Some years ago on our Dodge trucks, we used to place a 10K ohm resister inline on the IAT sensor to make the ECU believe that intake charge was about 40* F cooler than actual. This had the effect of influencing the fuel/air ratio and timing. Essentially, the ECU believed it was cold outside, and would not retard timing or richen the fuel ratio as compared to the hot summer. Those ECUs depended on the IAT to prevent a detonation condition from occuring-- the ECU played it "safe" so to speak, and would retard timing and richen the fuel mixture, just because it though detonation MIGHT occur.
Naturally, detonation was a concern and was experienced by a very small number of folks in very, very warm climates. Most of us never experienced a problem, and the mod gave us a better throttle response, better fuel economy, and a small boost in HP-- at least during the summer months. Some folks would even relocate the IAT from the hot intake manifold, to their CAI, just behind the filter.
Those Dodge engines were not equiped with knock sensors. The IAT was the only sensor the ECU used to prevent knock, so one had to keep an ear open for ping/knock/detonation. I personally had great success with it, and never had a problem... even in 95* F+ summer, pulling a 4000lb trailer, uphill, with my A/C on-- honest!
I understand the MINI has knock sensors? If so, then would the ECU then retard timing and dump fuel when it senses detonation from the sensors? And if that's true, could we not play with IAT on our MINI's and achieve a similar effect?
I'm tempted to experiement, but would appreciate anyone's feeback before I begin.
Yes, exactly Ob. I found that with a pot resistor on my 2000 Dodge I could dial in how much temp offset I wished-- turned it off in winter, and turned it up in the summer. Using a multi-meter connected to the IAT, and probe thermometer in the manifold, one could generally plot temps to resistance, and find a resistance value that will have the IAT sending a value 10, 20, 30 degrees lower than actual.
Small/subtile detonation will not hurt anything as long as it is not allowed to occur often, or allowed to continue long-- hence my question about the knock sensor. Good to know its there to prevent knocking.
My overall goal here is to tame the fuel dump that occurs above 5k RPM with my 19% pulley while running my factory ECU. Manufacturers always build in a little fluff as a safety precaution. I'm thinking that I can take advantage of that?
I'm hoping someone has played around with this and can share their findings.
This shouldn't apply to the MINI or any modern cars with real knock sensors. It worked because the dodge did NOT have a knock sensor, so just always retarded things simply because of temp.
Modern cars have acoustical knock sensors that actually hear (just like you would listen) the first bit of a knock and make adjustments before you could probably even tell. But they only make them if the engine were in fact knocking, not all the time as in the case with the dodge.
Has anyone here actually tried inserting a resistor inline with either the water temp, air temp or pre-cat lambda sensors to fool the ECU and achieve a leaner mixture on a Cooper S?
Perhaps using a on board fuel/air ratio meter with an independant lambda sensor (oxygen sensor) tapped into the exhaust to moniter the results ( for those who don't have a rolling road).Interested to know the results of any experiments tried on CS,or cheap but tried and tested alternatives.
dansmini: Yep, similar trickery to the $10 ebay mod, which is really just a 29 cent resistor.
I haven't tried any of this... yet. I'll get around to it some weekend.
jwardell: I have to disagree, 'mate, but I do concur with your description of knock sensor operation. Adding a resistor to subtract 30* degrees F from the true temp signal would not necessarily cause knock/detonation to occur. Sure it could, but its not a given. Perhaps we'd only see knock on a 105* degree F day, with high humidity, going uphill with the A/C on, at full boost? In this case, the knock sensor becomes a safety device for exceeding the capabilities of efficient combustion.
On the other hand, if subtracting 30* from the temp signal produces immediate knock, then obviously this trick would be a bad thing.
Maybe this is all moot on a supercharged engine? As compression builds, so does the likelihood for detonation to occur. If so, then there isn't much point in this if we can't use all the boost through the entire rev range.
Still, I like hearing everyone's opinion! Keep it up!
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