P0304 Help

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Lastplace

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After a door was left open overnight the battery died. I tried jumping it with one of those Halo battery boxes, no luck. Jumped it with a car and it fired up. Within minutes the motor started missing and finally the CEL light came on. P0304, 4th cylinder misfire. This morning I replaced all of the plugs with no improvement, still misfiring. I'm thinking maybe I damaged one of the original coils (218K miles) jump staring the truck? Replace the coils and wires?

Your suggestions are welcomed...

Anybody use the generic coils sold on Amazon? Pack of 3 for $35.
 
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Lastplace said:
After a door was left open overnight the battery died. I tried jumping it with one of those Halo battery boxes, no luck. Jumped it with a car and it fired up. Within minutes the motor started missing and finally the CEL light came on. P0304, 4th cylinder misfire. This morning I replaced all of the plugs with no improvement, still misfiring. I'm thinking maybe I damaged one of the original coils (218K miles) jump staring the truck? Replace the coils and wires?

Your suggestions are welcomed...

Anybody use the generic coils sold on Amazon? Pack of 3 for $35.
Click to expand...

switch the #4 coil with another cylinder and see if the cel jumps with it.If it does then replace the coil.
 
Yeah 1 coil to 2 plugs, so maybe is the answer to will #1 miss along with #4. Many times coils don't go completely out, they work mostly then sometimes occassionally not, hence the 'miss'.

So yeah just swap coils and see if problems travels or stays still. It's most likely a wire, coil or both. Neither are expensive, just take your time. Luck and enjoy that Runner! Go with namebrand stuff like Denso for the coil and NGK for wires, many other good brands of course, just my favs. :cowboy:
 
The number 4 cylinder is the middle cylinder in the LH bank of the engine and has an ignition wire from the cylinder 1 ignition coil going to it. If the coil was bad it should set cylinders 1 & 4 misfire codes. (in theory) Unbolt the coils and with the engine running lift the coils up one at a time to see if the engine stumbles more or no change. You should also hear the sound of the spark arcing into the side of the spark plug tube when you lift it away from the spark plug if the coil is working. If the coil is bad there will be no change when you lift it away from the spark plug. If it starts to skip worse you probably just need a set of wires. You can also pull the wires on the driver's side out with the engine running to see if it skips worse and to see if you can hear the spark. Very unlikely that you have a mechanical or fuel injector problem. If you do replace the coil or coils, spend the money on Denso coils. Napa also has a product line called Altrom which is OEM parts for a reasonable price. (usually in between their premium and economy lines) When you changed the plugs did you use NGK duel ground electrode plugs? Highly recommended! Be careful pulling ignition wires or coils with the engine running, you can get a good jolt if you get your hand near the end of the spark plug boots.
 
Lastplace said:
This engine only has 3 coils, cylinder 1 also charges 4. Does that mean they both would misfire?
Click to expand...

Not necessarily. Yes if bad coil. No, if the wire discharges via short to the block, #1 would fire while #4 would not. And, of course, if the issue is valves, injector, head gasket, etc. only that cylinder would be affected.
 
MaineRunna said:
The number 4 cylinder is the middle cylinder in the LH bank of the engine and has an ignition wire from the cylinder 1 ignition coil going to it. If the coil was bad it should set cylinders 1 & 4 misfire codes. (in theory) Unbolt the coils and with the engine running lift the coils up one at a time to see if the engine stumbles more or no change. You should also hear the sound of the spark arcing into the side of the spark plug tube when you lift it away from the spark plug if the coil is working. If the coil is bad there will be no change when you lift it away from the spark plug. If it starts to skip worse you probably just need a set of wires. You can also pull the wires on the driver's side out with the engine running to see if it skips worse and to see if you can hear the spark. Very unlikely that you have a mechanical or fuel injector problem. If you do replace the coil or coils, spend the money on Denso coils. Napa also has a product line called Altrom which is OEM parts for a reasonable price. (usually in between their premium and economy lines) When you changed the plugs did you use NGK duel ground electrode plugs? Highly recommended! Be careful pulling ignition wires or coils with the engine running, you can get a good jolt if you get your hand near the end of the spark plug boots.
Click to expand...

Actually, bad injectors are reasonably common causes of misfires on our twenty-year old trucks.
 
jgue467 said:
Yeah 1 coil to 2 plugs, so maybe is the answer to will #1 miss along with #4. Many times coils don't go completely out, they work mostly then sometimes occassionally not, hence the 'miss'.

So yeah just swap coils and see if problems travels or stays still. It's most likely a wire, coil or both. Neither are expensive, just take your time. Luck and enjoy that Runner! Go with namebrand stuff like Denso for the coil and NGK for wires, many other good brands of course, just my favs. :cowboy:
Click to expand...

I already took it apart and back together this morning (plugs). Just ordered new NKG wires and one coil. Advanced Auto has a 20% off coupon. At 218k miles I got money’s worth out of the old parts. I’ll try pulling the coil before replacing, I’ll have the replacement handy. Hopefully this will fix it.

Thanks for the help.
 
Last edited:
New plug wires and coil in cylinder 1 and all is well. 2nd time around taken apart, plug wires replaced, coil installed and put back together in 1 hour.

Thanks for the help.
 
Looks like the plugs were due. Well screw it I can't upload the plug pics so I added one of my hot wife.
 

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TheDurk said:
Actually, bad injectors are reasonably common causes of misfires on our twenty-year old trucks.
Click to expand...
I just didn't think a fuel injector was the most likely cause of the misfire here where it went from running fine to a P0304 after a jump start. Been doing this professionally for a while, bought, driven and sold a few 4runners and I've replaced coils to injectors 100:1. One of the most common thing I find on Toyota trucks when they suddenly develop a misfire are carbon tracked spark plugs and coil boots. Usually only see injectors on very high mileage vehicles or ones that sat for a long time without being run.
 
MaineRunna said:
I just didn't think a fuel injector was the most likely cause of the misfire here where it went from running fine to a P0304 after a jump start. Been doing this professionally for a while, bought, driven and sold a few 4runners and I've replaced coils to injectors 100:1. One of the most common thing I find on Toyota trucks when they suddenly develop a misfire are carbon tracked spark plugs and coil boots. Usually only see injectors on very high mileage vehicles or ones that sat for a long time without being run.
Click to expand...

I didn't say most likely, I took issue with your "very unlikely", which might lead a poster to rule it out. 100:1 may be your experience, but I have been active on this forum for over a dozen years, I read every post on 3rd gen diagnostics and it is reasonably frequent and not only in the cases you cite. Certainly nothing like 100:1.

I'd put plugs first, wires second, and coils third. Once you rule out electrical, injectors are the next most common thing.
 
Lastplace said:
I already took it apart and back together this morning (plugs). Just ordered new NKG wires and one coil. Advanced Auto has a 20% off coupon. At 218k miles I got money’s worth out of the old parts. I’ll try pulling the coil before replacing, I’ll have the replacement handy. Hopefully this will fix it.

Thanks for the help.
Click to expand...

Which plug did you get from them? I looked at getting them the other day but they only had the cheap NGK ones in stock,,,they have 3 choices online...oh and when you buy stuff online from them,,,don't buy it right away and leave it in your cart...they'll email you with a new code that takes more off after an hour or so.
 
Plugs as a cause of misfires is very common. It's insane by modern standards, but these factory plugs only last 30k. That's a year of driving for a lot of people. Very easy to get overdue with changing them.
 
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