Power. We can't just get enough of it, and of course, we don't want to pay anything for more of it. :)
|
Dr. Zhivago from the
YotaTech forums has brought to light a trick that he
tells me has been around for a while.
This mod produces more power by causing the ECU to think that it's dealing with a cold engine. To deal with this, the ECU will richen the air/fuel mixture to compensate for the cold, thus getting more fuel into the cylinder, thus allowing more power to be produced. A side effect is that as the ECU increases the amount of fuel that the injectors shoot into the engine, it will also advance the timing to be able to burn the additional fuel. What's done here is to insert a 500 ohm "pot" (potentiometer, variable resistor) in series with the ECT sensor (Engine Coolant Temperature) and it's associated ECU input. When the pot is adjusted such that it's resistance increases, the voltage that's presented to the ECU will increase, and this will make the ECU think that the coolant temperature is lower than it actually is. The end result is that the ECU is fooled into reacting to a "cold" engine. But, since the engine is actually warm, then we get more power from a cleaner burn closer to the optimum crank position and having more fuel in the mix. The net result is that you'll get better off-idle response and more pull throughout the midrange. Cool huh? :) See this PDF paper for more info on how the ECT works on our vehicles. Also be sure to check out the thread on YotaTech about this mod.
In order to get clear access to the ECU, you'll need to pull out the glove compartment. Remove the door by taking out the two Philips screws that attach the hinge, if you leave the compartment closed and latched at this point, it'll make things easier. Then unlatch the door and set it aside. Drop the upper part of the frame by removing three 11mm bolts. The frame then comes out by pulling in on the sides and dropping it away from the dash. You may find a couple of wire bundles attached to it as well as the lamp for the glove compartment. Disconnect these from the frame, and put the frame aside with the door. NOTE: You may find a yellow harness on the left side of the frame. If so, do NOT disconnect the plug, only remove it from it's holder on the frame. This is the connection for the passenger side air bag and you don't want to run the risk of forgetting to reconnect it.
None of the wiring diagrams I had for my '96 Limited were correct when it came to documenting where the ECT sensor was wired into the ECU. With Dr. Z's help, I found the ECT sensor junction under the hood and used a ohm meter as a continuity tester to find the other end at the ECU. For my truck, this ended up being a Green/Red wire at position B21 on the ECU. It is highly likely that your vehicle will be different. There are four ways to find this wire: Option 1 of course is the easiest, but you'll want to check it with one of the other methods just to be sure. I figured that one of the three diagrams I had were correct, and I'm glad that I double checked! Option 2 is the most absolute. Find the ECT sensor under the hood. It will have two wires going to it, most likely a brown wire (common ground) and then a Green/??? wire. Attach one lead of an ohm meter to the Green wire - if your ohm meter has a continuity setting, turn it on. Doing so will cause the meter to emit a "beep" when the resistance drops to zero. Head for the ECU, and remove the first plug. With the other lead from the ohm meter, test each position of the plug that has a wire in it. You should be able to get the tip of the lead into the back of the plug far enough to make contact. You may have to push a bit, so don't be too shy. Test each pin position while listening for the "beep" from the meter, or watching for the resistance to drop to zero. If the first plug doesn't turn up any hits, then put it back into the ECU and move on to the next. Keep trying until you find the wire... It has to be there somewhere! :) The 3rd option above is "pretty" valid, but it can produce false positives. On my truck, the lead to the ECT sensor has a junction right as it comes off of the harness. In my case, it was easy to see the wire coming from the sensor up to the connector, but not from the connector to the harness. It is very important that if you're going to visually ID the wire that you make sure you're looking at the harness side, not the sensor side. The reason being that (on mine) the wire color on the sensor side was Green/Yellow and Brown - but the harness side was Green/Red and Brown! Making a mistake here will cause you to clip the wrong wire at the ECU. Be careful! Option 4 works, but can take some time hunting for a single dropping voltage across all the connectors. You might also mistake what may be the ECT wire for something else that reacts the same way such as the intake air temperature. This option is best used as a validation for one of the other two.
Once you've ID'd the right wire, it's time to splice the cable that will run from the ECU to your control. Take a deep breath and cut the cable at the ECU. Remember to leave yourself enough wire on both the plug side and the harness side to be able to work with. The harness is quite tight at this point and doesn't offer up a lot of slack. Tug on it a bit to get as much play as you can. Attach the new cable from your control into the wire that comes from the ECT sensor to the ECU. Technically, it doesn't matter which side of the ECU/harness wire goes to which wire of the control. You can use crimp-on butt connectors here, though I prefer to solder the connections and dress the results with heat-shrink tubing.
I chose to locate my control in the center compartment so that I could make on-the-road tweaks. So, I ran a length of 18 gauge two wire cable in a sheath from the ECU location to the console. Wiring to the pot is straight forward. A potentiometer has 3 lugs on it, numbered above as "1", "2" and "3". The center lug (#2) is the "wiper" and this is connected to the part that moves inside the housing when you turn the shaft. For our uses, we want the resistance to increase as we turn the knob clockwise, which will happen if we use lugs #2 and lug #3. When I went shopping for a pot, the lowest value I could find in the physical format I wanted to use was a 1k part. While this will work, it creates a very coarse control. To counter this, I used a bit of electronic theory to reduce the effective max resistance of the control to 500 ohms. Without going into the science behind why this works, it can be done by simply wiring a 1/4 watt 1k resistor across the outter lugs (#1 and #3) of the pot. With that done, I soldered the end of the cable from the ECU location to lugs 2 and 3 (technically, it doesn't matter which wire goes to which lug) and then mounted the pot in the console. Once the pot was mounted, I attached the knob and called it good to go. :)
To configure the mod, all you need to do is:
The pics show the results as viewed on a BR-2 OBD interface. Each pic is a screen shot taken while the truck was running at 2500 RPM in Park, i.e., a no-load condition. Starting at the baseline (idle=700 RPM, temp=185) note the "Short-term fuel trim percentage" which is -1.6%. As the control is adjusted to add more resistance, you can see a couple of things happening:
The latter point is what you're interested in. As this percentage goes up, that means that more fuel is being shot into the engine. More fuel can give you more power. The greatest increase I saw was around "idle = 1050". The short term percentage bounces around a bit, so it can be hard to get a solid upper-bounds. The 3.9% number was pretty consistant at this point - that's a real increase in fuel flow when compared to the root -1.6%!
For me, I found the largest changes when I kicked it at highway cruise speed - such as when pulling out to pass, or just playing around. Also, merging onto the highway is a better experience overall, with a nice smooth and consistant pull from 2200 RPM up to the shift points. My gut feel tells me that there's more snap when coming off the line, but I need to do some more playing to get a better idea of just "how much". One nice thing about this mod is that it's quite easy to trim on-the-fly, or to turn off altogether for comparisons.
Mark |
Back to the Main page