So, I removed the tuner and replaced the voltage regulator/rectifier. That fixed the tach drop and the radio fart. Both work great now. However, one engine code returned (code 25 - rear cylinder ignition coil). The code 24 did not come back. I also noticed that when I put a multi-meter to the battery terminals while the bike is at idle, all seems normal (e.g., it holds between 13.8 and 13.9) but when I rev to 2,000 rpms and hold it there the voltage generally looks good (e.g., moves to 14.2-14.3) but has sudden drops from 14.2 to 13.9 and then right back to 14.2. If you blink at the wrong time, then you will miss it dropping but it happens every 3-5 seconds, which was the same time interval for the radio farts and tach drops. Is that normal? FYI - The check engine light for the code 25 does not stay on for more than a second or two and is generally off for the ride.

Since I am only getting a Code 25, should I start by tracing the power from the ECM to the ignition. Not sure that would cause a drop at the battery terminals. Or should I start with the fact that the new voltage regulator has a 38 amp output but the manual says I need 41-48 at the regulator and see if a more powerful regulator will fix the issue. Any thoughts on how to approach this would be greatly appreciated.

 

My symptoms and application are totally different from yours but I installed a Cycle Electric 50 amp 3 phase in my EVO Road King last April. Their setup actually turns the output of the stator off when charging is not required unlike the factory 32 amp single phase unit. The increased physical size of the stator and regulator/rectifier made the install slightly challenging but I'm very pleased with the results. It was not cheap but the old adage of price, quality, service; pick two, applies here.

 

So, I was finally able to zoom in enough to see the language in the flow chart boxes. It says that voltage at terminal B of the coil should be equal to the battery voltage. My question is whether that means exactly equal? I did a voltage drop and got a 15% or (.15) drop in voltage. I typically would not lose any sleep over anything less than a volt, but maybe that is significant here. How would you interpret this? Is .15 volts equal enough?

 

You have two threads on this going. In the other thread you say that when the problem occurs you see it over-charging. In post 9 of this thread I asked if it was overcharging when this occurs.

The problem is not a .15V drop through the entire harness to your coils. When a tach is exposed to high voltage it drops out. If you are experiencing that and a radio noise and see 15+ volts I would say you need to focus on overcharging.

If you replaced the VR with a quality unit and not a kwality one from the Ch Ina company, look at the wire that goes from the starter to the main circuit breaker. Many times they are corroded under the insulation - especially on the starter side. This wire is integral for the VR to determine charge rate on that year bike. Also, all connections, grounds should have been checked by now for integrity. The battery should also have been tested and been proven good.

 

I said in post #21 above that replacing the voltage regulator fixed the tac drop and radio noise. Also in that same post, I explained that after fixing those problems I am still getting a check engine light, usually while engine braking, and the corresponding code is 25, which is low voltage rear cylinder. The code 24 never came back. So, I am now trying to determine why this is happening. UPDATE: I get 0 voltage drop from the battery to the fuel pump relay. I have not figured a way to test the voltage drop from the relay to the ignition with the bike powered on because I cannot access the bottom of the relay with the battery connected. Has anyone done this? Or would you just pull the relay and measure the resistance between the secondary terminals?

Also, with the new regulator I get a sudden drop of .2-.3 volts at the battery terminals every so often at 2000 rpms. However, there is no drop at idle. Maybe that is normal?

 

10-4 - post above is in white text and missed that - along with reading the other thread on this. If you know the voltage drop from the battery to the relay, and you know the voltage drop from the battery to the coil, the delta is the drop from the relay all the way to the coil.

 

So, I tried to isolate what was causing the voltage drop. According to the shop manual wiring diagram, my fuel pump, fuel injectors, and ignition all get power from the same wire and they are the only things on that wire. When I unplug the fuel pump and do the voltage drop test, the drop decreases from .15-.16 to .03. So, the fuel pump seems to be causing the drop, or at least the majority of it. So, could this cause the code 25 (low voltage rear cylinder)? What I do not know is whether a .15-.16 drop is normal because the fuel pump is running during this test (i.e., drawing current while the ignition and fuel injectors do not) or whether this indicates a problem with the fuel pump.

FYI - this bike is 26 years old and according to the previous owner this is the original fuel pump. My fuel gauge does not move from 43 psi regardless of whether I am at idle or 3000 rpms. Can a fuel pump have a short and still maintain pressure?