Info needed on blue top coolant temp sensor

[DmcL]

right.. going to try and cut a long story short here. i have some 19lb injectors im looking to install before saturday for a dyno run. ive had them in once already for a day or so and once warmed the engine did run better/pull stronger even without a proper tune for the injectors. problem is it was incredibly rich starting from cold so i managed to pick up a FMU of sorts.. its a variable resistor that was wired in to the CTS of a vauxhall cavalier 4x4 turbo a friend has. anyway he doesnt need it so he gave it to me.

im wanting to know will it matter which of the 2 wires to the blue top CTS i hook this thing up to or will either wire be fine? im wantig to use it as a temporary fix to lean out the cold start enrichment while im using these 19lb-ers untill i can map it properly for the injectors.

[thejlevie]

You need to know that the ECT is a negative temperature coefficient device. Meaning that the resistance of the sensor is high when cold and decreases as temperature rises. Adding resistance to the signal from the sensor will make the DME think that the engine is colder than it actually is. So this variable resistor is going to have the wrong affect.

[DmcL]

was half thinking that.. its a 25k ohm unit and someone was just telling me the bosch sensors are like 3.6k ohm at 30 degrees C which is up around 90-100F. looks like theres way too big a range of resistance in this thing anyway nevermind trying to figure out how to "reverse" it so to speak so it leans off rather than richens.

its crazy opening the thing up tho.. nothing more than a variable resistor in a AA battery box with 2 wires coming out of it and someone was knocking these out in 2007 as a FMU and probably making quite a bit of money on each one sold..

with that one out the window do u have any ideas how i could lean out the cold start enrichment? seems ok once warm with the 19lb injectors but it literally ate fuel when cold. i was running an alpina B3 2.7 chip at the time tho which might be part of the problem. i adjusted the AFM to lean out the mix a bit but that would have no effect on cold start enrichment. really hoping to find a temp fix so i can run the injectors untill i can map the car for them otherwise ill have to fit them for the dyno run and remove them after. im hoping the alpina C2 2.5 map im on now might be a bit more forgiving with how much fuel the car uses with the 19's on cold start but im still thinking it will eat fuel before warm.

[thejlevie]

Does your car have an O2 sensor? They were on all US cars, but I don't know if they were fitted for all european production. If the O2 sensor is good (useful life is not more than 100k), the DME should "learn" to run a leaner mixture after the car has been driven a few hundred miles. That might not eliminate the rich cold starting, but it should become less severe.

[DmcL]

nope.. no O2 sensor im afraid. have read up about people just throwing them in and it still running ok on here and r3v, etc. but i know all the cars they were doing that on had an O2 sensor.

on a side note.. since fitting this chip with the C2 2.5 map the car has felt as good, maybe marginally better than on a modified B3 2.7 map i was running. probably a little leaner on the C2 chip. anyway.. i had the plugs out a couple days ago and all were showing a pretty good burn but im wondering if u can tell if the mix is a tad on the lean side by looking at the plugs? they were a light brown colour. looked to me as if it might be a hair on the lean side but idk. was more of a chocolate-ish brown last time i pulled them when i was on the B3 map.