[Cruiseomatic]

My '89 F150 has the 300 Inline-6. When you crank it up,sometimes it wants to die from lack of power,If you floor it,it might continue running. And each time it does this,the volt gauge jumps back. Or if you turn something on,it'll go back. Heres a pic with EVERYTHING on at idle.



And here it is with only the engine running at idle. Sometimes its a little higher,depends on the RPMs.



I had autozone,Oriellys and a starter/Alternator/Battery place test it and they tested it from the battery. They all say its fine. If it was fine,it would'nt do this. Could the voltage regulator be giving out or something else? Any help is appreciated. Thanks guys. It died in the driveway and almost did'nt crank back up.

[oldschoolrods]

Did you have the shop load test the alternator? How much additional electronics are you running? Might need a bigger alternator. Docvette can probably shed some more light on this than me

[Cruiseomatic]

They put a machine and had the engine running.

[docvette]

Doc here,

first of all, you didn't mention if you had to jump start the truck or not...Is the battery going dead all the time?

With the battery discharging at idle as the photo shows, a few things come to mind.

The FIRST best line of defense, is check your battery cables, make sure they are clean corrosion free, and tight.

Next confirm the Battery ground goes to the Block at or near the starter..If not consider moving it there...and run another Battery cable with ring terminals on both ends from there to the frame and yet another set of 10 gauge wires ,one to the firewall, one to the alternator mount ground lug, or case mount bolt. Burnish the paint, and be sure they are grease free ... and use a star washer at each ground point.

After you Confirm or make those modifications, using a Volt meter, start the truck, at idle do you read 14.4 volts across the battery? If not rev it up a little, does it rise a bit? If so first look for anything that poses a high current load (or short) while running...

( frayed harness, lights running that shouldn't be and the like..pull all the fuses one at a time except engine control fuses, and watch the gauge at idle..If it rises troubleshoot that circuit)

Replace the regulator..If I remember correctly, that regulator is an epoxy brick correct? has no adjusting points? it's easiest to replace those. If it does have a lid and adjusting points, try to adjust the air gap and field points , about 14 thousands and 67 thousands respectively.

The second most common malady after cables and grounds in the charging circuit, when it shows a lower than normal rate of charge, is the Alternator diode pack...

Usually a diode will go bad and impose 1/4 wave AC into the DC system..this lowers the rectified DC voltage by about 25% ( or about 3.6 volts DC for a single diode)and replaces it with an equal or higher amount of AC voltage, which is not good for the truck electrical systems and accessories..

You Can check both Alternator and Regulator Back at your local auto parts store..where you had your load test done.

If it turns out to be a diode pack, you can replace the diodes for about 15 bucks and a little tear down and rebuild time, however I would also replace the bearings/ bushings and the stator brushes and spring followers, and clean the armature copper pads while in there.

The Kit runs about 25 bucks..and is an alternative to buying a new one, If the alternator is "High Priced" ... most rebuilds run about $35 nowadays..so it's usually not cost effective to rebuild it yourself..but if it runs into the hundreds then yes by all means rebuild it yourself. It's VERY easy to do!

So in review, After confirming your cables are proper and clean, Next take it to the Auto parts store and get a check on the charging system...if it checks out good then look for high current draw while running...

When you say it "Stumbles" while trying to accelerate, could be a sign that your electrical system IS not supporting the ignition system at the current rate of charge,(high current discharge while running) or a reduced rate of charge (bad diodes, AC into the brainbox) to the ignition/computer system with a discharged battery.

Or it could be a totally different other problem, like you need a good tune up as well as charging system service..Eliminate the Charging issues first.

You also said the battery checked out ok..but is it discharging all the time? Dead in the morning or after a few days sitting? Do you have to jump it all the time?

Let us know
Doc

[Cruiseomatic]

She does'nt discharge overnight,per se dead in the morning or after a few days. Never needs jump starting,The alternator was rebuilt sometime last year when it almost burst into flames. ( It was smoking and red hot.) Battery cables are clean,so is the solinoid on the fender. I grounded the computer to pull codes,got them,while still grounded,I cranked her up and she ran perfect. Had the electrical problem still,but not as bad.

[docvette]

Doc here,

Well in light of the massive alternator failure in the past, It could possibly be an erroneous Amp gauge, damaged in the failure, try an external gauge or inductive gauge,and see if it reads correctly..It may be charging fine, but showing depleted readings..

Since the battery seems to charge up, and hold a charge, I would check there....

You may in addition to that need a tune up, or have other sensors that have been damaged in the computer system that may need addressing.

Doc

[Cruiseomatic]

The alternator shop I took it to had me turn the headlights on while running to check the system,he said it holds a charge and is fine. He did mention it might be a "Module" in the engine causing the trouble,but with the EEC,that could be anyone anywhare. What type of sensors would/could cause this type of trouble? (If there isn't to many to list.) I replaced the plugs and wires last christmas. and the fuel filter last month. What does a "Complete" tune up consist of?
Also,if it tries to die,and you put it in gear,most of the time,it won't die. Sounds like the transmission is playing a part in this,I don't know. Its a Ford C-6.
But it has me wondering why she runs better when the computer is grounded to pull codes,and when you take the ground away,it runs like crap again. And by "Perfect", I mean she does'nt misfire bad,has plenty of pickup,does'nt stumble on acceleration. I grounded the computer to the negitive post on the battery. (If that helps.)
Thanks again.

[gemini86]

Originally Posted by Cruiseomatic

But it has me wondering why she runs better when the computer is grounded to pull codes,and when you take the ground away,it runs like crap again. And by "Perfect", I mean she does'nt misfire bad,has plenty of pickup,does'nt stumble on acceleration. I grounded the computer to the negitive post on the battery. (If that helps.)
Thanks again.

I think you just explained a lot right there. I'd look at your ground side and make sure everything is clean and secure.

[Cruiseomatic]

I probably did answer my own question,but whare on earth is the computer grounded at? I had it grounded at a place called "Self-Test In." The ground took care of the stumble,but is the A/c,blinkers,headlights,etc... supposed to draw the volt gauge back?

[gemini86]

the computer should be grounded through it's own case. If it looks dirty or if there's paint restricting electrical flow, you'll have problems like you mentioned. And the a/c turning on will draw a little bit, but shouldn't dip below 13 volts. If your alternator is good (including regulator) then there should be very little movement on your voltometer. I would also check your alternator output wire that goes to the battery, if you have an external voltage regulator, I'de check ground to it, and also, checkout your connections and wiring for you voltometer itself. Mine was acting up a few weeks ago, turns out it had some resistance in the connections.

[gemini86]

did this fix your problem? just curious...

[Cruiseomatic]

Yeah,just dirty connevtions is what caused the problems. Thx for the help