Hey Guys,

Well, I towed with my truck for the first time this weekend, but I'll save that for another thread.

Right after I bought the truck (about a month ago), I did a tune up on it, plugs, new boots, etc. Soon after that, it started idling rough and the SES came on, P0307 misfire #7 cylinder. I swapped #6&7 COP's to see if #7 was bad, problem cleared up and the truck ran like a top.

Truck ran fine on the way out, fine while out there (California desert) but when we left it started idling rough, the SES came on, same code, #7 misfire. I lifted the hood, wobbled the COP, started it again and it seemed fine. Started to drive back, it started shuddering and hesitating, no SES but when I pulled over I plugged in my code scanner and got P0300 Random Misfire. I swapped 6&7 back and went on my way.

Well, the idle seemed OK, but would get rough occasionally. The truck seemed to run fine, but I noticed with lower RPM's (under 2100) the truck would shudder if I gave it gas. If I downshifted and got the RPM's up, it ran great.

So, the question in this long winded post (sorry) is do I start with he COP's and work my way backwards? Replace 6&7? It now keeps throwing the "random" misfire rather than #7 misfire.

Thanks in advance for the help.

 

I wonder if it's your injector?

 

Thought about that, but wouldn't I get a "lean" code as well if it was an injector?

(Not sure, asking) =)

 

Not sure if you would get a code.

 

I have a bad injector and with 2 bottles of gumout from walmart it clears up, but it has not ever thrown a code or check engine light, its really frustrating because its not quite bad enough for me to work out which one it is, it won't miss consistently.
Gumout is cheap, 2 bottles and 20 miles mine usually comes right.
Andrew.

 

You may want to double check #7 COP harness to make sure you have a good contact .
Good luck.

Ken

 

Update:

Well, It's still running like crap. I hooked it up to the scanner again today, it still shows the "P0300" code, but shows a "pending" code for misfire on #7.

I'm of the mind that there's some sort of issue with #7, gonna start by replacing the COP and see if that clears the issue, I'll move to the injector from there. Anyone have any other suggestions?

 

Pull the plug also to make sure there's nothing wrong with it. New plug could be defective.

 

I have seen plenty of off-the-shelf bad plugs in the past few years. The resistor that is in the plug isn't what it used to be anymore. Change that single plug, replace the plug boot and try again.

If it turns out to be an injector, they can be had on ebay brand new for under $20.

 

I had this exact same issue on my '00 5.4 gasser----drove me nuts looking for a bad part when all along it was a damaged #7 connector. Quick trip to NAPA for their part number EC259 ($20 ea), one helluva time splicing it into the harness (E250 van) and all has been good since.

Seems the locking tabs are easily damaged when changing plugs/COP's or they break due age-----either way just one more thing to test and check.

 

Thanks guys, I'll start by changing the plug (just happen to have a spare set) and go from there.

I'll report back and let everyone know how it goes.

 

Update 2:

Well, I pulled #7 plug. It didn't look too bad, but maybe worse than i thought it should after 700 miles. Cleaned the COP & connectors, cleaned the injector connectors, put everything back together. Started it up, no sputter or anything like that. Took it for a drive around the block, it ran like a top, smooth idle, sounded great.

No SES light, but it still shows a pending code for #7 misfire, will that clear up over time or should I just clear the DTC's?

Not ready to cry victory yet, but things are looking better than they were yesterday!!

 

I would clear the codes and see.

 

+1

If you think you've fixed the condtion then clearing the code is the only way to know if the ECM agrees!

Of course if you effected the repair after 10 times of starting the engine without a code the existing one will clear itself. In the end its easier to clear it yourself and see what happens.

 

Another update: (and hopefully the last on this issue)

Well, cleared the codes and finally got to drive it today. Just drove around town and ran a few errands, truck seemed to run fine. Checked for new codes twice during the drive and when I got home, no codes.

Seems to have taken care of the problem at least for now.

Thanks for all your help guys.