Misfire on cylinder 5 - p305

[junker68]

We recently bought a 2002 Mountaineer, 4.6, 120,000 miles.
It has developed a misfire in cylinder 5 and a rough idle while stopped in traffic. There does not appear to be any issues such as a loss of power or performance other than the idle. There may be an issue but I do not notice it when driving, other than stopped in traffic.

So far I have done the following:

Changed the sparkplug in cylinder 5, along with the coil pack and injector - I used Motorcraft on all parts except for the Spark Plug where I used Autolite - Platinum.

Fixed a few vacuum hoses which were in need of repair. I added a can of Seafoam through the tank.

I cleaned the IAC and the MAF.

The IAC was cleaned twice and each time I cleaned it, the rough idle subsided, but did not disappear. The cel light would return in a day or so, when the idle got back to original "roughness."

I was thinking about buying a new Motorcraft IAC, but I wanted to run it by the fine people on the forum first.

Can a bad IAC cause a misfire in a specific cylinder?. Wouldn't it effect the entire engine? From reading past posts, it appears that people who have solved idling issues by replacing the IAC did not really have the same symptoms as me.

Thanks for reading this long post and thanks in advance for any replies.

Dwayne

 

[Number4]

I'd suggest doing a compression test on the engine.

 

[lincolnshibuya]

+1 on the compression test, a worn out piston ring or a leaky intake/exhaust valve could cause a misfire on a specific cylinder.
A bad IAC can cause stalling when you release the gas such as in turns or when stopping, IMO it doesn't cause misfire to a specific cylinder.
I hate to say this but I don't really trust seafoam, my cars don't use this snake oil sold in parts store. Try gum out fuel system cleaner, my 01 cougar developed a misfire on cylinder 4 and 5 every 3 days of driving and I have replaced the coil pack, plugs and wires with no effect. A bottle of it in the fuel tank eliminates the misfire. You could try that before doing the compression test. I believe my intake or exhaust valves are carbonized really bad. BG44K is also a good fuel system/induction cleaner, used by dealerships and not sold in parts store.
Don't let you engine misfire for too long, it will ruin the catalytic converters.

 

[fritz24]

IAC will not cause a misfire, neither your MAF. If compression test checks out fine, suspect the gasket on the intake manifold specific to that cylinder is leaking.

 

[junker68]

Thanks everyone...

I went to do a compression test, but my tester, an old fashioned one - probably about 40 yoa, didn't work so I bought one on Amazon, waiting for that to arrive.
I'll let everyone know when I get the results.

Additionally, when I did pull the spark plug on number 5, it looked nice and clean - nothing that would indicate a bad cylinder, but we'll wait and see.

Thanks!

 

[junker68]

One other question...

When I pulled the number 5 spark plug I noticed the threads were "oily", but the electrode was clear and as stated, it show no indication of fouling.

As I'm reading different scenarios on this site, I see alot of people have the cracked manifold, which leads to coolant into the spark plug well. Obviously I have to see if coolant is in there. But if there is coolant in there, how do I tell if it is a gasket or the manifold itself that is cracked? Do I just change the manifold, because the original is going to crack eventually because of the bad design.

Thoughts?

Thanks in advance.

 

[Number4]

If there was coolant in there, you'd have noticed when you pulled the coil and plug.

 

[junker68]

Just got done with checking the compression.
Compression in cylinder number 5 was 80, way below the norm, correct?
I added 30 wt oil into the cylinder and the compression shot up to 120.
So it looks like I'm looking at a piston problem.
Sound about right?

 

[fritz24]

It's either piston or valve seal.

 

[junker68]

I'm assuming that if I pull the valve cover I could tell if the valve seal is bad just by looking at it, is that correct?

I started the car this am. After sitting all night, there was a very small puff of blue smoke out of the exhaust. Then it immediately disappeared.

Would this condition cause a misfire?

To reiterate, there is no fouling to the plug when pulled.

Thanks in advance for any thoughts!

 

[dieselscout80]

It's either piston or valve seal.

If oil changes the compersion values it means the rings are the issue.

Oil will not make the valves seal better only the rings.

 

[Number4]

The blue smoke was most likely the oil you'd put in for you compression test.

 

[junker68]

Thanks everyone.

I'll let you know how I make out.

 

[lincolnshibuya]

there's a product called "rislone restore", it's an oil additive that sticks to the cylinder walls and temporarily fixes low compression (if the piston rings are worn). I haven't tried it but some people say that it works.

 

[junker68]

I was thinking about bringing the car to the mechanic first to get a true reading of what's going on in there before I start adding additives.

But, that was a consideration as a temporary fix, thanks.