Multiple misfires on 4.7L

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inkedmongo

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Sep 24, 2014
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Ram Year
2003
Engine
4.7L
I have an 03 4.7L with 139k miles on it. I purchased the truck with a misfire problem and the previous owner has replaced the following: TPS, Idle air control, Cam position sensor, Crank position sensor, COP for cylinder 1 (showed a code before) and spark plugs

When I start the truck I have to give it gas and I have to keep my foot on the gas for it to stay running. It gives off a strong gas smell and misfires badly.

We have sprayed around the intake with carb cleaner to check for leaks, checked all vacuum linee, and the only code showing is P0300 for multiple misfire.

While I had my friend holding his foot at a steady rpm I began to unplug from the COP's and the only cylinders that reacted to being unplugged was cylinders 6 7 and 8 . Next we hooked up a spark tester to cylinder 1 and it showed it was receiving spark when cranked over. At that point we pulled the plug and it shows black on the plug but when checking for spark outside of the cylinder it fired with both old and new COP.

I guess my first question would be if this is a fuel related issue as to where an injector isn't working properly would it kill the spark to that cylinder?

The only things that have not been checked yet is the fuel pressure and a compression test. I think with what I am experiencing that having low compression in 5 cylinders would be a slim chance? I am showing no coolant oil mixtures, no leaks from the engine, no oil or water in spark plug holes.

I am completely boggled at what's causing this and fearing its going to come down to taking it to a mechanic or a stealership.

Any knowledge and suggestions on this would be very helpful and if I forgot any information or have any questions please feel free to ask because I could be looking over anything simple as we all do at some point.
 

xb1230

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2020
Engine
5.7 HEMI
You have done much of the homework required to get to troubleshoot this code.

So the next step as you stated would be to test for Fuel Pressure. (You can also have a look at the Fuel Filter, especially if has never been changed it could cause low fuel pressure issues, then the fuel pump could also be a culprit if you find you have too low fuel pressure)

Really bad injectors are a possible cause of misfires. Check for Power to the injectors before replacing them. If the signal to "spray" gas into the combustion chamber does not get to them then you could have a PCM/ECM issue which would be the next thing to check.

I am not aware of any real way to test the PCM/ECM than connecting them to a Dealership troubleshooting tool or just getting a replacement and do a swap. (If someone has tips on this please chime in!)

I would still run a compression test even though as many cylinders low pressure is unlikely you could be facing Head Gasket issues or worst broken off valves/rocker arms/Lifters which is not uncommon on these high mileage 4.7L.

Hope this helps
 

JPT

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2015 Big Horn
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5.7 Hemi
When I had a jeep, I was chasing down an intermittent misfire for years. Turned out to be a hardened o-ring on cylinder 3's injector. Once I put in the new o-ring, all problems went away. Maybe not your problem, but something easy to check.
 
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inkedmongo

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2003
Engine
4.7L
Well I wanted to update everyone on what the problem was and thank those that replied. Mechanic found absolutely no compression on cylinder 2 (burnt valve.) I was quoted quite a bit to fix it, or I could have fixed it myself for around 6-700 dollars for parts and my own labor but being in Oklahoma, and hearing about cold weather coming in harsh this winter, I went ahead and sold the truck and picked up something else.

Thanks again for the help you guys.
 

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