When idling while drawing electrical power (like running the lights with the heater/fan/ac) my rpms dive and the motor struggles to run at 550-600 rpms. Any ideas? Is my alternator crapping out?

88 22 re.

 

No one? I've got a rare free day today and would really like to get this licked.

 

Check the voltage at the battery with all of those accessories running. Should be north of 13.25 volts at least. High electrical load with excessive resistance can cause the engine to run crappy.

 

Voltage is about 13.54- 13.6 with nothing on. 13.49 with lights and fan on. EDIT. DISREGARD. SEE UPDATED INFO BELOW.

 

is it the original alternator? if so, it's probably in need of either overhaul or replacement. i replaced mine at 175k with a 140 amp gm 1-wire. best thing is it's almost 100% bolt-on (you'll need a few adapters, but that's it).

my idle used to die a bit when my lights were on. i'd rev the engine and watch the lights get brighter. i don't have that problem with the new alt

 

Alt has been replaced by previous owner, but I don't know how old it is.

 

could be a cheap alternator they put in

 

I would get the battrey and alternator load test at a auto parts store. Then Proceed from that.

If those checked out, I would make sure your idle screw has not backed out any and adjust as needed.

If still not any of those, I would start looking at the idle air control valve and make sure the coolant lines are not plugged up. But based on your brief description, it sounds more like an electrical load bogging down the engine.

 

definitely take it to the parts store. an alt test is free

 

Battery is new. IAC valve is less than a yr old.

Right now I just have the idle turned up to just under 1000 rpms when warm. That way when I turn stuff on it only dips to about 750 rpms and idles OK.

I should also mention, this only happens when warm, once the fast idle has slowed to normal.

I guess pulling the alt is the next step. Was hoping to avoid that unless I could verify it was toast.

 

it's not too hart to do, just a bit awkward. remember to pull the battery cables off... the main wire is hot on the alternator (i almost welded a wrench to my block)

 

Im getting good voltage, but my guess is this is an amp problem. Why else would this happen while the alt is still putting out 13.5+ volts? Can the parts store test for that? What more does a parts store test for that I can't do with a miultimeter while it is still in the truck?

 

they put a calibrated load on the alternator when they test it, and they test the regulator at the same time. the alternator needs a voltage reference from the battery to maintain proper output. if the alternator gets a bad reference, the output can be affected. if there is no reference, the voltage will climb uncontrollably, and if it's too low, you might not be getting all that you need

 

UPDATE, some new info... Still a mystery.

I was doubting the readings I was getting from my multimeter so I went and bought a new one.

So now my new battery reads 12.74v at rest. All good there.

Motor running at idle (900-1000 rpms) with nothing on, I am getting 14.24 volts.

As soon as something electrical is turned on, it goes to 14.18v for a split second, then immediately thereafter bumps back up to about 14.22v with fan and/or lights on.

So what is this telling me? Seems like the regulator is working. Right? Still need to pull alternator to go get it tested?

I should also mention that it's not like the truck is sputtering and dieing. I just lose 200-250 rpms with all this stuff on. About 100 rpms if just lights or just fan. I just turned the idle up to about 950 with nothing on so that when I lose rpms it's not enough to make the motor struggle much. Seems to work just fine that way, but I know that's not exactly right.

 

maybe it's as simple as a bad positiveve alt cable connection. try cleaning that up.

that voltage (14+ volts) seems a bit high

 

Pulled the alt and took it to Napa to be tested. All tested good. So now what? This is confounding. Everything is running well, it's putting out good voltage, all connections that I can think of are clean... I'm thinking this is some sort of ECM issue? Why would I loose 200-300 rpms with an electrical load and on a good alternator/battery?

 

If your running a lot of things, drawing a lot of current its going to drag your engine down. More so with a smaller 4cyl which doesnt have much low end torque. The bigger the load you place on the alternator the harder the engine has to work to turn it. And without supplying more fuel to the engine to provide more power to turn the alternator your going to lose RPMs.

I would assume most vehicals are set up to correct the idle for accessories coming on such as AC and a bigger alternator load. If everything is working with your alt, batt and you connections are clean i would look toward your idle control. You would have to do some reasearch to see what device keeps your idle steady (electronic or mechanical) but if you just have a manual idle setpoint with no auto adjust i would think you may be out of luck.

 

It sounds like you didn't take it to the parts store for the FREE test. Okay, you took the alt out and had it tested, but the store can check the whole system while it's together. To me, losing RPMs with an electrical load means that you're drawing enough current to cause the alternator to work harder. It's not a voltage problem, but a current (amps) one.

 

Agreed. But doesn't that test check for amperage? The parts store guy said it checked "everything". Whatever that means. I'd rather not drop $200 on a new alt when I can't return it if that still doesn't solve the problem.