1992 Silverado p/u very strange problem

[pfindlay]

I have a 92 Silverado 2500 pickup (350 fuel injected, 4L80E trans) which has developed the strangest problem.

I pull a trailer with an antique car on it. When pulling up a hill, sometimes the alternator light will flash a few times and then the gauges and speedo will all flick and the transmission go into a neutral. As soon as I back off on the throttle it goes back into gear and all is normal again. If I back off as soon as I see the alt light flash I can usually avoid the subsequent symptons. It seems to happen at higher revs, such as if I have pulled it into second to pull up the hill. No memory codes are stored during this event.

I've never had this happen without a load on the back. I've disconnected all trailer wiring and it still happens, so it is not related to the trailer itself.

I'd be interested in hearing any thoughts on what could be causing this problem. Electrical? ECM? Transmission? Why does it always begin with the alternator light?

Just yesterday the SES light came on and a code 32 was read, but I don't believe this is related to the problem.

Peter

[SiCk_DiAbLo]

Probably telling you your alternator is going...I had a problem with my speedo, and radio had to be reset every other time I started the truck, it was the alternator...

[speedygonzales]

Could be the alternator. But then it could be the belt also. The tensioner, the battery or even a poor connection.

The first thing to do is a little investigation. See what the voltage across the battery is before starting, during cranking and after the engine is running.

Battery at rest with nothing connected to it will read 12.6V.
While cranking it's best not to go below 11 volts.
After running, the voltage at the battery should be at least 14V.

Most auto parts stores can confirm your charging system components.

FYI, I had a problem since the summer that the battery would go dead after sitting for while. I checked the above readings and they were fine. And I checked for a load on the battery when everything was turned off completely. No drain. It turned out to be a bad battery. But then it was 50 months old.

[ChevyTech]

Have someone sit in the truck, with the engine running ,and watch the alternator light, while you wiggle the battery cables and wire harness from the back of the engine to the firewall. Use care to keep your hands away from moving parts.

Also check for loose nuts at the junction block under the hood, on the passenger side of the firewall.

Another thing to look at is the ignition switches can fail so power only goes through some circuits at times. When this happens it causes transmission control issues.

My first guess would be battery cables that are breaking connection.

There should be a ground cable between the back of the passenger side cylinder head and the firewall. Make sure it is still connected.

I see it's your first post. Welcome to the board!!!

[pfindlay]

Thanks for all of these tips. I will start looking into the alternator and connections. I replaced the ignition switch about 18 months ago.

Does anyone have any thoughts on why it happens consistently when I am pulling a load up a hill, but I have never been able to make it happen without the load?

Peter