High RPM misfire - Dodge Challenger Forum: Challenger & SRT8 Forums
 
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post #1 of 9 (permalink) Old 03-10-2019, 02:37 PM Thread Starter
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Angry High RPM misfire

2012 392 93 octane Shell gasoline, with 16k miles on it. According to my time slips I've lost about 200 horsepower to "something" over the 2018 season.

Plugs are fouled, thick brown spoo. Needs to be changed what I need to know is can I put in the 5.7L 26.5mm plugs and clear the glass pistons? It really looks like it needs a hotter plug.

In searching for clues I came across a cracked Idle fuel injector, injector O-rings drying out, coil pack for #7 due to heat. Now reaching there is weak valve springs because lets face it, I'm shifting at 5800 to 6k and the rev limiter is at 6200.

I am pretty sure if the CEL is on, the ECU pulls timing no matter what.

So plugs will be changed one way or another next month. so does anyone know where to look for the raw misfire data / counter in the ECU?
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post #2 of 9 (permalink) Old 03-12-2019, 02:22 PM
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All of your plugs are fouled? Are you stock? What kind of change on your time slip? Engine compression?

2012 SRT automatic, PB 12.0490 with MT drag radials and trinity 93 octane tune.
PB [email protected], Magnuson supercharger 5.5psi, forged piston/rods, Hellcat injectors, 10/1 compression, tuned for 90 octane.
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post #3 of 9 (permalink) Old 03-12-2019, 02:27 PM
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Also what tuner are you running...HP tuners, Diablo trinity...or are you using a generic OBD scanner?


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2015 Challenger RT+ (non-STP)
8lb Magnuson w/ Innovate PSB-1 wideband/boost/shift light gauge
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post #4 of 9 (permalink) Old 03-12-2019, 03:28 PM Thread Starter
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All sixteen plugs have brown fouling that impedes function. It gets a steady diet of Shell 93. So I am surprised they fouled out so quickly. The engine is totally stock since it was under warranty until just now. Its had all the oil changes, injector and coolant flushes in the OM on time or slightly early.

The car slowed down from a 12.3 qtr to a 13.9 qtr so in theory it lost 200HP. Since the CEL is on my thinking is that the ECU is pulling timing, causing incomplete combustion and thus the fouling. There is still salt on the road so its not moving until the next rain storm.

Factory tune; Actel scanner / code reader.
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post #5 of 9 (permalink) Old 03-12-2019, 05:18 PM
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Originally Posted by skypilot View Post
All sixteen plugs have brown fouling that impedes function. It gets a steady diet of Shell 93. So I am surprised they fouled out so quickly. The engine is totally stock since it was under warranty until just now. Its had all the oil changes, injector and coolant flushes in the OM on time or slightly early.

The car slowed down from a 12.3 qtr to a 13.9 qtr so in theory it lost 200HP. Since the CEL is on my thinking is that the ECU is pulling timing, causing incomplete combustion and thus the fouling. There is still salt on the road so its not moving until the next rain storm.

Factory tune; Actel scanner / code reader.

I would not install hotter plugs. The plugs are fouling because there's a problem. Not because they are too cold.


You sure the gas is not stale? 93 goes off pretty quick. If the car has sat over the winter that gas needs to be used up by driving the car -- but *not* at the track -- or siphoning out the old fuel and putting in fresh fuel.



What is the error, or codes, associated with the CEL? Read active, pending codes. Get the freeze frame data and code. That's the one that triggered the CEL.
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post #6 of 9 (permalink) Old 03-12-2019, 06:58 PM Thread Starter
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The gas changes every week or less so once the salt is washed away this tank will go quick. The code is P0300 and its a stored or permanent code now, it just reset itself during warmup session. I fill the tank just before the first snow so I can run & jog it, till spring. So the present gas is three months old.

It has to go to the dealer for a Takata airbag recall. One of the guys there is pretty sharp, so I will have him vacuum the ECU and zero it out. The track opens in mid-April, so it will have fresh plugs, gas, oil, and air filter.

I'll have to go a back road to collect some freeze frame data.

Last edited by skypilot; 03-12-2019 at 07:00 PM.
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post #7 of 9 (permalink) Old 03-12-2019, 07:12 PM
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Got pics of the plugs? Trying to think what can cause "thick brown spoo"? Is it like #7 in link below?

https://www.ipdusa.com/techtips/1008...ur-spark-plugs
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post #8 of 9 (permalink) Old 03-13-2019, 09:12 AM
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The gas changes every week or less so once the salt is washed away this tank will go quick. The code is P0300 and its a stored or permanent code now, it just reset itself during warmup session. I fill the tank just before the first snow so I can run & jog it, till spring. So the present gas is three months old.

It has to go to the dealer for a Takata airbag recall. One of the guys there is pretty sharp, so I will have him vacuum the ECU and zero it out. The track opens in mid-April, so it will have fresh plugs, gas, oil, and air filter.

I'll have to go a back road to collect some freeze frame data.

As I said 93 goes off pretty quick it could have gone off in 3 months.


In a Hellcat this could easily account for the feeling the engine lost "200hp".



91 gasoline went stale in around 6 months in my sister's Infiniti. Engine started and idled ok. Car ran ok but the engine felt flat.


Being unfamiliar with the vehicle I just assumed it was a dog. But after the fuel tank got low and I refiled it with fresh Shell V-Power 91 which is what she used the engine was transformed. It was not a dog at all. The gasoline had just gone stale.


The P0300 is random multiple misfire fault codes. That a sign of a systematic problem. I'm liking "bad" gasoline more and more.


While the P0300 is now "permanent", after so many warm up cycles provided no more misfires the engine controller will then erase the code. In the meantime you should be able to clear it from active status and extinguish the CEL. However, if the light comes back with that code as the reason then the engine controller is detecting random multiple misfires.


If you continue to drive the car I would not push the engine hard until you have run the fuel tank level down to say around 1/4 tank and then had a chance to refill it with fresh 93 octane gasoline.


I'd replace the plugs with new factory recommended plugs unless you have a "tune" and the manufacturer of this has another plug recommendation.
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post #9 of 9 (permalink) Old 03-13-2019, 10:27 AM
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I'd tend to agree with the Guys here that it sounds like bad gas. What does the gas smell like and what color is it? It it has kind of foul, stale odor to it, then I'd change it. I've actually learned that the best way to fix something is to start with the simplest solution first.

My Lovely Wife actually taught me this after a TV problem came up and I tried to diagnose it and while trying to think of every possible solution, I found that the problem was it wasn't plugged in. Sometimes I'm not the brightest crayon in the box and in the words of Homer Simpson........DOH!!

P0300 is a generic code that might have been set off by the bad coil causing a misfire. I'd start by changing/fixing the injector/o-rings and the #7 coil pack first and then clear the code. Those parts being bad could cause that code to be thrown. I'd then clear the code and then drain and refill the gas tank and then see how she runs. It might take more than one good tank of gas to clean things up because gummed up gas is nasty on fuel injectors. They have some tight tolerances. The Shell gas is good too because of the amount of detergents in it.

Good Luck and Please let us know what you find out.
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