Here is an update on my 4-7 misfire:
Did a Seafoam treatment using the vacuum line. No help but was exciting to see all the white smoke.
Cleaned fuel injectors with OTC 7448 and 16 oz of 7000A-1 Inject-R-Kleen via schrader valve. The adapter fitting my schrader valve was 0.308x32.
Measured fuel pressure at 50 psi. Maybe runs a little smoother after injector cleaning?
After all the above, I wrote down DTC codes without clearing them:
P0300, P0304, P0307, P1300, P0327, P1551, P1510, P0301, P0302.
Maybe some of the codes came from the seafoam treatment or injector cleaning?
To clean the injectors, I disconnected a plug on the thing that bypasses the throttle body which I think is the idle control valve so I could get to the schrader valve easier and I left it off during the injector cleaning but then plugged it back in.
I then cleared the codes and now have only P0300, P0304, and P0307 sitting in my driveway at idle.
I measured misfires live on cyl 3 and 7 none on cyl 4 with a Hawkeye.
At 640 rpm idle, cyl 3 had 170 misfires in 30 seconds, cyl 7 also had 170 misfires in 30 seconds. I find this odd that the Hawkeye reports DTC misfires on 4 & 7 but then it counts live data misfires on 3 and 7 ! What the heck?
I need to think about the live misfire count. Each plug fires twice, once in power and once on exhaust. What does a OBDII misfire count ... each time the plug sparks or only when it sparks on a power stroke?

I did the spray mist treatment and could not see any arcs nor did the engine change pitch. Tried my best to spray the coil and plug ends.
I'll clear the codes again and take it for a short ride in the dark since my inspection sticker is way out of date awaiting a misfire fix. I'll post the codes I pull after my short ride.

 

I'm back from my short ride.
I first cleared my codes then went out for a ride.
SES light came back on during the ride.
The codes after the ride are:
P1300, P0304, P0307, P0300, P0327.

The coolant temp was reading 94.6 on the Hawkeye which sounds like Celsius (202F)
Driving slower temp hit 98.6C (209.5F). Dash temp gauge was steady at halfway.

 

-The dash temp gauge won't move until I believe around 230, that is why most of us use an ultragauge to get an eye on the temp. That sounds like temps from a stock or motorad T-Stat, but nothing super high to worry about at the moment.

-Sorry to hear you still have the misfires codes coming up. At least you can rule out plug, wires, coils, fuel pressure, and plugged injectors. Have you done a compression test on all the cylinders yet?

-It's interesting that the hawkeye is reading a #3 and not #4 misfire. Are you sure you have all the engine and vin setting input correctly?

-I read another thread that was having a similar issue with #4 and #7 misfire and his thought was a bad ECM. You might want to check connector C0636 of the ECM to make sure none of the pins are damaged, wires loose, and also check the ground for the ECM. https://landroverforums.com/forum/di...s-coils-42571/

-The new code P0327 is LH knock sensor 1 signal less than threshold. You can check to see if the nut holding the sensor on came loose and that the mating surface is clean and makes good contact. Here is how to check the KS: knock sensor.pdf

 

The Hawkeye does read DTC codes for P0304 and P0307 under the read DTC menu but it is under the read live data that the Hawkeye is counting misfires on 3 & 7.
With 170 misfires in 30 seconds, that is 340 misfires per minute. If the engine RPM is 680rpm, that tells me the cylinders are always misfiring since there are two revolutions per power stroke.
I'll eventually measure compression but first I'll check for spark on 3, 4, and 7 with an inline spark tester. I should have done this to start with!
An Acctron OBDII reads misfire on 4 & 7 so I think it is just the Hawkeye that is not reading live data correctly. I'll look into the setup. I did not change any settings on the unit since I bought the thing. Maybe I'll try to find a Hawkeye help line for the pricey thing.
After checking for spark I'll pull the ECM plug C0638 and measure C0638 pins to GND one at a time for pins 2 to gnd,6 to gnd,7 to gnd, and 8 to gnd. That will tell me if the wiring and coil primary are good or not. Pin 6 and pin 7 fire the driver side coils, not sure which one is for the 4-7 coil.
If no spark and the wiring checks OK, I must have a defective ECM. I'll then try to open the ECM cover and look for a fried output transistor. Any idea how I can find a schematic for the innards of the 2003 Disco 4.6L ECM unit?

 

before you keep looking for an electrical problem have you checked the mechanical? cooling system pressure and compression tests?

 

I have the Engine Management System Wiring Diagram.
Engine Management system wiring diagram.pdf

This part of the rave will tell you what each pin on all 5 connectors for the ECM are for.
ECM pin info.pdf

I noticed that cylinders 4 and 7 ignition share the same pin on the ECM (pin7 of connector C0638) and the same wire (White with Blue stripe) going from the ECM to the Coil.

It is possible that you have a short in the wire somewhere between the ECM and the coil. That would explain your relentless 4 and 7 misfires and why the previous owner got rid of the truck. It sounds like he may have replaced all the same things you did to try and fix the misfire and finally gave up. However, I would think that you would have zero spark on 4 and 7 if there was a major short in the wire. Checking for spark on 4 and 7 and compression should be your next move.

 

I did feel coolant hose and did not feel overpressurized. I have no coolant leaks.
Eventually, I'll get around to doing a compression check.

Thanks for the ECM pin info, this is what I was looking for in the RAVE manual. Pin 7 of connector 5(C0638) is what I'll check.

I should mention I need to clean up the inside of the truck because I have parts all over the place awaiting me to put my headliner back up. I had two leaking sunroofs I fixed. The front one had a broken nipple on the passenger side that the PO had tried to fix unsuccessfully so that drain was just pouring onto the headliner. The ECM is down below on that same side. I'll post what I find on the ECM connector when I can find time to work on it.

 

I measured spark last night on cyl 3 with a neon inline tester. 3 was nice and bright. Cyl 4 and cyl 7 had only a faint trace of light which I could barely see.
The ECM connector 5 ( C0638 ) contacts did not appear corroded nor did the ECM pins.
I measured continuity between pins:
2 to 8 = 1.2 ohms
6 to 7 = 1.5 ohms
It looks like the primary side of the coils are OK.
The 3 pin connectors on the coils connect together to Fuse 14 and get power through relay R211. I made some more measurements on the ECM connector 5:
2 to 6 = 1.5 ohms
2 to 7 = 1.6 ohms
2 to 8 = 1.2 ohms
6 to 8 = 1.4 ohms
7 to 8 = 1.6 ohms
I should be able to measure the high tension sides of the coils for plugs 4 to 7,
plugs 1 to 6, plugs 2 to 3, and plugs 5 to 8. I'll try to get to that this weekend.
Maybe I can measure compression this weekend too.

 

Have you checked the wire harness plug that goes into the problem coil?

The coil uses the same wire for 4 and 7 (white w/ blue stripe I think) and it may be loose in the plug or something. You will probably need to pull the upper intake manifold off to get a good look at the plug.

Although I think that your spark test would point to something electrical like a pinched or loose wire, you probably should still do a compression test on all the cylinders to confirm everything is fine and rule that out real quick.

 

Making some progress on my 4&7 misfire.

Measured the ECU C0638 connector pins with an oscilloscope while running at idle.
I only looked at pin 7 and picked one other to compare it to. I picked pin 6.
Pin 7 just sits at +14v and never gets grounded by the ECU.
Pin 6 sits at +14V then gets grounded and released which creates spark voltage on the secondary of the coil.

Opened my ECU and found the smoked transistor. It is a BOSCH 30021 transistor. The transistor next to it ( which connects to pin 8 thus cyl 5&8 )also looks burnt but I think it must only be the conformal coating that got burnt. Cyl 5&8 had no misfires so the transistor that connects to pin 8 must be working OK.

I'm trying to find an equivalent transistor to the Bosch 30021 but can't find a Bosch datasheet. I think maybe Fairchild's EcoSpark IGBT transistor might work. In the mean time, I took a risk and ordered a Bosch 30021 for $10 off Ebay. This thing should only cost at most $1 or $2.

I just hope that the failed transistor did not take out the chip that drives it. I'll give an update in about a week after I replace the transistor.

By the way, it is very easy to disconnect the ECU and then remove 4 torx screws and the ECU cover to look for burnt ignition transistors. I should also mention I came across a BMW discussion that looked to use the same Bosch ECU but with 8 ignition transistors instead of the 4 the Disco unit uses.