Insufficient Voltage problem causing rough riding / misfires

[eyedeekay]

I have a 2015 Infniti q70s 5.6

So have been having this issue where the car misfires because the voltage of the car keeps running really low (around 12.5 to 12.9 volts). I replaced the alternator as I found it made a clicking noise when the shaft was spun, but it seems like the issue persists. The dealer is stumped too as they found everything related to the engine such as sparkplugs, injectors, and ignition coils are all fine. the battery is also operating normally too. It just seems like the car is running 1 volt lower than it should which is why these misfires issues are sprouting out.

I should add when the car is running at a higher voltage from a cold start (13.5 to 14V) it runs perfectly, the voltage happens to just drops overtime and the misfires begin to happen)

I was wondering if anyone had this similar issue with their q70 5.6 or m56 by chance? thank you!

[Q70sGuy]

These cars have intelligent charging which I think is controlled by the IPDM? I would look at the FSM charging chapter and look for clues there.
Also, rebuilt alternators are rarely good in the first try. I wouldn’t rule out the new alternator if it is rebuilt.

[VStar650CL]

howto-disable-ecm-controlled-alternator-t623786.html
The "intelligent charging" is frequently unintelligent. That's very likely the OP's issue.

[VStar650CL]

Here's the wire to cut or detach, it's Brown. On a Q70 the IPDM is tucked in outboard next to the battery:

[Yoda's Master]

Definitely related to the not so intelligent charging.

cut the brown wire.

[Ilya]

One of the best 'mods' for these cars is removing this 'feature' lol.

I don't know what engineer dreamed this up or what singular use case they used to justify the existence of this feature, but it's one of the dumbest 'features' I've ever heard of in any car ever. Engineer, if you happen across this post because you are Googling your marvelous invention...you, sir or madam, are a freakin moron.

[eyedeekay]

Here's the wire to cut or detach, it's Brown. On a Q70 the IPDM is tucked in outboard next to the battery:


15 Q70 IPDM.jpg

So I attempted this and the issue still persists

So if anything it seems like the car is producing EXACTLY 1V less than it used to. So for example:

Cold start Voltage Before issue arose: 14.3V

Cold Start voltage After issue arose: 13.3V

Warm Start Voltage before issue arose: 13.9V

Warm Start Voltage after issue arose: 12.9V

What would cause the car to produce EXACTLY 1V less is what I am stumped on now. Like, perhaps a ground connection that’s bad? Or maybe the voltage regulator is receiving input that does not reflect the actual voltage it needs to regulate?

[Yoda's Master]

was it an oem alternator that you replaced yours with? what kind of battery do you have? The dumb feature likely damaged your battery. try take it to autozone to do a battery test. You might need to replace your battery also. I had to replace my new battery after 6 months cause the dumb feature killed it. If you have a AGM battery, then you could try using a battery tender or re-conditioner to try to restore your battery if it's not too badly damaged.

[VStar650CL]

Besides the "dumb charging", there are only three possible culprits for an underperforming alternator:
1) Resistance between the alternator and the battery. You can check that with voltage drop. Put a voltmeter on the lowest scale (usually 200 milliVolts) and measure voltage between the main output terminal on the alternator and the battery positive post with the car running and all the electrical loads on. The higher the reading, the more resistance is present between the alternator and the battery. Typical drop will be around 50~200 mV, anything higher could pose a problem.
2) Resistance in the field supply circuit. That's the Blue wire at the alternator plug and is connected to battery through a fuse in the IPDM. The field coils are basically electromagnets which leverage a few amps of current into many amps at the main output by enhancing the magnetic field around the stator and armature. They need to be able to draw reliable current in order to do their job, so resistance in the field wire supplying them will cause low output. You can check that the same way as (1) but you need to back-probe the Blue wire instead of the main output. You should also check the plug itself for blackening or corrosion.
3) Your new alternator may just be a POS. Remans are notoriously unreliable no matter who rebuilt them. I always recommend new if new ones are available.

[eyedeekay]

Besides the "dumb charging", there are only three possible culprits for an underperforming alternator:
1) Resistance between the alternator and the battery. You can check that with voltage drop. Put a voltmeter on the lowest scale (usually 200 milliVolts) and measure voltage between the main output terminal on the alternator and the battery positive post with the car running and all the electrical loads on. The higher the reading, the more resistance is present between the alternator and the battery. Typical drop will be around 50~200 mV, anything higher could pose a problem.
2) Resistance in the field supply circuit. That's the Blue wire at the alternator plug and is connected to battery through a fuse in the IPDM. The field coils are basically electromagnets which leverage a few amps of current into many amps at the main output by enhancing the magnetic field around the stator and armature. They need to be able to draw reliable current in order to do their job, so resistance in the field wire supplying them will cause low output. You can check that the same way as (1) but you need to back-probe the Blue wire instead of the main output. You should also check the plug itself for blackening or corrosion.
3) Your new alternator may just be a POS. Remans are notoriously unreliable no matter who rebuilt them. I always recommend new if new ones are available.

Okay so update, i was going to go ahead and do number q of your suggestions, and I found out the power steering switch connecting was completely broken, and it was dangling freely near the alternator. It seems like the alternator voltage regulator plug and the power steering switch are intrinsically connected, would you know this from the top of your head by chance? I was going to go ahead and replace the sensor since the plug of the sensor itself is completely destroyed

[eyedeekay]

Besides the "dumb charging", there are only three possible culprits for an underperforming alternator:
1) Resistance between the alternator and the battery. You can check that with voltage drop. Put a voltmeter on the lowest scale (usually 200 milliVolts) and measure voltage between the main output terminal on the alternator and the battery positive post with the car running and all the electrical loads on. The higher the reading, the more resistance is present between the alternator and the battery. Typical drop will be around 50~200 mV, anything higher could pose a problem.
2) Resistance in the field supply circuit. That's the Blue wire at the alternator plug and is connected to battery through a fuse in the IPDM. The field coils are basically electromagnets which leverage a few amps of current into many amps at the main output by enhancing the magnetic field around the stator and armature. They need to be able to draw reliable current in order to do their job, so resistance in the field wire supplying them will cause low output. You can check that the same way as (1) but you need to back-probe the Blue wire instead of the main output. You should also check the plug itself for blackening or corrosion.
3) Your new alternator may just be a POS. Remans are notoriously unreliable no matter who rebuilt them. I always recommend new if new ones are available.

Okay so update, i was going to go ahead and do number q of your suggestions, and I found out the power steering switch connecting was completely broken, and it was dangling freely near the alternator. It seems like the alternator voltage regulator plug and the power steering switch are intrinsically connected, would you know this from the top of your head by chance? I was going to go ahead and replace the sensor since the plug of the sensor itself is completely destroyed

https://imgur.com/a/Qb0TBG1

[Yoda's Master]

Try shove the connector back on and see what happens

[VStar650CL]

It seems like the alternator voltage regulator plug and the power steering switch are intrinsically connected, would you know this from the top of your head by chance? I was going to go ahead and replace the sensor since the plug of the sensor itself is completely destroyed

That's a pressure sensor, not a switch, and its only connection to the alternator wiring is that they run through the same branch of the F Harness. However, the most likely cause of your busted sensor is that it was broken by whoever installed your new alternator, so damage to the harness in that area certainly can't be ruled out.

[Q70sGuy]

Unrelated to your problem - I had a year 2000 Lexus Es which had the same issue your describing. Starts off strong but at idle would barely be able to hold 12v if any strong current pulling accessory was on (like the rear defrost or blower at max). I did every imaginable test, changed alternators multiple times (reman and new), and never found the issue. I was convinced it was a wiring issue somewhere but all the testing with the multimeter I did couldn’t locate a problem. And that car had pure dumb charging - it was a 3 wire alternator. So as others have said, before blaming the smart charging you gotta test everything and you still may not figure it out

Anyway, just a story with no happy ending , I sold the car as it was

[eyedeekay]

It seems like the alternator voltage regulator plug and the power steering switch are intrinsically connected, would you know this from the top of your head by chance? I was going to go ahead and replace the sensor since the plug of the sensor itself is completely destroyed

That's a pressure sensor, not a switch, and its only connection to the alternator wiring is that they run through the same branch of the F Harness. However, the most likely cause of your busted sensor is that it was broken by whoever installed your new alternator, so damage to the harness in that area certainly can't be ruled out.

Try shove the connector back on and see what happens

So last night I connected the exposed prongs of the pressure switch back to the wiring harness plug, and when I started the car on the voltage was showing 13.8V . FYI when the car was running prior to to connecting the exposed prongs, it ran at 12.8V..

It is worth mentioning prior to starting with 13.8V, I did disconnect and reconnect the voltage regulator harness plug as well.

Interesting as well the car did not throw a code related to the pressure switch being mangled

I wasnt able to run with it like this as autozone was closed, but I picked up a pressure sensor from autozone this morning and hopefully will have it installed during lunch

[eyedeekay]

Some other notes:

Found out the wiring harness metal holding bracket for f36 and f35 (steering pressure sensor and voltage regulator) was loose, so the metal bracket was resting on the alternator.

Plugged the pressure sensor (electrically only, so sensor just hanging outside of steering pump), and car ran up to 13.7 Volts.

I know it’s ill advised, but I disconnected the voltage regulator plug and put the car in idle. Even though the car ran at a very low 11.2 voltage, the idle ran fine without any misfires whatsoever detected even after revving

Many of the ground wires have a lot of surface corrosion, I was planning on cleaning all of them one by one when I get back from work

[Yoda's Master]

Some other notes:

Found out the wiring harness metal holding bracket for f36 and f35 (steering pressure sensor and voltage regulator) was loose, so the metal bracket was resting on the alternator.

Plugged the pressure sensor (electrically only, so sensor just hanging outside of steering pump), and car ran up to 13.7 Volts.

I know it’s ill advised, but I disconnected the voltage regulator plug and put the car in idle. Even though the car ran at a very low 11.2 voltage, the idle ran fine without any misfires whatsoever detected even after revving

Many of the ground wires have a lot of surface corrosion, I was planning on cleaning all of them one by one when I get back from work

Make sure you clean the battery terminal clamp also.

Sounds like you may have found the issue 13.8-14.4V is what i normally get after giving the dumb charger a lobotomy.

[eyedeekay]

Some other notes:

Found out the wiring harness metal holding bracket for f36 and f35 (steering pressure sensor and voltage regulator) was loose, so the metal bracket was resting on the alternator.

Plugged the pressure sensor (electrically only, so sensor just hanging outside of steering pump), and car ran up to 13.7 Volts.

I know it’s ill advised, but I disconnected the voltage regulator plug and put the car in idle. Even though the car ran at a very low 11.2 voltage, the idle ran fine without any misfires whatsoever detected even after revving

Many of the ground wires have a lot of surface corrosion, I was planning on cleaning all of them one by one when I get back from work

Make sure you clean the battery terminal clamp also.

Sounds like you may have found the issue 13.8-14.4V is what i normally get after giving the dumb charger a lobotomy.

So I cleaned all the ground points for the F harness, and I found one of them to be slightly loose. One of them the bolt completely broke on the chassis, so I stacked it on top of the other ground point. Also one of the lugs were completely corroded so I crimped a new lug onto it.

Replaced the power steering sensor with the new one shortly after and lo behold the car is running at 14.4 volts cold start . Drove it for a bit and the voltage stayed around 13.8 to 13.9 volts. also glad I cut the variable wire yall mentioned for the alternator.

Car feels way different now, I’m pretty sure the car has always been running at way lower voltage because of the broken sensor and grounding issues, cause it noticeably shifts faster and pulls harder. It always ran at around the low 13 to high 12 volts range since I bought it in May

Regardless thanks for the tips again guys! I will post photos of when I get a chance

[Q70sGuy]

What a strange outcome. The power steering sensor was bugging the whole thing??

[Yoda's Master]

Congratulations to resolving the issues. Definitely sounds like you'll be having more fun

[VStar650CL]

What a strange outcome. The power steering sensor was bugging the whole thing??

I'd be pretty sure the grounds he fixed were causing something to have foggy electrical glasses. There's no way a P/S sensor causes vagaries in the charge rate.