Ok guys, here's a brain teaser..... WHERE IS MY VOLTAGE GOING!

I've replaced my ECM 3 times so far over the course of the last 4 years of having my car. EVERY time i replaced it, i pulled my hair out trying to find out why i had an SES light because everything always checked out.

when i replaced the ECM they went away, the codes have always gone away, and not come back, and i've gotten a different code each time its happened.

this leads me to believe, there is something wrong with the car that is killing the ECM'S! The only thing i can think of, is that my VOLTAGE is not sufficient. I've also replaced my alternator 3 times, every time its went bad, it starts making a whistling sound, and then my voltage starts going way below 8 volts.

if i drive the car right now, it will have 12-13 volts, however when i use something like the blower motor for the heat, the lights, and use the switches for the windows, the voltage will go down to like 12-11, and stay there until i stop using the accessories, it NEVER goes below 12-11, unless the alternator is bad.

i think something is robbing my voltage..... any ideas? i've looked through most of my wiring in my car, i'd say 90% of it

 

Might want to check your grounds. There are several of them throughout the car.

 

yeah i know, i think i need some kind of wiring diagram taht tells me exactly where the grounds are throughout the car.

 

Start checking all powers and grounds.

Use a voltmeter for reference only and always measure battery first before testing.

That will also tell you the voltage drop the particular circuit is experiencing.

later
Jeremy

 

wait, so while the car is running i have to check everything that is using power with a voltmeter to make sure its not taking more power than it should??? ugh this is gonna take me a lifetime

 

yeah electrical problems are very time consuming but if you know what your doing you learn to love figuring them out. ok so when your car is running there should be 13.5-14 volts not 11-12. if the alternator is being replaced so many times it seem like its just being over worked because the voltage throughout the car is insufficient and it is being full-fielded and is burning up the bearings.

the thing to look for is the wire the alternator to the battery. its the big red battery wire. start the car and place a voltmeter on each end of the wire. one on the alternator post and one of the battery post. it shouldn't read more the .5v. what that means is that wire is dropping .5 volts from one end of the wire to the other end. if over .5 volts check connections, if everything is tight and corrosion free replace the wire because it is corroded inside where you cant see.
now if the drop is .5 volts or less then start checking grounds. check all the main grounds but from the sounds of it you have a large voltage drop from the alternator to the battery. you should be at 13.5 to 14 volts minimum at all times

 

wow man, that really helped/makes sense, i'm gonna try that next time i get a chance, but seriously, i really appreciate it!

 

I agree with checking grounds
I have had more than my fare share of electrical "GHOSTS" over the years and 95% of the time it came down to bad ground
Get some BIG cable and ground EVERYTHING
Battery to Engine
Engine to Chassis
Battery to Chassis
anything that stands still long enough !!!


GOOD Luck

 

bb454, i tried checking the voltage on the positve battery cable on both ends, and i didnt get anything on the voltmeter at all..... is this bad?

 

depends. did you get anything or was it like .1 or .2 v? if you got a real low voltage thats good. but if you didnt get anything at all there mey be a problem. you were on the main wire on the alternator and the positive wire on the battery correct? you should get something on the meter if your doing it correctly. make sure your on DC volts too and that the leads are in the right holes in the multimeter.

you said earlier that the voltage is at 12-13 volts while driving. what are you relying on a gauge inside the car cause those aren't very accurate at all. start the car and an idle the voltage at the battery should be 13.5-14. check that with the multimeter. just place it right there on the battery posts. if its not the only thing is a problem with the alternator, wiring controls for the alternator, or the main wire to the battery like we've been talking about. i have access to all the wiring diagrams you need at my shop so if we cant pinpoint it let me know and ill try to scan some diagrams for ya. one of the perks of being a mechanic. haha

 

yeah definitely man, well i would tell you exactly what i did, but i'm at work, so i'll have to summarize. i was using the same settings on the multimeter that i was using to check the voltage on the battery, and that read 13 volts, so think thats ok. what about if i checked the voltage on the post behind the alternator where the + battery cable connects, then checked the voltage on the actual battery, and then subtracted the two. would that also give me the voltage drop??? then again it might not be very accurate considering i'm using an analog multimeter, not a digital one...

anyway, i think we should move forward with this idea until i do the test correctly, i dont get home until about 7:00pm eastern time, so i'll check the settings on the multimeter then. and as far as the wiring diagrams go, that would be great if you could post them.

yeah, i'm relying on my stock voltage guage in my car, but its gotta be pretty accurate because it drops to like 10.5 sometimes when i hit a big puddle, which is a little weird but when it drops, my lights dim and everything for a second, so i know its atleast AROUND what it should be.

 

Wow bigchief you are definitley having some voltage issues. If a puddle might be affecting it you might also want to check your power wires to the starter. Also on many firebirds there are power distribution blocks near where the factory air intake sits mounted next to the radiator. Again check for corrosion on the wires make sure everything is tightened and check from there to the starter to make sure nothing has melted or broke.

Your major engine grounds are attached to the cylinder hads on the back of the motor. Not being the orginal owner who knows what bolts are holding them in or if they are sucured properly. Just keep chipping away at it and you will find it.

 

well i've pulled out the motor and checked ALL the harnesses in the engine bay and everything seemed to be just fine, this was about 3 years ago. but yeah, i think it might be the wiring on the starter, maybe since its an aftermarket starter (summit mini starter) maybe they made the harness wires kind of badly so that when it gets hit by water, it makes a connection between the ground and the power for a second? i dont know.... but i'm also having issues with my starter when i run my car for a long time, it gets too hot a lot of times if i idle it a long time and after i shut off the engine and try to start it right away, it just wont crank at all........

dont think my car is a pos b/c it isnt, everything works fine...... i think all these minor problems i'm experiencing are probably related, keep in mind i've changed the motor, and checked all the wiring pretty recently, but i think i've always had this dumb problem with the voltage, i can always remember my voltage going pretty far down close to 10.5 when i turn on my rear defroster

 

Well i read your profile and it mentions you have headers. If any of your power wires run from the starter to the front passenger side of the car to the distribution block then you may have a melted power wire that could be a huge cause for the ground. I have run into this problem before with uncoated headers and you must keep all of your wires several inches from them. This could also explain the poor starting after it has been running due to the power draw having the bare wire exposed. Anothertihing to do is run your car for a while and see how hot your starter gets, it may need a starter blanket or you wrapping the y pipe near it.

If you start checking connections and don't find an issue I can suggest upgrading your major power wires such as your battery to alternator, battery to starter, and so on.

Also upgrade your gounds as well. A good rule of thumb is to go on step bigger for your main ground over your main power so if you run a 4 guage power wire to teh starter then run a 2 guage ground to the block. These might help overall charging as well. I am not a big fan of the stock 105 amp alternaotr for our cars, the consistantly put out lower voltage than they are supposed to.

I realize this reply is getting very long so i will try and finish up hear. So I would do everything else first though before you spend the $150 on a 140 amp alternator.

Question? Do you have under drive pulleys on your car?

 

no, i dont have underdrive pulleys, all my pulleys are stock, i have the air pump, the crank, the alternator, a dead pulley instead of a compressor, a power steering pump pulley, and my water pump.

don't worry about the lengthy response, i can use all the help i can get right now, the only thing is, the only time i can work on the car is over the weekend, so we'll see if i can pull off all the wiring to the starter this weekend and make sure that everything is good, and not melted, i think that could probably be a possibility since i put the headers on the car. i also think that my y-pipe could be heating the starter since they are SO close together....... anyway, i'll check the wiring again to get that out of the way.

 

The other thing I would do as well after you check everything else is to hook up a battery charger and set it at the 2amp trickle charge and make sure your battery is at maximum effeciency. It is time consuming but go through everything slowly to make sure there are no bad wires. I do strongly suggest upgrading your power and ground wires though.

 

yeah that would probably be a good move, especially since my car has so many miles lol...... 261k+

 

Any luck checking anything so far? That is very high mileage. sounds like the car treated someone well.

 

yeah its been through a lot, but never in an accident any more than a fender bender. basically what i checked this past weekend was the wiring underneath the car to see if anything had been melted by the exhaust. everyting checked out, so this coming weekend i'm gonna rip the dash out, and check ALL of the wiring behind there, mostly becuase of a wire i found not too long ago that was getting cut and sparking behind the dash where it was sharp, but i fixed it a few months ago, i just have a feeling that the same thing happened somewhere else, so i'm gonna take a NICE good look through all of the harnes on the inside of the car by the firewall, should be a nice challenege ripping all taht stuff out

 

well, the last thing i've done was ripped out the ENTIRE dashboard, checked all the wiring and everything checked out. right now i have everything plugged in, and the car starts fine without the dashboard and everything is fully operational. my guage still reads below 13 when i start the car, and when i use something like the defroster, and the headlights at he same time, my guage goes down to about 11.5 and stays there until i stop using the lights/defroster. and god forbid i use the window switches, it'll probably go down another .5 volts

 

Did you trace down all of your main power and ground wires under the hood? Did you check what the voltage is at the battery, alternator, starter? I would go ahead and make sure these arent the problem areas and upgrade all of them.

 

i've checked the battery at the starter and the alternator, and they match the voltage i'm seeing on the interior gauge.... i think a possible solution would be to just buy a high output alternator, but i feel like thats just running around the problem......

where exactly are the MAIN power lines and MAIN grounds in the engine bay???

 

Well with all of your wires being good there are two possible things that might be going on. Your battery is low and it could either be that it needs replaced or your alternator is no longer putting out enough voltage. You can take your alternator off and take it to a parts store and have them test it for free. I never liked the output of my stock alternator supposed to be 105 amps but I had issues with mine as well. Could be as simple as a porr alternator. You should have several ground wires connected to the back of the cylinder heads. The powermaster 140 amp alt. that I got has never let me down and puts out plenty of juice at idle and low speeds even with my undrive pulleys. If you test it and it is bad I still suggest upgrading youtr wires to get the best results.

 

i have that same problem on my 87 gta the it charges ok at idle but when i turn on the ac or headlights or the fan comes the voltage drops to 12 or so and i just replaced mi alt but when i replaced it i remember reading a warning that was on a sheet of paper it said that on some of the gm cars with the side post cables that the cables were copper clad aluminum and what happened was that the cable would corrode from the inside out this will cause poor voltage readings and poor grounds if you still have the factory bat cables i would try this i haven't but i am this weekend.

 

oh wow really? maybe all i need is new battery cables then...... wow but from the dealership, they go about 100 bucks for the positive side!

 

i would try getting a shorter cable one for the positive and just run from the alt to the bat and you should be able to get a neg cable from auto zone or someware like that for about 20 bucks i believe that will be a direct replacement for the factory it just goes from the bat to the bottom driver side of the motor but the positive cable splits off there is a little wire going to the alt which seems weird to me and the big wire goes to the starter you would think with all the electronic devices you would want just as big of a wire going to the alt thats going to the starter

 

It wont be cheap by any means even doing it yourself. I switched to top post when I did my engine swap so i could make all of the wires myself. I ran 4 gage power to the start, 10-12 to the alternator and a 2 gage ground to the back of the drivers side head. I have no charging issues at anytime with everythign going at once. I did upgrade teh alternaotr but top post allow you to easily hook up aditional power wires and grounds.

 

Please let us know how it works out

 

shockerbird with everything going do you still get 14v at the bat and do you have the digital instruments and what did you upgrade your alt to

 

i'm sorry... what is top post???

 

its probably bad grounds.

and if its killing ECMS.. its because the ground is forced thru the ECM... and that eventually overloads the circuit traces, they break, and you need a new ECM.


make sure the block and chassis have atleast two big ground straps...

 

Yes i do. I am in the midst of upgrading my computer to a 411 but last i recall I had atleast 14 at the battery. I have an 89 Formula not with a digital dash. I have upgraded all teh wiring including the fuel pump power wires as well. Lights, wipers and radio nothing seemed to drain too much with the powermaster 140 amp alternator. Actually it is chrome which i normally wouldn't buy for an item that gets hot but it looked so damn good and the price at the time was $145 if i rememeber correctly.

 

there is two types of batteries, gm uses the side post cables most of the time if you have this type they are probly the orginal ones they are held to the bat whth a short bolt to the side of the bat, the top post bat has two posts that stick up out the top of the battery and you put the cable over them and tighten the cable around the terminal

 

I have a top post Optima battery since I was doing an engine and harness swap at once. Yes you are correct after time the side post terminals should be changed along with the cables. They can actually fix idling problems and all other sorts of issues.

 

i got another question where is the bat voltage distributed from ive traced the positive wire from the bat(stock cables)there is a small wire which runs to the alt and the the big wire runs to the starter i assume but where is the power distributed through out the car is it at the starter connection most newer cars have a power distribution box some whare but i cant find one on my gta

 

One Firebirds and Gta's there is a power distribution block near the passenger side headlight off of the radiator support. When i upgraded my wireing I found this unneccassary because it just made the wring longer but if you decide to run msd igniton or something else on the passenger side it does give you a close power source.

 

well i'm pretty much out of ideas, so i think i'm just gonna replace the positive battery terminal harness, and spend the 100 bucks.... hopefully that is it, i'll keep you all posted

 

when u say u've gone throu 3 ecms do u mean they were completly toasted or they wre just showing a trouble code cuz my car has been flashing code 36 for the past few years and with a bit of work it passed ontario emissions and seems to run good with a custom e-prom , does your car run shitty or u just don't like looking at the check engine light oh ya my car does the voltage drop thing to but it had the factory 85 amp alternator and now i have 105amp it seems to help alot but the volt meter just kept going down whenever i put the turn signals on or the headlights almost to 9-10 volts and my ecm has kept on going ,and ur describing all the same situations that i;ve had with me car let me kno when u figure this out

 

Dude!! Use punctuation. More specifically the period.....

 

**** i didn't kno i was being graded on this , why don't you search all the other threads for punctuality make urself usefull.

 

LOL

 

lol no need for the fire, gosh... ok well i'm using a factory alternator that i got from a nearby autobarn, its completly basic so i dont know if thats the problem either, but i know that my voltage is NOT very consistant, i'll have close to 13 volts sometimes, and other times i'll have 11.5.... not like its bouncing back and forth, but its just not consistant, and it doesnt matter if i'm using devices or not, the voltage still changes every so often. and when i hit the brake, i see atleast a .5 volt drop every time.

also to answer 87tpi, every time my ecm dies, it starts throwing a bogus code, and it wont go away no matter how many times i reset it or change the prom, it only goes away when i buy a NEW ecm.... the last time it happened i did a LOT of research to find out if it was definitely the ecm causing the code, and it was! i'll explain, it was giving a code 36, but all my MAF burnoff relay stuff was fine, so i traced a ground wire that activated the relay back to the ecm, connected a light to it, and to a 12 volt source, and the light NEVER turned on. once i bought the new ecm, i did the same test, and the light lit the 1st time i shut the car off, which is what its supposed to do.

 

What does this have to do with the thread?

 

Simply ease of reading. More help is given and received when you don't have to read the thread 3 or 4 times to figure out what's being said.

 

lol comon, topic people plzzzzzz

 

i'm having the exact sam problem with my car ever since i had the car i have had a code 36 . will never go away , only when i reset the computer but then comes right back the previous owner just pulled the check engine light , i put it back in so i can check the codes but i have never had a problem with drivebility of the car . well nuthing to do with the computer and i have a custom burned e-prom and tons of bolt on's but the car runs great i get about 14-15mpg in the city depending on how i drive it cuz i drive her like i stole it and i get about 600 maybe more km 360miles to a tank on the highway doing 120km/h/75mph i kno the city fuel consumption is bad but she seems fine. so if you can figure out what the problem is let me kno cuz i would be so greatfull but unless this problem is causing issues for you ie, bad fuel economy , or rough operating conditions i would have to say maybe let it go cuz i have spent 250$ for people to tell me whats wrong with it and the dicks at GM have no clue and i said f##k it , i was sure it was the ecm but the previous owner had replaced it 1or 2 times i was not going to throw more money at sumthing i kno could not be fixed . but to help you out check the ecm power connections and the fuseable links that are located right beside coolant bottle they sould be orange and some black with pink test resistance and continuity , they tend to corode. I hope this helps and good luck.

i thought T/A's were supose to be better than camaro's but we have the exact same problem i love all cars but GM makes it so easy to get pissed off

 

interesting, well today i got a code 32 which is egr while i was crusing on the highway at a constant 70mph. the egr is new, and so is the solenoid, so i guess i have a few things to look over. any suggestions?

 

check the rubber connectors on the vacume hoses test ur engine vacume to make sure your around 17-20 in-hg check the egr temperature sensor 1 black wire attached to the egr valve and check to make sure the diaphram opens and closes on the valve and test solenoid to make sure it holds vacume i had that problem to ,the solenoid wasn't holding any vacume. after that it passed emissions.

 

oh wow, alright then i'll get on top of that, thanks man

 

Good suggestions. You have an EGR temp wire?
Bigchief, you may also want to check the EGR passages in the manifold for crud.