I think either alternator, or voltage regulator. I'm hoping my alternator isnt on its way out. Then voltage jumps right to 14+ for about 5 secs then back down to about 10 volts for 5 seconds and then back to 14 where it will eventually stay. Battery still shows 12.4-12.6 at rest, however the alternator voltage at idle fluctuates between 12.4-13.9. Do you know what type of battery you have? 2) Turn car off, with engine bay hot. Like Indy said put the other pulley on or buy an overdrive pulley. If I turn on the fogs and heater blower the power fluctuation goes away and I return to ~14.3v. My 05 does the same thing with a new alternator and battery. it would fluctuate randomly sometimes every 5 seconds several times in a row to intermittently. Bringing the BMW community together. JavaScript is disabled. Then passed the control to DME, sudden raise in Rpm to 700 rpm and I could see the DME alternator voltage is 15.4 . 89 GT gr-40, KB2200(10psi), tweecer R/T,LC-1, 22gal cell, w/tailpipes. Initially I thought maybe my battery (bought a new one), then the alternator (had it checked several times), then possibly a vacuum leak off the brake power booster. When everything is totally off, the noise is 90% gone. Good alternators measure the voltage at the battery terminals and use whatever voltage at the alternator that is required to obtain good voltage at the battery terminals. Also stereo starts crapping out. There are two things that you are looking for. Now the system charges but at idle (stock rpm) it fluctuates like mad. This was all done at idling, very rare it would happen when not idling. If you want to learn how to make an alternator voltage check on your car, click here for a separate article on that topic or watch a video tutorial on our You Tube channel. You should see 11.5-12v depending on the battery and it's charge. A forum community dedicated to Ford Mustang owners and enthusiasts. GM has issued a technical service bulletin #07-06-03-009 regarding Voltmeter fluctuates GM Trucks. INPA ALTERNATOR VOLTAGE TEST AND SYSTEM BEHAVIOUR: When you command 10V and see 12.4-12.7, that's your battery itself, with the alternator not helping any. . When you are at idle, the alternator is not producing a sufficient charge in order to maintain the amperage load of your rig. The new alt. You did not state the specific brand of alternator in your Jeep. If the needle seems 'bouncy' while driving or at idle, then there may be a problem. You may have a battery or alternator issue. So I did the next thing changed the battery. Once moving, the voltage is rock steady at 14.1v. The replacements always come with the wrong pulley size for these cars. Backstory: I installed a 3G alternator out of a windstar or something in my 1990 fox, and used a 4 gauge power wire with the stock 10 gauge wires disconnected. Even if I put the smaller alt pulley on, it will be the same issue when that happens. I have a 1994 GMC safari van, when the cars on the voltmeter fluctuates between 13 an 18ish, and I hear a rhythmic wirrring sound that matches the movement of the needle and of course the pulsing lights. For a better experience, please enable JavaScript in your browser before proceeding. It seem that either the alternator is not regulating the current propoerly or there is something drawing a lot of volts on and off (like twice per second) down to maybe 12V then back up to 14.6V. What about when I throw on my vortech v1 with the 10 rib pulley. The battery meter dips from about 15 or 16 down to below 14 and then back up to normal. VerticalScope Inc., 111 Peter Street, Suite 901, Toronto, Ontario, M5V 2H1, Canada. This happens at idle, with accessories on. For a better experience, please enable JavaScript in your browser before proceeding. When fully warm at idle with new used alternator my voltage will drop all the way down to 12.6v and fluctuates up to 13.5v (back and forth). Voltage drop of output cable. Just replaced the 3 wire pig tail with a better one (sense wire = 12 gauge now). Whe only a few are used it will be as high as 14.6 volts driving and drops to 12.8 at idle and continues to drop as I … At idle, most charging systems produce 13.8 to 15.3 volts with no lights or accessories on. When I use alot of accessories the battery voltage drops to 10.5 volts. A forum community dedicated to BMW owners and enthusiasts. If you don’t see the recommended voltage when you check charging voltage at the battery with the engine idling, check the wiring connections at the alternator — not just visually or by wiggling the wires or connectors, but checking for excessive resistance by doing a voltage drop test. If I put all 4 windows up at the same time the lights dim for a second and then the voltage goes up to 14-15 volts. So lets rule out alternator spinning too slowly being the cause. Turn the key truck starts right up, battery gauge will be right around the 10volts mark for about 5 seconds. This comes and goes at idle or highway speed. Measure the voltage across the battery and the big bat alternator terminal to alternator case. saravan, as you saw, our BMW's certainly have separate regulator modules attached to them. The fluctuation only happens when I'm at idle with headlights on. If voltage seems to fluctuate during your test, switch your voltmeter to the AC voltage scale and take another output voltage reading with the engine still running. Behavior: Idle fluctuation little bit more between 640-670 rpm., voltage shown on cluster fluctuate between 12.40 - 12.70 v . Set the parking brake and your transmission to Park (automatic) or Neutral (manual). Many so-called alternator problems turn out to be nothing more than a bad connection at the alternator or a bad … But it has good charge, to run the car on its own. Since an alternator’s output can vary both up and down from 13.5V in real-world situations, it’s actual output limits will vary from the idle and rated numbers. Sometimes for a little time or for like 20 min drive. Put a voltage meter across the battery while running and voltage was fluctuating from 9 volts to 13.5 down to 9 again over and over and over. It is all in the details, my friend. This time, connect your meter's red lead to the B+ terminal on the back of the alternator, … My car has many short trips in it's history, so my brushes seemed to wear a bit early at 92K. The actual output voltage produced by the alternator will vary depending on temperature and load, and will usually be about 1.5 to 2 volts higher than battery voltage. Battery voltage swings from 14.5v to 12.5v pretty quickly, with all the lights dimming and rpm dipping. Asp makes a few. It's usually fine when I first start it, but gets worse after the truck gets warm. Voltage gauge fluctuates, but alternator checks out. In the city it is around 14 volts, when I get on the highway it drops to 11-12 volts. 2005 Chevrolet Silverado Voltage fluctuates. So, as a summary, you should be measuring the voltage at the battery terminals. 2006 530xiT 6MT - 150k miles - 3rd owner - sport & cold packages. You should have 13+ volts when the alternator is charging. I checked the battery with a volt meter while running and it fluctuates between 13.2 and 14.8 volts quickly so the battery is not discharging. Solutions include driving in a lower gear below 35 MPH, letting the engine idle with everything off for 5 minutes at the end of each trip or getting a float charger (1.5 to 2 amps should work fine) and hooking up the battery to it overnight each night. Low engine speed, lights and blower motor on full, rear defrost on, the alternator cannot keep up. What i observed from this test is , the DME - BSD communication to alternator is fine. Used a multimeter on the main cables to the fuse box and to/from battery to alternator, there’s no voltage drop and no obvious corrosion. I have no clue why this is happening. When the voltage does drop some lights will dim, the engine sound would change. When the voltage drop happens its pretty noticeable visually & audibly. From a 2011 BMW document "Power Management", The battery voltage can vary between 14 V and 15.5 V. The optimum charging voltage is set by the power module as a function of the state of charge of the battery, the battery. JavaScript is disabled. VerticalScope Inc., 111 Peter, Suite 901, Toronto, Ontario, M5V 2H1, Canada. 4,094 Posts. Just put a voltmeter to the battery when the car is not running. If the needle drops to 13 (or so) in about 10-25 miles of driving, stays there for a while, and then returns to a higher voltage (~14.5) and remains there for a while, that is not "rapid" - that's fairly normal. Check out ScottiesHobbies.com for more automotive videos.I am currently having a issue with my 1994 Chevy Silverado with a 5.7 L engine. Of concern are their brushes, which wear to intermittent contact -- but 80Kmi is a little low for this problem. Lately I have noticed the voltage fluctuating 13.9 - 14.1 at idle, in time with the idle itself fluctuating up and down a little. There the voltage should be … Come join the discussion about Bimmerfest events, production numbers, programming, performance, modifications, classifieds, troubleshooting, maintenance, and more! My 1990 ST still has the original RR and alternator, and usually shows a steady 14.1v. has a 2.5" pulley on it which is … Worked great for 2 years. The charging voltage should be between 13.9v to 14.4v. I'd say for the past 2 weeks now my truck started doing something kinda weird. The battery is getting about 13.7 volts at idle. Come join the discussion about performance, production numbers, VIN decoders, modifications, troubleshooting, power adders, DIY tutorials, and more! The crank pulley accessory drive is underdrive sized. Page 1 of 2 1 ... and the heater are running in the video. Adam: The voltage at the battery should not drop below 12 volts engine off for a healthy battery, and not go above 14.5 when running. Hi, I just started having some voltage fluctuations (according to to Volt gauge). It seems that it is surging a bit no matter what speed you are going and when it does this it actuallly causes the interior and exterior lights to dim and brighten along with the surging. The regulator for the alternator is built into the PCM, so there might be an issue there also. Disconnect 10mm nut holding down output of alternator. AGM charging voltage shouldn't exceed 14.8V. and voltage fluctuate agin between 14.7 - 14.8 along with idle fluctuate. GM says fluctuating voltage on the vehicle’s voltmeter is NORMAL and is not a reason to replace any parts. Voltmeter fluctuates GM Trucks The voltmeter fluctuates on my GM Truck. Discussion in 'Engine & Drivetrain' started by derekjl, Jan 17 , 2018. Truck is running idle at normal operating temps. Also the voltage at the battery and the voltage at the alternator should be within 0.5v of each other. Build The Wall Already! Oct 29, 2016. The voltage gauge fluctuates between 12 and 14 or so. I did check the diode pack before replacing and it was fine. Not … #2 • Aug 19, 2019. Tell us which alternator, one-wire or … One must define 'fluctuate' and 'rapid' first. Must have been a faulty regulator. Sorry for the delay, Just a quick update. My voltage started dropping from 14 to 10 at times, causing the engine to cutout. Disconnect negative and positive battery cables. Replacement made the BSD bus happy and stabilized my voltage. The battery shouldn't be bouncing much. I know the voltage should not decrease below 13.3V or so to the battery. It is more noticeable at idle, but you can "hear" the surge at any speed. The proper voltage output is from 13.5 volts minimum to 14.5 volts maximum. After a short time, the voltage decreases to approx. The fluctuating voltage is by design. Do you have a separate voltmeter you could connect, either at the battery or at the cigarette lighter (has a direct wire back to the fuse block)? AC voltage leak can cause your lights to dim and drain power from your battery, for example. Since then it starts up fine, but the voltage gauge fluctuates a bit, it increases then decreases just a little from the baseline. Usually, you can detect this leak by measuring AC voltage at the alternator. The last number is 13.5V, which is “VT” or the voltage that the alternator was held at during the test. Ok just to put this to rest, I just replaced the alternator on warranty and it fixed the issue. Does the voltage display bounce when the car isn't running? The yellow/white sense wire was connected to the stock harness as per the LMR instruction video. While driving and sometimes idle the headlights and interior lights while dim and then go bright and will repeat. 8901. Irregular Fluctuating Voltage. I have checked all the grounds and positive leads. I notice the volts on the gauge drop from 14.6V (Which I think is the normal running volts?) I figured if it was the alternator my battery would eventually die, but the truck starts no problem for a couple months now. For a second opinion, compared to the dashboard reading through the computer? By checking the alternator voltage output, you’ll know for sure if the alternator is “guilty”. 15.3 is too high if you have an AGM battery. #1. The voltage gauge will also fluxuate while driving. At first I noticed mostly when maneuvering in the parking garage - braking and turning. Start and let the engine idle. Hey everyone. I just bought a 2005 3500hd and it has a slight issue (at least I hope it's slight). This happens if either everything is on or everything is off (lights, heater, stereo) but after driving for a while the meter sits calmly at 14 volts. 12V or less (confirmed with a digital volt meter and read at the battery terminals). Could it be the alternator, starter or even the new battery?