RB20 S14 Swap- Not Charging

[dirty_dyer]

Hello all,

Having an issue with the charging system in my car. I cant seem to figure out why its not charging. Here's some details on the car, and the trouble shooting I've done thus far...

 

Car:1998 UDSM 240sx S14 (Factory Automatic) - RB20DET/5 speed swapped

*Lower harness is brand new, I believe it is from Wiring Specialties. Therefore, everything relating to the battery/starter/alternator and fuse box interface is likely not suspected

I have found and cleaned the following grounds and connections for the lower harness:

*One tying the battery ground to the battery tray from the lower harness,

*Ground that bolts to the top of the fuse box under the cover

*Alternator grounds: both the lead and the mounting bracket

*The alternator has battery voltage coming from the power post

* 75 amp fuse is good

*Battery is two months old

*Key off voltage is 12.8

*Engine running with no accessories 12.55v  W/accessories 12.43v

* No change in voltage with increased rpm

Here's is why I am a bit lost so far. I took off my alternator and got it tested at two different auto parts stores. I went to Autozone and they said is was no good. I went to Oreillys for a second opinion and they said it was functioning well. One thing I am suspecting is the circuit going to the dash. Its a bit odd, because with the key in the on position and the engine off, the battery light in the dash is on and goes off as soon as i start the engine, as it should if the system were functioning correctly. Looking for some guidance and more areas to check before I buy a new alternator. 

Cheers- Johnny

 

 

 

 

[Duncan]

It will be a bit tricky to check, but step 2 after checking voltage at the battery while running needs to be checking voltage at the alternator (post on the rear while running). 

BTW when troubleshooting never rule out something obvious (wiring harness) because it looks new. Could be installation issue, manufacturing issue or even damaged in some way since installation.

[dirty_dyer]

Okay I will do that. How will i go about testing the circuit for the dash light as well? 

[dirty_dyer]

UPDATE:

 

I hooked up alligator leads to my multi-meter to get the voltage of the posts of the alternator. I connected the leads to their respective power and ground posts. Here's what I got:

Voltage at battery before start-up: 12.76v

Voltage from the alternator posts before start-up: 6v-7v ... Thought this should be battery voltage.. Odd.

Engine running battery voltage: 12.4v no accessories

Engine Running alternator voltage: 16.2v drops to 15.7 with increased rpm and climbs back up to 16.2 when the engine returns to idle.

 

Sounds like the regulator is shot?

Also, please my excuse electrical ignorance,  I'm real bad with this stuff but I'm learning . Let me know if i did something wrong.

 

Cheers

[Duncan]

OK, so first up I'm no auto electrician, and you should probably ask one.

My understanding is the alternator post should have the same voltage as the battery, they are directly connected by reasonably heavy gauge wire. Further, the alternator uses one of the input wires to check the battery voltage as a reference for charging. If it is seeing way less than the actual battery voltage it would make sense for it to be trying to overcharge. And in any case, whatever it's doing is not making it to the battery since the voltage there doesn't change with the car running.

From my understanding....could be alternator, more likely to be an alternator wiring issue. Keep in mind the earth is key to seeing the correct voltage so a bad earth could also be the issue, not just a problem on the positive side.

[Duncan]

OK, so first up I'm no auto electrician, and you should probably ask one.

My understanding is the alternator post should have the same voltage as the battery, they are directly connected by reasonably heavy gauge wire. Further, the alternator uses one of the input wires to check the battery voltage as a reference for charging. If it is seeing way less than the actual battery voltage it would make sense for it to be trying to overcharge. And in any case, whatever it's doing is not making it to the battery since the voltage there doesn't change with the car running.

From my understanding....could be alternator, more likely to be an alternator wiring issue. Keep in mind the earth is key to seeing the correct voltage so a bad earth could also be the issue, not just a problem on the positive side.

[Slap]

Check connection
Engine earth to chassis?
Engine earth to battery?
Alt pos terminal to battery pos?

Any other shorts or recent malfunctions or mods?

Have you tried a different battery?

[Slap]

Possible that the gauge is a high amp gauge reading from low amp supply design ed for ecu reading and low amp gauge... guess?


Maybe i missed it but how long has it been this way?

[dirty_dyer]

@Slap

So I bought the car swapped at the end of November when I was at uni. I maybe had it running for a week, when I noticed the car start to run poorly. Had a long weekend coming up, so I decided to just bring it home. It was then the car died an hour from home which I then determined to be a charging issue. I bought this car fully knowing that the wiring was an absolute hack job and planned to re-do it when I had the time and money. Since i got it cheap, I figured the overall investment was pretty good, minus all the headaches of dealing with the previous  owners "work" ?. I'm not sure what you are referencing when you mention the amp gauge. However I haven't cleaned the battery ground to the engine yet, it was in a very tight spot between the sub-frame. I was suspicious of that. Also, I need locate the ground strap for engine to body. I remember seeing it on the exhaust side on the engine, but now I don't see it, maybe it fell off, who knows haha. Here is my new suspicion. I know that the lower trans harness is from Wiring Specialties, it looks good but as @Duncanmentioned, it's possible the alternator is not properly connected. In fact, I don't believe that the P/O bought the right trans harness. There is difference in the harness between cars that had a factory automatic or were factory 5 speed cars. I am contacting Wiring Specialties for diagrams to confirm this. This should allow me to determine if its A) The alternator is improperly  connected. B) The wrong harness C) Both. In the mean time, I am going to start doing more thorough detective work. Also, I'm planning on getting a full pro harness from Wiring Specialties, just because the old harness is in complete disrepair and will cause more long term cost and headache if it is not replaced.

 

This concludes my TED talk.

Johnny

[Slap]

Kool sounds like you will get it sorted.

 

I was getting at... the gauge in the dash may require higher power load than the set up is feeding it.

I remember reading somewhere not long ago about some wire from the alt was lower on the rb25 than the 30 and the dash wouldnt read correctly or something.

 

If ya havent sorted it out soon ill hunt it up.

 

 

[Slap]

Could be similar to the rb 30 prob.

[GTSBoy]

No charge gauge on any Skyline (or S chassis car). Exciter light is all there is.

Edited June 2, 2019 by GTSBoy

[niZmO_Man]

What's a charge gauge? Different to the volt meter?

[Slap]

My bad but beside the point i was getting at.
Light/gauge/tickler dont matter if the wiring is wrong.

No charge gauge on any Skyline (or S chassis car). Exciter light is all there is.

[Dose Pipe Sutututu]

Does the alternator work once you connect a direct +ve into the exciter input? Of course don't leave it connected!

[GTSBoy]

2 hours ago, niZmO_Man said:

What's a charge gauge? Different to the volt meter?

Yup, ammeter. Has to go in the main charging output from the alternator, which is kind of why they died a death after the 80s. Used to be one hanging under the dash of every hoon's HK Holden in the 70s.

[niZmO_Man]

Ahh right, man I haven't see one of those in a loooong time.

[dirty_dyer]

Hey all long time no post, (been very busy lol) but I'm fairly certain I have found my issue. So I'm not sure how it is on the R-Chassis but on the S-Chassis, at least the s14, the main charging cable goes into the fuse-box via ring terminal with the bolt. That goes through the 100 amp fusible link, back to the battery. I'll attach a screenshot from the FSM for a visual. So I did some poking around. Low and behold, the connector for the fuse box charge cable was melted. Intrigued by this I redid my voltage drop test. Hooking up my multi meter, one lead on the power output of the alt and the other to the ring terminal, I got a reading of about 4.3 volts, which was fairly steady. I haven't fixed it up yet because I'm exploring my options on replacing that connector, although I'm most likely just going to splice a piece of wire in its place. Bottom line things are looking good. Also seems like the engine is grounded pretty well, but i noticed i didn't have a dedicated engine to body ground. I got a voltage reading of .02 volts between the cylinder head and my strut tower bolt. If you guys have recommendations on best grounding wires and locations, let me know. There's a few threaded holes on the bottom of the block that look pretty good.

 

In response to @Slap, on the S14 the charge light circuit is critical as it is a voltage sense and commands the voltage regulator. If that circuit is open in any way, the alternator will not produce any power. 

 

@Dose Pipe Sutututu I'm not exactly sure what you mean there. What is +ve? Excuse my ignorance.

 

Cheers,

Johnny 

[Dose Pipe Sutututu]

The Charge Lamp warning, without that connected the alternator won't work.

This also means, if your cluster isn't in and/or the bulb is blown there's nothing to "excite" the alternator. A simple way could be to start the car and connect a bulb/resistor in series to the alternator labelled "L" to the positive terminal and see if that's raises the voltage of the electrical system.

[Slap]

@ dirty_dyer.

" I got a voltage reading of .02 volts between the cylinder head and my strut tower bolt."


Wouldnt that signify a low voltage short.