P0308 (Cylnder 8 Misfire Detected)
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From: Stillwater, OK
P0308 (Cylnder 8 Misfire Detected)
1998 Ram 1500 5.2L V8 Automatic 2 Wheel Drive.
I recently cahnged my plugs, wires, oil-0W30 Full Synthetic, oil filter, and air filter.
Arter changing those, cylinder 2 was not firing at all resulting in backfire, and the other expected consequences, and the codes reflected cylinder 2 misfire. I double checked all the plug gaps, and rerouted the wires, then it spred to random multiple cylinder misfire, cylinder 2 misfire, cylinder 6 misfire, and cylinder 8 misfire. I then replaced the cap and rotor, which appeared to fix the problem, despite that both showed minimal signs of wear, and neither showed any damage, tehre was a tiny bit of corrosion on the inside of the cap, but otherwise looked new but dusty. I then cleared all the error codes.
After repalcing those, reconnecting the wires, and and routing them properly, it is now somewhat hard to start, if I turn the ignition, it will crank endlessly. If I turn the ignition, and barely even touch the gas, it starts right up like there was no problem. Additionally, now it runs smoothly, but after driving a while, and nothign is consistent aobut the coditions when it happens, check engine light comes on, and it reports cylinder 8 misfire, but there is no impact on performance at all. If I clear the code, it goes away for a while, and then the same thing. Everything inside apears to be fine, no oil, no foul, no other error codes. The code can appear after driving 57 miles on the highway, followed by another 30 on the highway, and 5 in the city, with a couple stops. It can also appear after driving 15 miles in the city with a few stops. It can also not appear after drivng 20 miles in the city with several stops. The truck is not buring any oil, and is not smoking at all.
Yes, they are the right plugs and wires, yes they are gapped correctly, no I did not overfill my oil, no there is no oil in the tb, yes I checked my wire routing and connections, etc. etc., I am not stupid.
Any ideas?
I recently cahnged my plugs, wires, oil-0W30 Full Synthetic, oil filter, and air filter.
Arter changing those, cylinder 2 was not firing at all resulting in backfire, and the other expected consequences, and the codes reflected cylinder 2 misfire. I double checked all the plug gaps, and rerouted the wires, then it spred to random multiple cylinder misfire, cylinder 2 misfire, cylinder 6 misfire, and cylinder 8 misfire. I then replaced the cap and rotor, which appeared to fix the problem, despite that both showed minimal signs of wear, and neither showed any damage, tehre was a tiny bit of corrosion on the inside of the cap, but otherwise looked new but dusty. I then cleared all the error codes.
After repalcing those, reconnecting the wires, and and routing them properly, it is now somewhat hard to start, if I turn the ignition, it will crank endlessly. If I turn the ignition, and barely even touch the gas, it starts right up like there was no problem. Additionally, now it runs smoothly, but after driving a while, and nothign is consistent aobut the coditions when it happens, check engine light comes on, and it reports cylinder 8 misfire, but there is no impact on performance at all. If I clear the code, it goes away for a while, and then the same thing. Everything inside apears to be fine, no oil, no foul, no other error codes. The code can appear after driving 57 miles on the highway, followed by another 30 on the highway, and 5 in the city, with a couple stops. It can also appear after driving 15 miles in the city with a few stops. It can also not appear after drivng 20 miles in the city with several stops. The truck is not buring any oil, and is not smoking at all.
Yes, they are the right plugs and wires, yes they are gapped correctly, no I did not overfill my oil, no there is no oil in the tb, yes I checked my wire routing and connections, etc. etc., I am not stupid.
Any ideas?
Administrator
Joined: Apr 2010
Posts: 87,548
Likes: 4,230
From: Clayton MI
What plug wires did you put on there? (brand, diameter)
How many miles on the truck?
Have you looked into your plenum?
Possible cat going bad? (that will give you a cylinder 8 misfire when it starts to go....)
Is it just cylinder 8 now?
Have you pulled the TB, and cleaned the IAC valve, and passages?
How many miles on the truck?
Have you looked into your plenum?
Possible cat going bad? (that will give you a cylinder 8 misfire when it starts to go....)
Is it just cylinder 8 now?
Have you pulled the TB, and cleaned the IAC valve, and passages?
Grand Champion
Joined: Apr 2010
Posts: 5,011
Likes: 6
From: Meeker, CO
If they'll go, swap the #8 and #6 wires (on both ends, of course) and swap the #8 plug with #4. See if the misfire follows the wire to #6, the plug to #4, or stays with #8.
You won't necessarily perceive the misfire that sets the code, as it's a threshold of x% misfires over y time -- I don't know the actual values, or at least don't remember them and am feeling too lazy at the moment to go digging around.
As HeyYou said, a failing cat will show up in cylinder 8 first -- it's closest to the cat and eats the most heat when the cat begins to plug, which is what makes our Magnum heads infamous for dry cracks.
A partially plugged or lazy injector could cause a single cylinder misfire, too. If nothing else proves out, you might swap #8 out with another and see if it follows the injector. Just be careful of those o-rings. And of course that old plastic in the connectors that's just lying there waiting for an excuse to break.
Welcome to the forum!
You won't necessarily perceive the misfire that sets the code, as it's a threshold of x% misfires over y time -- I don't know the actual values, or at least don't remember them and am feeling too lazy at the moment to go digging around.
As HeyYou said, a failing cat will show up in cylinder 8 first -- it's closest to the cat and eats the most heat when the cat begins to plug, which is what makes our Magnum heads infamous for dry cracks.
A partially plugged or lazy injector could cause a single cylinder misfire, too. If nothing else proves out, you might swap #8 out with another and see if it follows the injector. Just be careful of those o-rings. And of course that old plastic in the connectors that's just lying there waiting for an excuse to break.
Welcome to the forum!
