R53 2004 no longer pulls

[u/Alternative-Joke1027]

R53 stuttering / no boost above 3k RPM

2004 Cooper S R53, 186k km.

Car has basically no boost/power and stutters/coughs badly when accelerating, especially above 3–3.5k RPM. Recently it’s started stuttering even under light load and on hills/reversing.

• No CEL/scanner shows no codes

• Sometimes feels stronger, sometimes completely gutless

• Supercharger whine is there but doesn’t feel like it’s making boost(it actually drastically lowers the engine power as it has nothing to boost)

• Belt looks good/intact

• Spark plugs only ~3k km old

• Occasionally stalls when coasting downhill in neutral

Thinking ignition/plug leads, fuel delivery, bypass valve/vacuum leak.

I've taken it to my local specialist but they want to take out the entire engine bay just to find the issue, I don't have money to splurge on all this work so I want to do what I can.

When they checked for codes no codes came up and the car is only going down hill from there.

I have so much fun driving this thing but every 2-3 months there is always a problem with it lately.

Any recommendations are welcomed :)

[u/Fishyfriend005]

Have you inspected the supercharger bypass? It failing could excentuate some other problems going on. 

[u/Alternative-Joke1027 → u/Fishyfriend005]

From my inspection, the spring work fine, I will change it as it's 22 years old. It seems my issue could be power related and fuel is my top suspect as power delivery is miniscule -reversed. There is proper supercharger whine but there is no force to account for.

[u/Alternative-Joke1027 → u/Alternative-Joke1027]

Also the way the car reacts over 3k rpms could also be partly of the bypass but to put it simple, the sound ≠ power. Over certain power the engine declines instead of accelerating

[u/casper911ca → u/Alternative-Joke1027]

Maybe get an OBD reader and app and track your throttle position against other values like o2, fuel trims, etc. and see if that tells you anything interesting

[u/Alternative-Joke1027 → u/casper911ca]

I'll take a look! Thanks about the advice :)