my boost problem

[Phil Rose]

My car still suffers from power loss--especially at higher RPMs.
Beside the seat-of-pants "measurement", this shows up as a
slower-than-normal build of boost, which reaches a lower maximum than
usual (the computer gauge now gets to 1.5 or barely 1.6 bar whereas
1.7 and 1.8 was typical). The Michelin Man hose is OK. No ecu codes
retained. Lehmann chip, all else is stock.

A possible explanation that just occurred to me related to the broken
cat-converter elements. I've listened to the rattle of broken
catalyst (on both sides) for several years, and I wonder if pieces of
catalyst have finally worked their way back and plugged the exhaust.
Would measurement of exhaust system temps be a useful diagnostic
method? Or...?

At 142K (rust-belt miles), I suspect a new exhaust system is about
due in any case.

Phil



At 12:55 PM -0400 7/16/03, Phil Rose wrote:
>First, here's my little problem: I'm trying to diagnose the reason
>for loss of top-end boost, which became evident only during my final
>run-session yesterday at WGI. The car's performance (Lehmann-chipped
>'91 200q) seemed normal for a day-and-a-half on the track, until late
>yesterday afternoon. Then, during my last red-group session on-track,
>I was being passed _much_ more often and was needing to downshift
>more frequently than was usual. It dawned on me that I no longer felt
>any significant "kick" from the turbo on the straights. I verified
>that the boost gauge showed at least 0.2 or 0.3 bar _less_ than usual
>(at max). This session was suddenly no fun at all. I pitted  a lap or
>two early out of consideration for my ailing vehicle and for the
>other drivers. The boost performance did not improve after cooling
>down (i.e., during the drive home), even though I did stop along the
>highway to remove the ECU fuses for a few minutes. Some WOT testing
>shows boost coming on more slowly than usual and topping out too low
>(by 0.2 bar). Between 3 and 5K RPM, the engine felt verrry slightly
>"uneven"--perhaps pulsation/missing is a better term for it.  No
>significant ECU fault codes were retained as of this morning's
>reading (unfortunately I was too weary on the trip home to bother
>reading fault codes). It could be a simple matter of hose-clamp
>leakage, etc., although perhaps something has caused the ECU to
>retard timing. I did add a large quantity of (allegedly) 93 octane
>fuel just before the second day of the event. Bad gas? The BPV is
>new. WGFV is just a few yrs old. I have naturally been concerned
>about the amount of life remaining in my old (140K) MM hose, and I'll
>certainly give that another close inspection--later today.
--

Phil Rose				Rochester, NY USA
'91 200q	(140K, Lago blue)
'91 200q   (64K, Tornado red)			mailto:pjrose at frontiernet.net