Good afternoon Everyone,

Last week, on a 2 hour drive I noticed that my 03 R53 mini wasn't performing to its usual standard. With the car in 5th or 6th gear it usually has plenty of acceleration to pass cars on the highway. Well on this day, it didn't have that acceleration. It felt much slower.

Over the last year I have installed: rebuild supercharger w/ 15% pulley, Detroit tuned bypass valve, accessory belt, and replaced my transmission.

I made a phone call to Detroit Tuned to ask them if there have ever been any issues with their bypass valves, and he said no. He also suggested that it could be the quality of the rebuild done on the supercharger that was installed. I doubt that this is the issue but I may be wrong. He also suggested that I could zip tie the bypass valve closed and see what happen, so I did. Using a OBD II Bluetooth adapter with my phone, I was able to see "Boost pressure." Now what i'm confused about is that, even with the bypass valve ziptied closed, i was still getting a negative pressure until I stepped generously on the pedal in which case it would go positive. Why would it go negative with the bypass valve ziptied shut?

So after doing this, the car still lacked power.

Upon some research it appears that these fuel pumps can go bad if the gas tank is ran dry (i've never ran it dry, but i'm not ruling out the pump). So I decided to check my Bank 1 O2 sensor voltage while I drove, figuring that if it ran rich, i would see it. When driving average the voltage stayed between 0.6-0.8 . When I would step on the Gas, the o2 sensor voltage would drop to 0.0 and would not change until I let off the gas a lot.


(I have attached a couple of photos. The first photo, is with the bypass valve ziptied shut and coasting at about 30mph. The second photo is with the bypass valve ziptied, in second gear and about 75% throttle.)



The most boost I can get, is about 12 psi in first gear. Does that sound right?


So what do you guys think, is it a fuel issue, or a boost issue?

If you need any more info, let me know

 

Boost is partly dependant on elevation.....how far above sea level are you?

 

12psi sounds a little low. Did you check your belt, or tensioner? Maybe it's slipping and you're losing boost from that. Not sure if a bad crank pulley could also cause low boost, but they're known to go bad so I would check that, too.

 

My towns elevation is 475'. My belt is about 1 year old and still looks good. I looked at the tensioner while the car was at idle and it looks good to me, it has a very little amount of bounce. I did notice that my crank pulley had some dry rot on the rubber last time I had access to it. Is there a definitive way to tell if its bad?

 

I was surprised by this initially too, but you will stay under vacuum at the intake under most driving conditions until you really step on it. You are getting boost, but not enough to move from vacuum to positive pressure. If you hook up something like a scan gauge II, you can see the MAP readout as you drive. It reads absolute pressure in psi, so 14.8 psi is atmospheric pressure at sea level.

I've had sluggishness like this when my map sensor got oil fouled. Try cleaning yours....

 

I would say if you plan to keep your R53, an ATI damper is a must and if you see rot, get it done sooner rather than later.

That said, Artoo, my 2003 MSC started loosing power under load and in the end it was a burnt valve that required a rebuilt head. Now it purrs again. But that is at 150,000 miles. And trust me Artoo gets loving care, is well maintained and only gets Top Tier gas.

So how many miles on yours?

///Rich

 

Should I still see a vacuum even when the bypass valve ziptied shut? Thanks for the MAP idea, i'll try that tomorrow!!

 

My mini has 174,000 miles, but runs nicely. Was you burnt valve visible via an endoscope?

 

Actually it went into limp mode twice going up a long steep hill on the highway. Otherwise it was running fine and always pulled well going up that hill. Anyway, both happened at the same location and both times, pulling it over and turning it off and on cleared the issue. But the CEL light and corresponding #3 or #2 I forget cylinder miss was there. Compression was fine when I checked and I changed the wires, coil and injectors prophylactically and hoped for the best.

Then a 1000 miles later, same hill same lights but this time I really had to limp it home as nothing cleared it up. And then a compression check had zero in one cylinder. I took it apart and here is what it looked like.

///Rich





150,000 miles. MCS burnt valve.

 

Yikes, yea burn valve alright. Can you see any stored fault codes with your app and scan ?

 

Great News Everyone!!!

I cleaned my MAP sensor and decided to take one more look along the intake for anything abnormal and caught a vacuum hose disconnected on the supercharger outlet horn. When i popped it back on it went on fairly easy so i expect it to pop off soon. I'll be ordering a replacement. The car seems to have its power back!!! My O2 sensor voltage no longer drops to 0.0 when i step on the gas. So thats awesome! I posted a picture below of the pesky vacuum line that popped off.

Thanks David.R53 for the MAP sensor suggestion and thanks for everyone's
input. Its truly awesome to have an entire community of people willing to help when in need. I greatly appreciate all of your help!

 

That is great news! Im glad it was nothing major.

 

Yup - that goes to your fuel pressure regulator....many people t that location for a boost gauge. I myself was a little shocked at how easy that hose unplugs.

 

Nice find and fix.

 

Where is this can you take picture from a distance and point in the direction?

 

It's under the left side (when facing the car) supercharger horn. Google install boost gauge r53 - most of them go here for boost pressure

 

Yes, you're still throttling the engine at low loads, so you'll see almost normal vacuum levels at very low loads (eg. Idle). The bypass is there to reduce supercharger work when boost isn't needed. This improves fuel economy.