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Discussion Starter · #1 ·
Hey gang:

Kind of a long shot on this post, but this is more an electronics question-

I have inadvertantly damaged my ECM on 2 occasions, on pin 13. Pin 13 is the grounding pin responsible for firing injectors on the odd bank (1-3-5-7) in a sort of square wave pattern. 12V (powered) down the line and it's closed... ground is on. It started to not ground the other day, and it just a 12V solid signal as read from the rear of the ECM harness. It was working quite fine 12 hours before, but the previous evening I was measuring resistances and voltages across the injector harness (at the injector) on both right and left banks. And, I had the ignition on for part of that. I unplugged the harnesses to read those, not from the back of the injector connection.

Is it possible to somehow fry the ecu at that pin without it first blowing the ECU main fuse? OR, is it more likely that there is a short in the wiring somewhere that is causing it to send amps back through the injectyor harness to the ECU? I thought it was safe to pull injector connections.

This has happened before, same pin, different ECU. That time, it blew and was stuck grounded, so the entire injector bank was stuck OPEN, dumping fuel at start up.

I think inside the ECU, it's as simple as a transistor that grounds the signal, and perahps I blew a transistor by sending too much current back through the ecu, but I really thought the fuse would have blown... and I've blown the ECU fuse before by accidently crossing injector wires.

Wanting to replace the ecu, and stop playing with readings.. but don't wanna blow another.
 

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This one is certainly running you ragged. I admire your tenacity in tracking it.

Hopefully to propagate discussion as way of gaining input for this.

Concept of the switch transistor used in those two bank injector channels, they effectively isolate the main current being switched on the injector rails from the eprom and other components in the ECU.
They are controlled, obviously, by the ECU logic in switching the injectors in timing required, but specification is to handle that load competently such that none of it passes through any sensitive components.
Meaning, that the earth line being switched should go in on the identified pins, to the transistor, which on command will connect it to a earth route. This earth supply would be a logical place to start looking as without that route to complete the process it can't ultimately operate.
Carefully identify and check any earth facility for the ECU to make sure nothing obvious is being missed.

They shouldn't ultimately put any load into the ECU main operation as there's no pathway. Switching and power load exist in the transistor but don't contact each other.
 

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Discussion Starter · #3 ·
Upon further inspection, I discovered this in the left hand injector harness where the TPS branches looks like this under all the tape. This is clearly a short happening now and then, here and there.
Automotive tire Motor vehicle Wood Gas Automotive exterior


I once accidentally crossed probes while measuring injector pulse and it blew the ecu fuse. So I know if something got shorted it’s a protected circuit. So a few thoughts here as well to start the discussion.

1: Is there a way that I could have probed with my DVM that it would have sent too much current down the wire and fried the ECU? Furthermore, when the injectors stopped working that morning, I immediately checked and got a resistance of about 250 Ω, and normal operation it's supposed to be 44 ish on the NO/YW line. That resistance was actually moving around a bit too...

2: Is it possible the ECU is still functioning but can't/won't send a pulse down a shorted line? I'm back probing the harness at the ECU.
 

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Just fix the wires…
It will run much better…
Some years back I burned my wireing and replaced them…
That fixed many problems …
From before the fire…
 

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Discussion Starter · #5 ·
The more I peel back, the more brittle I realize these wires are. Did you remove the whole harness and re-wire it?

Also, I have a harness connection removal kit, lots of shapes. How do I remove the 3-pin connectors from the TPS and O2?
 

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95 Range Rover classic SWB, 2016 RRS Td6
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That looks horrible. No wonder you had issues. I don’t know what TPS connector you have. Mine is the 3 pin flat type not the 3 pin round type.
I got new shells and pins from www.3waycomponents.co.Uk.
They are as follows
TE-Connecticity Econoseal 070
Female Pt# 344273-1
Female pins Pt# 345150-1
Male Pt# 344271-1
Male pins Pt# 345148-1
I think I used a thin flat tool and depressed the locking tab from the open side. I will check tomorrow and also look at the O2 plugs. I replaced everyone of my shells and it took all winter and was a royal pain.
Your harness looks very brittle. Mine was pretty good. It has obviously flexed but whether the insulation has been eaten or overheated I can’t tell.
 

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Discussion Starter · #7 ·
Heated for 30 years. Taped and re taped over decades. Anything exposed or only taped has cooked.

It really seems like most of the exposed wire is around the TPS and injectors... and mainly on the left. So, that would indicate something in the wiring is causing the left channel ECU pin to "blow," but I don't really get how that might happen since it's fused.

Is that, like, something that could happen. The YB wire - Yellow Blue - is a 12V pulsed signal. If perhaps the 12V (NO) wire and the 12V (YB) touched, that'd be double the current down the wire, and that'd be very bad right? But, I once blew the main fuse by accidently grounding a probe to the injector harness. Sparked and burned the fuse.

I'm sick to my stomach about blowing another ECU, but I can't understand how the fuse didn't catch this.

For sure I was taking DMV readings off the harness, resistance and volt waveforms... and there's been acouple of times that playing with the injector wiring kicked off the condensor fan cool off (10 minute timer)... which would also indicate there's some short/ground on the right side too... (NO) wire goes to the timer relay.
 

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I had a parts rover… I used that harness..
I would remove the bad wires…and matched them to the other and replace what was needed…
I would think if your connectors are good…
You should be able to just replace the bad wires..
 

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To describe your original main ECU fuse blowing.

The positive is obviously fiused as you know from working with it, that supplies the injectors when on with + supply. The negative line switched through the power transistor to control injector open time will be part of that fused circuit when activated. The injectors and wiring will have circuit resistance when active that doesn't exceed th fuse rating, so no blow. Plus some capacity in the fuse rating to cope with operating variables while running. That's all ok as expected and should run without trouble unless a competent fails to lift that circuit resistance above fuse rating, then pop out it goes.
By crossing over between the two injector wires with your probe you produced that short circuit (as if an injector had possibly failed and connected the two) the fuse failed as it should and protected the whole circuit. So although a fail it was contained properly with the fuse as contingency to avoid roasting parts.

Problem with the failed loom now is that you may have positive feed in there that can track back down through to ECU that is not protected by that correctly rated fuse on supply side of ECU, so that could have given an unconstrained supply relatively, and caused problems.

As others have posted above, you've really now got to fix the loom competently before you can move on.

If you fix and then test to see if you've any switching coming out of the ECU to assess that to see if it's still alive or not to get appraisal at that status and judge where you need to go.
 

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Discussion Starter · #10 · (Edited)
That's exactly what I was needing, so thank you for taking the time to thoughtfully explain. Basically, the power feed into the ecu is protected so if the component is tied to the whole circuit by ground it will trip the fuse, but if it's not tied into the whole circuit, that's the problem? (still getting my bearings on the way this works)

Below I've traced out what the 12v lines are (dashed is pulsed) that are in play in the harness where the damage is. Note that [NO] is the power feed to all injectors and also branches off to the condenser fan timer relay, which I have shorted as well and has kicked on while I was moving the injector harness on the right.

The orange dash is the most likely contact from brittle exposed wires, and would add 5V from the TPS to the Pulse [YU] on pin 13. That would basically make it a 17V spike down the line, with no path to fuse?

Schematic Line Font Engineering Parallel


Anyway, my plan is to shrink seal and tesa tape wrap up all these crazy exposed wires and get the new ECU in. Pretty certain the main culprit has been where injector 3, TPS, and Coolant temp sensor all split up (see pic) as whoever tape wrapped it last didn't get the junction right and all the wires were exposed on top of the engine. Interesting to note that as long as the wires are not exposed they have held up and are still flexible. Any direct exposure to heat and they fall apart.
 

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Apologies for delay in response. It won't be the 5 volts from TPS circuit as addedd to the 12 volts in the system it will still be invisible (just runs contained within the 12 volts) and so not accumulated in total.

There are 5 volt systems (TPS circuit for one) within the ECU though, and fed 12 volts wrongly down to a 5 volt system will likely cause problems, it's that sort of error that can be cause of failure. The opposing scenario effectively.

Absolutely you need no crossover within that (or any other) loom for the components to work without error and so this, fixing all insulation failures, being the only way forward.

All electrical systems are the same in simplistic terms;- capacity (design and spec of system components) routing (everything going to the right destination) and insulation (to stop any unwanted crossing or leaking) once those are accounted for you should have a working system.

The problem here for anyone not standing next to it and working in reality on it, is that we don't know for certain which components are being wrongly connected. The only clear way is to diligently eliminate all possible insulation errors first to give yourself the right path forward. Hopefully it's all accessible for you to get it sorted and then tentatively step it forward to running.
 

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Discussion Starter · #12 ·
I've been using a few items primarily : Shrink tubing and Tesa electrical/fabric tape. These combined are really the only way I can re-insulate the brittle wiring. Fortunately, the wiring only falls apart ahead of injector 7 in the loom. That just translates to everything sitting directly on top of the engine for 30 years. In fact, injector 7 wiring is flexible, so I'm starting the rewire from there forward in the loom.

I shrink-tubed all the injector clips from the terminals back, so there would be in possibility of damage about 4 inches up.

So far, I'm here - Engine temp sensor (not seen) 2 injectors, TPS, and ... you can see injector 5 wiring, which is a mess. 7 is behind it and super clean and ok.

Bag Grey Luggage and bags Fashion accessory Linens


After this, I'm going to add split tube over all the sections to protect it from heat an added step.

Then, I'll repeat for the right side. I may just address the over-fueling on that side as well! We'll see.

I'm still concerned about the idea of blowing pin 13 again, but this is really the only way forward, as you have said. Based on the fact that 13 is the only thing that has been getting sizzled... and this is what the electrical loom looked like inside, I can't imagine it being anything but.
 
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