GeneralDisorder Posted August 7, 2011 Share Posted August 7, 2011 I recently had a chance to try out the resistor mod on the EJ sending unit for a Brat I converted. 270 Ohm resistor shunted to ground from the sending unit is the commonly held value to correct for the EA gauge..... but with a hodge-podge of old and new parts that EA's almost always are - the actual value that will work correctly in each vehicle will NOT be the same. I took it a step farther and bought a 500 Ohm pot to dial in the exact resistance for where I wanted the gauge to read. Sometimes when working with these old parts (gauge, sending unit, etc) things aren't exactly where they ought to be from the factory. Turned out I needed only a 120 Ohm resistor to put the gauge exactly where I wanted it (on the 2nd line up from the bottom). The pot only cost $2 and told me exactly what value I needed to use *for that specific vehicle* to get a perfect gauge reading. I used the ECU's fan control and my laser temp gun to insure that the operating temp was exactly where it ought to be before dialing in the pot and then allowed it to cycle multiple times while watching the needle to see the deflection between fan cut-in and cut-out. Worked great. Figured some folks might like a more accurate gauge and since all the EA cars that are getting swaps are old - the tollerances of the sending units and the gauges and the power/ground supplies are getting a bit loose. The $2 pot test will give you an accurate gauge with no guess-work. GD Quote Link to comment Share on other sites More sharing options...
el_freddo Posted August 8, 2011 Share Posted August 8, 2011 270 Ohm resistor shunted to ground from the sending unit is the commonly held value to correct for the EA gauge. Does this mean it's wired in like which one of these: A) C) I'm thinking it's either a or c... And what exactly is a Potentiometer, and where can one find this device? I'm keen to do the same on my EJ converted L series. Cheers Bennie Quote Link to comment Share on other sites More sharing options...
GeneralDisorder Posted August 8, 2011 Author Share Posted August 8, 2011 Thanks for the diagrams Bennie - It's wired per your C diagram. A Potentiometer (or Pot for short), is an adjustable resistor - think of your stereo volume knob - what you are turning is a Pot and as you turn it from low to high the signal power is provided with progressively less resistance. You can find them at any electronics store - you just need a 0.5 watt Pot capable of 500 Ohms of resistance. Thus it's resistance is adjustable from 0 Ohms to 500 Ohms. Here's an example for $0.50 online: http://www.surplus-electronics-sales.com/Zencart/index.php?main_page=product_info&cPath=23&products_id=274 You first wire the Pot in temporarily, and then run the engine till you reach operating temp (fan's cycle if you are using the ECU's fan control) and then set the pot to where the gauge reads what you like. When you have the Pot set where you want it you take a resistance reading across it's terminals with a meter and that's the resistor you buy to shunt your sending unit. Simple right? GD Quote Link to comment Share on other sites More sharing options...
eulogious Posted August 9, 2011 Share Posted August 9, 2011 Good thinking man! Sometimes the simplest solution is the best one Quote Link to comment Share on other sites More sharing options...
LeoneTurbo Posted August 9, 2011 Share Posted August 9, 2011 I'm currently having an aluminium bung for the EA temp sensor welded to my EJ cross over pipe... Should I have known the above before... Oh well.# Quote Link to comment Share on other sites More sharing options...
bratsrus1 Posted August 9, 2011 Share Posted August 9, 2011 Hi GD This is Jerry, i have an EJ water manifold with the EA81 water temp sending unit in it. make me an offer Thanks Jerry Quote Link to comment Share on other sites More sharing options...
el_freddo Posted August 9, 2011 Share Posted August 9, 2011 Thanks for the diagrams Bennie - It's wired per your C diagram. No worries - I've had them sitting there waiting an answer from another fella who had done the same thing but with a 180ohm resistor, I had asked the same question... then run the engine till you reach operating temp (fan's cycle if you are using the ECU's fan control) That ECU's fan control - which wire is it? I'd like the ECU to control the fans when it wants to. I've got the wiring labelled for AC relay fan etc, is this the wire and is it earth switched (meaning needs accessories power on other side of relay trigger) or will it be a powered wire when switched on? Looking forward to doing this simple mod! Cheers Bennie Quote Link to comment Share on other sites More sharing options...
GeneralDisorder Posted August 9, 2011 Author Share Posted August 9, 2011 (edited) Hi GD This is Jerry, i have an EJ water manifold with the EA81 water temp sending unit in it. make me an offer Thanks Jerry . That's how I used to do them also. I have a freind that TIG welded the last one for me so it could be tapped for the EA sending unit. I find the resistor modification easier because by using the EJ's temp gauge wireing I can eliminate the manifold harness from the EA and by using a pot it allows adjustability so I'm not *only* correcting for the EJ sending unit but also calibrating the gauge - which would require a similar process if I were using the EA sending unit. Thanks for the offer though! GD Edited August 9, 2011 by GeneralDisorder Quote Link to comment Share on other sites More sharing options...
GeneralDisorder Posted August 9, 2011 Author Share Posted August 9, 2011 That ECU's fan control - which wire is it? I'd like the ECU to control the fans when it wants to. I've got the wiring labelled for AC relay fan etc, is this the wire and is it earth switched (meaning needs accessories power on other side of relay trigger) or will it be a powered wire when switched on? I can take a look at my diagrams and tell you - what year is your ECU? It's not the AC one - I don't use that (unless I were doing a swap w/AC - which I personally haven't done since none of the cars I've converted came with AC). As you surmise it is a ground signal for a relay that will need to be powered on the other side of the coil. The early ECU's don't have seperate fan controls so what I like to do is setup one of the fans I install using the ECU's control - this I call the primary fan. The secondary fan I wite to the vehicles existing fan/thermo-switch wireing so it is driven of a completely different system. The last one I did the ECU fan would come of first and only if the temp continued to rise would the secondary fan cut in. That way you aren't uneccesarily pulling fan power from the electrical system by running them in tandem. GD Quote Link to comment Share on other sites More sharing options...
el_freddo Posted August 10, 2011 Share Posted August 10, 2011 I can take a look at my diagrams and tell you - what year is your ECU? '91 model... It's not the AC one - I don't use that (unless I were doing a swap w/AC - which I personally haven't done since none of the cars I've converted came with AC). I've heard that you don't have to use this wire with the AC - the ECU automatically ups the idle when it senses the extra load. This is what I've heard from others down here that have done the EJ conversion and retained/retro fitted the AC as well. As you surmise it is a ground signal for a relay that will need to be powered on the other side of the coil. This is good to know - thanks! The early ECU's don't have seperate fan controls so what I like to do is setup one of the fans I install using the ECU's control - this I call the primary fan. The secondary fan I wite to the vehicles existing fan/thermo-switch wireing so it is driven of a completely different system. The last one I did the ECU fan would come of first and only if the temp continued to rise would the secondary fan cut in. That way you aren't uneccesarily pulling fan power from the electrical system by running them in tandem. This is probably what I'll look at doing as well - although I've got three fans squashed between a 3 core radiator and the front of the EJ, I used three as they're smaller and easier to mount around the various parts on the front of the EJ! I wouldn't go the 7 inch fan again though - the 9 inch feels (hand dyno here) like it pulls twice as much air! Thanks GD! Cheers Bennie Quote Link to comment Share on other sites More sharing options...
Gloyale Posted August 11, 2011 Share Posted August 11, 2011 (edited) That ECU's fan control - which wire is it? I'd like the ECU to control the fans when it wants to. I've got the wiring labelled for AC relay fan etc, is this the wire and is it earth switched (meaning needs accessories power on other side of relay trigger) or will it be a powered wire when switched on? 90-94 ECU's it's the Red/Blue stripe wire that then goes into the diode pack(to prevent backfeed when A/C and defrost run the fan), and then out as White/Red stripe to fan. The ECU controls the ground side, so you need to provide power to the fan, and the relay will provide the ground. I preffer to have mine on a realy, and the ECU triggers the ground side of the coil on the relay. Edited August 11, 2011 by Gloyale Quote Link to comment Share on other sites More sharing options...
GeneralDisorder Posted August 11, 2011 Author Share Posted August 11, 2011 I preffer to have mine on a relay, and the ECU triggers the ground side of the coil on the relay. Yep - that's how I do it as well. GD Quote Link to comment Share on other sites More sharing options...
xbeerd Posted August 19, 2011 Share Posted August 19, 2011 I got my 500ohm pot yesterday (i love ordering a 50cent part online and paying 7 times more for shipping it> LOL) i was gonna use my usb-obdii scantool to set the gauge. just curious what the temperature is when the gauge is at its normal position (slightly under half is what mine always was) i figure i can run the real time data scan program on my laptop, and then set the gauge accordingly and then put it the propper resistor(s) Do you think it would be worth it to mount the pot in a box under the hood with a knob? otherwise i already have the 500+ various resistor pack from radio shack so making the right resistance isnt a problem. Quote Link to comment Share on other sites More sharing options...
xbeerd Posted August 19, 2011 Share Posted August 19, 2011 (edited) Delete me. Edited August 19, 2011 by xbeerd Quote Link to comment Share on other sites More sharing options...
GeneralDisorder Posted August 19, 2011 Author Share Posted August 19, 2011 I would use at least a 3 to 5 watt resistor..... that pack of resistors are probably 1/8 watt or 1/4 watt..... might burn them up. I wouldn't leave the pot in place - too much vibration for such an animal. The red/blue wire from the ECU is not the one you use - you need to use the white/red wire coming out of the diode pack to protect the ECU. Or add a diode to the red/blue wire. I'm not sure if you are saying that your's is newer than 94 or? OBD-II would have two fan control wires - one for each fan..... GD Quote Link to comment Share on other sites More sharing options...
xbeerd Posted August 19, 2011 Share Posted August 19, 2011 (edited) im sorry, yeah mine is from a 2000. i cant find my diagram from the 2000, but it lists the same for the 2000impreza i found here below as far as this diode goes, then i would wire it inline as such? with diode the other way, wouldnt electrical flow be stopped thus no grounding out the relay. ECU--------Red/blue wire-------------|<- DIODE ------------red/blue wire------ negative side of relay coil------())))))coil)---- fused 12v+ Edited August 19, 2011 by xbeerd Quote Link to comment Share on other sites More sharing options...
GeneralDisorder Posted August 20, 2011 Author Share Posted August 20, 2011 Yep - that's what you want. You can use the green/red wire to control your second fan or use the stock wireing with the thermoswitch. GD Quote Link to comment Share on other sites More sharing options...
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