ECU pinout for 1995 D-90 - Defender Source
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  #1  
Old January 12th, 2006, 12:03 PM
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Tim Riccardi
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ECU pinout for 1995 D-90

My copy of RAVE has only the 1997 model year. It does have one for a 1995 Disco, but the tune resistor (K140) is not for NAS. Thanks Tim
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Old January 12th, 2006, 07:43 PM
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Shouldn't really be any difference between the 95 disco and defender as long as both are the hot-wire system with distributor. The tune resistor in the UK will be a different resistance, but wired in the same.

I can always look at mine tonight or tomorrow for you when I get home. What did you need to know?

-Hans
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Old January 12th, 2006, 08:21 PM
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Tim Riccardi
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Hans I found a pinout list on RPI, and it was the same as the DiscoI in RAVE. I now have 2 ?'s. Pin 33 (a/c comp clutch relay) and 36 ( a/c condenser blower motor timer relay), what are they used for? I have a/c, but when it turns on the RPM'S drop, should it or should the RPM'S rise? I don't think they are conneted. Was the a/c installed at the factory or the dealer, NAS? Where is the tune resistor? In the harness under the truck? Thanks Tim
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Old January 12th, 2006, 10:28 PM
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Tim Riccardi
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And pin 21 a/c pressure switch.
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Old January 12th, 2006, 11:07 PM
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Well, I'm still at work, so I can't check it just yet. I honestly haven't played around much with the A/C in defenders, mine doesn't have it at all. But the 110 guys should know more specifics about it since they ALL had A/C. But my book has both the 1993 D110 and 94 D90 diagrams in it, so I'll check it all when I get home to see what the deal is on the Defenders. If the A/C was installed at the factory or dealer, I believe that both ways was possible.

It is normal is for the RPM to drop a bit when you turn the A/C on. The compressor has a clutch in it that clamps and releases at need. When you turn the A/C on, that clutch locks up and this places an additional load on the engine, which slows it down.

Just from memory on the times I've seen the topics brought up, I believe that pin 36 engages or disengages the cooling fan in front of the condensor while the A/C is on. Pin 21 probably reads the pressure in the A/C system, which tells pin 33 to engage or disengage the compressor depending on the system pressure. But that's all just educated guesses.

-Hans
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Old January 13th, 2006, 12:29 AM
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Tim Riccardi
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Hans I though the ECU would raise the RMP'S when the a/c is on, if it doesn't then the RPM'S would fall. I'm trying to find the "tune resistor" because I just installed my WB O2 and want to play with AFR. My pin 5 is gray/black and with the ECU disconnected it reads 3.879 ohm's. Tim
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Old January 13th, 2006, 02:13 AM
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All I could dig up right now on the tune resistor is that it's between pins 5 and 27. Doesn't look too big at all. Might be wrapped under tape.

http://www.v8engines.com/carbs-2.htm#Tune-resistor
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Old January 13th, 2006, 10:39 AM
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Tim Riccardi
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I found a number on the main harness AMR3943 RISTS limited. Does this mean anything to anybody. If somebody had a schematic of this harness it would tell us were the resistor is located. Tim
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Old January 13th, 2006, 01:51 PM
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Ok, going over my book now, so here goes! First off, the A/C connectors into the ECU.

-One is Yellow with black stripe coming out of the ECU pin 21. Goes through the A/C connector to the pressure switch, then to the thermostat located in the A/C unit , then to the A/C on-off switch. Probably an on-off signal wire to tell the ECU when it needs to engage the compressor.

-Black/Slate wire coming from pin 33 goes to the A/C connector then to the compressor relay. I believe this is the signal ground from the relay that the ECU uses to switch the compressor on and off.

-Then you have a Black/green wire coming out of pin 36. This goes into the fan relay timer. Pin 36 is probably the wire that the ECU uses to tell the timer to turn the fans on and off.

You have 2 wires coming out of the fan relay before the A/C connector.
-one is black/red, runs through the A/C connector then to the condensor fan relay. Carries power from the relay, probably to tell the timer that the fans are on.
-the other is white/green and goes to the coolant temp switch, which I believe is the one in the thermostat neck. This one tells the timer to turn the fans on if the coolant temp gets too hot.

The diagnostics for the A/C mention nothing about engine RPM, so I don't think the idle valve does anything in relation to the A/C system at all. The idle valve should normally try to keep the RPM in a certain range of about 700rpm, but doesn't seem to compensate specifically for the A/C unit. What does yours drop down to when the A/C is running?

-------------

Now, on to the resistor

Located between pins 5 and 27. Pin 5 is black/white, pin 27 is black/slate. The black/slate seems to also branch into the diagnostic connector.

I checked in my own truck, it's wrapped under the electrical tape in the main harness, about 6" from the ECU.

-Hans
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