Fitting Omex Throttle Bodies to a Morgan Plus 4

After owning our 2012 Plus 4 (Ford Duratec 2.0 L) for a year I decided that I wanted just a little more performance. When I purchased the car directly from the factory I ordered the sports exhaust system similar to that used on the Morgan Plus 4 SS, however it always seems that whatever you have is just not quite enough.

Omex had already made a throttle body kit for the Morgan 4/4 but had never completed development of a proposed kit for the Plus 4. Last year Williams, the Bristol Morgan dealer, supplied a car to Omex to complete the development. I had been watching with interest and as soon as the kit became available early this year I placed my order.

The kit includes a mapped Omex 600 ECU, Jenvey throttle bodies and manifold, sensors and engine cabling. The Omex 600 ECU is supplied with a calibration developed for the Morgan but is programmable using the software that can be downloaded from the Omex site. A portable Windows computer and a suitable cable is required if you wish to make your own adjustments to the calibration.

Omex kit

Throttle bodies

This is the kit as it arrived.

Following the instructions included with the kit I removed the bonnet and stripped out the original parts. The thing that gave me most trouble was all the electrical connectors and the fuel line connection. Almost every one is a type of Chinese puzzle where you have to find the part to press to unplug them. Working in a tight space, sometimes with little light, and a back that was slowly going to pieces, just added to the difficulties.

Original parts stripped out and ready to install the throttle bodies.

Original parts stripped out and ready to install the throttle bodies.

I then completed installation of the mechanical items. I found it best to completely remove the throttle pedal to fit the cable. Standing on you head under the steering column and trying to insert a tiny split pin I found to be just impossible. Better to remove and replace the pedal; that is not easy either but at least it is possible.

The next stage was to the electrical connections. A bit worrying that a few wires need to be cut. It makes going back to original more difficult. Not impossible just more difficult. I don’t suppose I will ever want to go back. At least I hope not.

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Ready for the first start.

 

The small black object on the firewall above the ECU box is the atmospheric pressure sensor that is quite necessary for good running on the high mountain passes

The small black object on the firewall above the ECU box is the atmospheric pressure sensor that is quite necessary for good running on the high mountain passes.

 

On completion the electrics I tidied things up, put back the fuses (nothing went pop), and, with a certain nervousness, I turned the key and started the engine. It very quickly arrived at the point where it could idle, despite the throttle bodies being slightly out of balance. I then followed the instructions to get them balanced. The first, cylinder 2, I started to adjust as the engine was warming up. Once it was fully hot it required very little adjustment to get it correct. I then followed the rather tedious sequence to get them all balanced to the same air flow using the meter which I had ordered separately (it is not included in the kit and you do need it). The instructions that come with the kit are quite good and once you have achieved a balance between the two central throttle bodies the fine adjustments of idle air flow are quite simple.

Balancing the airflow

Balancing the airflow

Job done I then fitted the air cleaner and the car was ready for a test drive.

Air cleaner fitted. Not a lot of clearance to the bonnet. I can see a set of SS bonnets with a scoop in the future

Air cleaner fitted. Not a lot of clearance to the bonnet. I can see a set of SS bonnets with a scoop in the future.

On the initial test drive the outside temperature 8 to 10 degrees Celsius. I started the car and it idled fine but the moment I tried to increase the revs it wanted to cut out and started coughing back in the TBs. The conclusion was that the mixture was too lean. After a few minutes and when the temperature needle started to move it was possible to rev the engine but it would not run happily at about one tenth throttle opening again spitting back every so often. Once the revs rise to 2,000 rpm everything seemed fine. I suspected a lean mixture at small throttle openings. After consultation with the support people at Omex I discovered that the vacuum line to the brake system was not properly attached but also that the Throttle Position Sensor (TPS) was out of position by a small fraction. It had probably been bumped in transport. To adjust it is just a matter of loosening a couple of screws and rotating the TPS until the desired reading is achieved on the computer screen and re-tighten the screws. Not too tight so as to avoid damage. After rectifying those problems the throttle bodies needed re-balancing at which point the engine ran reasonably well.

Out on the road the engine pulls very well and the throttle response is very fast. Running through my favourite bit of twisty road I let the engine rev and there certainly seemed plenty of power on tap. In fact I felt I had to be careful not to overdo it on a public road, particularly with cold tyres and the occasional wet patch of road. I did not quite red line it but I did feel that there was a definite increase in power. The car was quite usable as it was but I felt there there was room for improvement. It is in the nature of Morgans that they are all slightly different and my car has a different exhaust system to that used on the development car so the calibration needed some fine tuning to match my exhaust system.

Using the logging software I was able to send the logs to Omex support and they made some fine adjustments to the calibration. After a few variations I gained the confidence to make minor adjustments myself. Simply put the logging system is able to monitor engine speed, throttle opening and other parameters together with the feedback from the sonda lambda sensor which is used by the ECU to increase or decrease fuel flow at a given engine speed and throttle opening. The trick is to try to maintain, at least for a period, a constant set of conditions to allow the log to record meaningful figures. One then returns to the fuel map and makes adjustments to bring the fuel flow corrections made the ECU, as far as possible, to within plus of minus 5%. Other adjustments were required for transient conditions, such as cold running and acceleration. I have, fortunately, the time and interest to refine the calibration beyond that which most people would require.

Example of a graph drawn from a log file.

Example of a graph drawn from a log file. Click to view full size.

The end result is just fantastic. The car takes off like a scalded cat and certainly produces enough power and torque to satisfy me on the narrow and winding roads I have to drive on around here. In fact I am very conscious of the need to not overdo it on a public road with no room for error. At the same time I have good power for touring on the open road. The sound on an open throttle is just superb and I am a bit inclined to give it throttle just to hear it growl. Power output is expected to be about 180hp and torque about 158 lb/ft at 5,500rpm.

All in all I am happy with the result. On a recent run of over 1,000 Kms the fuel economy over a variety of roads is quite good. An average of 7.6 ltr/100 km, or 37 miles/gallon (Imp), was achieved on a recent trip. I am very pleased with the result as I had expected an increase in fuel consumption. When I start driving it as though I had stolen it it uses considerably more, well fuel economy is not a consideration then, and you can’t get something for nothing.

I would like to thank Williams for making the kit possible by working in conjunction with Omex, and I would like to thank Omex for the excellent support in helping me fine tune the calibration to work well with my exhaust system. Getting it fine tuned has been a longer exercise than I had anticipated but it has been good fun and very interesting. In the end I am sure it has contributed to the bank of knowledge that will help others fit and adjust their systems to optimum performance. If anyone is considering fitting throttle bodies and needs more information I am sure the helpful and knowledgeable folks at Williams and Omex would be able to answer any questions that you may have.

Comparative dynamometer charts: standard Plus 4, Plus 4 with Omex Throttle Bodies, throttle bodies plus Omex fast road cams.

Comparative dynamometer charts: standard Plus 4, Plus 4 with Omex Throttle Bodies, throttle bodies plus Omex fast road cams.

Links: Omex Technology Systems Ltd, Williams Automobiles

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