[s-cars] 93 S4 running weird/rough
Keith Maddock
Keith.Maddock at trw.com
Wed Jun 19 04:11:23 EDT 2002
David,
Your most probable culprit is one of the PSO (Power Stage Output) devices, or one of your coil packs.
(some people will also refer to the PSO as the POS)
To diagnose, do the following:
Wait for a time your engine is running rough. Remove the long black plastic cover (held by two Allen screws) over the fuel rail.
The first thing to do is identify which cylinder is missing. One at a time, remove the Fuel Injector connectors. When you remove the connector on the cylinder that is missing, you won't notice a difference in the idle. When you remove any of the other connectors, the idle will be very rough because you've just turned your 4 cylinder I-5 into a 3 cylinder I-5...
Once you know which cylinder is not running, you need to swap your two PSO's They are small black plastic modules and are located on the firewall, under neat the black plastic cover that's held on with two quarter-turn plastic screws. One is mounted "upwards" and the other is mounted "downwards". Swap these two modules around.
Repeat the "missing-cylinder-identification" routine above. If the missing cylinder moves by 3 spots (From 1-4, 4-1, 2-5, or 5-2), then you need a new PSO. If the missing cylinder was #3, and all 5 cylinders are now running, then you got lucky (the 2nd PSO only controls cylinders #4, and #5, and has one unused input/output).
If the missing cylinder did not move or go away when you swapped PSO's, then it is most likely your coil. Swap the coil assemblies of the missing cylinder with another cylinder, and see if the missing cylinder moves with the coil swap.
If that doesn't do it ,try swapping FI's around...
Cheers,
Keith
-93 S4 with two new PSO's
*************************************************************
Keith Maddock, TRW Automotive, Livonia, Michigan
Slip Control Software Design, Traction Control Systems
(734) 266 - 3971 - - keith.maddock at trw.com
>>> "cuatro quattro" <quattropwr at hotmail.com> 06/19/02 12:49AM >>>
Hi all,
Have a strange problem that I can't quite resolve with my 93 S4.
The problem started about 2 weeks ago and is getting more frequent/worse.
ok, here's the problem..
The engine would sometimes run very rough like if it's running on 4
cylinders instead of 5. This happens all the time and is not boost or
engine RPM dependent. It happens while idling too. I'm not getting any
fault codes. Sometimes the engine would just run perfectly without any
problems.
So far, I've replaced all the spark plugs and the O2 sensor. Neither
helped.
any ideas? Much thanks in advance.
David
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