Dead battery. Replaced with new. Now won't start

[Clavurion]

Originally Posted by jagarundi

What is the 'BST'? This is really frustrating. How the hell can this be? A battery dies, you replace the battery and then the car won't start when it was running perfectly well before then? This is a RIDICULOUS problem with this vehicle!

BST = Battery Safety Terminal. It's on the positive battery clamp on the thicker wire coming from battery to engine bay. It's part of the restraint system cutting power to engine bay after collision. If you have normal voltage on the engine bay jump start point BST is OK.

[wpoll]

Originally Posted by Clavurion

… If you have normal voltage on the engine bay jump start point BST is OK.

Maybe.... but not always.

BSTs can "soft-fail" where they have enough of a connection for the low current draw (like from a multi-meter) to still allow full voltage to be apparent but when you draw a large current, the voltage loss at the BST become significant and the car won't start. The BST has in effect become a high-resistance joint.

I doubt this is the issue in this case though, as with a high-resistance BST the engine would likely try to turn over but not. Also the electrical load of simply turning on the ignition would pull the apparent terminal voltage down a lot too.

Which reminds me - we've seen a few high-resistance joints at the B+ terminal on the front bulkhead too - I guess this is another possibility? Not sure it matches the symptoms though - sounds more like an EWS issue.

[Clavurion]

Originally Posted by wpoll

Maybe.... but not always.

BSTs can "soft-fail" where they have enough of a connection for the low current draw (like from a multi-meter) to still allow full voltage to be apparent but when you draw a large current, the voltage loss at the BST become significant and the car won't start. The BST has in effect become a high-resistance joint.

I doubt this is the issue in this case though, as with a high-resistance BST the engine would likely try to turn over but not. Also the electrical load of simply turning on the ignition would pull the apparent terminal voltage down a lot too.

That is true. For this purpose you should also check the engine bay voltage while starting. But like you said if BST was on partial contact the starter solenoid would likely click even if there was not enough power to rotate engine.

[andrewwynn]

Originally Posted by wpoll

I doubt this is the issue in this case though, as with a high-resistance BST the engine would likely try to turn over but not. Also the electrical load of simply turning on the ignition would pull the apparent terminal voltage down a lot too.



Which reminds me - we've seen a few high-resistance joints at the B+ terminal on the front bulkhead too - I guess this is another possibility? Not sure it matches the symptoms though - sounds more like an EWS issue.

Only the starter and alternator are fed through the BST.

Either B+ loose or BST open with cause the symptoms. (among other possibilities) but it's an easy test: jumper from battery pos to B+ under hood. If it starts, likely BST open.

Make sure B+ is tight. When I replaced alternator recently I just removed the bolt from B+ to disconnect battery.

[jagarundi]

UPDATE

Got a mechanic to do a house call. He ran power directly to the starter and had me turn the key. The engine cranked right up. This rules out the starter and the battery. This leaves the connection between the key and the starter now. What can it be now?

[bhennrich]

Originally Posted by jagarundi

UPDATE

Got a mechanic to do a house call. He ran power directly to the starter and had me turn the key. The engine cranked right up. This rules out the starter and the battery. This leaves the connection between the key and the starter now. What can it be now?

IT LEAVES THE BST!!! Like you have been being told about since you started this thread!

[jagarundi]

Originally Posted by bhennrich

IT LEAVES THE BST!!! Like you have been being told about since you started this thread!

Can you explain those steps to me as if I were a small child? I really need to get this truck running.

[bhennrich]

Originally Posted by andrewwynn

Only the starter and alternator are fed through the BST.

Either B+ loose or BST open with cause the symptoms. (among other possibilities) but it's an easy test: jumper from battery pos to B+ under hood. If it starts, likely BST open.

Make sure B+ is tight. When I replaced alternator recently I just removed the bolt from B+ to disconnect battery.

Andrew already explained this to you! Why ask for help and disregard the help already given?

[jagarundi]

Originally Posted by bhennrich

Andrew already explained this to you! Why ask for help and disregard the help already given?

DUDE!! I'm NOT A CAR GUY so I don't understand what the below MEANS!!


jumper from battery pos to B+ under hood.


If you're not going to help WHY THE HELL RESPOND???

[bhennrich]

Originally Posted by jagarundi

DUDE!! I'm NOT A CAR GUY so I don't understand what the below MEANS!!


jumper from battery pos to B+ under hood.


If you're not going to help WHY THE HELL RESPOND???

Do you know what a "hood" is? Do you know where the battery is located? It has already been pointed out but under the hood on the firewall (that is the metal that separates you in the car from touching the motor) there is a metal post that has a red + on it, that is the B+ Under hood. You run a jumper from the battery positive terminal in the rear of the car to the B+ under the hood. If that lets everything start as normal you BST is bad. The BST is there to help reduce the risk of the battery grounding out causing a fire in the event there is a crash.