I was discussing the merits of taking a a compression test to make sure that all was well with my engine and the mechanic said if there was any significant
difference it would kick out a code. I've never heard that before.

 

I don't know, but that would be nice if it did. (Waiting for others to reply ...)

 

Anytime your down a good amount on compression it will kick out a misfire code. ie. 20-40psi down

 

What's considered good compression for our cars? I'm having issues under boost and I was told I'm getting blow by past the rings. I'm going to do a comp test on my own to actually confirm that is the case and just want to know what number I should be looking for. To cut off fuel, just pull fuel pump fuse correct? Which I'm assuming Is under the dash with all the other fuses?

Thanks,
Steve

 

Are you pulling any codes?

 

I don't really rember, I think it's 160'ish (do a search you'll find it)
As far as fuel, if you're just doing a compression test, no need, just unplug the coil.

 

I'm not getting any codes, no. As soon as I go from vacuum to boost the car starts hesitating like a stutter over and over again. Idle is fine and just using light throttle the car accelerates normal. Its as soon as I press the pedal down farther where it starts making boost, the engine falls flat on its face. The guy I brought it to said that the compression was fine during the test and that it held, but once it was under boost that it would start getting blow by causing the stuttering and blaming that on the piston rings being no good.

I don't have to cut off the fuel supply? I thought the injectors squirt during cranking? No? How else would the engine start?????

Steve

 

Healthy numbers range 160-200psi for stock bottom-end and head.

 

First:
I'm prob. wrong about the tech. aspect of this but my understanding on the comp. test is, no charge from the coil = no injector pulse, this being right or wrong I've done many compression tests this way with 0 issues.

Second:
If it were rings I would think you would have evidence ALL the time not just under boost, how many miles are on the car? You shouldn't be having ring issues on an '05.
Sounds to me more like a BPV or TB issue, or possibly a map sensor starting to go. (the map sensors get coated with oil and have been known to gradually fail.)
The strangest thing about all if this is that you're not throwing any codes. According to your sig. you have a DT/BPV, I think I would start there simply because it's the easiest, first check all your connections, (something could have just come loose) esp. the plastic hose to the S/C, they have been known to become brittle and crack or break, next if you find nothing simply swap it back with your stock one and see what happens. (Chad's BPV's have a reputation for being extremely reliable but anything is possible. Besides if that ends up being the problem just give him a call his customer service is second-to-none.)
Next, do you know anyone else with an r53 that would let you swap map sensors or T/B's with them, it may save you from buying something you don't need.

Still the strangest thing is that you're not getting any codes?

Edit*
I just re-read your last post again I've had both a bad MAP sensor and a bad T/B that caused similar problems, when my T/B went the car would perform normally only if you didn't throttle to hard, if you did it would fall flat on it's face till you backed out of it. (but it threw a code.?)

Good Luck

 

Hey everybody just a little update.

So I originally brought my car to this guy to have this problem looked at. First the head was pulled off because of low compression. Found the valves to be covered in carbon and believed to be not sealing properly. Had the head cleaned and pressure tested and put back on. Still doing problem. Then found the intake manifold gasket had a deformity in it and was leaking air past it. Changed the gasket out and hardware but still continued with the problem. It was a little better but def still there. He tells me I need a motor that I was getting blowby at the piston rings. After $1500 I told him I'm tapped on the money and I have to wait. I never really believed him that that was the problem.

So last Friday I backed the car out of the garage and it was idling very rough and smelt of raw fuel very bad. Sniffed the tailpipe and sure enough stunk of gas - running very rich (at idle!!). Popped the hood and took the IC off to snoop around a bit. When I took the IC off I got a really strong whiff of gasoline within the IC and the inlet horn to the intake manifold. So after looking around a bit I noticed a vacuum line was disconnected and dangling by the output horn from the SC tried to find where it went and while looking I saw the fuel pulse regulator was missing its vacuum line completely!! Turns out when the intake manifold was put back on he got the lines mixed up and hooked up the FPR line to the 3 way tee by the horn and left the other line off. I rerouted the line back to the FPR reconnected that dangling line to the place where the FPR line was connected to and put the car back together again. Took it for a drive and it runs GREAT now!!

So I'd have to assume the problem the whole time for the past two years was the intake manifold gasket. Still dont know why that wouldn't set off some type of code but it didn't. Anyways, thanks for the tips from everybody. I'm just so happy to have my Mini back to normal again! Time to start the modding process again! LOL

Steve

 

True.

 

True for any OBDii or newer car, the 20-40 part may vary but the rest is true.

 

i'm down in the 90-95psi range on 3 cylinders & 135psi on 4th...no codes.