Hi Everyone,
I have MINI r53 and just joined the forum yesterday, but was wondering if anyone might have had a similar experience. My car has around 90k miles and just turned up a P0301 code which is a cylinder 1 misfire. No other codes or anything. I replaced the plugs, wires, and coil. I brought it to the MINI dealer and they did a compression and leakdown test and said that my cylinder 3 was testing low at 135psi and 45% in its leakdown test. I am a bit baffled as there is no codes or anything leaning towards cylinder 3 and the codes point to 1 but it tested fine. They said they could pull the head and check my valves out. Does this make any sense to anyone? I am wondering if it could be injector or computer related, but i would have thought there would be more than just the one code if this was the case. Any insight would be great...

Thanks Guys!!

 

Not injector or computer related. They should be able to tell you if air was coming out tail pipe, intake or valve cover cap.

Jeremy

 

Yes, the MINI tech said he put a glove on the tailpipe and it was inflating. I did my own compression test and know that I have an issue on cylinder 3. I am just a bit confused as to why no cylinder 3 code yet a cylinder 1 code when 1 has 150psi and was about 5% on the leakdown test??? I guess i am trying to figure out if the code in three could somehow be caused by cyl 3. I know it sounds crazy but i know codes arent always an exact thing, you need to know how to interpret them.

 

Folks with cylindar 1 codes usually SEEM to end up with a valve issue....
Seems to start out mild, and worsens over a few thousand miles. Not sure why...but a couple mini techs and a memory of threads here kinda makes me lean that way.
Check your coil, clean it up, add some dielectric grease to the terminals, and keep an eye on it. It might be almost time to yank the head, and have a look, both at 1 and 3.

 

Well, my compression on all four cylinders is 150psi, i replaced the plugs (ngk 4 prong), wires and coil. I tried moving the injectors and the code still comes back to cylinder 1. The car runs great and aside from the cel I wouldnt even know there was an issue.

 

Well, my compression on all four cylinders is 150psi, i replaced the plugs (ngk 4 prong), wires and coil. I tried moving the injectors and the code still comes back to cylinder 1. The car runs great and aside from the cel I wouldnt even know there was an issue. I am still getting the p0301 code for a misfire on cylinder 1. If I allow the car to heat up then erase the code the car runs and drives and idles without returning the cel or the code. It isnt even a pending code, but if i allow the car to cool down and sit a bit and restart it the code comes back. So basically the code somehow returns when the car is cold and at idle. I am just wondering what you guys would recommend me checking next. I am thinking maybe engine coolant temp sensor, or map sensor, o2 sensor or possibly a leak in the exhaust???? Any help or advice would be most appreciated...

 

I see you had a leak down test done and it was 45%. That is your problem. Good cylinder leakdown readings should be below 5-8%. Typically if the leak persists and is well into the 20 percent zone, it might be worth the time to yank the head and repair the problem.

 

Just to be a little more clear, an engine that is in great condition should show only 5 to 10% leakage/loss. An engine that is still in pretty good condition may show up to 20% leakage/loss. But more than 30% leakage/loss indicates trouble.

 

The car passed its most recent leakdown test. The mechanic put some seafoam into the spark plug hole and let it sit overnight and it brought the compression up and gave it good leakdown readings on the #3 cylinder. He thinks there was some carbon causing the issue with #3 cylinder.
The cylinder that is returning my code cylinder #1 has great compression and did great in its leakdown test, it has new coil, plug, wires, the whole engine was tested for leaks. The only leaks were around one of my injectors and the o-ring was replaced. It just seems odd to me that the misfire that trips the code only happens when the car is cold/has been sitting. Otherwise there is no sign of a misfire or code.... thanks for the help everyone!! My inspection will be up in a little while and I am trying desperately to resolve this before then!!

 

A compression test is a dynamic test (engine moving), a cylinder leakdown test (C.L.T.) is a static test (engine at rest). The compression test measures how much pressure the engine can produce while cranking; in contrast to the C.L.T., which measures how much pressure is lost in the engine. In a C.L.T. the engine is placed on TDC of the cylinder in question and using a similar type of connector as the compression test, we fill the cylinder with pressure. The tester then measures the volume of air needed to maintain a predetermined pressure in the cylinder.

 

Oh ok, that actually makes a lot of sense. According to the mechanic everything looks good in the engine which is why I have started looking at sensors, exhaust leak, etc. Is it possible that it could still have an internal issue with cylinder 1 while having good compression and doing well on its leakdown test?

 

If air is leaking past the rings, or the valves, or the head gasket, you can directly read the amount of leakage and can easily find the leak. If there is air blowing out the PCV, you have a ring leak, if it's coming out of the exhaust, you have an exhaust valve leak, and so on...

 

Ok, well i guess that rules out an internal issue then. The mechanic said 150psi for compresssion and 5% in the leakdown in cylinder 1..so why a p0301 uggghhh!!! what would i check next?

 

IMO it is still head related and most likely valve related on the exhaust side. You might have no choice to remove the head and inspect. Take the valve cover off and see if anything looks out of normal. Then you may need to still remove the head. Just my 2 cents.

 

I'm with bram...like i said before, you can drive it for a while, the misfire will worsen over time till it will barely run...short of waiting for that, yank the head, and see what is going on...
Like i said before, the valves in cylinder 1 are the ones MOST COMMONLY burt from running lean, low octance fuel, etc....you have tossed a bunch of $$ and time at an item that cannot be fixed from tge outside....all the tests you have done is to SIMPLY TRY TO DETERMINE what is going on inside...YOU KNOW FROM THE MISFIRE SOMETHING IS AMISS, so just open it up, and look!! With the $$ you have paid in testing, you could have paid for half the cost to remove/replace the head.....then add the wires, and coil......not saying those parts will not help the car in the medium term, but short term is it NEEDS a mechanical repair on the inside...
Could be a hot spot, a piece of carbon, bad valve, crack...etc...
Back during a tech day at a mini dealer in RI, the mini tech basicly said misfire cylindar 1 usually indicates an exaust valve issue.....most common thing. Many folks have thrown tons of parts here at an issue...sometimes "fixing it" for a few months, then it returns, head comes off....nuff said. Good luck.

 

 

PS
The psi on compression is ONE test on ONE STROKE...
You have had both high and low tests, and an intrrmitant misfire...
Can you say on the stokes with good compression it runs good, but on the strokes with poor compression it misfires?
Just saying.....a valve that is not always seating propperly....etc. only way to tell is too....

 

ok gotcha, i guess that was what i needed to hear. I assumed i had some internal issues but those two tests both looked promising so i didnt want to jump to conclusions. i wanted to make sure i wasnt overlooking something obvious. Is it common for an internal issue to be more apparent when the car is cold and has been sitting? Thanks for all your help guys.

 

is there anythineg else such as an exhaust leak or bad sensor that could cause a p0301? i just want to eliminate those things before the head comes off.. thanks

 

Thanks to everyone for your help. Well I decided to take everyones advice and pull the head. As soon as the valve cover came off I found the problem. There was major pitting and a visible track thru the cam lobe on the camshaft. My cylinder one misfire turned out to be caused by excessive wear on the camshaft. Thanks to a couple members here I was able to pick up new roller rockers and a new camshaft. My car has been back together for a week now with about 400 miles on it and no check engine lights, the idle is smooth and it finally passed its inspection in NY.

Thanks Again!!

 

Glad the parts worked out for you. Like I told you I've passed on a few OEM cams this past month due to cam lobe wear. Now go enjoy your MINI!

Jeremy