So I've got two X300s...neither of which are currently running (so I can plunder to test).
In utter frustration my attention has turned to the red one which is cranking but not starting.
Battery is good (12.45 v), alternator is new and Crank Sensor is registering 200 rpm when cranking.
HOWEVER, when cranking, the battery dips into the red which I am given to understand means the ECM won't let it fire (I believe I read here that below 10v is a no go).
Any ideas what might be causing this?

Any help would be greatly appreciated as I am currently without car.

John

 

A fully charged battery is about 12.8 V, but if it isn't able to handle crankign current you might have a bad battery. Do you have another you can try?

Also take out a spark plug and have a look. I had an X300 that flooded and I wasn't able to start with wet plugs. It was surprisingly easy to flood it.

 

The starter solenoid attached to the starter motor is actually 2 solenoids in one package

you have a solenoid that engages the bull nose gear into the starter flywheel ring gear and a 2nd solenoid to hold it in place

To get this to work electrically involves a engineering compromise in wiring and solenoid manufacture

The wiring diagram does not represent this very well but I have it redrawn somewhere on a old computer

The final solenoid output post must have a certain amount of ground to the case but not too much that draws battery measured voltage down . This post is the lower one in the Bosch 110 series starter you have . Idealyt 100 % of the power at this post should go through the short pigtail in the picture to turn the electric starter . But this is not the case in design and possibly to a greater extent in your starting problem .

With a meter you may see different voltages based on a static or dynamic running system

In a static sense you may see the same voltage at the battery post as well as the starter solenoid battery cable post

But in a dynamic sense with high current flow a loose terminal will resttict this flow and lower the voltage seen with a meter

But before removing the starter there are some simple things to cover beginning from the battery and working forward

The battery can be removed and put on a large in the auto parts store back room load tester that is very heavy and not the small hand held device . This is a more accurate real world battery test

Do not tighten the battery positive post too tight as it will break a U shaped nut in half

A battery shim can help with battery terminal clamp stretch over the years , avail at the local parts store




The battery cable runs from the trunk have a couple of terminal post

As the positive battery cable turns down from the battery post there are 2 fuses in a bus protection black box that have the post nuts migrate loose



In removing the rear seat lower pan there is a small triangle cover on the right side that has a terminal post that can get loose . This is different then the rear seat heelboard area containing a fuse box and other relays that has another couple of battery cable terminal post






Moving forward from there the next terminal post is in the engine compartment rear right side on the wheel well




The last connection is the upper starter solenoid terminal post where a short battery cable goes forward to the alternator large B + post

This solenoid terminal post with the 2 cable tie in point can be gotten to with a 15 mm socket on a 3 inch extension

Editing

 

Wow thank you ever so much!

That is very helpful indeed.

John

 

Just finished my noon nap and will finish editing