2004 mini Cooper. Non turbo. 220k miles. No compression in cylinder 4. Getting 25psi. Other cylinders read 105-125. Dtc set for cylinder 4 misfire

I'm a mechanic. Though I don't know everything and car designs differ. So my guess would be a valve or lifter lifter no over heating. Runs and drives fine other than lack of acceleration. Already pulled injectors cleaned and swapped position, swapped plug wire, new plugs.

Any thing that would cause low compression for one cylinder? Not excessive noise from engine. Best guess is a valve/head job is needed. Haven't searched yet, but if there's a write up on removing the head feel free to link it.

Appreciate the help.

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Two things come to mind - there are things that pop up regularly on this forum:
1. Burnt exhaust valve - can be checked with a leak down test
2. Worn cam shaft lobe - easy to pull the valve cover and look.

 

Chipped/cracked valve in #4. Swapped on a used head. Head looked clean, valves in good shape, no noticeable issues. Car started and idled rough, then died. Have to give it gas to keep running holding at 1.5-2k rpm. Left off gas after about 5 secs and it'll idle rough without dying. If I move the car and disengage the clutch it'll stumble and die.

Drove down the street and back and got a random misfire code, along with the two codes below. Realized the nipple at the brake booster was broken. Fixed that but still runs the same, and have the codes below. Haven't driven again so not sure if I'll get the random misfire code again.

p2096 - lean O2 and p0301 - cyl. 1 misfire
I have swapped plugs with no change. Cannot swap plug wires as the #1 wire won't reach for any of the others, but don't suspect this as it wasn't an issue before. I'll proceed with swapping injectors and checking compression.

I did notice with the key on engine off I can hear a whining like a motor/pump is going. I hear it near the power steering fluid reservoir...come to think of it, it could have been the blower fan, I'll double check that.

 

Posted a reply last night but didn't seem to post.

Had a cracked valve, so I swapped a good used head in. Now I have a lean O2 code (p2096) and a misfire in cyl 1 (p0301).

Can't swap plug wires as cyl 1 won't work for other cyls. But highly doubt that's the issue. Swapped plugs, no change. Will perform a compression test and swap injectors.

Noticed that the intake had rubber gaskets while the new gasket is a paper type. Any issues with this? I feel the rubber ones would work better.

 

Check the vacuum lines. The rubber connections get soft and leak or come off.

 

All rubber hoses disconnected for head replacement are tight and in good shape.

Performed a compression test. #1- 0, #2- 135, #3- 135, #4- 150

Generally zero compression is a big problem related to a non moving piston or valve damage. Could also be a fuel injector concern I suppose if there was no injector or o ring present, so unlikely).

Did a leak down test for cyl 1. Using a screw driver to tell when piston is tdc. Got air coming out of #3. Rotated so piston fell and when back at tdc rechecked, then was getting air out of #2 cyl.

Sounds like a valve issue, cracked or warped head, or possibly a bad head gasket. When looking for specs I saw that the main head bolts are torqued to 30 ftlbs then 90 degrees. Smaller ones by timing chain are torqued to 25 ftlbs then 90. But I also saw that some said they get two 90 degree sequences.

Any advice on where to go from here and what to look at is helpful.

 

Took the head back off. Double checked and putting between cylinders and head gasket issues. Nothing visible. Decided to take valves out and clean them.

Noticed a few things1) there's a greyish build up on several as seen in the pics attached. There was more but I cleaned most of it off. Issues?
2) pitting on valve face going to lap them unless you guys think otherwise.
3) one of the rocker adjusters is different as seen in pics
4) one of the intake valves is different as seen in pics

 

Got all valves out. Looks like the two intake valves in #1 were bent. So that explains it. Intake valves were all pretty clean. Going to swap over two of the valves from the other head.

 

Following thread.

 

Got everything buttoned back up and no more misfire. Got a couple cores.for O2 sensor lean, but likely wiring issue as it's reading a voltage code for the sensor.

​​​​​​If anyone needs help doing a head swap/head gasket swap, etc. Shoot me a message. Definitely one of these easier head swaps ive done.

 

i think i have the same issue on cylinder 4. i did a leak down test and air is coming out the supercharger intake and zero pressure on compression test.
I'm not a mechanic to you think i could change the valves myself?
Will i need any specialized expensive tools.
im currently watching minimod to learn how to dismantle the mini.

Do my symptoms point to anything else?

 

The noise you’re hearing is the power steering pump low on PS fluid , they get noisy if fluid level is low or empty…