Discussion
After getting the exhaust back pressure valve sorted, I now noticed a bit of a stumble around the 3000 rpm range. I have read that others have this problem and that some of the upgrade chips reduce and in some cases fix this problem. However, I am quite happy with the current performance and don't want to do a chip upgrade. So, has anyone successfully fixed the 3000 rpm stumble without a new chip? By the way, freescan shows no error codes, but I havn't done logging yet to see if there is something obvious when this stumble happens.
Any advice?
Thanks
John
94 S4
http://24.31.219.162
Any advice?
Thanks
John
94 S4
http://24.31.219.162
I believe that rechipping is the only simple solution as it's a boost control issue in the ECU.
There's a great explanation of the issue on Kato's site:
www.lotusespritworld.com
The chip you'd want is the Improved Mark V.
The S4s Mark V still has the stumble...the next iteration does not.
All the higher boost chips (the 310 and 330) and the High Torque chip are based on that Improved Mark V code.
Of course, if you are adept at such things you can reprogram the code yourself...you'd want to start by looking at what exactly Andy Whittaker did to reduce the stumble in the first place. I'd imagine you can modify his code to reduce the stumble but still maintain the stock S4 boost limits.
>> Edited by madmike on Tuesday 15th July 18:42
There's a great explanation of the issue on Kato's site:
www.lotusespritworld.com
The chip you'd want is the Improved Mark V.
The S4s Mark V still has the stumble...the next iteration does not.
All the higher boost chips (the 310 and 330) and the High Torque chip are based on that Improved Mark V code.
Of course, if you are adept at such things you can reprogram the code yourself...you'd want to start by looking at what exactly Andy Whittaker did to reduce the stumble in the first place. I'd imagine you can modify his code to reduce the stumble but still maintain the stock S4 boost limits.
>> Edited by madmike on Tuesday 15th July 18:42
From memory:
The stumble happens because the boost control algorithm turns on at 2810rpm and shuts down the fun for a second. Suprisingly (to me, at least), the car can't use the MAP sensor below a certain throttle opening (94%?) and boost is actually bled off at part throttle settings based on a map in the ECU. That map is just a little bit off. IIRC, Andy's fix effectively shifted everything a little bit to the right.
Michael Sullivan accomplished the same thing mechanically by cutting the wastegate actuator vacuum line and connecting the two pieces with a bit of metal tubing with a few tiny (1/16"?) holes in it. He added holes until the problem went away.
I have Andy's chip and am very pleased with it.
The stumble happens because the boost control algorithm turns on at 2810rpm and shuts down the fun for a second. Suprisingly (to me, at least), the car can't use the MAP sensor below a certain throttle opening (94%?) and boost is actually bled off at part throttle settings based on a map in the ECU. That map is just a little bit off. IIRC, Andy's fix effectively shifted everything a little bit to the right.
Michael Sullivan accomplished the same thing mechanically by cutting the wastegate actuator vacuum line and connecting the two pieces with a bit of metal tubing with a few tiny (1/16"?) holes in it. He added holes until the problem went away.
I have Andy's chip and am very pleased with it.
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