How dangerous is lean burn ?

[krousdb]

Originally Posted by diamondlarry

On my car it seems to make a significant difference. But I think that some cars are set up differently. What I did was, I unplugged the IAT from the sensor and took two 220 ohm resistors and tied them together-this combination equals 110 ohms- then I shoved the ends of the resistors into the holes in the sensor plug. This makes my ECU think that the intake air temp is 242-247 degrees F.

Ouch! 242F? I would think that the ECU would assume that the sensor had shorted out and go into an open loop. But that might be a good idea for the WT sensor. It looks like 220 ohms would equal about 200F. I might make a setup where I can switch between the sensor and the 220 ohm resistor. After starting and getting underway, I could switch over. That would avoid starting problems. I might even have those resistors and a switch laying around somewhere. That would make it free.

[JanGeo]

In the old days with open loop fuel injection in my rabbit and in my carb engines the lean burn was not a big problem because of the low power levels that my engines had but you could see the increase in engine temps at highway speeds - that's when the water injection comes into play. Ideal fuel mixture for MPG is about 18 to 1 power 12 to 1 and cleanest emissions about 14 to 1 which is what the rabbit had been set to originally and got 27mpg in the coldest of winter and the hottest of summer. After I reshaped the AIR CONE of the CIS metering system, mileage was up in the 35-40mpg (80 rabbit 4 speed). You don't really burn up the engine until you start pushing the power up - under light loads it is not a problem. If you lean the mixture out too much it gets difficult to ignite requiring a bigger spark gap indexing etc.

[diamondlarry]

Originally Posted by krousdb

Ouch! 242F? I would think that the ECU would assume that the sensor had shorted out and go into an open loop. But that might be a good idea for the WT sensor. It looks like 220 ohms would equal about 200F. I might make a setup where I can switch between the sensor and the 220 ohm resistor. After starting and getting underway, I could switch over. That would avoid starting problems. I might even have those resistors and a switch laying around somewhere. That would make it free.

If I try to go ANY less than 110 ohms my ECU has a fit and throws a check engine light. I have thought about trying to mod my coolant temp sensor but I figure that the ECU would just freak out.

[SVOboy]

By the way, Dan-san, the IAT mod is the same thing as the WAI, however it makes the engine run lean rather than stoich, so I'd prefer to run the WAI. Look in my IAT tidbit thread, 6% for high temps are possible and we don't have any timing correction so no worries there.

[krousdb]

Originally Posted by SVOboy

By the way, Dan-san, the IAT mod is the same thing as the WAI, however it makes the engine run lean rather than stoich, so I'd prefer to run the WAI. Look in my IAT tidbit thread, 6% for high temps are possible and we don't have any timing correction so no worries there.

I don't understand why you wouldnt want to run 6% lean? Why not do both and use the same 220 ohm resistor for both Air and Water temp?

[SVOboy]

I don't understand why you wouldnt want to run 6% lean?

The issue with the IAT mod is it is 6% lean, which isn't terrible, but you want to lean out anyway, and 16% lean is a little unhealthy.

However, if you run the WAI inside of IAT mod you will use 6% less fuel, but not run 6% lean because you will have 6% less air too. In effect, the WAI allows you to run a safe 10% lean and use 16% less fuel, but the IAT would run 16% lean which is sort of unsafe for the same effects.

Coolant temperature I wouldn't make a constant, look at metros thread in the experiments section about his idea.

[diamondlarry]

I have been running my IAT mod since April(?)2005 and have seen no ill effects yet.

[SVOboy]

I agree that you would not because it's just a bit of leaning, but if I go an lean out the ecu more besides that then it'll get dangerous. Neither by itself is harmful, but if you can run two without double leaning I say that's better.

[krousdb]

Thanks to DAX for sending me the OBD training manuals. I'm on part 2 of PGMFI System Overview. I found this nice piece of info, I think it refers to the D15Z1:
"Certain Civic Models use a very special O2 sensor called a Lean Air Fuel Sensor. This sensor has 5 wires and can be controlled by the ECM to run the engine on A/F ratios as lean as 23:1"

I'm jealous!

[GasSavers_DaX]

Originally Posted by krousdb

Thanks to DAX for sending me the OBD training manuals. I'm on part 2 of PGMFI System Overview. I found this nice piece of info, I think it refers to the D15Z1:
"Certain Civic Models use a very special O2 sensor called a Lean Air Fuel Sensor. This sensor has 5 wires and can be controlled by the ECM to run the engine on A/F ratios as lean as 23:1"

I'm jealous!

Much welcome. And yes, the LAF sensor is often called the "wideband" or "5-wire" sensor. You will not be able to run one of these sensors unless you (a) get a P07 ECU and use a D15Z1 engine, or (b) buy a wideband controller. I am partial to the PLX devices, they are about $300. You can have a digital readout of realtime AFR and still emulate a narrowband signal to the ECU.