Voltage Drop

I have been having a cutting out problem for the last four months. I have replaced many, many parts including alternator. Today it was doing it again so I checked voltage at the alt to see it was at 14-15 then dropping down to 12 while it was cutting out. I'm lost! Most grounds look good. It's a new alt. Could it be bad?

The voltage could be dropping as a result of the engine slowly cutting out.(the alternator slows down) What is your fuel pressure doing when it cuts out?

GM Dealer just had it for a few days for diagnostic and they said no drop in fuel pressure when it happens. They said it was a Crank Sensor that needed to be done so it got done last Sat and still cutting out.

You could have a bad wire feeding voltage to the alternator, or a bad thermistor. The thermistor will restrict charging voltage based on battery temp if I understand it correctly. It's a small wire that runs back to the battery. The new alternator could also have a bad voltage regulator.

Is voltage dropping to 12 when the engine shuts down? When the engine 'cuts out' does the engine shut off or does it begin sputtering? If it shuts off like you turned the key off, 12 would be because it stopped spinning/charging.

rivparadise wrote:

I have been having a cutting out problem for the last four months. I have replaced many, many parts including alternator. Today it was doing it again so I checked voltage at the alt to see it was at 14-15 then dropping down to 12 while it was cutting out. I'm lost! Most grounds look good. It's a new alt. Could it be bad?

Did you ever check the wiring at the big connector at the firewall (and if not, when are you gonna)?

It sputters but doesn't shut off.I have checked the harness at the firewall a few times and voltage as well.

rivparadise wrote:

It sputters but doesn't shut off.I have checked the harness at the firewall a few times and voltage as well.

I understand. I still think you have a break in the wire that is hidden by the insulation, but you've checked. Crank sensors usually quit bad warm.

Did the dealer (ever) reflash the PCM to the latest calibration (that you know of)?

Funny thing, when the techs at my local GM dealer connect my car to the Tech II they tell it that the car is a Bonneville. I quit asking why.

They tell it its a Bonneville? thats interesting.I'll try that with my useless Actron.maybe it'll work?

Got to go and get the re-learn done next week.

rivparadise wrote:

Got to go and get the re-learn done next week.

I think Deekster may be onto something concerning the thermistor. You ever check yours?

Hint - if you don't have an original battery cable, that could be the source of *all* the problems.

I shoulda asked that sooner.

Albertj

Where exactly is it?

rivparadise wrote:

Where exactly is it?

FLip up the back seat, it's a little gadget on the positive battery cable. If your cable was replaced or resectioned (for instance to add a power take off for a big stereo) and it was not properly re-connected in teh charging circuit, that could be it.

Also you mention having replaced a number of parts, I kinda wonder if you replaced plug wires and if so what brand you used. Standard-spec wires will often cause a miss.

I changed the battery myself and don't remember anything not being hooked up. I used Belden Wires. Not sure if those are good. I replaced the MAF Sensor yesterday because it was never done, only cleaned.
The car ran good for 2 minutes then the idle shot up to 2k and would rise and fall two or three times then stall. Drove it down the road and ALL hell broke loose with lights flashing, ABS, Airbag, Traction Control lights coming on then off, bucking, cutting out, and heater displaying chinese symbols. There was for sure a relay clicking in the back seat while this madness was going on but I couldn't say which one exactly. The back seat was out so I could hear it clearly. My mechanic was in the car while it was doing this and thought at first it was a fuel issue but then after pressure test no problems with fuel. For sure an electrical issue. Going to drop off at another mechanics shop. I'M DONE! If this can't fix this, there will be a parts car for sale with LOTS OF NEW PARTS. I have spent over 2K on this with no success.

rivparadise wrote:

Drove it down the road and ALL hell broke loose with lights flashing, ABS, Airbag, Traction Control lights coming on then off, bucking, cutting out, and heater displaying chinese symbols. There was for sure a relay clicking in the back seat while this madness was going on but I couldn't say which one exactly. The back seat was out so I could hear it clearly.

Sounds like you have bad grounds or a loose connection to the battery. There are a few major connection points to inspect.

Check the voltage again - while running. Is it higher than 15v? A failing regulator (in alternator) will cause your symptoms. PCM should also throw a code when voltage is too high.

Why did you replace the MAF sensor? That's a pretty expensive part to just replace on a whim. Do you know the old one was bad?

Electric Connections, Ground and Lead wires are first on the list for the guys at this place to check. I replaced the MAF Sensor because it was cleaned twice and filaments looked hammered. All others in throttle are replaced. This will be the fourth time it has been at a shop!

rivparadise wrote:

I changed the battery myself and don't remember anything not being hooked up. I used Belden Wires. Not sure if those are good. I replaced the MAF Sensor yesterday because it was never done, only cleaned.
The car ran good for 2 minutes then the idle shot up to 2k and would rise and fall two or three times then stall. Drove it down the road and ALL hell broke loose with lights flashing, ABS, Airbag, Traction Control lights coming on then off, bucking, cutting out, and heater displaying chinese symbols. There was for sure a relay clicking in the back seat while this madness was going on but I couldn't say which one exactly. The back seat was out so I could hear it clearly. My mechanic was in the car while it was doing this and thought at first it was a fuel issue but then after pressure test no problems with fuel. For sure an electrical issue. Going to drop off at another mechanics shop. I'M DONE! If this can't fix this, there will be a parts car for sale with LOTS OF NEW PARTS. I have spent over 2K on this with no success.

Belden wires are good standard-spec wires but others have found that they are not good enough for the high-energy ignition on the Riv. I have used them in the past on other cars with no problems, and I would not use them on a Riv. I would use OE Delco wires, Magnecors, maybe Taylors on a Riv. End of my list...

Unless your mechanic is familiar with the Riv charging system (and has a Tech II equivalent, not just a scanner), his work is likely to run difficult. The Riv system is not difficult but is unusual because of the thermistor setup that lets the alternator put out a lot of juice under certain conditions, and he/she needs to check it. I suspect he/she will find the thermistor bad, along with a number of other components that the overvoltage took out. The thermistors don't go often but when they do the over-voltage situation kills off many of the car's electronics. The relay clicking in back is probably the one triggered by the thermistor as part of that quick-charge circuitry - is my guess, I am not the mechanic. My experience is most mechanics hate electronics.

If this is the case my guess is you will either need a replacement battery cable (pricey) or a mechanic that likes electronics and will do "surgery" on the old cable to fix it, basically check it all out and replace the thermistor. If you could do that "surgery" yourself it's like a $5.00 fix, because you can get the replacement thermistor from Radioshack, it's not exotic really. There is another post on this site that says more about that thermistor IIRC.

Good luck and sorry about your troubles.

Exactly where is this thermistor? Looked yesterday, dont know what im lookin for!

Check your system voltage. That's how you know if the thermistor might be bad.

Doing that today. Also, I now hear a ticking at the bottom of the motor and hope this is not a rod or bearing going bad.

rivparadise wrote:

Doing that today. Also, I now hear a ticking at the bottom of the motor and hope this is not a rod or bearing going bad. Started after my friend drove my car to the shop and beat on it all the way there.

Nice friend you have. Was it low on oil?

Not sure. Still at the shop and will have them check it tomorrow. Very rare that I'm low on oil. I check it every week and maybe lose a half a quart between changes.

Someone mentioned that you can adjust a crank sensor and that may be causing the ticking?

rivparadise wrote:

Someone mentioned that you can adjust a crank sensor and that may be causing the ticking?

I doubt that. Ticking from under the valve cover(s) might not be serious, but from the bottom end, not so. These engines are very sturdy. About the only way to hurt them is to over rev them, or run them low on oil, or to run more boost without supporting mods.

I couldn't make this up if I wanted too!
Mechanic called today and found a screw rolling around INSIDE the PCM! WTF! Called where I got it and they are going to get me a new one.
They have the problem isolated to the fuel pump circuit cutting out for a moment. The pump has been changed as well as two new relays. The relay clicks about 80% of the time.
Going to swap PCM, check fuel pump circuit and whatever else may arise.