Noticeable Engine Surge When Turning on Accessories

[211]

I've posted about this before but never really got a solid answer. Plus my issue seems to be getting more noticeable (or maybe I've just become more hightened to it).

 

In my original post I noted how the engine surges when the A/C is turned on. It will also surge whenever the compressor (or whatever is kicking in) kicks on and off.

But I'm also noticing it when I turn on the fan (no A/C just cold air). Happens even more in the defrost setting.

Now, when I say "Surge" I don't mean the car stalls or want's to die, its just a short "stumble", an obvious load on the engine.

I guess it wouldn't be a problem if this is normal but it's annoying because driving on the freeway the fan (defrost, A/C, or whatever) kicks in every minute or so so that "stumble" is felt every time. Needless to say it gets old.

 

anyway, my panic is this, I'm going camping this weekend and really don't need any surprises along the way.

[porcupine73]

What year and model Subaru is this? I notice on '00obw at idle it bumps up the idle about .5 seconds before engaging the a/c compressor. I don't notice the engagement much when it cycles while driving. I can feel it cycling on the '96 though. I don't notice it at all on the '94 but that's because the a/c doesn't work on the '94.

 

I wouldn't worry about it too much before going on a trip. I mean if the a/c clunks out or whatever, just remove or cut the belt to the a/c compressor and you're good to go.

[nipper]

Defrost will turn the AC comprssor on for a short time to lubricate the compressor (if I remember correctly).

 

The IAC motor is what kicks up the engine rpm when a load comes on the engine. Unless its more then a few 100 rpm i wouldnt worry about it. If it is more it can be a dirty IAC valve.

 

nipper

[211]

Sorry, It's a 2000 OBW manual trans.

 

I guess I'm mostly worried that it's a charging/battery issue. It's the original battery but seems to be fine (have not had any load tests or anything but starts up just fine). Besides it's all alternator output once I'm driving right? Or will a dying battery create loads on the alt causing the alternator to split it's output??

 

I've never had a car surge when an accessory was turned on. Are these alternators inherantly low output?

[porcupine73]

Are these alternators inherantly low output?

Good question. Nipper has a thread going on for this right now. I have noticed output as low as 12.8V sitting at idle (engine at operating temp) and no accessories on. These cars ('00OBWs) have DRL too so that probably doesn't help.

[nipper]

I'm not following your resoning.

 

The way a battery usually dies is that the plates inside the battery shed enough material from charge/discharge that the plates short out. This is why optimum dry cells are superior to wet cells. This makes the battery into a resistor, which can load up the altenator, or cause the battery to self discharge, or worse case damage the alt.

 

over 2000 rpm its all altenator. Under 2000 rpm it can be all altenaotr, or altenaotr - battery mix. It depends on what the load is and what the car is doing at the time. This is why when your in a catalysmic traffic jam in the summer, the first cars with thier hoods up are usually luxury cars. AC on full, all the gizmos running and the car is just ideling. This will kil the battery in a HUGE jam. Just reving the car up a bit keeps the battery charged.

 

The highest load on the car is when everything is on, your in gear (auto) and your foot is on the brake pedal. Manuals are a little bit better with this.

 

nipper

[montana105]

I can't think of any modern era car,less then 30 years old, that doesn't cycle the a/c compressor when either the defrost is on or you are using the a/c. On my 93 Leg wagon I can definitely feel it when the compressor kicks on and the engine does compensate for it when idling.I really feel it when cruising at highway speed,I can feel it kicking on and off,and it really drains engine power when pulling a hill or pass.I can see how it could drain down your electrical reserves at idle as my radiator fan kicks on at the same time,and the compensation the engine makes only is about 200 rpm,nowhere near the 2000 rpm needed for full alt output.So lets say it's hot out-you're running the a/c,plus the fan motor plus the radiator fan any media sources,and not to mention I've noticed lots of vehicles that have daytime running lights required or not and you're sitting at a stop light at maybe 800 rpm.total battery power. as far as your trip why not just replace your battery,it's overdue and not one of those things you want to have go bad out in the boondocks?

[211]

I can't think of any modern era car,less then 30 years old, that doesn't cycle the a/c compressor when either the defrost is on or you are using the a/c. On my 93 Leg wagon I can definitely feel it when the compressor kicks on and the engine does compensate for it when idling.I really feel it when cruising at highway speed,I can feel it kicking on and off,and it really drains engine power when pulling a hill or pass.I can see how it could drain down your electrical reserves at idle as my radiator fan kicks on at the same time,and the compensation the engine makes only is about 200 rpm,nowhere near the 2000 rpm needed for full alt output.So lets say it's hot out-you're running the a/c,plus the fan motor plus the radiator fan any media sources,and not to mention I've noticed lots of vehicles that have daytime running lights required or not and you're sitting at a stop light at maybe 800 rpm.total battery power. as far as your trip why not just replace your battery,it's overdue and not one of those things you want to have go bad out in the boondocks?

 

I think this reply answered a lot of questions.

 

So it sounds pretty common that a noticable surge is felt (in engine rpm and power). I'd feel better if others noticed this surge and commented as well, that would make it normal for these subarus.

 

As far as the battery, I should replace it although i'm not 100% sure it's OE, looks damn old though, definately not a "name-brand" on it anywhere. If nothing else I'll have it load tested before I leave for my trip.

 

I'm planning on brining my laptop and dc/ac inverter so the kids can watch movies along the way. That plus the A/C, daytime running lights, stereo, that seems like an aweful lot of juice for that tiny alternator to put out.