1st Gen R53 Cooper S NEED HELP figuring out low vacuum issue! Feel like I've tried everything....

Hey everyone, first post here on MA, sorry its a long one but I need all the help I can get on this. It all started when I had to do a head gasket job on my car. The head had warped around Cylinder #2, allowing coolant into the combustion chamber & vice-versa. So, I pulled the head, took it to a machine shop, had it leveled (was slightly warped around cyl. 2). They also replaced my exhaust valve guides and all valve seals. Re-installed w/ OEM Head gasket, IM & EM gaskets.

Firing it up, the car was very hesitant to start, but would eventually stumble to life after cranking for a while. The first thing I noticed was if the throttle was blipped up to 2-3k & let drop, it will either fall to 5-600 RPM, catch itself, then settle at a normal idle of 800, or just fall to 0 RPM & die. Also, my boost gauge is only showing 10 in HG at idle. I believe this should be closer to 15. The idle is also rougher than normal & loud - causes whole cabin to drone. First test drive, it threw a P1498 - unmetered air after compressor. Okay, a vacuum leak!

Listening around my engine bay with a length of hose up to my ear, I stuck it down behind the radiator & could hear the green gasket leaking. I ordered a new gasket, replaced it, still leaking. Okay, well, It's possibly time to replace the plastic inlet pipe. So, I order up one of those along with a new OEM green jam gasket. I put it all back together & it's running a little better, as in, it's not dying anymore, but it is still bogging & not reading sufficient vacuum.

I took it to a dealership & they ran a smoke test, found nothing. They reset adaptations & suggested driving it for a while. On my way home, I threw a P0303, Cyl #3 misfire. Cleared it & it hasn't come back.

I went to Home Depot, bought an air compressor & PVC cap to rig up my own pressure tester. Pressurized the system & right away the damn green gasket is leaking, not even holding 1 PSI. Also, I found that the BPV housing was leaking like crazy. So, I order a new Detroit Tuned BPV

Today, I installed the DT BPV as well as re-aligned the SC inlet pipe to hold as much pressure as possible. I was able to get it to hold about 5 PSI before leaking any air, which might be a record considering how terrible that gasket design is. I actually had to put 1/4" nylon spacers in between the TB & TB support bracket along with longer bolts in order to get the mouth at the bottom to align properly.

So then, I'm excited. I finally got the whole system to hold pressure & along with the new BPV, I should be off & running! FALSE! If anything I'm back to square one! Significant bogging when I let the RPM fall & pulling into my driveway from the test drive around the block, the engine didn't catch itself & just died. Still only pulling 10 in HG.

In addition to all this, we actually have another R53 & I have tried swapping coil packs & MAP/TMAP sensors between the cars. No change whatsoever. Also, i'm not sure if this is just a part of the


None of these symptoms were present before the HG repair. I apologize for the marathon post but i'm completely out of ideas. I feel like I've tried absolutely everything..... open to any ideas at all, this project started over 2 months ago & has taken up every weekend since

 

Correct, on the SC first, seated completely.

Yup, boost gauge is in Vacuum, but not enough vacuum. Should read at 15 in HG, mine hovers around 10, fluctuating back & forth depending on how warm the engine is (suspect wherever the leak is is contracting / expanding).

Did this, they didn't find anything. After realizing that smoke machines only pressurize to about 1 psi, that's when I bought an air compressor & rigged up my own pressure tester.

 

I think you may have just nailed it-

I just back probed my MAP & TMAP sensors. What I'm mainly wondering is - What is considered "out of spec"? How off from the OEM spec should a sensor read before replacing? These are the measurements I took vs. Bentley spec.

I have hi lighted the values from my sensors that I feel may be problematic-

Pin1/Pin2/Pin3/Pin4

MAP (Key On, Engine Off)
0.0/NA/4.99/4.06
(Idle)
0.0/NA/5/2.4

TMAP (KOEO)
0.0/1.31/5/1.95
(Idle)
0.0/1.3/5/1.12

Bentley-
MAP (KOEO)
0.0/NA/5/4
(Idle)
0.0/NA/5/1.8

TMAP (KOEO)
0.0/3.9/5/1.90
(Idle)
0.0/1.25/5/0.9

 

Hmm.... well, just swapped in a set of known good sensors & the car runs exactly the same.... So..... any other thoughts?

 

Yup, intercooler boots are seated properly. when pressurizing the intake system I made sure to soak them with soapy water to look for bubbles & they didn't show anything.

The engine is for sure in time. When I did the head gasket, I second guessed myself on the position of the timing marks so I pulled the timing cover & lined up the links & everything.

I sprayed that MAP sensor line with soapy water as much as I could but it's pretty difficult to see where it seats down into the black intake pipe.

Interestingly, the car has started running perfectly on occasion once it's had time to warm up. It doesn't always do this, but it seems possible that if there is a leak, once it's warmed up the material expands, seals itself and allows the car to pull proper vacuum. Reads at 15 in Hg, idle falls to a solid 800 RPM, everything. Unfortunately, it doesn't last very long. I'll go out to drive it the next day & it starts / idles like crap again.:mad2: