Hope someone can give me a hint. I've got an 87 4cyl 4Runner. No problems starting the engine, etc. However, sometimes, when I turn on the headlights or the turn lights (while driving in the highway, etc) the truck seems on the verge of shutting down (it has never shut down, it just appears there's no power but it recovers quicky); it lasts for half a second or so. Anyone experienced a problem like this?

The battery seems OK and I'm suspecting it is the alternator; anyone had a symptom like this?

Thanks in advance

MM

 

Have you had any warning lights on? Brake/Charge?

take it to autozone or Schucks, and have them test the battery and alternator. I know at Schucks they have a hand held unit that will test the starter, alternator, and battery all in one fell swoop.

 

If you have a voltmeter, check your battery voltage with the truck shut off. It should be about 12.6 volts. Start the truck, the voltage should be around 13.5 volts. Have someone turn on your headlights, then the blower fan and watch to see if your voltage drops below that. You can also have a parts store like autozone or napa check your charging system and if you have any luck the person who does the test knows what they are doing. Good luck

 

its usually the cause of a dead cell or 2 in the battery and its the battery is havin a hard time under load. I could be wrong but if your alt is puttin charge back into the battery while its runnin then its most likely the battery. But you never know when it comes to the electrial systems...so as stated above check everything before you just start hrowin parts at it

 

even with two Optima's, my truck drops about 150 RPMs when I turn my head and driving lights on; granted I have upgraded to composite headlights with H4 bulbs and run 100watt driving lights; probably wouldn't do it at all if it weren't for the original altenator

but yeah, take a multimeter to the battery posts while it's running, and have a friend turn the lights on and off and watch your voltage. If it drops below about 12.5v at idle with em on, I'd look into having the battery or altenator tested somewhere.

 

low idle speed can also cause this type of issue

 

Hi again and thank you for your input. I did the check mmR2 specified. First I measured the battery with the motor off; it measured like 12.6V. Then I turned on the engine and measured the voltage again, it was around 14.6V; I turned the lights, wipers and heating on and the measured voltage lowered to 14.4V.

It seems to me the alternator is delivering the voltage; I was tempted to disconnect the battery's negative cable while the engine running but I heard it was not a good idea; is it?

What do you guys think of the result of the test? Oh, I did/do not have any warnings on.

Regards,

MM

 

pulling the neg. cable is not really a good idea on anything that has a computer. I have heard that it can send a voltage spike to the computer and fry it. The results you had tell me the alternator is working fine and the battery is fully charged.

 

x2 on the alternator output being okay. also, not a good idea to pull the neg cable from the batt- the batt acts as a load on the alternator and absorbs most transient voltages. pulling the cable from the batt will cause the alt to go full output, which can momentarily exceed 15 volts without the load of the battery and consequently damage electronics, etc.... even blow lightbulbs.

given that, sounds like a ground issue (corrosion, missing, loose) between the accessories (lights, ecu, etc) and the battery.

 

Pulling the negative battery cable won't affect anything. All it means is the battery is not charging.

However, since he is getting 14.4-14.6V, there is no reason to pull the cable since the alternator is putting out a charge.

 

Hi Again. Just an update to my problem.

I got the battery tested with an automated multimiter-like device which showed the battery is in good condition. They tested the alternator as well with the same device and it gave a good reading. Beforehand I had cleaned the battery contacts. They said it might be a contact problem and to check the negative lead connection to the bottom of the car. I did and it looks OK.

However the problem persists; moreover, (I guess) because the cold weather, I have to give at least three tries before the engine starts in the mornings. This had not happened before even with severe cold weather. The battery does have the energy to keep the started running.

I was looking at the Haynes part on checking the alternator and I will follow the procedure sometime next week; it involves tapping into some connectors in the alternator itself.

Any additional suggestions/comments will be appreciated.