[NA] surging lights and RPM (automobile)

[TangoWhiskey]

I have a 2000 Volvo S70. It started doing something odd on the way home tonight. I got video of it after I got home:

The interior (dash and dome) and exterior (headlights) are pulsing while the RPM surges up and down a couple hundred RPM. I filmed it at both idle and with the accelerator depressed slightly.

Alternator is my first thought--but why would that affect the RPM? Any ideas??

No idiot lights are on, gauges are in range. 123,000 miles, recent oil change, passed inspection a week ago.

When I restarted the car to make this video, it idled just fine with no fluctuation in the lights... until I tapped the accelerator... then it started fluctuating and pulsing again, and I shot the video shown above. Note that the dash lights are pulsing in time with the exterior headlights, though it's hard to see that in the video.

I've sent the video to my Volvo shop mechanic too, so this is more for fun to see if somebody on the group can accurately diagnose the problem from a video...

 

[Capt. Geoffrey Thorpe]

I have a 2000 Volvo S70. It started doing something odd on the way home tonight. I got video of it after I got home:

The interior (dash and dome) and exterior (headlights) are pulsing while the RPM surges up and down a couple hundred RPM. I filmed it at both idle and with the accelerator depressed slightly.

Alternator is my first thought--but why would that affect the RPM? Any ideas??

No idiot lights are on, gauges are in range. 123,000 miles, recent oil change, passed inspection a week ago.

When I restarted the car to make this video, it idled just fine with no fluctuation in the lights... until I tapped the accelerator... then it started fluctuating and pulsing again, and I shot the video shown above. Note that the dash lights are pulsing in time with the exterior headlights, though it's hard to see that in the video.

I've sent the video to my Volvo shop mechanic too, so this is more for fun to see if somebody on the group can accurately diagnose the problem from a video...

Voltage regulator most likely. Could be (probably not for a 2000) that the alternator is controlled by the Engine Control Module and something has gone wrong in the communication network between them.

Looks like the alternator output is increasing making the lights go bright and increasing the load on the engine causing the engine speed to drop. The alternator gets turned down and the speed increases as the lights dim.

 

[wsuffa]

Could be a VR (which might be integrated into the alternator). If the engine RPM varies, it could cause the symptoms - there are various sensors that can cause engine surging at idle (idle is computer controlled on many modern cars).

One other thing to keep in mind: most newer cars will outright die if the battery goes dead. I had an alternator go out one night - the idiot light didn't come on, and the car just died when the battery discharged. Fortunately it happened on the exit ramp from the highway a mile from home.

You might want to stick an voltmeter on the car and see what the voltage is when the variation occurs. If it drops below 13.something volts at idle with lights on, you'd want to take a closer look at the electric system.

 

[TangoWhiskey]

Thanks guys, I'll throw a voltmeter on it tomorrow after work (carpooling in with somebody else tomorrow). I have a digital and an analog VM; I bet I'd see the issue better with the analog...

 

[Ted]

Potentially a combination of things here.

1) Most alternators (although less on 2000-ish vehicles) don't fully charge at idle, so it's normal to see the illumination increase when the RPMs go up. My mom had an S70 and I don't recall it doing that, so it wouldn't surprise me if the alternator was starting to go south. I wouldn't change it, though, so long as you're still getting a charge at idle. If it's still working and I've seen alternators last for years like that. It doesn't hurt anything.

2) Your engine surging is likely separate. While it could have something to do with changing voltage, more likely would be something like a vacuum leak or idle air control valve. The frequency that you're seeing makes me think vacuum leak. What can happen is a large vacuum leak is basically like having the throttle open more. This will cause the RPMs to go up. Above a certain RPM, the ECU will say "Wait a second, I'm in idle, that's too high" and then cut fuel. This will cause the engine to try to shut off, then it gets back in acceptable range and turns fuel on more. This loop will go on ad infinitum, but sometimes can be broken by carefully getting it into an acceptable range. The car starting itself might do that. The IAC may also just be stuck in a certain open position.

Check voltage with a multimeter to confirm alternator functionality, look for (and repair) any vacuum leaks and/or repalce IAC valve.

 

[Capt. Geoffrey Thorpe]

2) Your engine surging is likely separate. While it could have something to do with changing voltage, more likely would be something like a vacuum leak or idle air control valve. The frequency that you're seeing makes me think vacuum leak. What can happen is a large vacuum leak is basically like having the throttle open more. This will cause the RPMs to go up. Above a certain RPM, the ECU will say "Wait a second, I'm in idle, that's too high" and then cut fuel. This will cause the engine to try to shut off, then it gets back in acceptable range and turns fuel on more. This loop will go on ad infinitum, but sometimes can be broken by carefully getting it into an acceptable range. The car starting itself might do that. The IAC may also just be stuck in a certain open position.

A problem with the idle speed control valve was my first thought - but it appears that the lights don't go bright as the engine speed increases - there is a short delay, then the lights go bright and then the speed drops.

 

[Ted]

A problem with the idle speed control valve was my first thought - but it appears that the lights don't go bright as the engine speed increases - there is a short delay, then the lights go bright and then the speed drops.

I don't see the issue there. I'm saying the two are likely unrelated.

 

[SkyHog]

Lights - I'll bet a Voltage regulator (as others have said). Very, very common.

Engine surge: TPS perhaps, or the IAC. Could be a vacuum leak, but unless its an old car I'd bet not.

 

[TangoWhiskey]

Lights - I'll bet a Voltage regulator (as others have said). Very, very common.

Engine surge: TPS perhaps, or the IAC. Could be a vacuum leak, but unless its an old car I'd bet not.

Both problems started at the exact same time, so I doubt I blew a regulator or alternator AND developed a vacuum leak or killed another component at the same time.

If I turn off the ignition and restart the car, it idles fine (no surging) and the lights stay steady. It can sustain that state for as long as I leave the throttle alone. Step on the throttle and take it up to 2000 rpm or so, then back to idle, and the problem starts.

On restart, idling fine, battery voltage is showing 11.64, which is low. Stays steady until the throttle up/down, then cycles from 11.86 to 13.86 and the lights surge with the engine.

Odd.

 

[Ted]

Well, your 11-12V is not charging, and your 13-14V is. So first problem, your alternator isn't charging at idle, so you should fix that. That can be due to a few things. Check connections first (you could have a loose or corroded one). I'm assuming on that car there's a signal that goes to the alternator to tell it when to charge, in which case that wire could be bad and it's operating like a "1-wire."

Most likely, it needs a new alternator.

Fix the charging problem, see if the surging problem goes away.

 

[wsuffa]

Well, your 11-12V is not charging, and your 13-14V is. So first problem, your alternator isn't charging at idle, so you should fix that. That can be due to a few things. Check connections first (you could have a loose or corroded one). I'm assuming on that car there's a signal that goes to the alternator to tell it when to charge, in which case that wire could be bad and it's operating like a "1-wire."

Most likely, it needs a new alternator.

Fix the charging problem, see if the surging problem goes away.

With those voltages, I'd look at the electrical system. Alternator, voltage regulator (probably integrated) and maybe battery. And all the connections in between.

with electronic engine controls, low voltages can wreak havoc.

 

[Ted]

With those voltages, I'd look at the electrical system. Alternator, voltage regulator (probably integrated) and maybe battery. And all the connections in between.

Which is pretty much what I said.

with electronic engine controls, low voltages can wreak havoc.

Yep, agreed.

-Guy who does electronic engine controls for a living

 

[TangoWhiskey]

Thanks guys. Put it on the charger overnight so I could drive it into the shop this morning--waited for daylight so I could run with no lights, fan or radio--aviation principles of load shedding being applied!

Volts before start, off the charger was 13.10. Started up and headed the 20 miles to the shop. Surging was still occurring, but not as noticeably. Tests: turned on fan, fan motor surges at the same frequency as the lights were.

Interestingly, got halfway to the shop, and the problem stopped, so I came straight to work. Will take the car out in a bit and drive it with lights on and see if I can reproduce the problem. I'm thinking that without a load, the alternator got the battery charged back up, or I jarred an intermittent connection back into place on our infamously smooth Texas roads.

 

[Capt. Geoffrey Thorpe]

Interestingly, got halfway to the shop, and the problem stopped, so I came straight to work. Will take the car out in a bit and drive it with lights on and see if I can reproduce the problem. I'm thinking that without a load, the alternator got the battery charged back up, or I jarred an intermittent connection back into place on our infamously smooth Texas roads.

With no load and a charged up battery, variations in the alternator voltage won't produce much change in the torque required so you won't get much engine surge. Turn on the lights, rear defrost, defrost, max fan, and whatever else and watch it come back.

 

[gismo]

On restart, idling fine, battery voltage is showing 11.64, which is low. Stays steady until the throttle up/down, then cycles from 11.86 to 13.86 and the lights surge with the engine.

Odd.

That's not right. 13.86 sounds good for a steady state voltage but it shouldn't be cycling down to 11.64, in fact it shouldn't go below about 12.6 volts unless the battery is bad unless there's a significant load. Ideally you should measure the alternator current when it's cycling but that might be difficult to do. Does the engine RPM surge when the lights (and other heavy loads are off? If not what's the voltage at idle? My first guess would be something drawing a lot of current and cycling on and off. One candidate for that would be a power window motor or anything else that uses a self resetting CB instead of a fuse for overcurrent protection.

 

[TangoWhiskey]

OK, update: driving it home from work yesterday, the battery just BARELY got me home. It was dark, had to drive with lights on about 20 miles. Things were fine until about 2 miles from home, then the ABS light came on, followed quickly by other idiot lights illuminating and the dash lights getting dimmer as the voltage continued to drop... I had to hit the wipers to knock some drizzle off the window, and the wipers were SLOW.

Nursed it home, checked voltage, it was low 11's. Put it on the charger overnight. Took it to my favorite independent Volvo shop this morning (20 miles away). About 15 miles into the trip, when the battery's surface charge would have worn off, I stopped and put my voltmeter on the battery (11.32V) and ran it up to 2200 RPM and held it there; no change in V. Would have expected to see it jump up to over 13.

Dealer tested; the 18 month old Volvo-brand battery is fine, alternator isn't putting out anything. They checked the resistance on the other paths and cables (the B+ cable is notoriously a trouble spot on these S70's, but I had mine replaced with the battery 18 months ago), and they're all fine... they're confident a new alternator, which they are installing now, will fix it...

 

[wsuffa]

OK, update: driving it home from work yesterday, the battery just BARELY got me home. It was dark, had to drive with lights on about 20 miles. Things were fine until about 2 miles from home, then the ABS light came on, followed quickly by other idiot lights illuminating and the dash lights getting dimmer as the voltage continued to drop... I had to hit the wipers to knock some drizzle off the window, and the wipers were SLOW.

Nursed it home, checked voltage, it was low 11's. Put it on the charger overnight. Took it to my favorite independent Volvo shop this morning (20 miles away). About 15 miles into the trip, when the battery's surface charge would have worn off, I stopped and put my voltmeter on the battery (11.32V) and ran it up to 2200 RPM and held it there; no change in V. Would have expected to see it jump up to over 13.

Dealer tested; the 18 month old Volvo-brand battery is fine, alternator isn't putting out anything. They checked the resistance on the other paths and cables (the B+ cable is notoriously a trouble spot on these S70's, but I had mine replaced with the battery 18 months ago), and they're all fine... they're confident a new alternator, which they are installing now, will fix it...

Those are the symptoms.... you're lucky it didn't die coming home.

 

[TangoWhiskey]

...you're lucky it didn't die coming home.

No kidding; I could tell it was CLOSE to doing so.

They replaced the alternator, and things are working well again!