1989 gmc blue bird

[Veloc]

15v? Odd, should be seeing 13.2V on a good 12V battery. Are these actually 16V batteries? Also, when the parts store tested did they load test or put a multimeter across? A bad cell will show good voltage on a low load test like a multimeter but won't allow the amps a starter pulls to pass through. Another possibility, check all your grounds. Bad grounds will prevent amperage flow.

[cadillackid]

when you say "batteries at 60%" what does that mean? are you using a meter that has %? or is that what the parts stores are saying?


15 volts is high unless there is a charger connected at the time you are trying to crank it.. and a charger should nt be slamming 15 volts into a set of lead acid batteries.. 14 volts or right around that is generally what they get hit with.. over charging all night at 15 volts will easily destroy a set of batteries..



a little more than 16 volts and you can easily damage the TBI ECM.. (89 was a pivotal year for those so im guessing it has a TBI (Throttle body fuel injection).. or is it still carbed?



and when you say "one crank" how long are you leaving the starter engaged? I have a Single group 31 battery in my Superior with a 392 in it.. I can crank for 20 seconds and still have PLENTY left and here strong crankling.. off that single battery..



so if you have 2 batteries and are cranking just a few seconds and then down to 'Click click click" then id suspect the batteries have a load issue..

..


batteries can test with great CCA at a parts store which tests them for a couple seconds but that doesnt test their reserve capacity.. ie what happens when you pull heavy amps for more than a couple seconds..

[mainframe]

Load tested, my buddie is saying the bus because it was an ems vehicle it should be 24v so it’s wired wrong if it’s supposed to be 24v. I want to swap but before I do if anyone else has info cause I’d hate to burn anything up it’s not 24v. Here is the electrical diagram and it shows them wired in series which would be 24v. But it’s wired 12 v currently if I am to be correct.

[mainframe]

So it that may be the issue I’m going to look for info on the starter or alternator for voltage. Good news is it reads same at batteries and starter so probably not the regulator or bad grounds. This has been stored inside it’s entire life zero rust or corrosion

[cadillackid]

ive yet to see a GMC bluebird school bus run on a 24 volt system,.. an easy way to tell is to start looking at the voltage rating on components.. that diagram you sent with 2 battery system shows 2 batteries hooked in parallel.. not series...



you could always get the body number off of it and see if blue bird has any info on it.. I doubt its on Vantage but may be able to call bluebird and see but my guess is thats a standard school bus body on a B(C) 40/50 Frame..

[cadillackid]

Sometimes the ;arger school busses will have a separate alternator that runs 24 volts for the A/C.. but it doesnt look to me like that bus has A/C.. if it was truly built as an ambulance I might expect to see similar.. a separate alternator that output 24 volts for the ambulance body equipment.. but again to me it looks like a regular blue bird school bus body

[Veloc]

Originally Posted by mainframe

Load tested, my buddie is saying the bus because it was an ems vehicle it should be 24v so it’s wired wrong if it’s supposed to be 24v. I want to swap but before I do if anyone else has info cause I’d hate to burn anything up it’s not 24v. Here is the electrical diagram and it shows them wired in series which would be 24v. But it’s wired 12 v currently if I am to be correct.

If that diagram is on your bus, it's a 12V system. It shows the two (+) and the two (-) connected to each other, which means the batteries are wired in parallel. It also shows an optional single 12V battery connection. Connect it as a 24V system and you're going to get high off all the magic smoke your bus is liable to start puffing out.

Disconnect the batteries and check the voltage. You want to see 12.6 at a minimum, 13.2 is ideal, and 13.4 max. More than that and your batteries are overcharged. Should be enough to start though. You also want to check those ground points to make sure there's no corrosion preventing a good ground. The power has to travel to the battery and BACK, so a bad ground will stop you starting just as much as a bad positive will.

Can you describe your starting symptoms? You turn the key for X number of seconds and you get a...

[mainframe]

Jumped it from my truck and started right up so batteries are friend from over charging…. Now I gotta figure out why that happened… and buy batteries ��

[cadillackid]

Originally Posted by mainframe

Jumped it from my truck and started right up so batteries are friend from over charging…. Now I gotta figure out why that happened… and buy batteries ��

while it was idling after you disconnected the truck did you check the voltage? thats the first place to start.. in fact id probably set high idle or have someone run the engine speed up to say 1500 RPM and measure voltage at the batteries and see what you have.. if its in the 13 to say 14.2 range (cold) then you are OK.. but if its going up towards 15 or above then its over charging..



it could also be under-charging and you ran home on the batteries alone... so if you measure 12.7 or so and below then likely you are not charging at all or very little..



these are easy first checks you can do to get an idea of what is going on.

[mainframe]

Honestly I was so relieved to get it parked up at the top of my driveway I just bearded it up and turned it off. I had a long ass day. But thank you I will start there. You have a Venmo? Feel like I owe you a tip already lol

[mainframe]

Ok so I am getting 950 cranking amps 12.5 v and almost zero ohms resistance. So both batteries are good. On to figuring out if it’s starter, regulator or ground.

[mainframe]

For anyone still following I got a battery analyzer. They have full charge and full coke cranking amps. I discovered it’s a ground issue. If I jump it off my pick up it starts right up so it’s not batteries or starter. Battery to body ground is good. Motor to frame ground looks good. Starter terminals are corrosion free. Any clue where else I should look for a ground issue

[PhilipE]

Never go by looks when you are dealing with electrical connections.

Find your battery to engine ground lead. Remove from the block. Clean cable end and block connection. Reinstall.

If you can find a 12 volt clamp amp gage. Do a amp test on the starter while cranking. That starter should be a MT28 Delco brand. It should pull around 450 amps when cranking if its in good condition.

[LargeMargeInBaja]

Originally Posted by mainframe

...I got a battery analyzer. They have full charge and full coke cranking amps. I discovered it’s a ground issue. If I jump it off my pick up it starts right up so it’s not batteries or starter. Battery to body ground is good. Motor to frame ground looks good. Starter terminals are corrosion free. Any clue where else I should look for a ground issue

.
Two stories:
.
1)
1987 Jaguar XJS...
I removed the clunky V-12 and 3-speed automatic, I installed a Chevrolet 350 V-8 and a 4-speed automatic with over-drive.
Advantages -- weigh 300# less, gain mpg and off-the-line acceleration, simple repairs..
Good idea, right?
.
With the power-train installed:
* I installed ground-straps from each head to the fire-wall.
* I installed ground-straps from the lower engine block to the frame.
* I installed ground-straps from the trans tail-house to the frame.
* I installed grounding cables from the negative terminal to the intake manifold and to the starter.
.
Each time I walked toward my Jag, I admired a deeply-grounded vehicle.
.
As a fine-tune to complete the conversion, I took it to a muffler shop for a slight exhaust re-route to eliminate a squeak between one muffler and the frame.
After the work, I had a no-start.
.
You see where this is going, right?
.
My diagnosis initiated by examining recent changes -- always a good place to verify.
I noticed the muffler wore a clean spot on the frame, penetrating the paint and under-coat.
Oh!
Turned out, all my attempts at grounding were for naught.
The only completion of the circuit was the muffler -- temporarily -- rubbing the frame.
Cripes.
.
2)
1991.5 Dodge 2500 Cummins 4x4.
As we traveled through Nicaragua, we had erratic gauges on the dash.
.
In a tiny village on the coast, we pulled over to camp and fuss with the fiddlins.
I cleaned and re-set every wire and cable, I chased every potential with a multi-meter, I re-cleaned all my connections, and yet, the issue persisted.
.
Around suppertime on our second day at camp, the hood still raised, an antique flat-bed farm-truck stopped to inquire about our situation.
Three little 'Mosquito' Indians climbed out, yabbering and gesticulating in some unknown local dialect.
.
Using the international Redneck language of pointing and making 'explosive' noises, I shared my thoughts on the dilemma.
They offered sympathetic murmurings, grabbed a few obvious cables and wires to verify my side of the story...
... and sign-languaged 'try the ignition'.
So, I did...
... and all the dash guages returned to normal factory-new.
.
Giving the fellows a look of utter incomprehension, I signed 'show me!'.
The driver of the old farm-truck pointed to a tiny wire from the negative post to the radiator support.
That tiny wire -- probably a 12-guage -- carried the entire full-time responsibility of grounding the system.
Criminy.
.
.
From then on, I honestly truly believe in magic and pixie dust.
Nothing else explains it.

[mainframe]

Starter is a 2012 replacement…here is battery to body mount. I sanded the underscore off of this… maybe I need a way bigger gauge going right to the frame? The other pics are of motor to frame. I can’t find any other grounds.

[Veloc]

There is a battery to body, which is typically a small gauge wire like 12-14ga. The main battery ground cable goes to the engine block. Need to check it, and by check it I mean remove it, sand it, sand the block, bolt it back together. Use no sealers or anything. There is also engine to frame, and engine to body, and body to frame. Ground it all, with bare metal to bare metal. Paint anymore is basically spray-on plastic, and plastic is an amazingly good electrical insulator.

[mainframe]

Thanks, I’ll get under there and start looking for mor grounds.