[s-cars] BOOST BACKOFF- was: Help!!!! Intermittant boost (kinda long)

[Paul Gailus]

Brian,

It may help to diagnose what's going on if you
can monitor the drive signal that the ECU is applying
to the wastegate frequency valve under the operating
conditions you describe.
If the duty cycle doesn't change significantly when the
boost jumps, then the ECU isn't forcing the jump and
you can probably rule out problems from the sensor inputs
to the ECU. In this scenario there could be a wastegate
problem or a boost leak.
If the duty cycle does jump, them something that the ECU
is sensing and processing is causing it to do this
(could be the knock sensor, etc.).

How to monitor the WGFV drive signal?
A portable battery powered oscilloscope or scopemeter
would be best. Barring those you might be able to use a
dwell meter (if you can still find one) or a cheap analog VOM
to detect a significant change in the waveform duty cycle.
A VOM could be more difficult to use because of needle
vibration due to the pulse-train, but if this is a problem
you could filter it with a resistor and capacitor.
Obviously, having someone in the right seat to make
the measurements would be very helpful.

Paul


----- Original Message -----
From: brian bilotti <vinnieb2 at yahoo.com>
To: <s-car-list at audifans.com>; christopher leal <cleal at internap.com>
Sent: Thursday, November 07, 2002 1:41 AM
Subject: [s-cars] BOOST BACKOFF- was: Help!!!! Intermittant boost (kinda
long)


> Dear S-Heads,
> My boost(or lack of) issues continue. I've ruled out
> ECU problems (I've used 3 differest ones), changed out
> the wastegate frequency valve. Symptoms, on boost to
> 20-25 lbs sometimes will hold but often will back off
> to 10lbs or stays at 10 lbs then will all of a sudden
> jump to 25+ lbs. I was just at a QClub event at and
> this was really evident, seemed worse coming out of a
> corner but maybe this is coincidental as I am
> experiencing same while on the fway. Really
> frustrating having to let a spec Miata pass me :-( Oh
> and Mr. Leal's Ford Lightening? Nothing like having a
> very large truck with pitiful brakes, snip, suck up to
> your rear bumper and hack a lugey on the way by :-0
> Seriously, this is really gettin' to me, I got big
> hardware, a Happersized RSB w/ Pederson adapto plates,
> serious sware, and all I get is a measly 10 elbows. I
> appeal to all you s-heads for any and all suggestions,
> no matter how obvious, so I can try to figure this
> issue out.
>
> Later
> Brian "Boostless in the Bay Area" Bilotti
>
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