My s40.
Have two codes p0303 p0304. wires run 1wire-4coil:2wire-3coil
Compression test (Roughly)
#1-90
#2-15
#3-25
#4-120
Holds these pressures on the gauge.

Symtoms;
-rough idle.
-rough start, sometimes not starting.
-start up, rpm bounces a little.

She drives fine once we're going. I can not hear mechanical noises, apart from the "misfire", does not have traces of oil in coolant or coolant in oil, she's not burning oil… Any suggestions would help. Thanks for reading.

 

You held the throttle butterfly wide open while conducting the compression tests? You trust those numbers? Because they indicate serious wear. All numbers should be within 10% of each other. Did you test wet or dry cylinders?

 

Do a cylinder leakage test. It will tell you more.

 

I did not hold the throttle open. I think dry. This was my first compression test.
What I did was, disconnect electrical form the spark plugs, pulled fuse for fuel pump, and then cranked it over 8 times per cylinder. Repeating the process. I waited and the gauge stayed at those numbers.
Did I do the test incorrectly?

 

I will look up how to preform a leakage test, and do that next.

 

What kind of compression tester did you use? The type you shove into the hole or the type you screw in? I'm thinking you didn't get a good seal with the tester. With the results you got in #2 and #3 the engine shouldn't even run, let alone "drive fine once we're going."

 

Sounds like you did the test right, was the motor warm? I think you have a small burn in a valve or a bad head gasket between 2 & 3.

Here is a video. After doing the test dry, wet it and see if the numbers jump.

 

I agree with atikovi- the engine would never run well with those numbers.

 

Yes, you should be getting misfire codes for #2 & #3. And I could not imagine the car running on 2 cylinders.

 

I will look up how to preform a leakage test, and do that next.

 

I used the one that screws into the hole. I used an extension and a socket to get it in, just like a spark plug. This was my first time could have preformed it incorrectly. Maybe it's running on hopes and dreams lol

 

Atikovi, ES6T, Rspi, and ziyixue,
It was a screw in tester I borrowed from the auto parts store.
The motor was warm, after driving I pulled my car into the garage and started working on it. I followed this video just did not have the oil. I will do it again, also the leakage test.
My codes are in #3 and #4. I understand those are "dead cylinders" with those numbers.
Why I am scratching my head…
Would any of you happen to know/recommend a shop in Utah?

 

The codes are for a misfire. The problem is that with 1 coil firing 2 cylinders the ECM can report the incorrect cylinder. In reality it could be 1 or 4 and 2 or 3. Normally a misfire in the 2000-2004 models means you need a tuneup. 2 coils, 2 wires, and 4 plugs.

 

I wouldn't trust the generic code to accurately tell what cylinder is misfiring. Using VIDA at the dealer, we can't tell which cylinder set the code.

 

Well, the compression numbers on the cylinder will not lie. Cold hard facts...

 

Exactly. But those numbers cannot be correct if the car runs fine when hot.

 

This is true. The I5 runs ok with 1 dead cylinder, I doubt one would run with 2 dead.

 

Umm, the OP's car is a 4 cylinder engine.

 

and a 5 cylinder won't run "ok" with a dead cylinder. It will have a very noticeable misfire.

 

I didn't say good, I said ok, meaning that it won't stall. I know of people that have driven their I5 for months on a dead cylinder. I doubt that one would idle with 2 bad cylinders.