Well, here's a head scratcher...
1998 GMC Jimmy with a buzzing / whistling noise coming out of the dash. Changes with RPM and causes the dash display to pulse. (odo and PRNDL) It's intermittent of course but goes away if you unplug the alternator. Failing alternator right? New alternator did not fix it. Noise goes away if both radio fuses are pulled which also kills the cluster. Pulling the gauges fuse alone does not stop the noise. Removing the radio and leaving the fuses in does not stop the noise.
I always get the weird issues.....
Does this thing have an instrument panel voltage regulator?
Is the speedo cable driven or??
I had a diode trio go bad in the alternator of my '81 X-11, which caused a relay under the dash (on the same circuit) to buzz at 3000 to 3200rpm. That was back when you could rebuild your own alternator. Any chance the diode trio would be separate from the alternator? I know some people who have gotten a bad 'new' alternator too.
L5wolvesf said:
Is the speedo cable driven or??
Its electric. Noise is rpm dependent and will do it when not moving.
racerfink said:
I had a diode trio go bad in the alternator of my '81 X-11, which caused a relay under the dash (on the same circuit) to buzz at 3000 to 3200rpm. That was back when you could rebuild your own alternator. Any chance the diode trio would be separate from the alternator? I know some people who have gotten a bad 'new' alternator too.
The trio is in the alternator. Yes there is a chance of getting a bad new unit, but one with the very same issue?
Also, good choice on the X-11. Such an under rated car.
I have replaced an alternator for noise issues and the new one had 600mv of ripple. The old had 400.
How old is your battery? How clean and tight are the battery connections? The battery works as a voltage stabilizer in the system and many noise issues can be traced to a battery with high internal resistance.
Also, and this may sound crazy, but if your truck is missing the ground strap to the hood, reinstall it. That is there specifically to combat RF noise. The hood is a big antenna on top of a whirlwind of RF mumbo jumbo.
Is the door chime/buzzer played through the radio on those, or was that later GM? If it's a separate buzzer, try unplugging that?
The door chime does not play through the radio. I'll look into those grounds some more.
I really would like to find a good wiring diagram.
Ok, updates.
Was making the noise good and loud this morning, pulled the radio out of the dash, but left it plugged in. Could hear the noise coming from the radio unit itself, not the speakers. Unplugged radio, no more noise. Plugged in different radio, it made the noise too!
Previously I posted that the noise continued with the radio out, maybe I was mistaken about that?
Sounds like old school antenna not grounding issue.
Steve_Jones said:
Sounds like old school antenna not grounding issue.
Radio stations come in fine, noise does not change with speaker volume, just engine RPM.
Gearheadotaku (Forum Supporter) said:
Steve_Jones said:
Sounds like old school antenna not grounding issue.
Radio stations come in fine, noise does not change with speaker volume, just engine RPM.
I'm going from late 80s memory, but I remember there used to be an issue on radios which caused a faint "whine" for lack of better terms, that changed with rpm. The cure was a suppressor on the antenna wire where it hooked into the radio. Does this one have a separate antenna wire into the back of the radio? If so, unplug it and see if it goes away.
if you can, post a video that has the noise in it
In reply to Steve_Jones :
....and this is why they ground the hood, I now think. Keeps the hood from transmitting the RFI to the antenna.
Automobiles are amazingly noisy electrically, with all the voltage surges from the ignition system and relays and injectors powering on and off, collapsing their magnetic fields and creating voltage spikes in the process.
Unplugging the antenna didn't make the noise stop for what that's worth. Didn't see any extra wires related to it.
The hood never had a ground strap. Wouldn't the hinges provide a ground path? I have seen other cars with straps there before though.
Finally found a proper wiring diagram, the excite wire for the alternator goes through the PCM. Any thoughts there?
Radio and gauge cluster share a power source, Radio-Bat fuse #19 hot at all times.
Shortly before this all started, I replaced the blower motor which involves moving the PCM out of the way. I did not unplug it, but maybe a wire is now compromised and causing the issue?
Ok, so antenna is out. Can you get to that regulator, and does it unplug?
Regulator? The voltage regulator is inside the alternator in this application.
I remember a similar issue on a 98 Isuzu hombre. Ground strap from rear of engine was corroded, and once fixed noise was gone. (Or maybe the bad seals and leaky heater core distracted me)
I did finally find the ground cable for the hood, it seems fine.
Learned how to test the diode in the alternator, its working as it should.
Is there some kind of ignition noise suppression device in the harness somewhere? I'm guessing, seriously just guessing, that there is and it's not doing its job anymore.
Pulled out the battery and followed the cables to various connections. Thoroughly cleaned and tightened everything I could find and the noise has been gone for a week. Lets hope it stays that way!
