Low Vaccum Light Trouble

[yugoner]

New Fuso owner. Calgary, Alberta Canada.
2007 FG140. 70,000km on it.
Drove 1000 km after pick up, next morning I go start it and low vaccum light, in combination with battery light flashing on and off after start. Also accompanied by screeching sound coming from front area of engine block.
Proceeded to keep flashing and making hissing noise for a while tilI I shut down truck. 2 hrs later I started it up again and nothing flashing anymore, proceed to drive, same thing 10 minutes into drive, flashing and hissing noise again.
Lasted for 5 minutes or so, pumped brakes very hard and the noise cut right out and dash light went out.
I can't see any visible leaks on the vaccum pump system.
Looking for advice on what the next rational step to making sure this things good before seeing light/ hearing sound again? Thanks!

 

[yugoner]

Realized squealing was coming from alternator.
Tested my battery bank while truck was at 900rpm idle, all lights on, AC on, etc.
Got 12.14 voltage on meter & dropping.
Realizing that the vaccum pump as an electrical component would no way be able to function with voltage in batteries that low.
This has led me to outsourcing a new alternator. Will install it tomorrow, and figure out it that's my only problem.

 

[gait]

the squealing may be as simple as loose belt tension,

but also may be alternator reluctant to turn,

I haven't looked but the vacuum pump on the back of the alternator is mechanical, its just a convenient place to have it,

there may be a problem with either alternator or pump,

I would look at the belt tension first, or if belt can be slipped off the pulley does the alternator turn freely - its usually obvious if its a bearing (the usual failure).

having said that the lack of voltage points to alternator failure, possibly the electronics which are at the back before the vacuum pump.

 

[unkamonkey]

Yep, I was going to mention the belt. I know mine makes strange noises when it gets loose.

 

[SkiFreak]

I haven't looked but the vacuum pump on the back of the alternator is mechanical, its just a convenient place to have it,

On the FG84/FG140 (4M50 engine) the vacuum pump is on the bottom of the engine, on the opposite side to the water pump.

Realizing that the vaccum pump as an electrical component would no way be able to function with voltage in batteries that low.

The vacuum pump is mechanical, not electrical. It's a safety thing.

 

[gait]

thanks Owen,

which either means the vacuum light was on because the alternator wasn't providing enough volts or there's a second problem.

I'd go for the alternator. Loose belt / stuffed bearing / stuffed electronics / stuffed brushes. The belt squeals if loose and alternator trying to output all it can, or squeals because the alternator won't rotate. Voltage suggests latter.

 

[trackadda]

may be completly differant but on my isuzu nps while i was working on it over several months the batteries ran down and every time i started it there was a few lights on on the dash, after i put on battery charger for a few days no more lights when i start it. may be low voltage warning

 

[yugoner]

Thing Is I drove for 700kms over the course of 10 hours the day before this happened. Should have been ample time for batteries to get charged by an adequate functioning alternator.
In the morning for me (8-10hrs) I'll throw a new (rebuilt) alternator I got yesterday in and keep you all posted.
Thanks for tips/ advice

 

[SkiFreak]

I'll throw a new (rebuilt) alternator I got yesterday in and keep you all posted.

It may be a pointless suggestion, given that you have already purchased a replacement alternator, but a simple test to see if any of this is a voltage related issue would be to charge the batteries fully with an external charger. Basically, take the alternator out of the equation.
As I see it (from what you have described) there are two issues here: 1 - the squealing you have heard and 2 - the lights on the dash.

The first, as suggested, could be just a loose belt or at worst a seized/semi-seized alternator.
The second might be a low voltage issue, as mentioned above, but you won't know until you have good battery voltage.

In my experience of fault finding any problem, resolve what it obvious and see if that has any affect on the other issues.
If the lights coming on is in fact a low voltage issue, then fully charging the battery should resolve the problem, at least until the voltage drops again.

The squealing is something that definitely should not be ignored either. Firstly, just do a simple check of the belt tension to see if it is loose. If it is tight, something else may be wrong.
As mentioned by Gait, there could be a problem with the alternator, Remove the belt and test that the alternator spins freely and that you cannot feel any roughness as it turns (indication of worn bearings).
With the engine running you should see about 14.5 volts at the battery using a multimeter, if the batteries are not fully charged. If you are seeing noticeably less than that then there is likely an issue with the charging system.

By the way...
Welcome to the forum.

 

[yugoner]

Replaced Alternator, Refurbished Alternator was used. This solved the problem of both noise, low voltage to batteries, and low vaccum light.
However, now faced with the problem that engine will not shut off once key is turned to off position and pulled out of ignition.
No Fuses in both fuse boxes are out, starter is totally fine. Just will not stop unless I stall the motor out.
Anybody have this happen?
I removed which I thought to be the solenoid, that just gave me a check engine light and did not shut the vehicle down when key was turned to off.
Fuel injection problem? Im lost here.
Im getting my exhaust brakes to work, so I dont think it its a problem with vaccum.
Thoughts?