[s-cars] Baffled over boost

[chris chambers]

Bruce,

Not there able to listen to the car I must say it sounds like what mine
was doing. My problem was a weak coil, under boost it would cause a
miss which almost sounded like I had a tire running on the warning
strips by the side of the highway.



HTH

Chris


--- "Mock, Bruce J (Bruce)" <bmock at avaya.com> wrote:
> Hi Guys:
>  
> This list is truly priceless.  I've been on this list almost since
> its humble beginning and have soaked-up immeasurable bits of wisdom
> to the point where I feel like NO matter what goes wrong with my '93
> S4,  (and at 175,000mi it really has not been much at all! )  I can
> tackle the problem.  I know most all of us would agree about the
> great worth of this virtual community.  Thanks guys.
>  
> This little problem has me completely stumped:
>  
> Again:  '93 S4 w/ 175,000mi stock expect for MTM stage 1 chip and RS2
> Ex. manifold.
>  
> Car runs fine until boost builds past ~15psig (I have an Autometer
> gauge on the A-pillar)  Normally boost would continue to build -
> depending upon what gear I am in - to ~20-21psig.  But now, at
> approx. 15psig, instead of the boost building - the car goes
> Drrrrrrrrrrrr.  (technical term, I know)  Seriously, It sounds like a
> toned-down, quieted-down version of what a Diesel big-rig sounds like
> when they throw on the Jake-brake"  Drrrrrrrrrr.  If I keep my foot
> to the floor this behavior continues. Drrrrrrr.  If I pull my foot
> off the gas it stops and the car runs fine - BELOW that magic
> threshold.   Behaves this way in 2nd, 3rd, 4th and 5th gears. 
> Behavior is very consistent -whether the motor is hot or cold.  Again
> car runs, starts etc. just fine, no hint of anything wrong...  until
> you put your foot down hard and let the boost build up - no boost
> beyond ~15psig. Drrrrrrrr.
>  
> This has been going on for quite some time now.  I can't pinpoint
> when it actually started.  I went to to get on the highway one day -
> got on the gas hard- and this happened. It'd been like this ever
> since.  So... At least it's not an intermittent problem!
>  
>  
> Here's what has been done to troubleshoot so far:
>  
> Tested for boot leaks by pressurizing the intake tract  - everything
> is tight.  As I increase pressure up past ~12psi the oil cap seal
> starts hissing slightly. (I have Samcos and and a high-dollar MTM
> Michelin-man hose)  I also inspected boost lines near the moisture
> trap, etc.
>  
> Multiple high-quality tanks of gas have been run through - so I don't
> believe that it is "bad gas"  Also, the fuel pump was recently
> changed due to a 'no start' problem.
>  
> Waste Gate Freq. Valve changed out for a known-good unit.  No change
> in behavior.
>  
> Near-new plugs changed-out for brand new ones.  No change in
> behavior.
>  
> MAF cleaned/inspected. No change.
>  
> Swapped-out the waste gate spring with a known good unit.  No change.
>  
> Disconnected the exhaust at the down pipe thinking that the CAT(s)
> was possibly clogged and restricting exhaust flow.  Man was THAT a
> loud test drive  :)   No change.
>  
> Throttle Pos Sensor tested per Bentley  (Resistance, etc. checks)  No
> change.
>  
> Wholesale swap-out of all 5 coil packs/spark plug boots/wiring - by
> this I mean I removed and swapped the entire aluminum cover section
> (the one that says "20V" and houses the coil-packs/boots, etc.) that
> sits on top of the valve cover with a unit from another car.  No
> change.
>  
> Swapped ECU with known good (stock chip) unit from another car.  No
> change.
>  
>  
> With all the recent discussion re knock sensors, I will check to see
> if they both are tight.  The rear knock sensor looks to be a real
> bear to get to.  Any suggestions on how to get to this guy?
>  
>  
> Well... there you have it.  I feel like I know my car pretty well
> thanks to this group.  But this one has me beat!
>  
> Appreciate any thoughts on where to go from here from the collective
> wisdom pool!!!
>  
> Bruce
>  
>  
> _______________________________________________
> S-CAR-List mailing list
> S-CAR-List at audifans.com
> http://www.audifans.com/mailman/listinfo/s-car-list
> 

AUDI - Accelerates Under Demonic Influence.

__________________________________________________
Do You Yahoo!?
Tired of spam?  Yahoo! Mail has the best spam protection around 
http://mail.yahoo.com