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Back on the wiring diagram above tiled battery you will see a second 250 amp fuse link
This fuse link is under the right rear seat pan behind the RH heelboard fuse box at the rear passenger foot area
If you lift the seat pan without removing he pan from the car you will see a triangle plastic cover on the right side covering the fuse link and its terminal nuts
If you slide the seat pan out of the car you risk damaging the felt door surround trim
This fuse link is before the 2 terminal post for the left and right engine fuse box in the blue colored areas
But is not for the starter cable run in red color
The splice point is were we split the problem in halve before removing the seat
If you read the voltage sag during starter rotation at the terminal post for the starter cable on the right wheel well you would see the area of interest being a high case ground from the starter solenoid output terminal to the starter motor pigtail
Instead of 100 % of the battery power going down the pigtail wire to the brushes for starter rotation , which it does . It grounds to the case of the starter solenoid which further drops the battery voltage to run the ECU properly
This is the case with my car as well as the example at the salvage yard
9.0 volts is my reading from a good load tested battery with the proper sized test equipment
With the solenoid removed and in free air with no wires attached the output terminal post to case ground is a very small 1 ohm
The 2 new solenoids I ordered do the same thing with the 1 ohm case ground along with new different sourced starter motor assemblies with the different new solenoid attached
The starter motor is a common Bosch 110 series with robust brushes and bearings and I took it apart to inspect and sand the commuter ring with cutback
Last edited by Lady Penelope; 04-02-2019 at 07:04 AM.
Reason: ng the felt material on the door trim
Back on the wiring diagram above tiled battery you will see a second 250 amp fuse link
This fuse link is under the right rear seat pan behind the RH heelboard fuse box at the rear passenger foot area
If you lift the seat pan without removing he pan from the car you will see a triangle plastic cover on the right side covering the fuse link and its terminal nuts
If you slide the seat pan out of the car you risk damaging the felt door surround trim
This fuse link is before the 2 terminal post for the left and right engine fuse box in the blue colored areas
But is not for the starter cable run in red color
The splice point is were we split the problem in halve before removing the seat
If you read the voltage sag during starter rotation at the terminal post for the starter cable on the right wheel well you would see the area of interest being a high case ground from the starter solenoid output terminal to the starter motor pigtail
Instead of 100 % of the battery power going down the pigtail wire to the brushes for starter rotation , which it does . It grounds to the case of the starter solenoid which further drops the battery voltage to run the ECU properly
This is the case with my car as well as the example at the salvage yard
9.0 volts is my reading from a good load tested battery with the proper sized test equipment
With the solenoid removed and in free air with no wires attached the output terminal post to case ground is a very small 1 ohm
The 2 new solenoids I ordered do the same thing with the 1 ohm case ground along with new different sourced starter motor assemblies with the different new solenoid attached
The starter motor is a common Bosch 110 series with robust brushes and bearings and I took it apart to inspect and sand the commuter ring with cutback
If I'm interpreting you correctly, are you saying that my starter might be going bad?
I took the mass air flow sensor out and squirted starting fluid into the intake as my sub cranked...she fired but didn't run...just caught and died! This means I'm not getting an injector pulse. Right? So, if the starter is going bad and sucking voltage as I crank, this would result in a low voltage situation and not enable the injectors. Right?
As near as I can tell, my Roadi scanner disabled the injectors when I cleared the codes on Saturday. Tonight I threw caution to the wind and figured I wouldn't do any more harm if I hooked it up again and fiddled with it. One of the selections was "fuel ready". On a whim I selected it and tried the key. She fired right up.
That's good news that you're up and running. Well done.
I've never heard of a scan tool disabling an engine start on any car, and certainly not on the X300. I don't know how it would do that. It would be good if you could try and repeat the scenario as a learning exercise for us all
That's good news that you're up and running. Well done.
I've never heard of a scan tool disabling an engine start on any car, and certainly not on the X300. I don't know how it would do that. It would be good if you could try and repeat the scenario as a learning exercise for us all
On second thoughts just leave well alone.
Well, I'm repeating it. Ugh. It's not firing again. I'll keep messing with it. Maybe the scan tool was a coincidence. Who knows when it comes to 'trons?
There was the case where someone found something messed up in the OBD 2 connector
The fuse # 10 is the " control " power to close both fuel pump relays to allow " power " from a different fuse to power the pumps
The ECU provides a ground to command the relay closed
If it was a data bus wire that was data corrupted I can see how this could interfere with the fuel pump relay enable in the ECU
Does the # 1 pump run with the reader in the OBD 2 port ?
notice the control power for the relay goes through the BT4 connector above the fuel tank in the trunk , this connector can come loose if the lock over bar is not tywrapped closed
Last edited by Lady Penelope; 04-02-2019 at 09:49 PM.
As near as I can tell, my Roadi scanner disabled the injectors when I cleared the codes on Saturday. Tonight I threw caution to the wind and figured I wouldn't do any more harm if I hooked it up again and fiddled with it. One of the selections was "fuel ready". On a whim I selected it and tried the key. She fired right up.
I do think this was just a coincidence. From what I know of the Roadi scanner, it is a conventional generic OBDII DTC reader and not a bi-directional diagnostic tool capable of changing settings in vehicle ECUs.
The "Fuel Ready" you noticed was probably a reference to the Fuel System Continuous Monitor, which is one of the monitors that is always ready, unlike the Non-Continuous Monitors.
I agree with Parker that your cranking voltage is far too low - maybe when it started it happened to surge enough for the ECM to trigger ignition and fuel. It is quite common for batteries to lose their cranking amp capacity over time, especially if they've been deeply discharged.
Have you cleaned your battery power connections and ground points, including the engine ground strap Parker mentioned? Corrosion at those connections adds cumulative resistance that can pull down your cranking voltage. It may do little good to just tighten the nuts and bolts if you haven't disassembled them and cleaned the studs, bolts nuts washers and eyelet terminals on the wires with a small wire brush and zero-residue electronic cleaner.
If I'm interpreting you correctly, are you saying that my starter might be going bad?
I took the mass air flow sensor out and squirted starting fluid into the intake as my sub cranked...she fired but didn't run...just caught and died! This means I'm not getting an injector pulse. Right? So, if the starter is going bad and sucking voltage as I crank, this would result in a low voltage situation and not enable the injectors. Right?
The starter motor could be shorting out as a possibly , but on mine I find with the pigtail removed I have the 1 ohm short to case ground
In my judgement I can see a 30 ohm resistance if it reads though one of the 2 coils in the solenoid . This as a design would be an engineering compromise to make the assembly work and maybe 95 % of the current goes down the pigtail for starter rotation
This case ground eventually goes down the large engine ground strap
This ground strap is good to clean for other engine regulation issues , so no wasted effort
If you put your finger on the large # 5 ECU controlled relay , do you feel it click that it's getting the close command , this power sitting on the injectors at all time and the ECU providing a very precise timed ground so current flow through the injector for fuel spit
on mine the relay control wire was nicked and insulation removed
Last edited by Lady Penelope; 04-02-2019 at 11:15 PM.
There was the case where someone found something messed up in the OBD 2 connector
The fuse # 10 is the " control " power to close both fuel pump relays to allow " power " from a different fuse to power the pumps
The ECU provides a ground to command the relay closed
If it was a data bus wire that was data corrupted I can see how this could interfere with the fuel pump relay enable in the ECU
Does the # 1 pump run with the reader in the OBD 2 port ?
notice the control power for the relay goes through the BT4 connector above the fuel tank in the trunk , this connector can come loose if the lock over bar is not tywrapped closed
I struggle with electrical diagrams so I'll be asking incredibly stupid questions. You've exceeded my ability to figure out what I need to look at. LOL
In your diagram I see what you're showing me on the BT4-31 connector. What I am not so sure of is what it physically looks like. Could you guide me a little bit? This is a huge liability with me...correlating the electrical diagram to the real world/physical part. I *think* you are showing me that from the #10 fuse (the 5 amp one), I need to follow the WK wire to the BT4-31 connector.
I do think this was just a coincidence. From what I know of the Roadi scanner, it is a conventional generic OBDII DTC reader and not a bi-directional diagnostic tool capable of changing settings in vehicle ECUs.
The "Fuel Ready" you noticed was probably a reference to the Fuel System Continuous Monitor, which is one of the monitors that is always ready, unlike the Non-Continuous Monitors.
I agree with Parker that your cranking voltage is far too low - maybe when it started it happened to surge enough for the ECM to trigger ignition and fuel. It is quite common for batteries to lose their cranking amp capacity over time, especially if they've been deeply discharged.
Have you cleaned your battery power connections and ground points, including the engine ground strap Parker mentioned? Corrosion at those connections adds cumulative resistance that can pull down your cranking voltage. It may do little good to just tighten the nuts and bolts if you haven't disassembled them and cleaned the studs, bolts nuts washers and eyelet terminals on the wires with a small wire brush and zero-residue electronic cleaner.
Cheers,
Don
Don, yep. Actually, it's a brand new battery that the previous owner put in just a couple weeks ago.
Did you check the voltage that you have at each of the engine bay power fuse box studs? What is that showing there compared to the voltage at the battery?
You said you checked the ground strap but did you also check the +ve studs on the firewall for corrosion/tightness?
It's important to confirm that you have good connections all the way from the battery to the engine bay and there are no high resistance connections.
Did you check the voltage that you have at each of the engine bay power fuse box studs? What is that showing there compared to the voltage at the battery?
You said you checked the ground strap but did you also check the +ve studs on the firewall for corrosion/tightness?
It's important to confirm that you have good connections all the way from the battery to the engine bay and there are no high resistance connections.
Nothing wrong with double checking those. I'll do that again.
Did you check the voltage that you have at each of the engine bay power fuse box studs? What is that showing there compared to the voltage at the battery?
You said you checked the ground strap but did you also check the +ve studs on the firewall for corrosion/tightness?
It's important to confirm that you have good connections all the way from the battery to the engine bay and there are no high resistance connections.
The voltage readings are each of the fuse locations are within 0.2 volts of each other. I'm getting 13.2ish volts without load and 11.2ish while cranking.
I also loosened, cleaned and tightened the positive battery points under the hood at each fuse box. I used a brass brush and electric cleaner.
Hunting down a mysterious no-start situation? My 1995 XJR had a bad story which I wish to share with you. Eventually the ultimate cause was a loose cable connection, as shown above in Parker's diagram above - the lock pin broke when trying to remove the fuel tank. This went unnoticed so contact, power and signals were unstable.
04-02-2019, 05:30 AM
