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High Engine Temp on 07/08/09 Bikes
2007/2008/2009 Harley-Davidson High Engine Temperature Behavior
(Editor Notes: We have learned a lot since this article was initially published. While the nature of the article is essentially correct and we stand by our observations, there are some techncial details about the workings of the HD ECM that we feel we got wrong. We will be correcting these in the near future as we find better information. We have found that HD has had a natural evolution of improved programming in the ECM's resulting in much better engine behavior in high temperature situations. There are also hidden tables that are beyond those seen by SERT/SEST, which control some aspects of the HD engine behavior. These hidden tables may account for some of the wild card actions we have seen in the past, but it is more likely that we just need to be more observant and gather a bit more data. We make the best observations and conclusions we can with our limited resources. We will update and correct as new information comes available.)
It doesn't take long after purchasing your new HD to figure out 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.
lDuring engine warm up the HD engine runs in open loop mode at a 12.5:1AFR. 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 hot) 14.6:1. Normal idle speed is 1050.
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 14.7:1 which is too lean. This means that the smallest amount of throttle will lean the engine out as long as the ECU is operating in "high heat" mode.
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. (Update: This behavior was not a true engine overheat. It was not consistent with HD's desert testing. This is probably better described as an engine cooling mode to make the rider more comfortable. We were not watching the AFR and temps on both cylinders to verify this.) 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) 14.7:1 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 14.7:1 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.
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.
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