98 Expe EB 5.4 - Last week I changed out all the COP's. Noticed an improvement right away. It was slightly rough between 1200-1500 rpm before the change. Now that went away. Throttle response felt a bit better. Well last night the wife says its running real rough and the whole truck shakes when driving. Today I start it up and notice a rough idle and I took it for a drive and yes the truck shakes slightly when driving. It feels like one cylinder isn't firing. When I blew a spark plug a couple of years ago, the truck drove the same way. Its just not making the loud popping sound it made from not having a spark plug in the hole. I rechecked all the connections. All COP plugs are tight. All injector plugs are tight. I checked all the hoses where I had to squeeze my hands through to make sure I didn't crack or disconnect any. They are all good. For a few seconds I thought I smelled fuel while I was looking at the passenger side. I couldn't see any leaks. The smell went away, though. New COP's are Accel from Summit. There is no CEL so far. I don't know if I should take it for a drive until one pops up. I don't feel comfortable driving it. Any thoughts, suggestions?

 

I unplugged 4 injectors 1 at a time to see if I noticed any changes. The engine still had the same rough idle each time. Maybe its there is some other problem.

 

What about the other 4?

 

Not sure I understand what happened, but I did the rest of the injectors and didn't notice any change. Then I did the COP plugs 1 at a time and they each ran worse. I unplugged some of the vacuum hoses and those made it worse too. I'm just flying blind right now doing random things.

 

OK, sometimes I'm a dummy. I was shutting the truck off as I unplugged each connection. then restarting every time. I just went out and checked each connection with the motor running the whole time. Every one got worse till I got to #8. That stayed the same. I pulled the new COP and put an old one back in. Truck sounds fine now. Only now the CEL came on. I'm guessing it was gonna come up because of the bad COP. I disconnected the battery. I'll hook it up in an hour and check it again.