3.2 JTS Conundrum - my final solution.

Started by Ascari32, December 14, 2022, 06:12:46 PM

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Since my 3.2 JTS has been back on the road after a fully rebuilding the engine, I have been dogged with continuous issues surrounding the Autodelta manifolds, Supersprint exhaust system, including the 100cpi sports - cat, and the  Colombo Bariani Camshafts.

The issues appear to revolve around the choice of MAF and the now defunct NTC Sensor function.

Firstly, the Standard MAF body has a slatted screen across the central Venturi, in which the MAF sensor is fitted. In order to create a laminar air flow across the MAF sensor "Window ", it needs to be very restrictive. With the air inlet ducting forming a ram - air feed, there is more than sufficient pressure/airflow there under normal circumstances. In conjunction with the standard valve timing, this is more than adequate.

However, when one takes into account the changes to airflow, the modifications have made, effectively, it starves the engine of much need air, these modifications were intended to promote.

Confirmation of this came when  a Petrol Chip device was employed to adjust the operating point of the MAF Sensor "Bridge". In essence, any adjustment was superficial and the problem persisted.

After much research and talking to some authorities involved with performance engines, and as I had a spare MAF body, I decided to remove the slatted screen. The consequences of this was a very great increase in the Petrol Chip's ability to adjust the Sensor Bridge. Thus the output signal to the ECU could be greatly adjusted. As the MAF output level had increased, the range it could be adjusted down was greatly improved and with "vernier accuracy ".

This procedure made it possible to use different MAF Sensors in place of the Standard Alfa one. In essence, the problem has been resolved.

As for the second issue, the NTC Sensor, it appears from all experiments, its sole purpose is to provide a reference value to the ECU, indicative of engine/catalytic converter temperature. With the removal of the Man - Cats, and the Secondary Cats, that function is now redundant. However, the consequences of improved airflow is much lower temperature, even when the car has been driven for several hours, non stop.

Disconnecting the NTC sensor and fitting a fixed value resistor, indicative of 87deg.C., the engine performs extremely well, with much lower exhaust noise and minimal "gas - burner" like sounds from the sports cat, on acceleration.

However, the recent cold snap, with temperatures as low as minus 8 - 10deg.C., the car is impossible to start. It is behaving as Port Fuel Injection engine; it requires choke - enrichment.

Reconnecting the NTC directly, and the engine springs to life on the very shortest of ignition button use, and this is at those very low temperatures I have related too. On a warm engine, at these low temperatures, it is significant how switching from the fixed value, representative of 87deg., and normal NTC function, the torque/power increases. Which ties in with established principles about performance engines running richer.

The weather is still damned cold, which now affords me time to fabricate my modifications, to be mounted unobtrusively in the cabin. Essentially it will be a switch to select normal NTC function in position one, for cold starts; a second position which disconnects the NTC and substitutes it for a value representative of 87deg.C., and a third, intermediate value; yet to be determined, which will give a lift to performance, without going to full enrichment that the below temperature NTC affords.

It really is fortuitous, the way a problematic element to 3.2 JTS modification can be turned into, not just an advantage, but a genuinely positive function. It is particularly advantageous given the NTC performs no other function than enabling the ECU to accurately dose the cylinders with extra fuel to maintain catalytic Light-off. The dash temperature gauge is of secondary importance to this and will be replaced by another device, fitted into the water jacket. It at least will perform the function of providing an accurate value that my modified engine now runs at.