I have a few threads i have posted here of time trying to find answers to several problems i HAD with my 2000 4wd 2door 4.3L. I had problems with weird changing fuel mileage,surging at highway speeds, erratic acceleration, power loss or slight bogging, headlights, instrument and cab lights flickering. IT WAS THE ALTERNATOR!!!!I had a feeling my alternator was making AC voltage because of the lights flickering, so i checked,it was putting out 1.2-1.4 AC VOLTS.....which didn't seem like much until i found some new information on this very vehicle's alternator that says the AC voltage present should not be more than 300mv!! FINALLY!!!! So i changed the alternator and EVERY SINGLE PROBLEM I HAD WITH THIS TRUCK WENT AWAY!!!! as i had suspected the small amount of AC voltage was enough to confuse the ECM causing all of my problems!! I hope this helps alot of other people that has had the same or some of the problems that I've had. I think that some people may not notice their lights flickering or their lights maybe flickering very slightly, but they seem to have the same problems at the same time like i had. So if you have the same performance issues i had, you might want to check your alternator for AC voltage. REMEMBER it must be below 300mv!!! I have been trying to trace these problems down for 6 months or so!!!! ANYWHO I hope this helps!!!!

UPDATE: after replacing the alternator which solved the erratic performance and my headlights and interior lights flickering, i still had a sputtering problem only at 1800 to 2000 rpm while cruising at 60-65 mph, and while accelerating in each gear when the engine would get to 1800-2000 it would sputter and hesitate then smooth out. I have already replaced the cap, rotor, plugs and wires 1 time in november of last year because of this sputtering problem and believe it or not the problem stayed EXACTLY THE SAME!!! because like a hard head i did not listen to what the administrators and other people that know these trucks very well said to use ac delco cap, rotor, plugs and wires!!!

BIG MISTAKE!!!......

I used the cheap wires and they immediately caused the same problem i already had!! WTF???? so naturally i thought IT CANT BE THE WIRES OR PLUGS OR CAP OR ROTOR.....WRONG!!!

So I saw the tool man again today and told him thank you and told him about the good news about how his scanner told me the correct info on the alternator and how it fixed my issues except for the little annoying sputter at 1800-2000 rpm. So he let me use the scanner again and I drove my truck with the scanner hooked up and lo and behold when it would start sputtering and missing cylinder no. 4, 5, and 6 were all missing at 1800-2000 rpms Every time!! Oh yeah and BTW I had the greatly feared PO300!!! when we first hooked up the scanner and i never had a MIL light NEVER..well i have searched this forum day after day and looking for anybody that has found an answer to the problem i HAD, WELL I FOUND MINE!!


I hope this helps people who are having all the same problems i had as i have tried to be very informative, sorry for the long post......I will never again used CHEAP FREAGGIN IGNITION PARTS EVER AGAIN!!!!

 

did u test this using a multimeter? i just went out to test mine because i have been having similar performance and light flickering problems as well as my battery light coming on and off and i used a multimeter on the 200V AC setting and came back with 31.4V AC at all engine speeds? this is a new rebuilt alternator which i just installed. i have never before had any light flickering until i installed this alternator but never tested my old one for AC Volts

 

Just out of curiosity I went and checked mine.. 13.7v DC and 30.4v AC. I too have been experiencing some weird things with mine as well. So I guess that a new alternator is in the cards.. Thanks for the tip. That explains a lot of issues I have been having.

 

yes i used a multimeter....but OMFG!!!both of you guys have over 30 AC VOLTS?!?!man its a wonder your ecm isn't fried! i would ask if you were sure you had it set on the right scale, but both of you guys are saying about the same thing WOW!I would put the multimeter back in the tool box and run ASAP to the parts store for a new alternator! Good luck to the both of you! Oh and DaveC i dont know if you remembered or not but MAKE SURE you disconnect your negative battery cable before you change your alternator this time, maybe you didn't the previous time before and could have very easily touched the positive cable to the alternator housing taking out your diodes hence causing your AC voltage from a new alternator!!

 

I used a digital multimeter set on the 200v AC scale. The readout said 31.4. So I am assuming that means 31.4 volts. I'll get a pic of it tommorow. It sounds like a shorted diode. Time for a new one.. What's surprising is that I don't hear it in the radio. I will take it to autozone tommorow and have it tested.


UPDATE: I went out this morning and tried the meter on a 2000 Focus.. Same result about 32v AC. I'm not sure if its just the way the meter reads it.

 

well i went and got another brand new rebuilt (traded the old one in) and i am very happy to report all light flickering and battery light flashing has disappeared and I tested this alternator for AC Volts once again on the 200V AC setting and i came back with a 3.1V reading. far lower then the last one which was 31.4V but still not under what you said the recommended AC Voltage of .3V but im not gonna concern myself it makes 14.5V DC and the lights never dim or flicker and the battery light does not come on anymore so i hope all is well now.

 

can someone describe the steps needed on how to test the alternator.

 

Po300 fixed!!!!!!!!

 

im pretty much having the same issue with a 90 fullsize chevy. i did the same thing changed distributor cap and rotor and even the distributor itself, also new wires. all brand name stuff still nothing. i cleaned every terminal on battery and cleaned every ground and i changed the alternator with a used one i had laying around same thing. ill check to see if its over 300mv like you said.

 

Davec i dont think you have your multimeter set on auto-range, you can also just set whatever scale you want it to read manually. I think what you are actually reading is 314mv!! just set at wrong scale though.

abig84 i think you might wanna do a compression test, i bet that 350's head gaskets went out and corroded the exhaust valves from burning coolant so they dont seal like they should and possibly burning a couple of exhaust valves also.

Also check your timing!!!!!! is it at 8 degrees?