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Engine ECU diagnostics

PostPosted: Tue Oct 27, 2009 3:47 am
by stuclark who here has played the diagnostics game with their engine ECU?

On "other" RRs of the same age, there's a diagnostic port (socket) built into the ECU loom, which you can plug a gizmo into and read (and subsequently reset) the fault codes out of your ECU. However, on my CSK, I haven't been able to find the diagnostic port - the ECU loom doesn't look anything like the same under the seat.

Does anyone know if this port even exists on the CSK? The chap who I've borrowed the diagnostic reader from isn't sure...

Re: Engine ECU diagnostics

PostPosted: Tue Oct 27, 2009 1:39 pm

Re: Engine ECU diagnostics

PostPosted: Wed Nov 04, 2009 12:35 am
by stuclark
That's the full Rovacom connector.

Some / all RRs from 1990 onwards(especially US market ones) had a secondary connector "for the owner" to be able to check the codes. From the wiring diagrams in the workshop manual, it seems the CSK should also have this connector, but I can't find it in the correct place on the wiring loom on my car :(

Re: Engine ECU diagnostics

PostPosted: Wed Nov 04, 2009 4:56 pm
by Jeremy
The only ones I was aware of are the ABS ones that should be under the passenger seat from memory

Re: Engine ECU diagnostics

PostPosted: Wed Nov 04, 2009 7:54 pm
by stuclark
Yep, ABS stuff is under the passenger seat.

The connector I'm talking about should definitely be part of the engine ECU loom, next to the tune resistor (which *IS* in the correct place under the drivers seat)

... I'm guessing it just doesn't exist on the CSK :(

Re: Engine ECU diagnostics

PostPosted: Fri Nov 20, 2009 4:06 pm
by diffwhine
Just picking up on this thread - all CSKs were built to UK spec as per the equivelant 1990MY 4 Door EFI units with the exception that the ECU was ungoverned. The wiring harness for the ECU should therefore be exactly as per a standrad EFI CLassic of that era with the white 14CUX diagnostic connector under the RHF seat. It is usually (should be) capped with another white connector. There is no other location for this connector on this era vehicle. I should know - I used to build them...! :) If you need help with sorting this, PM me and I'll dig out all my wiring training notes. All the best. Mark (or email me on

Re: Engine ECU diagnostics

PostPosted: Sat Nov 21, 2009 4:18 pm
by stuclark
Mark, that's what I thought...

The white (5 pin) connector is indeed there, plugged into the male / female equivalent, with one wire (1 pin) shorted between plug and socket. (no other connectors on the trailing connector)

I've been told (and indeed proved on a '93 model) that this connector is the "serial link" and can be used to reset / clear fault codes on the ECU. It's identical to the one fitted to a friend's '93, except that his has 2 pins shorted on the trailing end of the plug.

The diagnostic port I'm referring to isn't this one - it's another 4 pin, black, rectangular connector which on the '93 model (and according to the '90 wiring diagram) comes off the same bit of ECU loom under the drivers seat.

I've a feeling that as the RRC wasn't being sold in the US in 1990, the port isn't on the vehicle even though the wiring diagram says it should be. (there was an optional "customer fault code reader" available for US customers which plugs into this port and allows the lamen to read the ECU fault codes. There's a corresponding clip on the underseat bodywork on a '93 model to accommodate it's fixing)

Edit: I'll get / take photos of the connectors I'm referring to if it helps to describe what I'm on about.

Re: Engine ECU diagnostics

PostPosted: Mon Nov 23, 2009 12:10 pm
by diffwhine
Stu, I think you are correct. NAS vehicles had a Fuel Injection Fault Display Unit fitted which was mounted beside the ECU, so that all you needed to do was remove the lower seat trim to view fault codes. From what I remember this plugged into the connector you describe. I'm not sure though if this could be used on a non NAS ECU. NAS spec vehicles had a dedicated ECU capable of triggering MIL events long before the EU demanded this. Your white plug should have the white keeper plug, as I think there might be an issue with storing fault codes if the keeper plug is not refitted (or at least my old training notes suggest so...) Is there a specific reason why you need to do a diagnostic, or is this a case of theoretical investigation? If the former, let me know where you are, and I'll try to help. I have the original diagnostic tester (See the current RRR magazine - Ed Pascoe's articles), and also TestBook / T4 / IDS, so could download if need be. If you are too far away, can take you through the processes using multimeter checks. All the best. Mark

Re: Engine ECU diagnostics

PostPosted: Mon Nov 23, 2009 8:35 pm
by stuclark
Thanks for that, I think we're talking about the same bits of kit and connectors. What's "odd" is that the UK / Europe wiring diagram shows the existence of the "EFI diagnostic plug" but it plainly doesn't exist on my CSK in the same location (normal location) as on my friend's '93 model. (incidentally, the ECU on his, which I think is the same part no. as mine, IS able to read and reset the fault codes using the NAS code reader)

The reason for reading the codes on my part is / was mostly for interest only. I know I have a sticky idle valve, and had a faulty temperature sender (now changed) so merely wanted to see if these had flagged up in the ECU and reset the faults if they had. Having done similar things on the '93 model, it made a significant difference to the vehicle's performance, so I hoped the same might be true of mine.

The only outstanding "fault" I have is that the car is still running somewhat rich. However, there's still a few things I can check (plugs, disti, rotor arm etc).

Re: Engine ECU diagnostics

PostPosted: Tue Nov 24, 2009 2:38 pm
by diffwhine
Stu, Thanks for this. Have checked the factory database - the only diagnostic plug for the 14CUX was the white five pin jobby with the keeper (under the RHF seat) That was the only one used for diagnostics in all markets apart from the NAS code reader. If you are anywhere near Guildford, let me know and we can plug in and check. If further afield, might be a problem! If the IAC valve (idle control) is giving you problems, you will see it pretty quickly - stalling issues etc. Quick test - with a warm engine, clam the IAC bypass hose idle speed should drop to about 525RPM +/- 25 RPM (base idle setting). Should not stall! If it does, make sure throttle butterfly is very clean and set properly, and that timing is correct. Then adust base idle to those figures. If it still can't maintain idle properly after this, suspect the IAC (stepper motor)valve. Old Rover dealers had a test tool for this, but usually taking it out and giving it a good clean solves the problem.