8ad alternator/voltage regulator affect EFI?

rusty ol ranger · Nov 16, 2018

Can a bad voltage regulator/alternator affect EFI performance?

Since the whole system is dependent on voltage readings i could see it happening.

Input?

bobbywalter · Nov 16, 2018

Uncle Gump · Nov 16, 2018

Most components in a 12 volt system are designed to work and survive between 9 and 16 volts. But once you get outside of the normal 12 to 14.5 volts... strange things can happen.

rusty ol ranger · Nov 16, 2018

Heres why im wondering....

Ive always thought the charging system in this truck was kinda funky, but the battery never went dead so i didnt think much about it...

But i noticed this morning the truck started acting up sooner then normal, but i also had the fan on high, hi beams on, my phone charger in, the radio on and the wipers on high.

When i got to the shop i let it idle while i fired up the semi, climbed in and noticed my fuel gauge had dropped 1/8 tank, the charge needle was still centered, but ever so slightly toward discharge, and everything was dim.

I revved the motor and held it there (pry about 1500rpm) and the charge needle jumped to the 2nd dash, avd never dropped again till i let off the gas. The lights brightend up, etc etc, untill i let off.

Im wondering if all these damn issues ive been having is related to voltage spikes/drops.

Uncle Gump · Nov 16, 2018

Doubtful... but anything is possible

Put a real voltmeter on it and do some driving while monitoring your meter.

When symptoms arise... see what the voltmeter tells you.

adsm08 · Nov 16, 2018

Voltage readings that are low or erratic can mess with the EEC system.

The sensors all use something called Reference Voltage, or VREF for short. It is a set standard voltage that all the sensors are supposed to receive. On the first iterations of electronic engine control VREF was 12V but the engineers quickly realized that is caused issues when the alternator went bad because if system voltage was lower than 12 it would throw off the readings off all those sensors. So VREF was changed to 5V because 5 is the minimum the fuel pump and coil need to work, so the readings wouldn't be affected until the battery was so discharged that the engine couldn't run anyway.

I can't remember for sure what year Ford made the change, but I think yours is a 5V VREF system. You can verify it by looking for key-on power coming into the throttle position sensor or the MAP sensor. A 12V system will match the battery, a 5V will usually give a reading of 4.95V.

Also, when you get a real volt meter on it, with the engine off look for AC voltage, should be 0 because batteries don't make AC voltage. Then start the engine and see how high it jumps. Your vehicle's electrical system needs DC to work properly, but the alternator makes AC, and then runs it through a series of diodes to turn it into DC. If those diodes are getting weak they will allow AC bleed through, and that can cause all sorts of weird things to happen for seemingly no reason. And since the return phase of an AC pulse will work against the next DC phase it will lower system voltage.

rusty ol ranger · Nov 16, 2018

Mine is a 5v reference. Atleast thats what i got when i attempted to check the TPS. However that was with the key on, but engine off.

Ill pull it in the shop when i get back today and check what you said about AC voltage.

As far as checking it going down the road, some wire stuck in the battery terminals ran thru the pass side door seam should work correct?

Uncle Gump · Nov 16, 2018

Battery voltage is a constant where ever you test... just hook it up to a Battery voltage source inside the cab.

adsm08 · Nov 16, 2018

rusty ol ranger said:
Mine is a 5v reference. Atleast thats what i got when i attempted to check the TPS. However that was with the key on, but engine off.

Ill pull it in the shop when i get back today and check what you said about AC voltage.

As far as checking it going down the road, some wire stuck in the battery terminals ran thru the pass side door seam should work correct?

Then yours is a 5V VREF. That's what I thought it should be, but I wasn't 100% sure.

There are a few ways to test voltage going down the road. If you want to just see the usable output from the alternator, go get a true volt gauge, I have this one in my truck and B2, I just used add-a-circuit fuse holders to tap it into a key-on source.

If you want to be able to test AC as well go to the pars store and get one of those 12V lighter socket ends, something like this

and put some wires on the end that you can clip to with an alligator clamp and plug into your lighter socket. Aside from going through a fuse that is hooked right to the battery, which is where you would be taking those readings.

rusty ol ranger · Nov 16, 2018

Ok. I will do that with the cig lighter. Seems a bit more foolproof for someone like me who is iffy with wireing.

Ill get back to ya guys with what i find out.

rusty ol ranger · Nov 16, 2018

Ok heres what i came up with...

Now granted the truck was still cold, and it only acts up when warm...but...i know electronics can break down as they heat up...

On a regular old charging system test, no load, i got 14.2V at idle, no change with RPM.

Charging system test, under full load (headlights, heater, etc) it dropped to 12.2V, when revved it slowly climbed to around 13.9, then began to drop, to around 12.9, then back to 13.3 or so.

Tested for AC, got .20, then 0, then .21 and the rythm repeated, engine revs had no effect. With engine off i had no AC volts.

I also noticed my neg battery cable is almost worn in half.

Im thinking the alt is shot for sure, i need to get one of those cig lighter things to see what it does when it acts up. Turning on any heavy electric puts a noticable bog on the motor at idle

Thoughts?

adsm08 · Nov 16, 2018

Replace the damaged battery cable. Electricity needs a full circuit to work, so ground is just as important as the hot side, but often over-looked.

When you replace the negative cable all three legs from the original need to be there, or the computer doesn't get it's ground.

That alternator is getting weak, you are right, but the diodes seem to be working. It actually looks like you have a weak winding.

rusty ol ranger · Nov 16, 2018

adsm08 said:
Replace the damaged battery cable. Electricity needs a full circuit to work, so ground is just as important as the hot side, but often over-looked.

When you replace the negative cable all three legs from the original need to be there, or the computer doesn't get it's ground.

That alternator is getting weak, you are right, but the diodes seem to be working. It actually looks like you have a weak winding.

So prolly a no go on it fixing my other issues then. I knew it was a longshot.

But hey, whatevers causing it is getting worse. I cant even make it home from work now without stopping for 30 seconds, shutting it down, taking off, tben after 2 miles it starts coming back to life.

I did notice a weird rattle today though right before it started acting up coming from the cat area. But i hit it with a mallet before, and it passed a vaccuum test. Once it started doing its thang, the rattle quit and i didnt hear it again.

adsm08 · Nov 16, 2018

rusty ol ranger said:
So prolly a no go on it fixing my other issues then. I knew it was a longshot.

I have an axiom for times like this.

It may not be THE problem, but it is definitely A problem, so fix it and see what happens.

bobbywalter · Nov 16, 2018

adsm08 said:
I have an axiom for times like this.

It may not be THE problem, but it is definitely A problem, so fix it and see what happens.

one thing to add to that axiom with 80's wiring. exposed to the rust belt.

https://www.speedwaymotors.com/Speedway-Universal-22-Circuit-Wiring-Harness,229874.html

8ad alternator/voltage regulator affect EFI?

Im a Jeep guy now.

TRS Technical Staff

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Im a Jeep guy now.

Token Old Guy

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Im a Jeep guy now.

Token Old Guy

Senior Master Grease Monkey

Im a Jeep guy now.

Im a Jeep guy now.

Senior Master Grease Monkey

Im a Jeep guy now.

Senior Master Grease Monkey

TRS Technical Staff

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