Thread: D2a Td5 misfiring & cutting out (engine harness)

This post is about a problem I had with my D2a Td5 almost (2) years year ago. It has been covered in posts in other forums –although in various bits as the saga progressed—thus some of you may have read about it before. At any rate reckoned it would be helpful to consolidate and post here.
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A few months after acquiring it, the Disco started misfiring and cutting out upon releasing the throttle, this would happen randomly (any load, any speed, etc.). The engine would re-start normally as if nothing had taken place. Being our 5th Td5 (no, I am not affected by a learning disability) could tell this was not the classic 1 cylinder misfire caused by oil in the loom but something graver. Upon interrogation of the ECU, Nanocom would show a scramble of the following faults:

FAULT 27-01 injector 1 peak charge long (CURRENT)
FAULT 27-02 injector 2 peak charge long (CURRENT)
FAULT 27-03 injector 3 peak charge long (CURRENT)
FAULT 27-04 injector 4 peak charge long (CURRENT)
FAULT 27-05 injector 5 peak charge long (CURRENT)
FAULT 28-01 injector 1 peak charge short (CURRENT)
FAULT 28-02 injector 2 peak charge short (CURRENT)
FAULT 28-03 injector 3 peak charge short (CURRENT)
FAULT 28-04 injector 4 peak charge short (CURRENT)
FAULT 28-05 injector 5 peak charge short (CURRENT)
FAULT 31-01 injector 1 open circuit (CURRENT)
FAULT 31-02 injector 2 open circuit (CURRENT)
FAULT 31-03 injector 3 open circuit (CURRENT)
FAULT 31-04 injector 4 open circuit (CURRENT)
FAULT 31-05 injector 5 open circuit (CURRENT)

The injector harness had been replaced quite recently yet it was replaced again and at the time verified that all the connectors between the block and the ECU were absolutely clean. Also checked continuity in all 7 conductors (5 injectors + 2 grounds) from each individual injector connector to the corresponding pin in the red ECU plug & found no interruptions at all (even immediately after the engine cutting out!). Due to the apparent electrical nature of the problem, also verified battery, fuse boxes (ECM and fuel pump associated relays & fuses), alternator & grounding at various points, all to no avail. Pulled the ECU apart just in case... also completely dry & looking good in the inside.

While drifting in the dark replaced the fuel pump, fuel pressure regulator and CKP for working ones but still no joy.

The cutting out gradually worsened over time to the point at which the engine would stop altogether (without any previous misfiring) under high load and the check engine light illuminated. The fault code retrieved in this scenario was:

FAULT 28-07 topside switch failed pre injection (CURRENT)

This new evidence pointed the finger towards the ECU so started looking for a replacement unit. At this point the Disco was barely drivable and the substitute ECU in transit from the UK & still a few weeks away, thus took advantage of the sit time to carry out several low key but time consuming jobs in preparation for a future remap. Pulled out and cleaned intercooler, radiator, hoses, etc. Blanked off EGR, modified exhaust manifold, changed out studs, replaced oil cooler, oil centrifuge & oil filter housing gaskets. Replaced suspicious clips, secured cables, installed silicone hoses; cleaned plugs, changed out engine mounts, springs, shocks, track rod, link rod, etc.

It was during this process that I noticed that the section of engine harness conduit going from the back of the battery compartment to the engine, had been rubbing against the ACE lines (right below the coolant reservoir), and it was literally mounted on top. Concerned about a potential leak developing in the upper ACE line, wrapped it with a slit piece of hi temp rubber hose (engine harness getting moved around in the process).

Anticipating a frustrating journey drove the Disco to town for a wheel alignment session but experienced no misfiring or cutting at all. Drove it around lightly for another 5 days, still good! Got her on high speed black top and pushed it the limit but still not a single miss. Though uneasy about not knowing what the problem truly was or how it got (involuntarily) fixed, declared the Disco once again healthy.

Soon came a planned long weekend family trip and the now well behaved Disco was the vehicle of choice. Drove about 70 km on a paved road and took a shortcut through a rough mountain pass with plenty of corrugated dirt sections, pot holes and rock outcroppings. About 30' into it the engine started cutting out again. It became progressively worse & to the point where even a small bump would cut the engine out! The difference this time was that the misfiring and cutting out were not random but in response to road surface features! Turned around & managed to get home although not without giving the starter motor the day of its life, as well as infuriating the wife & kids…

With the replacement ECU yet to arrive and evidence that the problem could well be something else (although ECU was still ‘top-siding’ under heavy load and continuity was re-checked good between ECU and each injector… in static conditions), resolved to try out a different approach... Disconnected the plug going into the engine (C0171) and peeled off enough tape & conduit on the main harness as to expose some 8 inches on the 7 wire bundle coming from the said plug. Cut these cables, ran heat shrink on each, soldered new wires, heat shrank, ran into 1/4" slit conduit, and taped & zip tied in place. The conduit was ran along side the engine harness and into the ECU compartment where the corresponding conductors were cut off on the red plug, soldered, heat shrank, etc. Effectively laid out a parallel engine/injector harness.












Fired her up and never again did she miss a beat let alone cut out! I nevertheless ordered a new engine harness founded on concerns about the long term integrity of the soldered connections.

Here's where the engine harness had been chaffing against the ACE lines & suspect the conductors had been damaged:




It's a low point therefore if any oil or dirt built up between partially peeled conductors then that could explain the ECUs topside switch failures (partial shorting between conductors at higher loads) and why they disappeared after the ‘bypass surgery’.

Whilst experienced no more misfiring issues, soon enough the A/C compressor ceased working and tracked it down to a lack of conductivity between the compressors clutch connector and the red plug. Again had to cut cables off the engine harness and lay out in a parallel loom.



Shortly after that happened to take the Nanocom for a ride and it came to my attention that fuel temperature remained still at 30°C...

Fortunately the new engine harness had arrived at this point and proceeded to replace it. Needless to say, the fuel temperature issue was immediately solved.



As previously stated, had suspected the engine harness had become damaged by sitting over & rubbing against the ACE lines as marked by the red arrows:







And seen from below:



And was right... this is how the harness looked:




After being cleaned out:








Note the yellow cables are the injector conductors (no wonder the misfiring problems and shorting between injectors!)


This diagram I put together to assist in matching the conductors at each end of the new injector loom:



The full resolution version can be downloaded from this link:
http://picturestack.com/617/586/vNhC0158toC01MGt.jpg

Rgds
Matt

So my 01 td5 had gotten so bad, you'd have to put the foot to the floor just to get up a small hill or pull out at a intersection.

Also it would have a miss that would get worse, and could be made better by cleaning plug at head, but would always be there in some amount.

Also large black smoke when taking off in morning, and generally stuff all power...

No oil at the red plug, or in the ecu.

Common codes mentioned in opening posts after some time, but one that would come up straight away after clearing and go for another drive:
(i think the others would reappear given enough time)

FAULT topside switch failed pre injection (CURRENT)

well might as well try loom replacement first,

omg, i cant believe the difference,its like new again
(i was hopeful, but doubtful it could be something so simple in my case, thinking it might more an ecu or engine harness, going by my fault code and the opening post)

so i take the old one out, wtf! it had been sealed too (like i had just done to my new genuine loom), had the car for nearly 100kkm , hmmm, not mentioned in the service history.... it must be a common fault, and need doing every so often. maybe my past owner read aulro too, also not sure if loom was sealed from new or later.

any way from outside, it looked well sealed (not pictured) time for dissection...

notice oil ingress circled along wire outside between it and sealant....


oil all inside plug internals:


time to go deeper, yes there's oil in the wire itself:


wether it's an issue or not, its there. (wish id made resistance measurements of new and old loom wiring to compare...)


These splices are in the plastic shroud, i think they would be earth or negative going by the colour, but im sure they are soaked with oil, maybe an issue, maybe not:



would be interesting to see how some of these epoxy seal jobs turn out....