Compare the screenshot above to the one below. These two screenshots are a mere fraction of a second apart. Right after 3,740 RPM, the ECU snapped the throttle back to idle. You can see below that the throttle is on its way down to idle and is currently at 40.4%. The peak engine speed was 4,009 RPM as shown in the top graph in red. The third graph row shows TPS in green. You can see that in a moment the TPS would reach idle setting, about 16%. The throttle opening immediately after that, along with the corresponding rise in engine speed was Dan pedaling the throttle trying to see if the engine would still respond or if limp mode had kicked in again. Clearly the engine responded, so it wasn't limp. Here we had a limiter, or a cut-off issue.

The ETC table is for Electronic Throttle Control cut-off. The factory calibration leaves the Park/Neutral (P/N) setting at 4,000 RPM. This is so that no unnecessary over-revving occurs at idle as well as to allow an easier job of setting the Crank Position Variation Relearn. For Crank Relearn, part of the task is to goose the throttle and hit the rev-limiter. Why do that at 6,600 RPM when you can do it at 4,000? So the setting goes. However in this case, we believed that the ECU didn't correctly understand that it was in gear and moving after the engine swap had been performed. A forgotten pin or sensor input, perhaps? Maybe, and the technician who installed the engine was going to find out. In the meantime, you can see in the screenshot above that the value was now changed to 6,600 RPM; same as the other gear cut-off settings. With this change saved and loaded into the ECM, the car was sent around the track again...

The data above proves that this change hit the nail on the head. This time around, the car easily eclipsed 4,000 RPM as can be seen above. The engine hit 5,124 RPM while hydroplaning the fronts in the monsoon that was coming down. That was all that we needed to see and Dan brought the car back into the pits. With no windows, we figured that the laptop and equipment would be floating in a small pool by the time Dan turned in a lap, but at least the job was done, the problems were solved and the car stayed off the wall. So the next time you encounter a limp mode condition, remember these helpful little hints. Check the Diagnostic Trouble Codes first to determine if there is a sensor malfunction or some other potential issue, and if not, proceed to making the appropriate changes to the calibration. The example above was for the P01 controller, but you'll find most controllers, including E38 and E67 have similar diagnostic mechanisms. If you disable the diagnostic mechanisms, your race engine should hum along happily once you've tuned it properly. That was our next step with this little race car, but that will wait for another sunny, dry day. MET

limp mode fix

getting your swagger back

To solve this issue, open up the Engine section, and then go to Fuel, and then Cutoff, DFCO in the calibration file. Here you'll find the engine speed limiter settings. You can see in the screenshot below that the RPM Limits are set to cut off at 6,600 RPM and Resume at 6,599 RPM. That all looks fine. However, in the ETC table, under Cutoff RPM vs. Gear, we figured we'd make a change...

Cobbles set firmly in place, the car was run on our home track at part-throttle for the first half of the lap to be certain that the air/fuel ratio was acceptable and that the engine oil temperature and pressure checked out ok. Once on the back straight, Dan opened up the throttle. At full throttle, the limp mode issue was solved, but we still had a cut-off issue at 4,000 RPM. The data log can be seen below. Notice how the engine speed and wheel speed don't match in many areas? That's some serious hydroplaning! But the part we're really interested in is the white cursor line. You can see in the screenshot below that at 3,740 RPM, Dan still had the throttle pegged. Immediately after that, Dan's foot was still to the floor, but the ECU had closed the throttle up and ended the party at 4,000 RPM.

You can see in the photo to the right that we installed our wide-band O2 sensor along with our trusty HP Tuners VCM Suite to get the data we needed. The wide-band O2 will serve to verify that the air/fuel ratio is within acceptable limits for us to carry out some minor testing.


Unfortunately on this particular test day, the sky had opened up and rain kept falling. In fact, it was pretty much a deluge, but we soldiered on despite having no rain tires present. Old, hard slicks combined with a cold day (for Florida; it was 45 degrees F - Ed.) meant that there'd be a lot of slipping and sliding about but that we could nonetheless get the data we needed if we had the stones for some full throttle runs while hydroplaning. Isn't tuning fun?

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