Car not starting

[bcredliner]

When the BST connection blows it forces the cable back. If you push the cable toward the battery and pay close attention you can feel it move a bit. However, even if the cable has be fired back the engine should still start but not have enough voltage to support systems such as airbag. Make sure the new ignition switch is the correct part number for your vehicle and their isn't a problem stemming from the install. I have seen exactly your problem and it was caused by the ignition switch. And, recall that everything was fine for 3 weeks after you installed the new switch and symptoms are now the same as the old switch.

[upallnight]

Originally Posted by bcredliner

When the BST connection blows it forces the cable back. If you push the cable toward the battery and pay close attention you can feel it move a bit. However, even if the cable has be fired back the engine should still start but not have enough voltage to support systems such as airbag. Make sure the new ignition switch is the correct part number for your vehicle and their isn't a problem stemming from the install. I have seen exactly your problem and it was caused by the ignition switch. And, recall that everything was fine for 3 weeks after you installed the new switch and symptoms are now the same as the old switch.

Once the BST has blown, you will not be able to start the engine. The biggest draw on the electrical system is a starter. The starter circuit is feed from the BST cable. The airbag would have received the energize signal from the DME at the same time the BST cable would have received it signal. Some circuits such as the door lock and unlock circuit are not on the BST circuit so that they can still operate once the BST cable is blown. The fact that you can only start the engine thru a jump from the engine compartment jump terminal lead me to believe that you are back feeding the circuit from the battery jump cable.

[upallnight]

Originally Posted by bcredliner

When the BST connection blows it forces the cable back. If you push the cable toward the battery and pay close attention you can feel it move a bit. However, even if the cable has be fired back the engine should still start but not have enough voltage to support systems such as airbag. Make sure the new ignition switch is the correct part number for your vehicle and their isn't a problem stemming from the install. I have seen exactly your problem and it was caused by the ignition switch. And, recall that everything was fine for 3 weeks after you installed the new switch and symptoms are now the same as the old switch.

How do you explain that if he jumps the X from the battery jump terminal in the engine compartment, he can start the engine? Now I'm assuming he is using the same key and the same ignition switch to start the engine, and not a remote starter.

[80stech]

Yes, and IF the problem is the BST connector, It's not because it's blown, it's that it has developed some resistance from corrosion/oxidation. Once the OP figures out the relationship between current and voltage he'll have the problem pin pointed probably quicker than most of the mechanics at the dealership.

[StephenVA]

Others have experienced cables, connectors and etc not being locked down or corroded causing multiple issues. Like the one where the issue was the wiring at the starter itself due to oil saturation and icky crap deteriorating the wire and poor connections.

At this point on my life I would recommend a walk through each connection, clean, and reconnect process. Battery (physically pull it out), cables, wiring at the jump points under the hood (loose) etc, etc. A jump start allows a engine start means the cables from the back to the front (assuming he is jumping at the engine, NOT the battery) are NOT allowing current flow. Poor grounds? bad cable, short due to positive cable explosion? Who knows as only a resistance/volt drop test will tell.

Ten years of salt, wear & tear and vibration takes it's toll. Plus who knows who touched what it the poor X's life?

[bcredliner]

Originally Posted by upallnight

How do you explain that if he jumps the X from the battery jump terminal in the engine compartment, he can start the engine? Now I'm assuming he is using the same key and the same ignition switch to start the engine, and not a remote starter.

The only thing I could think of when it happened to me was that the jump voltage was enough more that spark arched across the ignition contact points remaining gap, that that particular ramp on the ignition switch had worn to leave a very small gap.

[bcredliner]

Originally Posted by upallnight

Once the BST has blown, you will not be able to start the engine. The biggest draw on the electrical system is a starter. The starter circuit is feed from the BST cable. The airbag would have received the energize signal from the DME at the same time the BST cable would have received it signal. Some circuits such as the door lock and unlock circuit are not on the BST circuit so that they can still operate once the BST cable is blown. The fact that you can only start the engine thru a jump from the engine compartment jump terminal lead me to believe that you are back feeding the circuit from the battery jump cable.

https://www.youtube.com/watch?v=c26Jq1O1m0M

Worthwhile content begins at 1:34,

[upallnight]

Originally Posted by bcredliner

https://www.youtube.com/watch?v=c26Jq1O1m0M

Worthwhile content begins at 1:34,

More bad info being posted from the net. People should do more investigation about how our X work instead of posting bad info on top of bad info.

Here's a diagram of the power distribution from Bentley Manual.



If you can read a diagram you will see that the BST circuit is only for the starter. Once the BST is blown, there is no more power being supplied to the starter. Like I stated before because he is jumping the car from the jump terminal in the engine compartment so he is basically backfeeding power to the starter. All the other circuits are not on the BST circuit so they will still function.

[upallnight]

Originally Posted by bcredliner

When the BST connection blows it forces the cable back. If you push the cable toward the battery and pay close attention you can feel it move a bit. However, even if the cable has be fired back the engine should still start but not have enough voltage to support systems such as airbag. Make sure the new ignition switch is the correct part number for your vehicle and their isn't a problem stemming from the install. I have seen exactly your problem and it was caused by the ignition switch. And, recall that everything was fine for 3 weeks after you installed the new switch and symptoms are now the same as the old switch.

When the BST is fired it forces the cable back and springs tabs prevent the cable from moving forward again to provide electrical contact. See diagram.

[SeattleBimmer]

Update: Tested voltage drop under load.

1) Confirmed battery was charged. Battery read 13V at terminals under the hood without load. Started the car to confirm problem still existed. No start.

2) Pulled the spare tire to get to the battery. Inspected the BST. There weren't any signs that the BST was triggered. Wiggled the cable to see if it was ejected by the BST. It was solid, no wiggle at all.

3) Connected the leads of my DVOM to the positive battery terminal directly on the battery in the trunk to the positive terminal under the hood. Voltage read 0v (without load). Held the key in the ignition position and the voltage jumps to 11.10v for about 2 seconds then drops to 4.5v and continues to stay at 4.5v even after turning the key off. Can someone explain that???

4) Left the DVOM lead connected at the battery positive terminal and moved the lead under the hood to the the ignition switch. Tested both sides of the ignition switch (power supply pin, and starter pin). Under load, the voltage reading showed between .1-.2 volts which I understood is within specifications.

So If i'm understanding this correctly, the voltage didn't drop beyond the specified range from the battery to the ignition so we can rule out everything in between. From the bentley diagram, the BST appears to be on a parallel circuit so that has not been ruled out beyond visual inspection. Can someone confirm that? Is the engine bay terminal connected to the battery by one long continuous cable? If so then we can probably conclude the problem is somewhere on that cable or at the end connections of that cable.