Introduction

As a start one might wonder why we have used an older vehicle to conduct these tests when most vehicles on the road are Fuel Injected?

The answer is really quite simple, managing the fuel system in an older car provides direct insight into the changes required with fuel injected system, even though the method by which these changes are done is different.

With an older car we could also push it to its limits without fear of damage, so you don't have to.

To get the most out of this study you may wish to review this Youtube video, which explains how the system is configured and installed in this vehicle.

Datsun 120Y - 1977 - 1.2 Litre Motor

The vehicle was used for every day driving on both city and HWY trips to establish a baseline for average fuel consumption. It blew a little bit of smoke, particularly when cold and transition between normal and open throttle driving. The vehicle was well tuned to begin with. Timing was confirmed at factory settings at 7° Before Top Dead Centre (BTDC) at 650 RPM whilst vacuum advance was removed.

Averages obtained over a 3 month period. (Results recorded were both higher and lower)

Almost immediately after the installation of a single (1 litre per minute (15 AMPS)) system, the vehicle when started, began to spew black carbon from the exhaust in the form of moist pieces, there was no noticeable difference in idle RPM through the engine seemed a little quieter and smoother. The exhaust had a distinct rich odor to it.

Driving the vehicle again over a 30 day period with the most noticeable difference being a feeling of greater responsiveness and a noticeable reduction in throttle position to maintain the same speed.

Over a period of approximately one week of continued driving the carbon being ejected through the exhaust settled down and the volume of smoke when cold reduced.

During the testing the Datsun continued to run rich and no modifications to the fuel system or timing were made.

Conclusion from this phase:

Testing with the Datsun further confirmed what has been observed with other engine tests. The addition of HOH gas to the combustion event does not have a direct effect on the amount of existing fuel used by the vehicle, as vacuum and air fuel relationships remain unchanged. It has re confirmed that an increase in mileage is through changes to throttle position whilst driving only.

Managing the combustion event:

It was obvious from this point that we needed to begin to manage the fuel system to see real and sizable gains  with this vehicle.

Many changes to the fuel system were made with each change requiring a calibrated test run over a pre-determined circuit consisting of 50km measuring precisely the fuel consumption used for each trip. We were not looking for 5% improvements, which can be explained with differences in air temperatures and traffic conditions but large leaps in economy (20-30%). We did use the small changes to guide the overall direction of further changes.

Retarding the timing:

Tests were conducted from 7° BTDC through to 0° BTDC, which resulted in a noticeable increase in fuel richness and reduction in power. This also resulted in a reduction in mileage.

Advancing the timing:

It was established that this vehicle could be advanced up to around 17° BTDC before it would begin to ping excessively at speed. Timing was advanced incrementally from 7° BTDC to 15° BTDC with a slight but noticeable reduction in the richness of fuel, which can be attributed to the increased combustion time. Advancing the timing also had an effect on throttle position, which saw minor improvements in mileage, with the optimum performance and mileage being around 12° BTDC

It was clear, as suspected, that greater levels of intervention with the fuel system was required.

Modifications to the Carburetor:

The carburetor in the Datsun is a twin barrel, consisting of a Primary and Secondary Jet, each with its own air bleed and slow jet.

Changes were only made to the primary jet system, as the secondary was avoided during testing and is only engaged at near full throttle. The standard configuration of the primary jets; throttle 0.97mm, air bleed 0.8mm, slow/idle jet 0.5mm

Tests were conducted on the primary throttle jet from 0.55mm through to 0.9mm and air bleed from 0.8mm through to 1.0mm.

On the smaller throttle jet sizes 0.55mm to 0.85mm the vehicle choked whilst in transition from slow/idle jet to primary jet, though once through the transition the car ran reasonably well with a slight reduction in power in the 0.55mm to 0.8mm range. The idle/slow jet size was tested from 0.5mm through to 1mm in an attempt to overcome the transition issues with little success.

0.9mm primary jet was then used as this removed the choking effect and idle/slow jet was returned to normal, being 0.5mm. Mileage testing resumed from this point, as there was little point testing mileage on a vehicle that was not running properly to start with. Mileage testing continued whilst slowly increasing the primary air bleed. 0.85mm, 0.9mm, 0.95mm and 1mm. Each of the tests saw proportional increases in mileage, with the testing concluding at this stage with the following stablised results.

Conclusion from this phase:

Even though we believe there is more room for improvement, as the Datsun is still running a little rich, our baseline target was to achieve an increase of 50% then document our findings.

It was clearly noticeable when the combustion efficiency was increasing, as the vehicle continued to run quieter and smoother and the overall responsiveness increased. The primary Air/Fuel mixture adjustment on the carburetor needed to be finely adjusted between each change for proper idle and transition between idle/slow and primary jets. As the efficiency increased through a leaner burn, the combustion temperature continued to fall in small increments, with the HOH gas acting as a combustion aid.

How sweet it is: Once these parameters all fell into place, the little Datsun ran like a train, with a quiet and smooth operation, clean burn coming out of the exhaust and a responsive throttle. My wife even commented. "I had to look out the window, because I didn't think it was you pulling into the driveway"

How does this information relate to Fuel Injected Vehicles:

It is obvious from these tests that in the most part smaller gains of around 15% can be achieved without modification to the existing fuel system, simply by throttle position change. This is given the O2 sensor does not dramatically over compensate for the detected change in oxygen levels and send the fuel system into open loop where mileage could get worse overall.

Advancing the timing by a further 5° BTDC can help aid in a cleaner and more complete combustion, without loosing performance or increasing engine temperature. Reports received indicate that this is particularly important with Diesel Engines, along with a slight reduction in fuel supply.

For fuel injected petrol vehicles, the installation of the a device like the EFIE produce by Eagle Research is required to ensure that maximum fuel efficiency can be gained. http://www.eagle-research.com/store/index.php?main_page=product_info&cPath=2&products_id=16

This device will help to lean the fuel back to the extent allowed by the ECU, which in turn increases your mileage further.