Throwing P0300 code

[JHC14]

I had the local AutoZone pull codes today as the Check Engine light has come on.
It threw up a P0300 which says it is a misfire. It also said to check the "Engine Valley Cover". I was not aware I had a valley, much less a cover for the valley.
From reading here, it seems several have had a misfire when water gets on the engine and corrodes a spark plug. I changed my plugs out about 6 weeks ago. One of them had signs of a little water getting to it. It was not terrible and not enough to make the CE light come on.
I was at 100k miles so I replaced all my plugs. The plug closest to the firewall had signs of water. I put in a new plug, the original coil pack back on, and the engine cover back on and went on with life. It has been running a bit rough, but nothing terrible. Averaging 20-21 mpg
Is there a way to discover if this is the problem?
I was wondering if I could purchase one coil pack and replace #4 and see what happens. If it doesn't help shift the old #4 to the #3 spot and see if it gets better or worse and keep trying till I see if there is any improvement.
Would this work or do I just replace all four or even worse take it to the Dealer? Of course, this happens the week before vacation so I need to get this fixed quickly.

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[deleriumtremor]

I believe P0300 is a random misfire (versus say P0301), so my guess would be a problem with the new plugs.

 

[RangerBill]

I had the local AutoZone pull codes today as the Check Engine light has come on.
It threw up a P0300 which says it is a misfire. It also said to check the "Engine Valley Cover". I was not aware I had a valley, much less a cover for the valley.
From reading here, it seems several have had a misfire when water gets on the engine and corrodes a spark plug. I changed my plugs out about 6 weeks ago. One of them had signs of a little water getting to it. It was not terrible and not enough to make the CE light come on.
I was at 100k miles so I replaced all my plugs. The plug closest to the firewall had signs of water. I put in a new plug, the original coil pack back on, and the engine cover back on and went on with life. It has been running a bit rough, but nothing terrible. Averaging 20-21 mpg
Is there a way to discover if this is the problem?
I was wondering if I could purchase one coil pack and replace #4 and see what happens. If it doesn't help shift the old #4 to the #3 spot and see if it gets better or worse and keep trying till I see if there is any improvement.
Would this work or do I just replace all four or even worse take it to the Dealer? Of course, this happens the week before vacation so I need to get this fixed quickly.

If you took the spark plug out nearest the firewall (or removed its spark coil) you may not have gotten the spark coil completely back onto the plug, causing a poor connection to the plug. That one is difficult to fully seat on the plug because of the obstacles around that plug. Double check that plug's coil. I would also check all the plugs to make sure that the spark coils are fully seated onto the plugs.

If there was significant water infiltration into the plug wells, the spark coils or boots may be damaged and need replacing. A careful visual inspection of these should be done.

 

[Rp930]

You can certainly swap coils to diagnose it.

 

[JHC14]

If you took the spark plug out nearest the firewall (or removed its spark coil) you may not have gotten the spark coil completely back onto the plug, causing a poor connection to the plug. That one is difficult to fully seat on the plug because of the obstacles around that plug. Double check that plug's coil. I would also check all the plugs to make sure that the spark coils are fully seated onto the plugs.

If there was significant water infiltration into the plug wells, the spark coils or boots may be damaged and need replacing. A careful visual inspection of these should be done.

The plug by the firewall was difficult to get reseated. I think I got it put back correctly. I have put 8,000 miles (plus or minus a few) on it since changing the plugs.
Shouldn't it have shown up as a misfire much earlier if it wasn't seated good?

 

[JHC14]

I believe P0300 is a random misfire (versus say P0301), so my guess would be a problem with the new plugs.

The problem was probably more with the plug installer than the plugs themselves. ?

 

[RangerBill]

The plug by the firewall was difficult to get reseated. I think I got it put back correctly. I have put 8,000 miles (plus or minus a few) on it since changing the plugs.
Shouldn't it have shown up as a misfire much earlier if it wasn't seated good?

All I can say is double check your work.

 

[JHC14]

All I can say is double check your work.

It was double and triple-checked, but without being able to see down in there how can we really know? It seemed to be seated good, I thought it was seated good. It felt like it was seated good...maybe it wasn't seated good. ??

 

[deleriumtremor]

It was double and triple-checked, but without being able to see down in there how can we really know? It seemed to be seated good, I thought it was seated good. It felt like it was seated good...maybe it wasn't seated good. ??

I was thinking along the lines that you may have gotten some knockoffs, etc. A while ago there were a few forums people were complaining about fake brands. If I recall the way people were nailing it down were the gaps being all over the place out of the box. Also subtle mistakes on markings, etc.

Good luck.

 

[JHC14]

I was thinking along the lines that you may have gotten some knockoffs, etc. A while ago there were a few forums people were complaining about fake brands. If I recall the way people were nailing it down were the gaps being all over the place out of the box. Also subtle mistakes on markings, etc.

Good luck.

I read those same threads. It convinced me not to get them off Amazon. I got mine at AutoZone. They were Motorcraft brand. I picked them up at the local store. I hope they were not knockoffs.

 

[shovelhd]

You can certainly swap coils to diagnose it.

^^^this

Swap #3 and #4. If the code changes, that's your issue. I'm not familiar how Ford coil packs are wired, but most have a wiring connector. Unplug them one at a time. The engine should throw a code and run like crap each time. The one that doesn't is the problem cylinder. Also, if there was water and rust in the #4 spark plug hole, you might have a ground problem.

 

[airline tech]

You have to do a Live Data - Monitor and see which cylinders are picking up a misfire, as a P0300 is multiple cylinders and can be a list of numerous things that will trigger that code.
With 8,000 miles since plug R&R, and not showing an individual cylinder. I suspect something other than a single coil or plug.
However, if the misfire is bad enough a single cylinder misfire can be picked up across 2 cylinders via the Knock Sensors.

1st question - Are you losing Coolant?
2nd question - Did you Torque the Plugs to Specs?
3rd question - Did you do anything else, when you replaced the plugs?

I would do a Live Data monitor and double check all the plugs and cop connectors, if all that is good - a deeper check is required for possible vacuum leak or injector control issue.
The vacuum leak - is where the Scan Tool is a generic statement - Check Engine Valley Cover (Aka) Intake Manifold is referencing as a blanket statement.
A Live Data Monitor is NEEDED, without it you are just throwing darts blindly.

 

[JHC14]

You have to do a Live Data - Monitor and see which cylinders are picking up a misfire, as a P0300 is multiple cylinders and can be a list of numerous things that will trigger that code.
With 8,000 miles since plug R&R, and not showing an individual cylinder. I suspect something other than a single coil or plug.
However, if the misfire is bad enough a single cylinder misfire can be picked up across 2 cylinders via the Knock Sensors.

1st question - Are you losing Coolant?
2nd question - Did you Torque the Plugs to Specs?
3rd question - Did you do anything else, when you replaced the plugs?

I would do a Live Data monitor and double check all the plugs and cop connectors, if all that is good - a deeper check is required for possible vacuum leak or injector control issue.
The vacuum leak - is where the Scan Tool is a generic statement - Check Engine Valley Cover (Aka) Intake Manifold is referencing as a blanket statement.
A Live Data Monitor is NEEDED, without it you are just throwing darts blindly.

So, basically take to someone who has a diagnostic machine? I sure don't have a Live Data machine, but I agree. It may be something much deeper than just a bad plug or a faulty coil pack.
I haven't noticed any coolant leaking out, but I will check it again.
I did change the oil at the same time I did the plugs, but I don't think that would have anything to do with it.
But, now that you mention it, I also changed the EGR DPFE sensor not too long after I did the plugs. I bought it from a local dealer.

I will probably try swapping a few coil packs or taking one off and see how it goes. It can't hurt to much before taking it to a mechanic with a machine to see what he can pull on it.

I appreciate the advice.

 

[JHC14]

Well, the saga continues.... on Thursday the CE light just went away. I turned the truck off for about 90 minutes. When I pushed the start button, the light was not on. It had been on for 5 days but now it's gone. So, what the heck does that mean? It is not misfiring anymore? Did a bad spark plug heal itself? Has the coil pack that was having issues get therapy?
How can I truly fix this now? It has done this twice now. Both times on an extended trip. The first time was 1 week after changing the plugs. It was after 4 hrs of driving (light stayed on for 100+ miles) and this time after 3 hours of driving (stayed on for 4 more days).
Could it be something besides the plugs, the computer or something else much more expensive?

 

[dtech]

Well, the saga continues.... on Thursday the CE light just went away. I turned the truck off for about 90 minutes. When I pushed the start button, the light was not on. It had been on for 5 days but now it's gone. So, what the heck does that mean? It is not misfiring anymore? Did a bad spark plug heal itself? Has the coil pack that was having issues get therapy?
How can I truly fix this now? It has done this twice now. Both times on an extended trip. The first time was 1 week after changing the plugs. It was after 4 hrs of driving (light stayed on for 100+ miles) and this time after 3 hours of driving (stayed on for 4 more days).
Could it be something besides the plugs, the computer or something else much more expensive?

Of course it could be a number of things, misfire codes can clear , you could have a bad ignition coil that occasionally has shorts in the secondary windings, if so be patient and it will expose itself

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