poor performance above 4000 rpm
07-19-2002, 12:24 PM
#1
2nd Gear
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Location: France
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poor performance above 4000 rpm
Hi,
I posted a couple of months ago a topic concernnig my 87 S4 which had problems accelerating above 70 or 80 MPH and 4000 RPM.
A certain number of leads where kindly provided by Wally Plumber,and others whom I thank here again:
bad coils, plugged exhaust pipe, clogged injectors,dirty spark plugs, fuel filter, varied ignition problems etc.
Salvation came from a Rennlist member in Switzerland, Antoine Comte, who had experienced the same problem with his GT.
Both of us are used to disconnecting the battery when we expect not to drive our cars for long periods of time.
This is the origin of the problem, and the solution was in his GT owner's manual:
After connecting the negative wire of the battery, just let the engine run 10 minutes at idle to let the engine computer ( which one i do not know, specialists will understand what i am talking about, probably one which has something to do with ignition of fuel management)find its original settings.
The result was dramatic, and this procedure hasd saved me more frustrating trips to the dealer:
my old 87 S4 accelerates like a brute, like on day one, and drives smoothly with all its power back, a true delight, a feewling i had not experienced for years. and a testament to the other qualities of these cars, which to me are so beautiful and special that i brought mine from Miami to France and still endure the grotesque red tape which goes with the certification of an imported car.but this too is another story. Would you beleive that to register this car in France and have legal livcence plates, iI have to prove that I HAVE PAID MY TAXES in the USA???.
Anyway, thank you Antoine Comte in Switzerland, and thanks to the Rennlist.
Claude Marchal
87 S4
I posted a couple of months ago a topic concernnig my 87 S4 which had problems accelerating above 70 or 80 MPH and 4000 RPM.
A certain number of leads where kindly provided by Wally Plumber,and others whom I thank here again:
bad coils, plugged exhaust pipe, clogged injectors,dirty spark plugs, fuel filter, varied ignition problems etc.
Salvation came from a Rennlist member in Switzerland, Antoine Comte, who had experienced the same problem with his GT.
Both of us are used to disconnecting the battery when we expect not to drive our cars for long periods of time.
This is the origin of the problem, and the solution was in his GT owner's manual:
After connecting the negative wire of the battery, just let the engine run 10 minutes at idle to let the engine computer ( which one i do not know, specialists will understand what i am talking about, probably one which has something to do with ignition of fuel management)find its original settings.
The result was dramatic, and this procedure hasd saved me more frustrating trips to the dealer:
my old 87 S4 accelerates like a brute, like on day one, and drives smoothly with all its power back, a true delight, a feewling i had not experienced for years. and a testament to the other qualities of these cars, which to me are so beautiful and special that i brought mine from Miami to France and still endure the grotesque red tape which goes with the certification of an imported car.but this too is another story. Would you beleive that to register this car in France and have legal livcence plates, iI have to prove that I HAVE PAID MY TAXES in the USA???.
Anyway, thank you Antoine Comte in Switzerland, and thanks to the Rennlist.
Claude Marchal
87 S4
07-20-2002, 09:05 AM
#3
Three Wheelin'
Join Date: May 2001
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As we all know, our cars have PCM’s {power control modules .LH EZK) which are computers. Any computer needs memory to function properly. There are several kinds of memory. PROM (program read only memory) and ROM (read only memory). They hold (library) the basic set of instructions (map) on how the input from sensors (O2, RPM, MAF) will be handled, and also vehicle specified data (weight, axle ratio, engine type, etc.
Maps are programs stored in the PROM and ROM. Maps are a set of instructions for different driving conditions. An example: if you push the gas pedal to the floor the PCM knows the car is under a load by inputs from the RPM, MAF, and TPS sensors, for these set of conditions the PCM will advance the cars timing.
RAM (random access memory) and KAM (keep alive memory) is where temporary information from sensors are stored, updated and rearranged. It’s a journal of driving and operating conditions that have been recorded. Fault codes are also stored in RAM and KAM. Even though the PCM has a map, it also has the ability to relearn new strategies. It learns from systems or sensor failures. An example would be the 02 sensor, having a lazy reading due to age. The PCM “looks up tables” (map) to find the adaptive setting for fuel injector pulse and timing. The PCM can’t compensate for a total electronic or mechanical failure. This information is stored in the KAM as fault codes. If the battery were disconnected in this example the adaptive strategies would be lost on startup, which would cause a rich or lean drivability problem until the PCM reads the O2 sensor is out of range and adapts to its new setting.
928 S4’s have adaptive memory strategy for idle speed and CO level. “Due to the storage of carried-out curve displacement in the memory, the engine will have to be run about 10 minutes at first after an interruption of the permanent pulse to the control unit, e.g. caused by disconnecting the battery or pulling off the 35-pin plug on the injection control unit, which cancels the displacement, in order to permit correct adaptation to the nominal values.”
If any electronic sensors on the motor, which would set a code, were changed the keep alive adaptive memory would have to be erased for the PCM to return to its factory map setting. If you don’t have a scan tool that can clear codes, you should disconnect the battery and touch the disconnected negative cable end to the batteries positive disconnected cable end. This will discharge any capacitors in the system and remove the adaptive information stored in the KAM.
In conclusion, disconnecting the battery on any computer control vehicle will have an adverse effect on the vehicles performance until it has relearned its adaptive strategy or map values.
Steve C
The great white
Use a computer memory safer when disconnecting your battery
<a href="http://www.eastwoodcompany.com/cgi-bin/sgsh0101.exe?&UID=2002072007032958&SKW=TEL3&FNM=20" target="_blank">http://www.eastwoodcompany.com/cgi-bin/sgsh0101.exe?&UID=2002072007032958&SKW=TEL3&FNM=20</a>
<img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />
Maps are programs stored in the PROM and ROM. Maps are a set of instructions for different driving conditions. An example: if you push the gas pedal to the floor the PCM knows the car is under a load by inputs from the RPM, MAF, and TPS sensors, for these set of conditions the PCM will advance the cars timing.
RAM (random access memory) and KAM (keep alive memory) is where temporary information from sensors are stored, updated and rearranged. It’s a journal of driving and operating conditions that have been recorded. Fault codes are also stored in RAM and KAM. Even though the PCM has a map, it also has the ability to relearn new strategies. It learns from systems or sensor failures. An example would be the 02 sensor, having a lazy reading due to age. The PCM “looks up tables” (map) to find the adaptive setting for fuel injector pulse and timing. The PCM can’t compensate for a total electronic or mechanical failure. This information is stored in the KAM as fault codes. If the battery were disconnected in this example the adaptive strategies would be lost on startup, which would cause a rich or lean drivability problem until the PCM reads the O2 sensor is out of range and adapts to its new setting.
928 S4’s have adaptive memory strategy for idle speed and CO level. “Due to the storage of carried-out curve displacement in the memory, the engine will have to be run about 10 minutes at first after an interruption of the permanent pulse to the control unit, e.g. caused by disconnecting the battery or pulling off the 35-pin plug on the injection control unit, which cancels the displacement, in order to permit correct adaptation to the nominal values.”
If any electronic sensors on the motor, which would set a code, were changed the keep alive adaptive memory would have to be erased for the PCM to return to its factory map setting. If you don’t have a scan tool that can clear codes, you should disconnect the battery and touch the disconnected negative cable end to the batteries positive disconnected cable end. This will discharge any capacitors in the system and remove the adaptive information stored in the KAM.
In conclusion, disconnecting the battery on any computer control vehicle will have an adverse effect on the vehicles performance until it has relearned its adaptive strategy or map values.
Steve C
The great white
Use a computer memory safer when disconnecting your battery
<a href="http://www.eastwoodcompany.com/cgi-bin/sgsh0101.exe?&UID=2002072007032958&SKW=TEL3&FNM=20" target="_blank">http://www.eastwoodcompany.com/cgi-bin/sgsh0101.exe?&UID=2002072007032958&SKW=TEL3&FNM=20</a>
<img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />
07-20-2002, 11:42 AM
#4
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Two things to add to Steve's excellent post: 1. Only the '87 and later cars have this "fuzzy logic" ability to learn and adapt their maps, and 2. I suspect, after experience with my previous car [Corrado VR6; LH-Motronic 2.7] that if your car behaves badly right after you reconnect your battery, then your computer is having to adapt for some component that might be on the way out. I disconnected the battery several times on that car, which was fairly new at the time, and noticed little difference afterwards.
Normy!
'85 S2 5 speed
Normy!
'85 S2 5 speed