voltage too high pegs my voltage meter at or near 60mph or 3000 rpms

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rugerberetta

rugerberetta

10 Year
Joined
Apr 6, 2011
Threads
43
Messages
189
Location
Defiance Missouri
I have q 71 FJ40 with the F engine it does have a painless wiring harness and Dolphin gauges. I was on my why home from a trip out west from St louis after driving straight through from Brice Canyon NP I made it to KC during rush hour. It was getting light out so I turned off my headlights my FJ started backfiring and died. I was able to limp off to the side of the hwy. I found out later that my voltage had gotten high enough to fry my electronic ignition I pull off the distributor cap and it had a very thick layer of black carbon dust covering everything. Well I had a to trailer it from KC to St louis. Since then I have replaced my ignition my voltage regular and my alternator and battery (to a gel battery) still if I drive at 60mph (close to 3,000RPMS) for any more that a few minutes my voltage spikes to over 16 volts. I have checked the ground of the regulator I even added a separate ground wire from the regulator case to ensure a good ground. I have the 3 wire regulator. I checked my engine, body and frame grounds all good. I thought maybe I gotten a bad regulator so I even purchased another one same result. I had driven my FJ 15,000 miles with no issues prior to driving out west so this was not an issue prior. My voltage is between 12-15 volts at 0-50mph once up near 60mph (3,000 rpms) for more than a few minutes and my voltage meter pegs over 16 volts. I have hooked up a voltmeter and it got to 17.5 volts before I turn on my headlight and brought the voltage down. If I turn on my headlights it drops back to 12-14.5 at high speed and between 10.5 to 12 at low speed 0-40mph. Right now if I have to drive on the hwy I keep my headlights on. I though maybe the pulley on the new alternator was a bit smaller so I swapped it with the pulley from the old alternator same result. My logic was first to change the regulator check the ground on the regulator still pegged the voltage, thought maybe the alternator was going bad replaced it still pegged the voltage, checked all grounds no issues. I do have electronic ignition and a high output coil but I do not think that would have anything to do with it. I would really like to get this issue fixed so any suggestions on where to look next would be appreciated.
 
Verify wiring from alt to voltage regulator and get a new regulator.

That is it for things in the charging system, unless you have something else you are not sharing.

:beer:
 
I checked the wiring the plug on my alt 3 pronged only 2 wires was pretty bad so I changed that out rechecked my grounds. Ran the engine at 2700 RPM voltage spikes to over 16 volts verified at the battery. Rechecked my wiring from Alt to battery based on the painless guide everything looks good. This problem seems to be getting worse I did not notice it right after I put in the 2nd new voltage regulator but I had to drive 20 miles or so on the HWy last week everything was fine on the way but then on the way back it spiked as soon as I reached hwy speed 60mph. Could it be the alternator it is remanufactured I got it online from autozone, how would you test that? I assume the faster it turns the more volts it generates could it be putting out too much that the regulator cannot handle?

I checked the voltage right after I installed this new regulator and it was fine but just like the last one. I drive for awhile the voltage spikes at high RPMs. When I say drive awhile I mean maybe 200 miles max before this starts again. I got this regulator from a well known landcruiser parts place so it should be of good quality. I do not want to just keep buying new regulators just to have them die after a few hundred miles. What really makes me scratch my head is the FJ was fine for 15,000 miles then this started. Maybe I got a bad alternator. I thought that was the original problem with the old alternator putting out too much voltage frying the regulator so that is why I purchased a new one but that did not correct the problem for long.
 
The VR is "watching" the voltage on its IGN terminal. If the voltage ( from the battery, to the fuse block, to the ignition key, to the IGN terminal) on the VR is too low, the VR is still sending out the FULL CHARGE command to the alternator.
In plain language; if there is voltage loss between the battery and the IGN terminal on the VR...... you're in trouble.
Clear as MUD ?!?!?!
Check the wiring from battery + to IGN terminal on the VR. Should be less than 1 Ω (ohm).
Look for bad (corrosion) contacts, connector(s), frayed wires, etc. etc.

My guess..... bad ignition key or broken wire from Ign key to IGN terminal on the VR.
On second thoughts..... your ign coil burns up do to high voltage but that also comes from the IGN key so..... that leaves a broken or bad wire between ign key and VR.

Rudi
 
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Thanks. I will check the wiring from the battery back to the IGN terminal on the VR. I also purchased another VR tonight did not know they could be adjusted as the one cover screw has the sealant so they can tell if you opened it if you send it back. This VR was fine 200 miles ago when I first installed it then voltage went over 16 the exact same thing happened to the previous VR so I hope I fine something wrong with the IGN wire. Thanks again
 
I would also check that the E terminal on the regulator is making a good ground. A poor or no ground would produce the same scenario as Rudi explained. This diagram might help ya.

altreg03w.webp
 
I tested IG wire and it has lots of resistance. I followed the wire and actually had to unbolt the fuse box and flipped it over which exposed a big issue. My IG wire had fried all the insulation off of it a good 3-4 inches. I called painless to see if there was a way to extract the wire and install a new one. The painless guy said they are put together at their plant and even with special tools chances were not good. He said my option was to buy a whole new harness. I guess bouncing around on all the trails in Utah allowed the voltage regulator to loose ground just long enough to fry the IG wire where it enters the fuse box. I ran a new IG wire and installed in the fuse box as best as I could drove my car 8 miles to he store and the voltage pegged once so I had to turn on my lights. On the way back my voltage held between 12-13 volts without the lights on and never spiked so I do not know if my patch job is working or not. I guess it depends on what direction I am headed. I think I need to rewire and get a new Harness but I hate spending the money on a painless harness again. Has anyone used an EZ harness they look about the same but way less money. I also looked at the one the JT has for $299 cheaper than painless but still hurts. I am not very skilled at wiring I did put the painless in my FJ and I know I could do a much better job the second time around. It is this type of system where if you loose ground wire fry pretty much standard in older cars or unique to toyota and is there anything I can do to prevent this from happing when I re-wire?
 
The FJ40 is no more susceptible to damage from losing a ground, than any modern vehicle. Also, I don't see how losing the regulator ground would have caused the ignition wire to fry without blowing the ignition fuse. You have something else going on here. One thought: Since it seems to be RPM related, have the alternator tested at HIGH RPM. This may reveal the culprit.

Your best bet? Rip the Painless harness out, and replace it with an OEM harness that you can easily troubleshoot and fix with the knowledge base we have here.
 
Coolerman, the painless system the IG wire goes directly from the voltage regulator into the fuse box . So from the Alt to the voltage regulator to the fuse box then back to the ignition switch. I have not decided what to do yet. I am far far below your level of expertise .
 
fjc-man said:
Definitely don't continue to drive it like that. Could start spewing electrolyte or worse yet the battery could explode.
Click to expand...

Ah, my FJ40 battery exploded when I second guessed the previous owners' gauge alterations. The explosion sounds like a shotgun blast hitting the rig - luckily the damage isolated to a new battery and voltage regulator.
 
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