MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB GT V8 Factory Originals Technical - Tach and Electrical

OK, here's my problem; I'm getting a little frustrated working with professionals who supposedly know there stuff.

I have a 1980 B with a 3.9 Litre engine. A Glenn Towery Electronic Fuel Injection (with Electronic Control Unit), picture attached.

The wiring is a mess, electrical tape all over the place, a few crimp connections and nothing solder.

I've decided if you want something done right, do it yourself. I'm in the process of replacing all the electrical connections that are twisted and taped with solder and shrink tubing.

Where can I get an electrical schematic of the car?

I've just got my speedometer and tachometer refurbished from Nosingers in New York.

The speedometer seems to be pretty accurate to the speed of the GPS on my phone, a lot better than before I had it refurbished.

I'm having a problem with my tachometer however; I'm getting a rpm of 3,000 while idle, I believe should be 1,000 (the car's is definitely not idling at 3,00 rpm's). The information I got from Nisongers is that the tach connection should be one of the follow:

1. With Electronic Ignition and no control box....
2. With Electronic Ignition and control box....
3. With Points Ignition Systems....

My question, is the Electronic Control Box of the EFI part of a electronic ignitions or do I still have a points ignition system and how do I go about getting the correct connection and correct rpm displaced?

Thanks for the help, I'm sure I'll be back with more questions.

Richard Cohen


ricmgb

"Do I still have a points ignition system"?

Surely you are the one to tell us that. EFI is Electronic Fuel Injection, you could have almost any ignition system with that, depending on which era of car the engine came from. The original age of the MGB is almost irrelevant.

A 'control box' - to me - is what would have controlled the output of the dynamo on early cars, in which case the 'no control box' option is likely to mean an alternator, and you could have points or electronic ignition with either. Electronic ignition could mean anything from an after-market module like a pertronix under the distributor cap replacing points ignition, an after-market system with a trigger under the cap and a module bolted to the inner wing, or one of several OEM electronic distributors that came with the engine.

Is the tach the original one from the car? If so that should use a 12v trigger wire connected to the coil -ve, which is the wire that goes to the points, or one of two wires where the points have been replaced by electronic ignition. It probably goes to the same place if the engine came with a OEM electronic distributor with mechanical and vacuum advance, but if it is a more modern engine with a full engine management unit or ECU controlling spark timing as well as the injectors, it will depend on the ECU.

Was the tach recalibrated from a 4-cylinder to a V8? If not it will read double.
PaulH Solihull

In addition to what Paul says, a 3.9 Rover engine should have a conventional distributor with a Hall effect magnetic pick-up instead of a contact breaker points assembly. That's what it left the factory with, but a previous owner could well have changed things.

Your tacho obviously is not suitable for an 8 cylinder engine. I have the same ECU on my 3.9 and mine idles at 800 rpm, come rain or shine. The ECU you show looks like the standard Lucas item, and if so it is nothing whatsoever to do with the ignition. It simply controls the fuel injection.
Mike Howlett

This thread was discussed on 19/10/2011

MG MGB GT V8 Factory Originals Technical index

This thread is from the archive. The Live MG MGB GT V8 Factory Originals Technical BBS is active now.