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RE: S4 high speed miss

This sound remotely similar to a problem I had with a friends 94 S4 with an
IA stage 3 set with RS turbo and manifold and K&N filter and tube replacing
the OE air clear housing and filter. I am a bit vague on the details since
it has been 9 months or so. In a full throttle run in third gear it with cut
out at 6000 rpm and put its self in to limp mode until the engine was shut
down and restarted. Using the Car Comp diagnostic tool we determine the
computer was calculating and over boost condition based on the air mass
sensor readings not an actual excess of pressure. We thought possible air
leak under boost and basically pressure tested each intake component to find
no leaks, many other leads were chased and nothing found. A lead from a
Porsche 944 Turbo owner that had gone through similar problems with his
highly modified car, (3.0L w/mass air flow sensor). We found what we believe
to be excessive turbulence in the air flow through the Mass Air Flow Sensor
causing it to give a false reading. The ECU was seeing reading that
indicated more air that the engine could flow for the RPM and boost pressure
so the ECU assumed the boost was higher than was safe and shut everything
down. We reinstalled the OE air cleaner housing and corrected the problem.
The boost could continue to climb passed the point the problem would occur
and not stumble or problem. We assumed the air needed a longer track before
the Mass Air Flow Sensor in order to smooth out the flow.
Jim Dupree
 <mailto:dupree@alldata.com> dupree@alldata.com
Technical Editor II
Database Development
(916) 684-5200 Ext. 3346
Fax: (916) 684-5225

	-----Original Message-----
	From:	Frank Amoroso [SMTP:FAmoroso@svbank.com]
	Sent:	Thursday, January 21, 1999 5:33 PM
	To:	quattro list; S list
	Subject:	S4 high speed miss

	Calling all q heads!

	Hello all,

	I am having a problem with a high speed, high load, high boost miss
/ buck 
	that my S4 experiences on occasion.

	It is a '93 S4 with 65,000 miles and a Hoppen Stage III RS2 kit. It
is very 
	strong and runs very  well for the most part, and it is a ton of
fun. The 
	one problem I do have, however, is a miss under heavy load w/ high
boost. I 
	get 30 psig max boost in the higher gears and on a continuous
incline with 
	wide open throttle I can get a rather abrupt miss / stumble, it
almost feels 
	as if an IC hose has blown. I am off the gas immediately so I don't
know if 
	it would continue missing. Back on the gas and the boost builds back

	Driving solo with less than a quarter tank of gas and the miss does
not seem 
	to come into play. Several people in the car, full tank of gas,
uphill, 5th 
	gear, WOT, 25+ psig of boost and the miss comes back.

	Major service 5,000 miles ago including the proper F5DPOR plugs. I
	checked the rubber boots on the ignition coils and they seem good. I
	yet to hook up a fuel mixture gauge to see if I get a lean condition
	miss / buck. The computer seems to back off boost the way my TAP
	did (albeit with a max of 30 psig as opposed to 22 psig). Two of us
	running the same setup (a S6 too) and we both have the problem since

	stepping up to the Stage III setup.

	I know the 3B motors running elevated boost levels have had problems
	that the conjecture has to do with the ignition rotors. How about
the AAN 
	motor with its distributor-less ignition? Potentially a weak coil on
my AAN 
	motor? Is there a way to check the coils?

	Any suggestions would be greatly appreciated. Is 30 psig (3.04 BAR)
just too 
	much boost under load? I tried running some octane boost to see if
it made a 
	difference, but it did not. One would think that if the miss is
	related to the high boost levels that running higher octane would
	lessen the severity of the miss / buck ar at least its frequency?


	PS I am off the list so please respond directly.