2.3 Cylinder 4 Misfire! What else can I try?

[Jermy]

Hello, I am in need.

I've got an 03 9-5 with 160k and a constant cylinder 4 misfire.
-Only codes are 0304 and 1304
-Misfire seems to stop at high rpm
-New DIC, plugs, new crankshaft position sensor, new vacuum hoses, new heater bypass valve
-Compression is 150-160 psi for all cylinders
-plug 4 sparked fine when I turned key with grounded plug sticking out of DIC
-Car starts up and runs reliably, just surges and shutters
-Brake booster seals well, holds vacuum/pedal movement doesn't affect idle

There is also a hissing somewhere around the fuel rail, but I didn't get any surging when held a butane torch around there.

Where do I go from here? Do injectors fail like this? fuel filter?

[GeoffR]

Check the vacuum line to the fuel pressure regulator for leaks.

[Jermy]

Vacuum line to pressure regulator is good.
I just swapped two injectors, 3 and 4, and am still getting p0304 as before. I also tested fuel rail pressure and it was over 30 psi. The misfire also seems to vanish when I rev up above 3k, which leads me to believe its some kind air fuel mixture problem, But I'm not sure what else I can do.
Any advice greatly appreciated, Thanks

[Mike Brennan]

The crankshaft sensor signals the fuel injection computer or the ignition control when the cylinders are firing. This causes the ignition coil to provide a spark and the injector to inject fuel into each cylinder at the right time.If either sensor isn't working correctly, the car will run rough and the engine will be less efficient. In later car models, the car's computer can usually keep the vehicle running, but the engine warning light on the dashboard goes on to warn the driver. (Lifted off the net)
you say your is new, installed correctly? I would double check that,
or, you just might need a new gas cap
seems I remember someone having to replace a brake booster.

[Jermy]

Thank you, already replaced DIC and cps, brake booster line is also 100% sealed.

[Biggsjam21]

Hissing can be from timing belt.
On the 4cylinder engine if the belt slips a little bit you will get misfires. I have a v6.... any slips with my belt im Bucked lol

[GeoffR]

Hissing can be from timing belt.
On the 4cylinder engine if the belt slips a little bit you will get misfires. I have a v6.... any slips with my belt im Bucked lol

The 2.3 Saab engine uses a timing chain, they neither hiss nor slip.

[Biggsjam21]

Serp belt maybe?
On my v6 im getting a hissing i thought it was a vac leak of even a tire popped and was going flat.
Had an idea and sprayed very little wd40 on serp belt and the his went away immediately.
I think my alternator is wiggling a bit and ac is definitely siezed 😒😒

[BeardedFool]

When I bought my wagon, it had a loud noise when running. I noticed that the tensioner would shake or wobble when running. I replaced the tensioner, both idler pulleys (yes I have the long belt). And it still made alot of noise when running. Was told to relieve the tension on the belt while its running, if the noise goes away then its the water pump. So I swapped out the water pump. Still had noise...
Out of frustration I figured it could only be 1 of 3 more options, a/c compressor, power steering pump, or alternator. I did find a post somewhere about replacing the bearing on the a/c clutch. It was relatively easy to replace and the bearing only cost like 13-14 dollars from autozone. Just dont go in there to look it up by vehicle year make and model. That may be a fix for your seized AC.
Down side for me was that the noise was still there... I discovered it was the alternator the whole time. The bearing I side of it was shot. My wife cousin showed me by holding a long narrow peice of wood against it and then holding it up to his ear. Worked just like a "mechanics stethoscope". Luckily I have a garage full of scraps of wood.
The lesson I learned after spending way too much on parts that probably didn't need to be replaced is to get a stethoscope or long narrow scrap of wood. Hold it against parts of the engine while its running and try to narrow down where the source of noise is.

[BeardedFool]

Forgive my fat fingered typos in there. I just read over what I posted last night and find myself laughing at where I said "my wife cousin showed me..." Where it should have said "my wife's cousin".