strange voltage prob?

[BoostedSUV]

Been doing this for a while, not a big deal but I'm kind of curious what's going on.


Sometimes I will look a my voltage gauge and it will be reading around 14v and 10 mins later it will be reading below the middle line. If I flip the fog lights on, which really "spikes" the volage on the gauge, and turn them back off the gauge will go back up to 14ish. Datamaster master shows 13.8 at all time because the ECU is wired to alt. off a relay so its not alt. voltage. Besides I tested the alt and its good. Any ideas? I know the gauge gets a "true reading" because the truck runs better as soon as the voltage is where it should be.


Also the fog lights drop the gauge to under 12 volts when they are on and damn near stalls the truck at idle. The truck also runs like sh*t when they're on. Not related but I know that's not normal!

 

[NecroWolf]

Re: strange voltage prob?

sounds like there might be a short in the fog light wiring?

 

[BoostedSUV]

Re: strange voltage prob?

sounds like there might be a short in the fog light wiring?

Possibly but it doesn't blow any fuses? It does heat up the fuse itself though. I never leave them on anymore, I just use them to "spike" the voltage system. Seems to kick the alternator into high gear. At least at the gauge.

 

[Syclone#2960]

Re: strange voltage prob?

You need a better ground connection.

 

[WyoSyclone]

Re: strange voltage prob?

Possibly but it doesn't blow any fuses? It does heat up the fuse itself though. I never leave them on anymore, I just use them to "spike" the voltage system. Seems to kick the alternator into high gear. At least at the gauge.

If something heats up like that it's usually a bad ground... check the battery and alternator grounds (including for corrosion).

Might want to take it by an autoparts store and just have them do a quick check on the battery and alternator.

 

[BoostedSUV]

Re: strange voltage prob?

Battery is new, battery cables are new, alt was tested at autozone and had no problems.

Another thing I noticed was when I shift from drive back to park when the lights are on the volt gauge bounces. Kind of weird... Ground is my guess too but I'm trying to centralize which one and where.

 

[BoostedSUV]

Re: strange voltage prob?

If I remember correctly the ground for the foglights is the same the one for the head/marker lights. I don't get anything irratic when I turn on the lights. Its only the fogs...

Still doesn't explain why the voltage drops and it takes a "spike" from the fog lights to bring it back to normal?

 

[BoostedSUV]

Re: strange voltage prob?

Dave to answer all of your questions.

Is a TY, I relocated battery to the driver side. 4ga battery cable ground goes from the batt to the block through the alt bracket bolt. Tried it off an intake bolt and it didn't matter. I don't and never had anything from the frame to block?

Ground strap from fire wall to back of head is intact, also have 10ga wire from batt ground to fender and rad support.

Voltage drops way down below middle mark on volt gauge with fogs on and is above it with them off.

Never tested volts off of back of alt with multi-meter but I will and get back to you on that one. Reads 13.8 - 13.9 on DM but alt tested ok at autozone..

 

[BoostedSUV]

Re: strange voltage prob?

Oh, stock replacement battery and alternator..

Another thing I should mention, I have an electric fan as well. DM reads 14.1-14.2 until fan kicks on at 170 degrees.

 

[cloneman315]

Re: strange voltage prob?

make sure the bulbs in the foglights are right,also the voltage mod will help make your votage more solid

 

[BoostedSUV]

Re: strange voltage prob?

Ok I did some volt/ohm testing when I got home from work. Let me know if this tells anyone anything...

12.5 volts across batt terminals with truck off, 13.8 with truck running. I've also got 13.8 at terminal post on firewall with or without lights/fogs on. If I let the truck run for a while the voltage jumps all over the place, anywhere from 13.8 to 17.1 and sometimes spikes higher. Turning the fog lights on at idle drops the idle 250rpms but doesn't change reading at the battery. Gauge in dash drops below 13 I would guess.

Ohm tested the grounds, I have .14 from ground terminal to block, and .80 from ground terminal to firewall and inner fender grounds.

 

[BoostedSUV]

Re: strange voltage prob?

make sure the bulbs in the foglights are right,also the voltage mod will help make your votage more solid

if you're talking about the voltage mod to the ECU it's been done. Used to drop to 12.1 at WOT but now it reads a steady 13.8 at WOT. Just changed fog light bulbs recently and it did prior to and still.

 

[NJ93TY]

Re: strange voltage prob?

Sounds like your alternator is going bad IMO. Charging at 17.1 V is not good. Alternator should be 1-1.5V over battery witch is 12.6 Give or take with what accessories are running.

 

[BoostedSUV]

Re: strange voltage prob?

Sounds like your alternator is going bad IMO. Charging at 17.1 V is not good. Alternator should be 1-1.5V over battery witch is 12.6 Give or take with what accessories are running.

Nick it generally charges at 13.8volts. Its just seems to jump around after the truck is running for 5 mins. not sure if it's a false reading or not. Gauge in the dash doesn't move and it reads 13.8 at block on firewall. Alt was tested and came back ok

 

[hatrik8]

Re: strange voltage prob?

I don't have extreme cases like you, but I do get a drop in voltage turning the fogs on and off. A little drop is understandable, but a noticeable drop seems wrong. It seems like more often when the truck is warm. I probably just need to clean up some ground connections. Give us an update if you solve it.

What bulbs do you run in the fog lights? I replaced mine a long time ago so I can't remember what I put in there.

 

[BoostedSUV]

Re: strange voltage prob?

I don't have extreme cases like you, but I do get a drop in voltage turning the fogs on and off. A little drop is understandable, but a noticeable drop seems wrong. It seems like more often when the truck is warm. I probably just need to clean up some ground connections. Give us an update if you solve it.

What bulbs do you run in the fog lights? I replaced mine a long time ago so I can't remember what I put in there.

I am going to run a ground strap from the motor to the frame this weekend and also clean up some grounds I can find. I'm sure is a ground issue.

As for the fog light bulbs I'm jus using standard 55watt H4 or something like that? Can't remember what part # but they're just stock replacements.

 

[BoostedSUV]

Re: strange voltage prob?

Update: I ran a new 2 ga ground cable from the battery to the intake manifold, a 2ga ground strap from block to top of shock tower (chassis), an 8ga ground from battery to radiator support. I also spent 2 hours pulling off every underhood ground I could find, sanded down the metal and put them all back on. Still same issues...

I actually caught my fuse box on fire a few years back when I used to drive with fog lights on all the time. Melted the fuse and box until it caught on fire! I replaced my entire under dash harness in my 92 ty with one from a 93 (what a nightmare!) And this problem still persists. I can see by the voltage drop there's an issue with the fogs so I don't use them.

I can have high beams, front and rear wipers, radio blasting (2amps and subs) , with the blower motor on and the volts hardly move. When I flip on the fog lights the truck damn near shuts off! Doesn't blow fuses and fogs are on but it really drops the voltage! I'm out of ideas other than never using the fogs. Should I wire up a relay to them and bypass the factory wiring? Where is the fog light ground specifically?

 

[Flyin Ryan]

Re: strange voltage prob?

Should I wire up a relay to them and bypass the factory wiring? Where is the fog light ground specifically?

I was going to suggest this although that really sucks.. I can't see this being really necessary unless you have higher watt bulbs in there and there maxing out the tiny factory wiring. Why don't you try some bulbs that have weaker out put that'll prob pull less amperage? Just shooting ideas at you

 

[BoostedSUV]

Re: strange voltage prob?

I was going to suggest this although that really sucks.. I can't see this being really necessary unless you have higher watt bulbs in there and there maxing out the tiny factory wiring. Why don't you try some bulbs that have weaker out put that'll prob pull less amperage? Just shooting ideas at you

I was thinking that as well but they are the stock spec bulbs? Nothing special. I'm going to stop on way home and see if I can get lower wattage bulbs but I feel like that's just a band-aid fix and not not solving the problem I may just rewire the fog light light system with a relay and make it look factory. The factory fogs only use like a 16 or 18ga wire...

 

[Flyin Ryan]

Re: strange voltage prob?

I was thinking that as well but they are the stock spec bulbs? Nothing special. I'm going to stop on way home and see if I can get lower wattage bulbs but I feel like that's just a band-aid fix and not not solving the problem I may just rewire the fog light light system with a relay and make it look factory. The factory fogs only use like a 16 or 18ga wire...

I agree about the band aid comment but it was merely a suggestion. I personally would rewire them up with higher gauge wiring and be done with it.