When i bought my car the voltage reads above 14 but the guage is bobing up and down between 12 and 16. I removed the alternator and had it check twice it checked ok. The battery is good tje alt is good what could cause this. Its causing all my dash lights and head lights to surge. Any thoughts?

 

Failing voltage regulator........which means getting a new alternator.

But might be loose ground wires also......check the bolts on the back of the passengers side head.

Corrosion build up on battery terminals.

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Ya me and my brother thought it might be the regulator and a friend told me it might be a bad ground somewhere. The only wires I've checked so far was the one going to the shock tower from the battery. There both tight and corrosion free. But the guy I bought the car from did port the heads so maybe when he put them back on he forgot a ground. If one of them is uhooked would that cause it or would it even run at all if there's one not connected.

 

If it was left off the engine would only run on one side......or so terribly you would shut it off right after you started it. It cN also fry the PCM if you run the engine too long with a loose ground. Happened to me......

Reach back and feel the two bolts behind that head. I think some years had three bolts.

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No it runs like nobodys business. Ill check them when I get home. If there loose or coroded that would cause it to miss or run a little ruffled wouldn't it?

 

Loose is just bad usually........

I've had what you mentioned in your original post....the lights surging up and down like it was phasing........it just went away and never came back. It did it for about 2 months with no ill effects on engine performance or battery power.

Not saying to ignore it.......but ai think its the voltage regulator freaking out. It may go away, it may burn out at any time too.....

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I just checked the back of the head for the ground and there isn't even anything hooked up to it. But I can feel where there's two holes probably where its supposed to be. If I put another cable on it where does it go from the head? Or where should I bolt it down to?

 

Did you look for a sliping belt?

 

is there a ground wire going to the back of each cylinder head?
are you saying if you had a ground going to the passenger side head but not the driver side head that the driver's side head spark plugs won't fire ?

 

LOL.......no, no, no......

I'm just saying my 427ci one day started running horribly. I was out driving. I got home and pulled into the driveway, left the engine running. Poppe the hood and took a look and everything sounded and seemed normal. But when I revved it a little bit the engine would buck and shake the front end. I turned it off and asked a friend to come scan it. We started diagnosing things. One thing we did was to check to see if some of the cylinders were not firing.

We found that after we started it up only the passengers side 4 cylinders were firing. The drivers side 4 headers were ice cold. Nothing firing on the drivers side.

The guy that came over let the car idle while he moved all the wireing harnesses around to see if it made a difference. Sure enough, when he moved the wiring harness bundle that is immediately coming out of the PCM the engine idled differently.....the drivers side started to fire on all 4 cylinders. He would move it again and that side would stop again.

He narrowed it down to a shorted out PCM-to-head ground wire. Instead of reaching back there and messing with the bolt on the back of the head and tunneling through the harness to dig out the bad wire he simply cut that ground wire right at the short, removed the bad piece of wire were he located it in the wire bundle about 3-4 inches from the PCM. Spliced and soldered a new wire in there and ran that new wire all the way over to one of my valley cover bolts and wrapped it with a black wire covering conduit. Done.

It ran perfect again. So, I'm just telling "LSx bird" that a loose ground wire that attaches normally to the back of the passengers side head can cause cylinders to not fire. In my case, it caused one bank not to fire while the other bank was fine.

And the craziest thing, the car drove pretty good with one side of a V8 engine firing and the other side was dead. I would think that would make the engine torque all over the place....but it was smooth running.

I'm not aware that ground wires even attach to the drivers side head, just the the passengers side.

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That sucks. That means someone repositioned them somewhere else to ground the PCM.

You need to get a wiring guru to come out and trace the ground wires from the PCM wire bundle to see where the ends go and where they are bolted to the engine. They have to be going somewhere, otherwise the engine would not run, because he PCM would not be able to operate.

Learning from my issue a few years ago. That PCM-to-head groun wire starts at about the 16cm spot in that wire bundle coming out of the PCM. It's two wires that splice into one large wire. It's the largest wire in the bundle in that area. That's the wire that is supposed to bolt to the back of the passengers side head.

This is what I recall from watching that guy fix my PCM-to-head ground wire years ago. I watched him do it all in my driveway.

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I shoved my hand Ollie the way back but there's no ground going to the back of the head there's not anything back there just two bolt holes. Not it seems to idle fine and it seems to run fine but I bought the car with the heads and cam already on it so I dnt really know how it should run if the wire was ro be hooked up. So what ur saying is I need to trace the ground from the pcm on the passenger side to see where its going? If its grounded somewhere else I need to relocate it to the back of the passenger side head?

 

There's probably an easier way to go about this. You could hook a single jumper cable from the engine block to the negative battery terminal to confirm if that's really and issue, right?

Did you try the easy stuff like checking the belt, tensioner, and exciter wire? (Although, as LS6427 pointed out above, a high voltage would indicate a regulator problem.)

 

Well, if someone relocated it, that's cool too. As I mentioned, mine is now attached to one of my valley cover bolts....not to the back of my passengers head anymore. So as long as its attached somewhere on the engine, it will work the same.

But maybe wherever it is attached.....it's coming loose.

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The belts not slipping and all the wires are fine. Ill have to check and see if the wire coming from the pcm is even connected to anything. Right now I'm just trying to fix the voltage problem. But more than likely id say its probably a bad regulator.

 

Trust me, it's definitely connected somewhere. If it wasn't the engine will not run at all. I mean...no start and no readings on any scanner either.

But it could be loose.

Bad regulator seems like the most likely cause.

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It wouldn't be unheard of for an alternator "test" to miss a bad unit. For example, if the rig is just confirming the voltage is above 12, it may be saying you are "OK."

 

i would go with LS6427, get a wiring diagram and
check ALL of your grounds just for the hell of it.

look for any black wire out of harness and ECM.

fix what needs fixing and then recheck
to see if you really need the regulator.