[s-cars] Car runs like crap under load

[chris chambers]

Jason,

if it only happens under load I can think of two things to check.

1. boost leak - fix is to find boost leak and fix. In order to do this
you will want to build a boost tester, which is basicly household PVC
fittings with an air pressure valve on it. Here are pics of my first
one.

Basicly it's a pvc cleanout -
http://img.photobucket.com/albums/v48/chrisanjenn/Audi%20S4/Press_Test_1.jpg

Assembled with your choice of air inlet valves, be it a tire stem or
air tool coupler.
http://img.photobucket.com/albums/v48/chrisanjenn/Audi%20S4/Press_Test_3.jpg

With this version of the tester you disconnect the house that attaches
to the outlet of the MAF and clamp the hose to the tester. This allows
you a way to pressurize your boost hoses and look for leak(s). Now I
found that the MAF hose tended to leak, and not being a pressurized
hose that didn't matter. So I added a reducer to the cleanout with a
section of ~2"pvc pipe and connected mine to the hose that normally
is connected to the outlet of the turbo. Sorry I don't have pics of it.

2. failing coil - What is happening here is that the coil is weak, it
puts out enough spark to fire with no boost, but when under boost it
missfires and the car develops a miss. If it feels like the car is
missing you will want to check your coils. The easiest (non pro) way
I found was by using a adjustable spark tester (as pictured below)

http://www.thegrillstoreandmore.com/image/products/big-pics/375319b.jpg

What you do is remove the bolts holding the coil pack in place and 
flip the coil pack over, I placed mine on a piece of wood. It's also
been advised to pull the fuel pump fuse to prevent washing your
cylinders with fuel. Connect a ground cable to the end of the tester
and press the other end into the cpark plug connector. What you will
be doing is have a partner then turn the engine over and check for a
spark jumping the gap. Check each cylinder and then increase the gap,if
you have a bad coil eventually you will get a gap large enough that one
of the coils won't have a spark and the other 4 do, at this point you
have determined which coil is the weakest.


Obviously other more informed S-car gurus will point out any error(s)
in my suggestions, which I welcome.


HTH
Chris



--- Jason Butler <jwbutler at wispertel.net> wrote:

> I have somehow pissed the Audi gods off, within the last three weeks
> I've 
> had a timming belt that slipped three teeth a blown tire a bad fuel
> pump and 
> now this.  The car is a '93 S4 with stock everything.   It Idles fine
> and 
> drives ok with no load on it but if I get over 5 PSI boost it cuts
> out and 
> stumbles.  I get a code of 2342 which is O2 sensor, ignition problem,
> fuel 
> tank empty (it's not this one), air leak etc..  anyone have any BTDT.
> 
> things I've done in the last three weeks
> 
>     Replaced timing belt.
>     Replaced water pump.
>     Replaced Spark Plugs.
>     Replaced Fuel pump.
> 
> 
> Any advise would be apreciated
> 
> Jason
>  
> 
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> 


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