Edmunds dealer partner, Bayway Leasing, is now offering transparent lease deals via these forums. Click here to see the latest vehicles!

Help with misfire at idle, and extremely low compression

trevheadtrevhead Member Posts: 1
edited March 2021 in MINI
Hi, I’m seeking advice for a persistent issue that I thought I’d have fixed by now with all the work I’m about to run you through. This will be a long post, apologies in advance, but I want to provide all the details in hopes that someone is patient enough to check this out and offer some opinions.

Car is a 2004 Mini Cooper S, 153,000 miles. I’m the original owner and it’s my son’s daily driver now. This is the supercharged 4-cylinder, not turbo. The engine is the same as what was in Neons and I think several Mitsubishis in the 90s.

We had, and still have, a code for cylinder 2 misfire. I DIY most of the work on this car, and I got help from the mechanic we've trusted with all our cars for the last 15 years. Here's a quick list to run down what's been done:

  • trouble code: Cylinder 2 misfire
  • trouble code: EVAP minor leak
  • loss of power at low revs (infrequent)
  • rough idle (frequent)
  • blinking engine light, rough idle, engine dies (infrequent)
Troubleshooting & Repairs Specific to the Misfire:
  • me: swapped plug wires, no change
  • me: new plug wires and new coil pack, no change
  • me: new spark plugs, no change
  • shop: bench tested injectors, all passed
  • shop: replaced injector seals, all were looking old
  • shop: smoke test, found vacuum leak at intake manifold
  • shop: borescope through intake manifold to look at valves; found burned valve on cylinder
at this point, it seemed like they found my problems! We decided to take the car home and get the cylinder head to a machine shop for a valve job, and to sort out the vacuum leak with new gaskets when everything went back to together.
  • me: pulled the cylinder head
  • machinist: valve job, no new parts, all machined and new valve seals installed. he said he wasn't entirely sure the valve was actually burned, but that it looked like maybe it was on way. felt like he'd seen much worse before.
  • me: re-installed cylinder head and new head gasket
  • me: new gaskets on everything that came out - exhaust manifold, intake manifold, valve cover
Additional Work "While I was in there" not specific to the misfire:
  • new oil pan gasket (was leaking)
  • new oil filter housing gasket (was leaking)
  • new crank position sensor o-ring (was leaking)
  • new lower engine mount
  • new crank pulley, 2% larger, lightweight, non-dampened
  • new supercharger pulley, 15% reduction
  • new cooler spark plugs to compensate for heat from the added boost from the new supercharger pulley
  • new idler pulley
  • new belt tensioner assembly and pulley
  • new timing chain
  • new chain guides
  • new chain tensioner
  • new accessory belt
Current problems and behavior after re-assembly:

the bad after this work:
  • trouble code for cylinder 2 misfire
  • loss of power at low revs (infrequent)
  • rough idle (constant)
  • audible missing at idle
  • blinking engine light, rough idle, engine dies (infrequent)
  • shop: compression test reads 60psi on all four cylinders

this seems like a huge problem. this engine runs low compression anyway because of the supercharger, but it is supposed to 90psi.

the good after this work:
  • extremely responsive and peppy under power
  • rough idle improved after putting on a shorter accessory belt - stock is technically okay for the new pulleys I put on, but 15mm shorter is better for the 2% crank and 15% supercharger pulley. the low and rough idle cleaned up a lot with the shorter belt but I can still hear it missing, and it still loses power and bogs down or dies at idle.
  • fewer oil leaks but still some more to track down
  • shop: smoke test found no vacuum leaks
  • EVAP leak code is gone
Not sure what to do next, thinking about the following:
  • I haven't touched anything with the fuel delivery - maybe fuel pump and fuel filter?
  • maybe cylinder 2 injector really is bad regardless of what my mechanic thought they tested and confirmed as good?
  • maybe the piston rings are too old and tired to keep up with the top end being 'new' and tight after the valve job? but that wouldn't explain why the cylinder 2 misfire was present before the cylinder head came out.
  • maybe my timing chain slipped a tooth on the first start-up? I'm 100% positive with photographic evidence for my own sake that the chain and sprockets were properly aligned and timed when I put the timing case cover back on. but that also wouldn't explain why the cylinder 2 misfire was present before I replaced the timing chain, guides and tensioner.

So with all these details of what I changed, I’m not actually sure any of it matters – I’m right back where I started. Cylinder 2 misfire, regardless of the valve job.

So that’s the long, long story, which probably could have been as short as “I have a misfire” since all this additional work hasn’t changed a thing. Thanks for reading this and if anyone has any ideas for me, I’m all ears.


  • docjdocj Member Posts: 6
    You need to get to the bottom of 60 PSI, Thats way too low. 90 isn't even that great
    Surprised this even runs. Unless of course the shop did the test wrong. Supercharger engine are known for burning valves.
    As far as the misfire #2....Did you check to see if you even have spark at #2 , even with new plug, wires and coil?
    Bench tested injectors.....did you check to see if the PCM is pulsing the injectors? Noid Light?
    Swap injector to see if misfire moves?
    Its all moot if compression is at 60...
Sign In or Register to comment.