Multiple missfires

[Pgazz]

I have a 2004 Baja turbo and I was getting a lean bank one code. I cleaned the maf and cleared the code and never came back. I got a green light and it passed emissions. I decided to clean the engine and after that it started missfiring. It only will do it when its warmed up and only cylinders 1,2, &3. I checked the plugs, replaced the coils, did a compression check, all around 150. My question is, would a bad maf cause this? If so, why no missfires on #4? The fuel lines under the intake have been replaced at some point before I got the car. It has 196k. The cats are not clogged by the way. I pressure checked the coolant system and no issue there.

[tomato_88]

Have you had a chance to check your fuel pressure?


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[Pgazz]

No I have not. Why would you think fuel pressure if it happens when it is warmed up? And it's not happening to cylinder #4. Wouldn't fuel pressure affect all cylinders?

[kamesama980]

No it's not likely to be fuel pressure but it is possible and not terribly hard to check.

vacuum/boost leaks.
time for new plugs (They can look good and be bad). Turbo engines are particularly sensitive.
Do you use premium gas?

Under what conditions does it set the code? driving light? driving in boost? idling? Can you pull freeze-frame data with the scanner available to you? Does it do it consistently that you can feel the miss or is it only at the threshold of the ECU noticing?

[joedavex]

I had sporadic misfires on my 2005 Turbo baja for a while.
My problem ended up being a vacuum leak from a cracked vacuum line under the throttle plate. Only way I found it was by doing a smoke test on it which wasn't as difficult as I expected.
I made a smoke machine from a $5 Walmart soldering iron and a glass jar. I used this video as the basis of my smoke machine: https://youtu.be/L9CDZ9lu6Rs

It's definitely easier with 2 people to find the problem. Use a flashlight and a mirror to look all over the engine.

I used the the same method after getting a misfire following a head gasket replacement. Come to find out I had loosened the #4 injector and it was sucking in air through there.

[w.rohr]

I have had two Subies with misfire and turned out to be bad spark plug wires, also I was told egr issues can sometimes cause misfire on one of the cylinders (I think 4). But I am no mechanic so take anything I say with salt.

[ryu]

I had the exact same symptoms (running lean, followed by CEL for misfire) on my 2003 at around 195,000 miles. My cat's seen better days, but they don't do emissions tests in my state so oh well I'll get to it. Replacing the plugs and wires did nothing for me, then I replaced the knock sensor and now it's happy.