it was the #8 COP, the bolt holding it down had loosened and the coil wasn't seated.
Never dealt with a COP and I really could not tell if I had the plug wire on the plug or not. I pushed it down as far as the manifold would let me, still have the miss, maybe the plug went bad because of the loose coil. Going to get a new set and install tomorrow and see what happens.
Last edited by kilr95ss; 11-01-2013 at 06:04 PM.
11-02-2013, 04:23 PM
#6
Thread Starter
Join Date: Oct 2013
Location: AL
Posts: 37
Little more diagnosis, disconnected each coil one at a time while running and each made a difference in engine rpm. Pulled the plugs and they looked great. Seems as if the miss is only under load and not at idle, could it be a coil even though they ohm good?
Tomorrow going to pull each coil and check them really good for bad boots and look for any coolant in the plug valley.
Tomorrow going to pull each coil and check them really good for bad boots and look for any coolant in the plug valley.
Last edited by kilr95ss; 11-02-2013 at 05:23 PM.
11-03-2013, 07:32 AM
#7
3rd Gear Member
Join Date: Nov 2012
Location: North Carolina
Posts: 574
When the engine is under load the coils have to work harder to produce spark. This is usually when you would stress test them but that requires some inductive pickups and an oscilloscope. You're gonna need to narrow down the cylinder that's misfiring and then swap that coil to a different cylinder to see if the miss follows it. They're too expensive to just shotgun parts at it.
I've also seen fuel injectors cause a miss under load but it' less likely than the coil.
BTW how did you pull out the spark plugs without looking at the COP boots?
I've also seen fuel injectors cause a miss under load but it' less likely than the coil.
BTW how did you pull out the spark plugs without looking at the COP boots?
11-03-2013, 09:10 PM
#8
Thread Starter
Join Date: Oct 2013
Location: AL
Posts: 37
BTW how did you pull out the spark plugs without looking at the COP boots?
Ordered a couple cheap COPs off ebay to swap around to check for a problem. If I find a bad coil, I'm going to order a quality COP then.
11-06-2013, 03:18 PM
#9
Thread Starter
Join Date: Oct 2013
Location: AL
Posts: 37
Problem found, started pulling plugs just to make sure and the #6 is broke! Now I'm in a worse situation because I can not get it out. I must be completely broke just above the threads and the element is the only thing still connected because it just spins and I can wiggle the top of it with a screw driver but will not come out when pulled on with needle nose pliers.
What do I do now!
What do I do now!