By Gadget, using info introduced by Lumir F. Bakota
and originally posted to the Delphi Vulcan Forum By Leo Holzman
A common complaint among Vulcan (and some other big twin) owners involves pre-ignition (aka "knocking" or "pinging") when rolling on the throttle especially in warm weather. There may be multiple causes in any given engine ranging from lugging the engine to a buildup of carbon in the combustion chamber (often caused by lugging) but it can also be caused by a lean mixture.
I'll be providing all the tech stuff below but here's the nuts and bolts of it. First, this should be considered a temporary fix, an experiment to determine if a richer mixture will end that "marbles in the combustion chamber" noise. If it does then I'd strongly suggest trying to eliminate ping by adjusting your throttle position sensor or buying a Dobeck Performance TFI or other aftermarket computer that can be used to add fuel when and where you actually need it rather than all the time as this fix will do.
The Vulcan FI Electronic Control Unit (ECU) determines the mixture of air and fuel to be sent to each cylinder based on information from several sensors. Coolant temperature, Air Temperature, Air pressure (altitude), Throttle Position and RPM. The ECU uses pre determined maps and when all the above items fit into a part of the map the ECU sends a certain amount of fuel through the injectors. If that amount of fuel is actually a little less than what the engine could actually use then combustion chamber temperatures go up, fuel ignites prematurely and you have the dreaded power robbing and engine damaging pre-ignition (knock or ping).
And so the fix. You could spend over $100 on an aftermarket computer like a Techlusion TFI just to fatten up the low end of the rpm range and that's highly recommended if you've modified your intake to flow a lot of extra air. For about 25 cents you can add a simple resistor between the air temperature sensor and the ECU. This tricks the computer into thinking it's a little cooler than it actually is by increasing the resistance number being sent by the sensor. A little extra fuel will be sent to the injectors, the engine won't run lean and you'll have an end to (or at least a lot less) pre-ignition. As noted above, if this trick works then give serious consideration to the purchase of an aftermarket device like the TFI or Power Commander. If the resistor trick doesn't work then you've saved some money.
Assuming your eyes haven't already glazed over, this is a very simple and reversible mod. Please note there is some chance that with this modification your FI light might come on somewhere around 32 degrees Fahrenheit (0 degrees Celsius) because at that temperature the resistance reading being sent by the air temperature sensor might be higher than normal range causing what the ECU considers a fault. The engine won't quit on you, don't worry.
What You'll Need
1- 470, 800 and/or 1000 Ohm Resistor, preferably 1/4 watt. At least one Vulcan 1600 owner has used the 800 ohm and reports it worked well on his engine that pinged very badly before the fix while another says it took a 1200 ohm resistor to make is bike run like the proverbial scalded cat he expected. You might want to start with the 470 and work your way up. Remember this fix will make your engine run just a little bit richer at 'all' rpm's so you don't want to over do it. You might even want to install a switch so you can bypass the resistor when you're just cruising down the highway, lookin' for adventure and don't need the extra fuel. How much richer will your motor run with the resistor you ask? Well, thanks to Mike Masse of Montreal we just happen to have an absolutely 'over the top' Excel spreadsheet that shows the link between resistance and temperature and fuel added to what would be the stock amount. Here ya go fellow techies, enjoy. (Note if the link doesn't open you probably don't have MS Excel on your computer.)
How To Do It
Look near the bottom right of your stock air box backing plate (right side 'air cleaner' cover) and you'll see a brass colored device. (#9 in drawing at left). That is the temperature sensor which varies its resistance reading to the ECU as air temps rise and fall.
You will be cutting the wire from that sensor (either a couple of inches from the sensor or at the ECU) and soldering the resistor into the wire. It is STRONGLY suggested you cover the resistor and any exposed wire with shrink tubing even if you only slide the tubing over the parts and zip tie the ends (makes changing or removing the resistor simpler later)
If you choose to put the resistor near the ECU just note the color of the wire coming off the sensor (usually pink for Vulcans) then look for that wire color at the ECU plug.
Test this mod with a ride under conditions that usually cause some pre-ignition in your engine. Typically that would be a warm day, rolling on the throttle heavily in (usually) too high a gear. Even if you generally keep the rpm's up go ahead and lug it a little for testing purposes. Hey, this is science ya know! If you still get a bit of ping you might want to try the next step higher resistor (aren't you glad you didn't shrink that protective tubing?)
If you really want to get fancy you could add a 1000 ohm potentiometer in line instead of a simple resistor and vary the resistance until you find the sweet setting. Then measure the resistance you end up with and get the next closest resistor to solder into the line. As mentioned earlier you could also bridge the resistor with a switch so you could turn the resistance on or off depending on riding conditions.
You'll find some duplication of some text above in the material below. The following though is far more technical and goes into much greater detail. Enjoy techies !
Causes of pinging/knocking on 4-stroke engines.
The pinging is usually caused by some kind of uncontrolled ignition that occurs too early in the engine’s compression cycle. Apart from running with no oil, the engine ping/knock is probably the second worst thing that can affect the longevity of an engine. There can be quite a few reasons for the engine pinging/knocking like a lean air/fuel (AF) mixture, too advanced spark timing, wrong spark plugs, engine overheating, carbon deposits, high compression ratio, poor fuel and possibly others. The only cause that I want to address in this article is the lean AF mixture, as this can be corrected by simple (or complicated and expensive) modification of the bike’s FI system.
The useable AF mixture on which the 4-stroke engine can run is quite wide. It can be as high as 17:1 for the most complete combustion, minimum emissions and best fuel economy and as low as 12:1 for the best engine power. An optimum AF ratio is usually considered to be 14.7:1 or 14.7 pounds of air for 1 pound of fuel. Running lower AF mixture not only gives you more power, but it is safer for the engine as the extra fuel is cooling the cylinder and cylinder head components. Different engine operating conditions and load may require different AF mixture, so on carbureted engines, where the mixture cannot be precisely controlled, the manufacturers tend to set it overall a bit richer and you seldom have a pinging problems.
On the FI engines, there is much better control of the AF mixture as the bike’s sensors supply the ECU (electronic control unit) all the needed information like the engine and air temperature, air/ambient pressure, throttle position, engine load and others. This, combined with the environment protection concerns, is making the manufacturers to push the limits of engines combustion setup towards more lean AF mixtures = more complete, less emissions combustion.
Unfortunately, some manufactures seem to program/map their ECUs towards excessively lean mixtures (especially on liquid cooled bikes where it is more safe) which inevitably results in pinging/knocking usually under low RPM, heavy load and hot operating conditions. Instead of optimizing bike’s sensors and ECU program/map the manufacturers make the owners solve the problem - pay a premium for a high octane gasoline.
This is especially true about the large FI Kawasaki V-twins. As far as I know, all the 1500+ cc Kawasaki V-twins have 9:1 compression ratios, which in no case should require high octane gas. There is quite a few FI bikes with 11:1 or more compression ratios which are rated by manufacturers for a regular 87 octane gas. An example is the above mentioned Suzuki V-Strom with 11.5 : 1 compression ratio.
Most of the V-twin cruiser owners are making the AF mixture issues worse by installing open pipes and air kits that tend to lean out the AF mixture further and make the pinging worse. The only solution for situations like this is some kind of ECU program/map modifying devices like the Power Commander (PC) or Techlusion’s TFI. The cost of these “gizmos” is quite substantial, usually $400+ in Canadian dollars. I am not familiar with the design of these devices and I do not know if they modify the AF mixture only or if they modify things like the spark advance as well, and I am not going to comment on their pros and cons.
Solving the pinging/knocking with air temperature sensor modification.
Your FI bike’s ECU has a certain program/map which tells it how much of fuel should be injected depending on operating conditions. One of the most important “condition” is the temperature of the air, which mixed with the fuel facilitates the combustion. The air (including the oxygen in it) is a weird yet predictable “animal”. Depending on pressure (and that depends on elevation) and temperature, the same mass/weight of the air will have a different volume. As we are going to tinker with the air temperature sensor, the air temperature effect is what I will try to explain a bit more. Have a look at the graph below showing the relationship between the air pressure (mass/volume) and the temperature.
As the temperature goes up, the air gets “thinner” and there is less oxygen in it to facilitate the combustion. To keep the proper AF mixture, your FI bike has an air temperature sensor and at higher temperature (= lower air pressure) it will tell the ECU to correct/lower the amount of fuel added per volume of the combustion air and vice versa.
The air temperature sensor on Kawasaki FI bikes is a thermistor that is changing its resistance depending on temperature. I have the resistance data for the 2003/2004 VN1600 Classic and they are identical for the Mean Streak. I would assume that the sensors are the same on the other Kawasaki FI bikes but I cannot guarantee it. The graph below shows the sensor’s resistance versus temperature:
As you can see, at low temperatures the resistance is as high as 6000 Ohms while at higher temperatures it is as low as 500 Ohms. For us the most important resistance range is somewhere between 1500 and 2500 Ohms, corresponding to 20 to 40 deg.C engine inlet air temperatures as measured by the sensor. I am assuming that the engine inlet temperature will be some 10 deg.C higher than the actual ambient temperature as the air will warm up going in between the cylinders before it hits the sensor – your guess is as good as mine.
Our objective is to eliminate/reduce the pinging by making the AF mixture richer. This can be achieved by a simple trick – adding the resistance to the air temperature sensor. If we add the resistance, we are fooling the ECU into thinking that the engine inlet air is cooler (= more mass and oxygen per volume) and the ECU will increase correspondingly the addition/injection of fuel. Unfortunately, there is one issue here with adding a fixed value resistor in series with the air temperature sensor (thermistor). Both the air pressure vs. temperature and the sensor resistance vs. temperature curves are not linear, so the same resistor (say 500 Ohms) will have a different effect at different air temperatures. As I will demonstrate in next two examples, that might actually be to our benefit. The two examples are exact calculations for 500 Ohms resistor with an air at 80% humidity at elevation of 800 meters above the see level (most of Alberta).
Example 1:. Ambient temperature is 10 deg.C, engine inlet is 20 deg.C. The sensor/ECU is reading 2560 Ohms, air pressure 0.06813 lb/ft3. Added 500 Ohms - the ECU is now reading 3060 Ohms, corresponds to 15.4 deg.C = air pressure 0.06925 lb/ft3. Air pressure increase is 1.7% the ECU adds 1.7% more fuel.
Example 2: Ambient temperature is 30 deg.C, engine inlet is 40 deg.C. The sensor/ECU is reading 1210 Ohms, air pressure 0.06245 lb/ft3. Added 500 Ohms - the ECU is now reading 1710 Ohms, corresponds to 30.4 deg.C = air pressure 0.06530 lb/ft3. Air pressure increase is 4.5%, the ECU adds 4.5% more fuel.
Evidently, the higher the ambient/engine inlet temperature, the bigger the effect of the 500 Ohms resistor will be. As mentioned before, that might work OK for us as at higher temperatures the engine is much more prone to pinging and it needs richer AF mixture to eliminate the pinging.
Bottom line facts.
Assuming that the Kawasaki FI engines are as stock rather on a lean side in the AF mixture, they can make use of the fuel ratio increase by up to 20%; let’s be conservative and say 15% max (and this is with the stock exhaust). Based on the data presented above, I would say that a fixed resistor in range of 500 to 1500 Ohms (added in series with bike’s temperature sensor) would work best for the most common operating temperature range to eliminate the pinging. I am using presently the 500 Ohms resistor and planning to go to 700 Ohms. Ideally, a 1500 Ohms potentiometer could be installed to vary the resistance for an optimum performance. Remember, too rich AF mixture will not harm the bike, too lean mixture will.
I have not seen any deterioration in fuel consumption with the 500 Ohms resistor, in fact I think it got about 5% better. Going to 1000 or 1500 Ohms you might see some fuel consumption increase, but your bike will not “complain” for sure.
You can buy resistors in Radio Shack, they come in values 470, 690, 1000 and 1500, there might be some values in between, I am not sure. The cost is less than $1 per couple. Buy preferably the ¼ Watt ones, but the miniature 1/8 Watt are OK as well.
I’d suggest that you do not attempt this fix unless you have at least basic skills with the soldering gun, ask a friend for help if this is a case.
Lumir F. BAKOTA, Crowsnest Pass, Alberta