Just wanna throw this out there, you do have lean spool disabled right? Also check/clean the terminals of the alternator, the battery clamps, and the cable that runs from the positive battery terminal to the fuse box. Also make sure sure your chassis grounds are all good. The chassis grounds are what would effect the ECU readings. So just to re-emphasize this, you need good grounds from the chassis to the battery, the engine grounds do not count for this. The alternator gets its ground connection to the battery through the engine, but all the instruments ground through the chassis to the battery. The battery being the focal distribution point of the stock electrical system. If your getting different voltages at the Alternator then at the ECU harness that tells you right there you are having some kind of a problem creating too much resistance for the amount of current you are drawing.

 

Update:

I was after the Voltage drop. As you can see in the logs it drops to 10.5 V ! . This can happen at both idle and high revs. No consistent pattern.

I started with Voltage Drop tests :

1. First test between Alternator and Battery, both for positive and negative sides (no/minimal drops)

2. Negative drop test between Battery -ve and Ecu Pins (13,26,91,92) Evo 5 pinouts. Max reading 0.15V on one of the pins here. Rest was 0.05V

3. Positive drop test between battery +ve and Ecu Pins (12,25,80). Yes it does drops. 0.75-0.82 on idle. Reving to 1500-2000 takes to 1V drop! . I think this is my issue? After all i am chasing for a drop around 2-3V at the ECU.

After this i looked at the fuse box. I could see 2 Hot cables underneath, tested +ve drop there 0.04V.

What should be next step?.

I am kind of confused here. Not good with electricals.

Am i looking at a bad ground or a bad +ve wire?

Why there is a drop on all three +ve wires that go into the ecu?

 

You should be measuring the voltage at the device you are testing, both positive and negative. If you are using the negative of the battery then you are omitting the entire ground path from your testing.

Edit: Sorry I was a little confused by what you wrote. What you really should be doing is measuring resistance across the different legs of the circuits. You want to see very low resistance, < 500 milli-ohm

 

I am trying to measure the voltage "drop" at the ecu from the battery. Am i on the wrong path?

 

I read somewhere its better to measure the drop on a live circuit rather measure resistance in a closed circuit especially for automotive where resistance technique does not work accurately perhaps due to small values not sure.

 

Well if you are going to measure voltage it has to be under full load. I've never heard about measuring resistance not working, but maybe with crappy equipment it might be a problem.

 

So, i should be measure resistance between all +ve and -ve in the ecu against the battery +ve and -ve. Where to you set your resistance dial normally? i can see different settings like (20k etc)...i think my meters Chinese crap lol

 

You can measure the voltage at the alternator from the lug to the alternator chassis, then measure voltage at the ecu using the power and ground cables in the ecu pigtail and compare. Also try just measuring resistance from the ECU + to the + battery terminal, and from the ECU - to battery ground. Wouldn't hurt to check that the ecu chassis ground is good and tight while you are at it.

 

Let me try this and ill get back soon..thanks

 

Yah you do kind of need a decent meter, we are talking milli ohms which is less then 1 ohm. You should be under 500 milli-ohms (1/2 an Ohm). To elaborate on this a little at .5 ohms and 14 volts the most current you can draw is 28 amps. If you draw more you will see voltage drop (Ohms law). Remember that all the chassis grounds are shared by the wire going back from your chassis to the battery, and its that connection that can be a real bottle neck when you start upgrading stuff. This is a classic rookie stereo installer mistake. They run a fat power cable for the amp, then ground the amp right to the chassis, but they don't add additional grounding from the chassis to the battery. So now all the current from the amp has to go through what ever the factory ground connection is and this effects everything that is chassis grounded. Same thing with adding additional fuel pumps or anything else heavy on current. If your running dedicated power to a high power device you gotta make sure you upgrade that return path as well. </rant>

 

Update:

Tested all grounds and positives for resistance. All under 0.6

I opened the wiring diagram. Traced the voltages to the ECU via a relay. There are actually two relays, one for ecu and one for fuel pump under my dash.

1. The +ve from the fusebox on the ECU relay shows the same as the battery voltage 14+

2. The wire which is powering the ECU on this relay, reads 0.6 volts lower then the above, at all times i.e with the car off or on

3. I replaced the ECU relay with the fuel pump relay (they are exactly the same). Same results

4. I disconnected the ECU plug, checked the voltages they are same as what comes from the battery.

5. I borrowed a different ECU and checked on that, same results

What am i missing here? Is it possible that the alternator is putting out good voltages and yet less amperes which may cause voltage drop? not sure what am i saying :/

 

I think you might be mistaking one of those relays see here:



Those are both fuel pump relays. The stock system actually uses 3 total relays for the fuel pump.

 

Not exactly. I am talking about the third relay behind/under my stereo side. Take a look at this:

http://uploads.tapatalk-cdn.com/2016...a02d80c58e.jpg

One of them is for ECU other for fuel pump. I have traced the +ve from this relay to the ECU successfully. The confusing part is , this relay gets its full voltage from fuse box yet it can't put the same to ecu. This means the wiring from alternator,battery,fusebox up to this relay is perfect. It's something else. Should i just replace the alternator?

 

oh you have an evo 6? Yah thats a horse of a different color lol. The thing is the alternator is trying to stay at 14 volts, and it pumps out current (amps) to keep it there. So if the voltage never drops at the alternator it doesn't "know" that it needs to supply more power. That being said though an evo 6 at this point is pretty old and there could be some issues with the brushes etc in the alternator that are showing up under high rpm etc. So it could be an issue with the alternator but I hate advising people to spend money on parts unless you know its the problem. Unfortunately i dont have evo 6 diagrams (ill see if i can dig some up). Can you explain to me how you are testing the voltage like literally brake down where you are placing your meter probes etc. Like give me a step by step of what you are doing and the results of that.

 

If you are pulling out the relay and placing your probes into the socket and getting X value, but then you pull out the negative and place it to a metal chassis ground do you get a different higher value? The idea behind this test is you are measuring the voltage across the ecu circuit to ground, then directly to ground. If you get a higher value then that means there is some kind of grounding issue with the ecu, or maybe something with the positive wire going to the ecu.