Noise for the first minute of start up when cold.

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89325iturbo

Joined
Sep 8, 2019
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Location
Northeast Ct
97 80. Upon start up when cold, it makes a noise I took a video. But I believe it's electrical based like battery or alternator. The dash lights will dim, and worse if I turn the lights on right away they will really dim and even more noise.
I tested the battery it's low at 12.1 when I tested it cold. 14.7 when running so the alternator seems fine.
Could it just the low electrical charge at start up? But what's causing the noise?
 
Can you take a long thin rod or a section of heater hose (both to your ear) and while the engine is running carefully touch (or get close to with the hose) the alternator (approach the rear of the alternator from the left fender side),
then the starter (from the left front wheel well). Try to isolate where the noise
is coming from.

One guess: starter engaging, pinion gear hitting flex plate/flywheel teeth, bouncing back??

Have you been having trouble with the starter, clicking and no cranking at times??
 
I can give it a try, but since it's probably still warm from driving a couple hours ago. I doubt it'll make the noise.
No issues with starting, or starter clicking or not working.
 
I don't really hear a whine, it's buzzing a little louder but in conjunction with the clunk.
Plus this is a cold start so the idle is higher.
The clunk has something to do with the starting/charging system.
Since dash lights will dim with the clunk, and if lights are on the clunk with last longer. Plus they will also dim quite a bit.
It'll last for like a minute or so, and go away as the engine idle back down.
 
This may be a stupid question but is your alternator loose? Not the belt but the bolt in the mounting bracket. Just a wag.
 
Each time it clunks, I hear a change in RPM. Sound to me like an intermittent short when wires are cold. When warmed up they make better connection.

Start with ignition such as loose coil wires, loose battery connection and or loose connection on the alternator wires.

What's you tach doing during this noise? It it slamming to zero and back up?
 
Initially checked to see if the alternator felt loose, it doesn't.
Went to start it to try to listen for a source of the noise with a rod. Since it's still a little warm. (Drove it a few hours ago.) There wasn't a noise to hear.
The tach moves some, but nothing drastic.
an intermittent short does sound like something it could be.
 
89325iturbo said:
97 80. Upon start up when cold, it makes a noise I took a video. But I believe it's electrical based like battery or alternator. The dash lights will dim, and worse if I turn the lights on right away they will really dim and even more noise.
I tested the battery it's low at 12.1 when I tested it cold. 14.7 when running so the alternator seems fine.
Could it just the low electrical charge at start up? But what's causing the noise?
Click to expand...
If your battery is reading 12.1 then it's not holding a charge. 12.1vdc across the battery terminals is a dead battery. A properly charged battery will read 12.6 to 12.7 at rest across the terminals.
 
Maybe pull your battery and have it tested (or drive the truck to O'Reilly or equal) and have them load test it. At 12.1V, maybe it has a bad plate in it and is doing a direct short, killing your electrical system. It will at least eliminate that from the equation.
 
jonheld said:
If your battery is reading 12.1 then it's not holding a charge. 12.1vdc across the battery terminals is a dead battery. A properly charged battery will read 12.6 to 12.7 at rest across the terminals.
Click to expand...
Let me rephrase that. 12.1VDC is a 50% discharged battery, depending on what type of battery you have.
In either case, your alternator is working hard to charge that battery.
 
Agreed the battery definitely does have an adequate charge and is essentially dead.
(Although it can sit for a week and still fire right up)
But yeah maybe it causing a short across like bilt4me said.
I'm gonna get it checked. But before work I put it on the trickle charger.
If the rotor was wobbling would it only do it for the first minute or so?
 
Does the sound go away after about one minute when the engine starts to idle down?
Does it sound like this from inside the cab?
 
89325iturbo said:
^^ what was the cause on yours?
Click to expand...

It still happens periodically. I had a little success with messing around with the TPS, but the noise came back. I've been working from home the last 4 weeks so I really have not driven anywhere in the 80. I resolved myself to going through the whole intake from air filter to the block, replacing every vac hose along the way, cleaning out the passages etc as I'm also fighting a P0401. Reading some of the suggestions on this thread has given me some things to look at once this rain lets up.
I'm sorry that you are experiencing this odd issue that does not allow for much of a troubleshooting window, but I'm also glad that I'm not alone with this. I was feeling a little crazy.
 
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