Hey guys, got a weird issue here. Just changed my spark plugs out and when I took it around the block the CEL came on. It's a 94 f150 4.9L. Old plugged were auto lights that looked like they werent changed in 100,000 miles. I picked up some motor craft coppers and gaped them to .45, installed them, started it up and everything seemed okay. Truck did seem to idle a little high. Took it around the block and CEL came on. I will check the codes tomorrow (it got dark) but I just wanted to see if anyone had any ideas on what could have caused it. Coil, wires, cap, and rotor are all new and all motor craft. When I was installing the new wires last week I noticed on of the plugs was really loose so I pulled it just to see how they looked.

Is it possible that the ECM was just "used" to the extreme gap on the old plugs and the new ones threw it off? I looked over everything thinking maybe I knocked something loose but it's all okay.

Any input is appreciated,thanks.

 

I know if you touched or bumped a 20+ year old nylon line, it will trip the CEL for you. It will no matter how much you think it won't. Those tight bends look fine, but if you look closely, then you'll see the hairline crack from just twisting it.

I'm not saying it's your problem, but most plug changes result or general maintenance can trip the CEL and it could be just a loose wire for sensor or sensors.

 

Pull the codes and see what the computer is complaining about.

 

Just got done pulling codes this morning. Only code stored "332" insufficient EGR flow. So I figured maybe I broke a vacuum line by the EGR when I removed the vacuum bank on the valve cover so I could get to plug #6. But everything looked okay. No leaks found. EGR was replaced a couple years ago so as I was looking it over just to be sure I noticed a gap where it connects to the intake manifold. I could probably fit a quarter in it. I tightened it up nice and snug, took it around the block and no more CEL. Don't see how new plugs would suddenly trip the ECM code 332 but it was probably just coincidence.
Thanks for the input guys.

 

Correct definition for Code 332 (CM): EGR valve opening not detected.

There is no way for the computer (PCM) to measure EGR gas flow, the feedback is position based. I suspect you will find a cracked vacuum line in the EGR circuit that may rear it's ugly head again or the connector to the EGR Valve Position (EVP) sensor was loose.

Glad to see you got it whipped for now!

 

I see, the chiltin manual says insufficient flow. Same thing i guess. All vacuun lines are tip top. I've replaced almost all of the brittle solid lines with rubber. I am picking up a new EGR gasket today just to be safe ( I'm sure the old one got a little burned up)