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Diagnostic plug on an RV8
The anonymous member who contributed this article has the full range of hand-held equipment and databooks needed for electrical component testing and fault diagnosis on the MG RV8. He warns that although the RV8 may look like a cosmetically-reworked variant of the MGB with a V8 engine, it is in fact full of modern electronic systems which need training and sophisticated equipment to carry out relatively routine servicing tasks. (Sep 01)

In common with all modern vehicles, the MG RV8's ignition and fuel injection systems are combined to form a single integrated Engine Management System (EMS). To enable routine servicing and/or fault diagnosis to be undertaken, the vehicle is fitted with a diagnostic plug - also referred to as the "serial diagnostic port" or the "data link connector" (DLC). As the RV8's EMS is pre-1997, the DLC is not the newer, standard 16-pin variety nor does the vehicle have European On-Board Diagnostics (EOBD) protocol which is now mandatory on all vehicles type-approved after 1st January 2000.
Diagnostic plug on the RV8. (Drawing: Anon)

The DLC on the RV8 is manufactured in white engineering plastic for ease of identification. It is approximately 1 inch long by about ½ inch wide, and is configured in a 3-pin arrangement. It is located above and behind the bonnet release catch and, in the case of the Japanese specification cars, can only be accessed safely by completely removing the evaporator unit and its associated pipework in the passenger footwell. You will find the diagnostic plug is loose and not particularly easy to plug in to.

You can gain access to the plug by undoing a couple of bolts on the cover to the air-conditioning equipment located in the passenger legwell and let it drop down. This cover (cloaking strip) is approximately one inch wide by one and half inches long. Take care as it can fracture if mishandled and be costly to replace.

Now three cautions with this diagnostic plug:

1. Diagnostic plug is fragile and cannot take too much rough handling
So if you have any doubts that mechanics handling your car are very familiar with servicing RV8s, make sure you stress that they should be particularly careful when plugging in and handling the plug. Why? Well the plug seems to be not available as a replacement part - it only comes with the complete wiring harness! Unlike the 16-pin EOBD DLCs referred to earlier, the RV8's 3-pin DLC is not fixed to the fascia or bodywork and tends to "dangle" loosely from some relatively thin wires. It can often be found to have been tucked away behind a fairly bulky section of the main wiring harness and can thus be invisible in the darker recesses of the upper footwell area.

The RV8's DLC requires very delicate handling indeed because any pulling or rough handling could well result in breaks in the connecting wires which will prove extremely difficult to rectify owing to the severely restricted access under the nearside of the dashboard. The pattern of plug is, we believe, the same as fitted to the Rover 820 models.

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2. Connecting to the DLC
The RV8's DLC will only interface with either the Lucas Laser 2000 handheld diagnostic tester and the matching Lucas 3-pin serial connection cable used on the Rover 820 (part number YWB 757) or the Rover Testbook and/or T4 interactive computer systems which are held by all MG Rover and Land Rover/Range Rover franchised dealerships. Any attempt to "cobble together" other diagnostic/test equipment and their connectors in order to achieve some sort of makeshift interface between the instruments and the DLC risks destroying or "blowing" electrical components within the ECU and elsewhere.

3. Additional access difficulty with Japan spec RV8s
With Japan spec RV8s the air-conditioning kit is fitted in the passenger legwell and makes access to the DLC much harder. The evaporator closing panel, referred to earlier, must be removed in its entirety in order to gain access to the DLC. Removal is the essence of simplicity. It only involves the removal of two 8mm bolts which fix the upper part of the closing panel to the fascia immediately below the glove locker, lifting the rubber mat and/or carpet out of the way, and then pulling the carpeted lower section of the panel clear of the evaporator unit and its pipes. However the point at which lack of knowledge, pressure of time or downright laziness can create serious pitfalls for the unwary! If the 8mm bolts are removed, leaving the closing panel in position, proper access to the DLC cannot be achieved without bending or forcing the panel downwards to such an extent that the panel itself will fracture and/or "pop" some of the rivets on its component parts.


Rover Testbook/T4 equipment set up alongside an MG in the workshops. (Photo: Brown & Gammons)

A couple of years ago, when my knowledge of the RV8 was somewhat limited, this is precisely what some impetuous technicians did to my own vehicle on two separate occasions with the result that the closing panel became irreparably damaged. In those days, instead of stopping them, I rather foolishly winced and hoped everything would be all right. Well it wasn't and a replacement panel later cost me £180!! It is worth bearing in mind that items such as an evaporator closing panel could all too easily become "no longer available" - so, be warned, watch both your actions and especially those of others like a hawk!!

Finally it is worth checking that as part of the service the mechanic did make a connection with the diagnostic plug! It is so awkward making the connection you need to keep in the back of your mind it might have been overlooked if everything seemed to be running well!

Other RV8 Workshop Notes
on this and related subjects are RV8NOTE118, RV8NOTE122 and RV8NOTE123.


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