Nightrider Technical Notes

2007 HD High Heat Behavior

Posted by Stephen P Mullen on 1/1/2007 to HD Tech Notes

2007/2008/2009 Harley-Davidson
High Engine Temperature Behavior

What is the LC1 Wide Band O2 sensor upgrade?

Nightrider has found a Wide Band O2 sensor upgrade that works in place of the OEM HD narrow band O2 sensors. This upgrade will allow the HD engine to operate in closed loop mode at a richer air fuel ratio. Richer air fuel ratios in closed loop mode will significantly reduce the exhaust temperature and improve throttle response. The AFR the engine will operate at is fully programmable by using a personal computer. This upgrade can be applied to any 07 and later bike or 06 Dyna by removing the OEM NBO2 sensors and installing the WBO2 upgrade.

The kit will consist of Wide Band O2 sensors to replace the two sensors used by the OEM ECU. Installation consists of removing the OEM O2 sensors, install the new WBO2 sensors, locate the control boxes under the seat or on the frame, connecting the O2 signal wires to the HD wiring harness and connections to a switched +12V power source.

The upgrade are fully compatible with any 06 stock Dyna, all stock 07 HD's, all HD "Stage" downloads, HD stage upgrades (103, 110, etc) or with SE Race Tuner, although no other HD product is required to use our upgrade. The WBO2 upgrade is also compatible with aftermarket ECU mapping devices like the PowerCommander or TFI if you use them without the O2 eliminators connected. has line of products that alter the OEM narrow band HD narrow band O2 sensor signal and richen the closed loop fuel mixture at a much lower cost than the LC-1 WBO2 upgrade. The XiED line of products is based on Patented technology that can richen the fuel mixture from 14.6 to 13.6:1. These products are much more cost effective and usually recommended over LC-1.
(Originally Published in 2007. Updated comments are in Italics.)
It doesn't take long after purchasing your new HD that this is a very hot running engine. One of the most common complaints about the new bikes is the heat that comes off the engine and exhaust system. These high operating temperatures can be mostly attributed to the new closed loop operating mode of the EFI system. The OEM closed loop operating mode relies on narrow band oxygen sensors to keep the air fuel ratio at 14.6:1 at idle, under normal riding circumstances and while cruising on the highway.

Most Riders are also aware that HD engine EFI acts a little differently when the engine even gets hotter than normal. The conditions that trigger a high heat condition include trying to idle for long periods of time, under very slow riding conditions or when the ambient temperature starts getting above 85 degrees. When the ECU senses hot engine temperatures, it goes into a overheat/high temperature mode of operation that is sometimes referred to as "Parade Duty" mode. Knowing that this overheat mode exists and recognizing what is happening as the engine temperature goes up are completely different issues. During development and testing of the LC1 Wide Band O2 sensor Upgrade, the behavior of the OEM ECU was observed and data logs collected by our laboratory instruments. Listed below is the sequence of events and engine behaviors noted as the engine warms up, gets to normal operating temperature and goes into high temperature mode.

lDuring engine warm up the HD engine runs in open loop mode at a 12.5:1 AFR. No matter what the engine temperature, this is the AFR that occurs at starting. If you disconnect the O2 sensors on the engine, this is the default idle AFR for the HD engine until the engine warms up.

Once the ECU determines the engine is warmed up, it goes into closed loop mode and will idle at a very lean (and rather warm) 14.6:1. Normal idle speed is 1050. It must be noted that technically an 14.6:1 AFR is not lean, but it is not an ideal fuel mixture for an air cooled motorcycle engine.

In high temp mode the engine RPMs drops to 950 and the ECU goes to open loop mode, richening the fuel mixture to 12.0:1 in an attempt to cool the engine. As soon as the engine RPMs hits 1200, the ECU goes back to closed loop mode at 14.6:1 which could be considered a bit too lean for an air cooled motorcycle. This means that the smallest amount of throttle will lean the engine out as long as the ECU is operating in "high heat" mode.
This tested was done on an 07 Softail. On this bike, it was specifically noted that the ECM did richen the fuel mixture considerably as engine heat increased. We theorize that this is a similar level at which the FLH's would have gone into parade mode or rear cylinder shutdown. It must be stressed that the engine behaviour seen was not a true 'overheat', but would have been uncomfortable for the Rider. The ECM did show how it richens the mixture under adverse situations to cool itself.

If the bike tries to accelerate, the engine stumbles and the continuation of the lean AFR condition can drive engine temperature even higher.

lDuring testing in controlled conditions with data logging instrumentation attached to the engine, the overheating engine behavior was captured. The OEM engine will go into this "high heat" mode in about 10 minutes of idling at 78 degree ambient temperatures in shady conditions. Exhaust pipe temperature will get as high as 750F degrees about 6" down from the cylinder heads as measured by a thermocouple. Temperatures of 194+ degrees were measured at the heat shields of the same location by IR thermometer.
lThe graphs below summarize testing done. The OEM engine (top) ran at 14.7:1 until it overheated and the AFR richened to 11.5:1. Exhaust temperatures peaked at 750 degrees and averaged 600 degrees during the test duration
lThe lower graph represents an engine with the LC1 WBO2 upgrade. The AFR is centered on 13:1 as programmed into the LC1. Temperatures at the exhaust peaked at 660 or 90 degrees less. Average exhaust temperature during the test was 540 degrees or 60 degrees low. Temperatures at the heat shield were 150 degrees or over 40 degrees lower.
lWith the LC1 WBO2 upgrade in place, the HD engine was 15-20% cooler under the same operating conditions and never went into high temperature operating mode.

The ECU forces the engine to idle at a very lean (and hot) 14.6:1 in closed loop mode. Normal idle speed is 1050. In high temp mode the engine RPMs drops to 950 and the ECU goes to open loop mode to richen the fuel mixture to 12:1 in an attempt to cool the engine off. Give the engine some throttle and as soon as the engine RPMs hits 1200, the ECU goes back to closed loop mode at 14.6:1 which is too lean, it drives engine temperature even higher and the engine stumbles.

During testing of the LC-1 WBO2 upgrade, data logs were captured the OEM HD engine/ECU behavior with various test instruments for RPMs, Exhaust Temperature and AFR. The OEM engine will go into this "high heat" mode in about 10 minutes of idling at 78 degree ambient temperatures in shady conditions. Exhaust pipe temperature can get as high as 800F degrees about 6" from the cylinder heads. Temperatures measured by IR Thermometer at the heat shield was 194+ degrees.

With the WBO2 upgrade in place under the same conditions, exhaust pipe temperatures averaged almost 100F degrees cooler after 15 minutes of idle and the ECU never went into high temperature mode. Temperatures at the heat shields were a little over 150 degrees, or 40 degree drop.

Engine Setup >

Test Results

OEM Engine with Narrow Band O2 sensor
14.7:1 AFR
Engine with Wide Band O2 sensor upgrade
13.0:1 AFR
How much cooler?
Maximum Temperature 749 661 88
Average Temperature 597 542 55
Heat Shield Temperature 194 158 36

Max and Avg temp measured by thermocouple on exhaust header 6" below exhaust port. Heat Shield temp measured by IR thermometer over thermocouple spot.

Temp measured during 16 minute idle test. About 10 minutes into the test, the engine when into overheat/parade duty mode. In  high heat mode the ECU richens the fuel mixture to 11.5:1 and lowers the idle speed to 950 RPMs. Temp measured during 15 minute idle test. The engine never went to overheat mode. Even with the OEM engine in high heat mode trying to "cool" the engine down, the WBO2 upgrade kept the engine significantly cooler.

While installing the LC1 WBO2 upgrade can not guarantee that the engine will not go into high heat mode, it does make it more resistant to high temperatures. Should the engine go into high temp mode, when the RPMs reach 1200 the WBO2 sensor will make sure the fuel mixture is a richer fuel mixture to prevent stumbling.

LC1 WBO2 Test Results Summary

Here are the summary graphs for an OEM engine during a 16 minute idle test. On the AFR graph on the left notice the two peaks. One peak is around 11.5 and the other at 14.7. This displays the ECU behavior as it tries to cool the engine as it overheated. During the test the average temperature was 597 degrees with a maximum temperature of 749 as measured by thermocouple on the exhaust pipe located about 6 inches down from the exhaust port. Temperatures were also measured at the heat shield over the thermocouple at 194 degrees

Below are the summary charts for the same engine with the closed loop AFR set to 13:1. Note the AFR remains centered on 13:1 indicating the engine never went into overheat mode. The average temperature was 542 degrees with a maximum of 661 degrees. Temperature at the heat shield was 158 degrees

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