‘01 4.4i misfiring when cold

[Jakal702]

Originally Posted by upallnight

Since you have multiple misfire with fuel cutoff, goes away once the engine is warm I would say that it is not an ignition misfire but a weak cylinder misfire. A weak cylinder misfire is when the cylinder doesn't produce the same amount of power as the other cylinders. The computer can determine this quite easily by the rotational speed of the crank once the spark plug has fired for that cylinder. All the other cylinders could be rotating the crank at 700 rpm but one could be rotating it at 650 or 630, etc... You will not notice the difference but the computer wil know.

In that case I should definitely take it to my mechanic. Hopefully it’s not that (sounds expensive&#128530 the thing is that it’s random cylinders... would they be all be weak then?

[upallnight]

Originally Posted by Jakal702

In that case I should definitely take it to my mechanic. Hopefully it’s not that (sounds expensive&#128530 the thing is that it’s random cylinders... would they be all be weak then?

A weak cylinder could be a cylinder with low compression (expensive fix) or a vacuum leak (lean mixture) could cause a weak cylinder. The fact that it goes away when the engine is warm leads me to believe it's a vacuum leak. Could be a hairline crack that opens up when it is cold (material contract except for water) and closes up (expand when it is hot).

[Jakal702]

Originally Posted by upallnight

A weak cylinder could be a cylinder with low compression (expensive fix) or a vacuum leak (lean mixture) could cause a weak cylinder. The fact that it goes away when the engine is warm leads me to believe it's a vacuum leak. Could be a hairline crack that opens up when it is cold (material contract except for water) and closes up (expand when it is hot).

I’m beginning to think it is a vacuum leak. I let the car get cold and just started it up with the hood open and I hear a hissing sound... from past experience I know this could mean there is a vacuum leak, but is a hairline crack still a possibility? The hissing sound eventually goes away and is only heard when the hood is open, but it is currently not misfiring.

[CapeX5]

you have to do a "smoke test" of the intake system. Try to break this down into one thing at a time, systematically. As I said in one of my earlier posts, gas, air, spark. Verify one at a time. Go on Youtube for a description of what a smoke test is

[upallnight]

Originally Posted by CapeX5

you have to do a "smoke test" of the intake system. Try to break this down into one thing at a time, systematically. As I said in one of my earlier posts, gas, air, spark. Verify one at a time. Go on Youtube for a description of what a smoke test is

The cheapest smoke test can be found on Scotty Kilmer's Youtube Channel. Cheap as long as you stay away from the Cohiba. LOL

[x5Alpine]

My bet is the intake manifold gaskets. When mine started to go bad it would run like crap on cold start then smooth out as it got warmer. replaced the gaskets and all was fine.