P0305 Mis fire on #5 cylinder

[Monsoon]

Hey Gang:
I've been on X-mas vacation and traveling through the Rocky Mountains when I got a P0305 MIL. I did some research about the P0305.

When I got my P0305 MIL the engine wasn't under a load, I was going down the back side of a hill foot off of the accelerator.

Since I was traveling I got gas at various locations.

I want to get to the root cause why the P0305 tripped.

Only thing I can think of right now is bad gas (water in fuel), the coil pack or vacuum leak.

Right now I'm thinking vacuum leak or intermittent coil pack. If it is a vacuum leak can anyone give a list of the top 10 locations to check on a 1997 Duratec engine?

My Motorcraft spark plugs have 30K miles on them. Thanks.

Monsoon

[sheila]

Vac. leak(s) should trip po171/174 lean codes. Most common 1 on your eng. is the upper u-shaped pcv hose directly under the throttle body. Check/replace plug(s), wire(s) or coil for misfire code(s).

[Jeff K]

Do you have a scan tool with you that will show fuel trims? If so, they will tell you if you have a vacuum leak or not.

[Breeves002]

Well it probably isn't a coil because coils either don't work at all, or have issues under load. It would probably miss under load as well if it was a coil. (or am I wrong?)

I agree check fuel trims, but you probably don't have a vacuum leak if you don't have the P0171/141 like Sheila said.

Go ahead and read the misfire sticky, should help you out: How to Understand and Diagnose Misfires

[behlinla]

PCM runs a misfire check when you're coasting. It would probably be fuel or vacuum related.

[Monsoon]

Originally Posted by behlinla

PCM runs a misfire check when you're coasting. It would probably be fuel or vacuum related.

behlinla:
I think you nailed it. I've cleared the P0305 code and it hasn't returned. I'm going to look for the elbow piece beneath the throttle body and check for cracking / dry rot. Thanks gang.

Monsoon