Running rough under a load.

[Bob 03]

My truck runs rough under a load. I got a code of 0300 say several miss fires. Not sure witch ones are doing that. Can someone maybe help? thanks Bob

 

[Fast69Mopar]

My truck runs rough under a load. I got a code of 0300 say several miss fires. Not sure witch ones are doing that. Can someone maybe help? thanks Bob

There are several things that can cause a P0300 Multiple Cylinder Misfire. Most of the time P0300 is accompanied by a single cylinder misfire DTC as well. When it is just P0300 by itself it makes it hard to diagnose without a scan tool but there are some things that you can do without a scan tool to eliminate some of the things that may be causing the misfire.

First things first, what is the condition of the spark plugs? Have they ever been changed in the time that you have owned the truck?

What RPM does the engine begin to run rough? Above 3000rpm, below, etc?

How long has this been going on?

Next, check the condition of all of the vacuum lines. A vacuum leak is one of the most common causes of a P0300 because a vacuum leak can affect every cylinders performance.

Had the motor ever had any major mechanical repairs?

I need some more info to help you out. Lemme know brother.

 

[Bob 03]

It seems to happen more on the lower side. I have not put any plugs in it. Just checked one look good. Let me tell you what I did to it. I tried to replace the stock wires with talyor short ones. It did not like them. Put new stock ones back on it. The truck just has not run right since then. I will check for any bad lines.

 

[Bob 03]

It is a coply of the one message.

 

[Bob 03]

To many messages.

 

[Bob 03]

It seems to happen more on the lower side. I have not put any plugs in it. Just checked one look good. Let me tell you what I did to it. I tried to replace the stock wires with talyor short ones. It did not like them. Put new stock ones back on it. The truck just has not run right since then. I will check for any bad lines.

 

[Fast69Mopar]

It seems to happen more on the lower side. I have not put any plugs in it. Just checked one look good. Let me tell you what I did to it. I tried to replace the stock wires with talyor short ones. It did not like them. Put new stock ones back on it. The truck just has not run right since then. I will check for any bad lines.

Are you sure you have the plug wires back in the correct location? Do you have a diagram for the plug wires?

The way they are installed is as follows:

1/6
2/3
4/7
5/8

 

[Redtruck-VA]

A P300 code is determined by a minute change in rotational speed monitored by the crank sensor and if I remember correctly with engine temp above 160 degrees and rpm's above 1800rpm. Typically a cylinder is identified by the cam sensor. In your case my money is plugs need to be replaced. Standard gap is .044", if you have performance adders then you requirements will change.

 

[Fast69Mopar]

A P300 code is determined by a minute change in rotational speed monitored by the crank sensor and if I remember correctly with engine temp above 160 degrees and rpm's above 1800rpm. Typically a cylinder is identified by the cam sensor. In your case my money is plugs need to be replaced. Standard gap is .044", if you have performance adders then you requirements will change.

You are correct in that engine temp has to be above 160° and the engine above 1800rpm.

 

[Redtruck-VA]

You are correct in that engine temp has to be above 160° and the engine above 1800rpm.

Thanks for confirming that, back in the good ole bad days of trying to tune the 03's misfires were common mostly associated with big cams. This was before it was recognised that swapping 05 pcm was the fix...

 

[Bob 03]

It did get hot. My fan clutch is bad and I just got one. I will replace the plugs all so.

 

[LeesEvoX]

It did get hot. My fan clutch is bad and I just got one. I will replace the plugs all so.

Is there a way to tell when the fan clutch goes bad?

Sent from my SM-G950U using Tapatalk

 

[Bob 03]

I seen mine just not turning much at all. When it was not running you could speen it like it was nothing. Plus it was leaking some oil.

 

[Bob 03]

I have no performance items on it. All stock.

 

[Bob 03]

Replaced the fan clutch and it temp runs 160.

 

[Bob 03]

Replaced all the plugs and coil packs. It runs great. Thank for the help.

 

[LoneWolf3574]

Is there a way to tell when the fan clutch goes bad?

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Take a rolled-up newspaper or magazine and try to stop the rotating fan with it. Just don't put your hand in there, whatever you do.

Replaced the fan clutch and it temp runs 160.

That seems a bit cold, the stock thermostat is 203F and there is 180F out there for those that want them. At 160F you are going to be running really rich, end up having fouled plugs, and garbage for fuel economy as the PCM is going to dump extra fuel in to get the engine up to temperature.