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Check Engine Light Flashing

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Hope somebody can help. My 2005 Ram 1500 Hemi had a check engine light on. 68K miles so I put in iridium plugs and new wires. Then the engine light started flashing and truck ran poorly, tach jumping around. Then I read here that I should have used stock plugs. So I replaced the plugs with standard Champions. But I still occasionally have a flashing engine light and poor running. This seems to only happen when the truck is cold and once warmed up, the problem goes away. Does anybody have an idea what could be wrong. I've also read here that maybe I should unhook the battery and reset the computer. Thanks for any help.
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A flashing check engine light is bad. You shouldn't drive the vehicle. You need to get the codes and post them here and we can help you.

P0420 means catalytic efficiency below threshold. Either one of the downstream O2 sensors is faulty, the connection or wiring is faulty, or the catalytic converter is faulty.
 

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Ya the code i got was 0420. The guy i got off said that its because he put regular gas in it. He says i needed to run with 89 octane becasue of the emisson is that why its on?
No that's not correct.

How many miles are on the truck? Any running issues at all? If it's running poorly it's probably a clogged/faulty catalytic converter. If it runs fine it's probably a bad sensor.
 

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What's a km????? :)

That's roughly 100,000 miles and that's a fair amount of mileage. It is possible the sensor is faulty. Also possible the cat is clogged.

If it's running fine I'd try the sensor. Although you don't really need to replace them if it is running ok and the light doesn't bother you too much. It's just an emissions thing, it doesn't effect the truck in any other way. Now, if the truck starts running poorly it could be a clogged cat.

I'd guess a new downstream sensor is ~$50 to $100.
 

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^it depends. If it's an upstream O2 sensor then yes it will effect mpg. But your code is a downstream O2 sensor, which has no effect on anything except monitoring emissions.
 

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Changing the muffler or adding a cutout will not effect the engine light.

An 05 hemi ram should get somewhere around 15mpg avg.

P0420 signifies a downstream(post cat) sensor. It could be either side if there are two(probably is two). It's either the sensor(s), the cat(s), or a wiring/harness issue.

There are other possibilities but unlikely. An exhaust leak, coolant leak(into the engine), etc can cause this. But if you don't have any running issues they are highly unlikely.
 

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that'd be my guess. Best place to start is to inspect the harness to look for frayed wires or loose connections. Disconnect and reconnect the downstream sensors and see if that helps. You can also clear the code and see if it comes back.
 

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I'm sure you can find the exhaust pipes right? Crawl under there and trace the exhaust pipes all the way from the engine to the muffler. I'm pretty sure on your truck you will have 2 exhaust pipes(one on each side of the engine) that lead to a y pipe where they merge in to 1 pipe and then go off to the large muffler. Somewhere between the engine and y pipe you probably have 4 O2 sensors and 2 catalytic converters. You probably have an O2 sensor in each exhaust manifold near the engine(upstream sensors) then an O2 sensor in or just behind each catalytic converter. You want these sensors that are at or just behind the catalytic converters. It should be self explanatory how to unclip the connectors.
 

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you should get a turn down pipe and clamp or weld it on and direct the exhaust down and if possible out from under the truck. Yes it will get in the cab if you sit still.
 

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A muffler only reduces sound level. it is very dangerous to breathe exhaust fumes(one of the stars from the show "buck wild" and some of his friends/family just died from this while mudding, actually). I don't know exactly what happened but I'd guess there was exhaust leaking into the cab(windows up since mudding) and they all passed out in the cab. Your body doesn't get enough oxygen and you pass out and eventually die.

Not having a muffler has no effect on this. What's important is to keep the exhaust out of the cab. Many people "dump" the exhaust under the bed, just use some common sense. Try to at least point it away from the truck.
 

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P042 is not a real code. Do you mean P0442? Or P0420?

P0420 should have no effect, assuming the problem is not a clogged cat.

P0442 could have an effect, as there is a leak in the EVAP system.
 

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sorry man I'd have to do some math to convert km to m and I do math all day so when I get home that's the last thing I want to do lol. But if you get 15-17 average mpg that's about right. I've known quite a few people with 3rd gen hemi rams and that's about right. A good friend bought a used one last week, quad cab, 2wd, hemi, with mds, and he's getting 17 mpg average but it's more highway.
 

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msd is a brand of ignition, it stands for multiple spark discharge.....

but MDS(the thing I was talking about) is the "4 cylinder mode" on newer hemi's. Allows them to get better economy.
 
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