Repositioned NTC Sensor For 3.2 JTS.

Started by Ascari32, May 11, 2023, 06:54:24 PM

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My engine has long been modified so it is increasingly difficult to judge it against the standard version. However, despite everything that has plagued my project, I have no regrets and frankly there is nothing to recommend a standard 3.2 JTS over my now modified one.

If anything stands out about it at all, it was discovering just how many different "Theoretical Emissions Control Techniques" Alfa incorporated into its design. In my opinion, over half of them could have been omitted and the engine would still have passed emissions regulations. Most of their techniques were taken from a E.U. funded research document - I certainly have read most of them - where the resulting conclusions were based on extremely limited data from tests never fully proven over long term employment on vehicles.

It is hardly surprising that to this day, very few understand how they all work and many "Blaise'" descriptions are offered, without going into exactly how they work in theory or practice.

For things to work, there needs to be a focal point - at least one constant, around which all else can take a reference. Theoretically, that should be the ECU. But that depends upon what the software engineers deem to be the most critical to enable ECU routines to function properly. The fact that some of those that do remapping cannot possibly understand the interrelationship of so much data which the multitude of sensors on an engine such as the 3.2 JTS is reflected in the paltry improvements in performance that is gained by remapping.

I myself make no claims to understanding the workings of the 3.2JTS, but I do recognize that there has to be at least one reference point around which the engine can function. And it seems to me, the most important parameter is temperature, and in essence, I mean engine temperature.

Ideally, an engine should be maintained at a constant temperature where fuel can achieve optimum combustion. That is the sole purpose of the engines thermostat, to maintain water temperature at a constant value, to assist correct combustion. It is also the function of the choke to enrich fuel to achieve optimum temperature on cold starting.

Crucially, the temperature of the charge air should also be optimum, or at least any engine management system, should at least be aware of what it is. Hence the sensor fitted to the Bosch HM5 MAF.

Get these two factors correct; water and air temperature, and it is possible to create the correct conditions for proper combustion. In doing so, emissions can be controlled.

So, why then did Alfa chose to base emissions control techniques around an NTC Sensor, located close to an exhaust port which in no way reflects the true core temperature of the engine? Not only is the difference between that of the exhaust port and the water jacket, relatively huge, that based upon the exhaust port located sensor is continuously unstable, greatly effected by deterioration of any manifold catalytic converters deterioration!!! Even neglecting Catalyst deterioration, the temperature at the exhaust port is continually changing due to the vagaries of engine performance and the ECU is continually trying to compensate, for those vagaries!!! In doing so, it is continually modifying other parameters in an attempt to correct it. Technically speaking it believes it is optimizing performance, when in fact it is detracting from it.

The degree to which it detracts is evidenced in the coarseness of the exhaust sound when under light/moderate load from the throttle. It induces the exhaust system, noticeably around the main catalytic converter, to produce a very untidy sound almost as if raw fuel is detonating in it. This phenomenon is most obvious when manifold cats are replaced with straight through headers and a single sports cat is mounted in place of the Alfa Twin - cat.

It is so bad, although there are issues in regard of the MAF Sensor, it can persuade one into believing the problems are entirely related to the MAF Sensor.

A Water - jacket fitted thermostat, which takes its reference from the combined temperature of the water in both banks of the engine provides a reading which is stable, but when changing, changes gradually. Not only that, it is free of the sort of "Jitters" the exhaust port mounted NTC Sensor suffers from continually. In essence it smooths out any short duration fluctuations.

By fitting an NTC Sensor into the Thermostat housing - a technique employed by other car makers, the ECU is provided with a reference temperature which is both accurate wrt engine core temperature and stable enough to be used by it as a constant. In fact it enables the ECU to employ "Standard Deviation Techniques". And in conjunction with the MAF air temperature sensor, will enable it to set accurate engine parameters, optimal for the driving conditions pertaining at that instance.

Further testis are ongoing. However, the difference is remarkable. Engine temperature, as indicated by the newly located NTC Sensor is lower and fluctuates much less. The preliminary warm - up process for the manifold - cats: now no longer fitted, is much less dramatic, exhaust sound is much "cleaner" and the sound one normally gets when under hard acceleration, is very, very, very much more subdued when applying light throttle touches.

So much so, I would very much suggest, anyone who has a 3.2 JTS 159, Brera or Spider, they think more about the engines performance and longevity and move the NTC Sensor from its current position and relocate it within the Engine's Thermostat Housing. Worrying about manifold temperatures is an unnecessary exercise; they can take care of themselves and whatever the do not capture, the secondary cats will. Plus the valve timing is such that HC's are re - ingested and burnt which is more than sufficient to meet emission regulations.



A test run, some 80 - ish miles, there and back took us to Old Felixstowe and the Ferry-boat for a Guinness and a Latte.

It was patently  obvious, the engine was responding with even the slightest adjustment of the throttle, with corresponding small growls coming from the engine. When cruising, the engine was virtually silent, with no noise from under the bonnet. Engine temperature indicated between 60 and 70 deg.C. There certainly seems sufficient cooling capacity in the radiator. This was when on the motorway, but temperature climbed to 80/5deg.C. on the urban roads around the town.

Both economy and acceleration were good, despite the engine appearing to run cool. The reason for this; I believe, is due to the ECU correcting the AFR much more accurately as the NTC Sensor fitted into the thermostat housing is working in a fashion not too dissimilar to the one in the Bosch MAF Body.

Which makes sense as the AFR should be adjusted over the whole range of the engine and not just when the Manifold-Cats reach "Light-Off".

Having now; I believe, resolved the issue surrounding the NTC Sensor, fitted in close proximity to No.2 Exhaust-Port, I will revisit the various Bosch MAF Sensors I have previously tested, to see if there is yet still more optimisation to be gained, with the NTC Sensor now located in the thermostat housing.

Currently, a GTV 2.0 Litre MAF Sensor is fitted and the above observations are made on the basis of it. However, judging by exhaust tip deposits and the indicated economy the car returned on this outing and the "Quietness" of the engine, I believe small adjustments with the Petrol - Chip device fitted, may well result in fine tuning the AFR. I probably need to borrow a Lambda probe to analyse the exhaust gases.

A further exercise will be to fit a NTC temperature display into the original sensor position and compare the difference between the two. This is purely an academic exercise simply to quantify the error between the two, i.e., the ECU parameters being adjusted for a temperature which is not that at the engine's core.

A compensating resistor does not need to be fitted to the new NTC sensor as the instrument on the dash is now indicating the true core temperature of the engine, which the ECU appears to recognize as correct and thus is adjusting to the various sensor information correctly and trimming the AFR accordingly.


I have come to the conclusion the MAF element that works best is 0 - 280 - 218 - 019 as fitted to a 2.0 GTV. It seems the characteristic response is such that the "Chip - Tune" device I bought can be altered such that many of the "Symptoms/effects" seen with the other elements I have tested, can be emulated by varying its settings. Other elements appear to limit adjustment in one direction only, whereas the 019 can be adjusted centrally.

What it also seems to suggest, when not "optimized" - for want of a better expression - if the Chip - Tune operating point is moved away too far, the exhaust noise can be provoked to sound similar to that of the other elements, suggesting the noise is a function of a weak AFR and not a rich one ?????

I find that very confusing. However, I have repeated this exercise so many times there seems to be little doubt in my mind this is the case, although don't understand why? Is it due to something peculiar to the JTS design or is it due to MAF Element incompatibility?

Alfa do state the engine functions in lean burn, up to 1500 rpm. However, I believe that is a function derived from valve timing in conjunction with the MAF. With the Colombo Bariani camshafts, NVO has been eliminated and the conjoined banks at the input of the Sports - Cat ensure there is a very high air flow charging the cylinders from 0.5deg. BTDC. The consequence of this being a huge increase in bottom end torque. So clearly, the ECU is capable of increasing fuel dose rates at low rpm, based on the air flow at low rpm.

I believe I can dismiss the Porsche element as although it is superb at high rpm, there is little point if its performance is lacking on take - off. Equally, the correct JTS MAF element, whilst being sharp at the bottom end, seems to run out of steam as the revs climb. equally, the element from my 3.0 GTV, although having a greater range, has lower voltage outputs by comparison to the 019. The 019 is consistently 100mv or greater at all quoted flow rates than the 0 - 280 - 217 - 531 element of the 3.0 GTV. Although the range of the 019 is 480kg/hr as opposed to 640kg/hr for the 531, it seems to cope well at high rpm.

The newly installed NTC sensor appears to be functioning well and I am convinced the exhaust sound is cleaner as the sensor is less prone to the constantly changing temperature around number two exhaust valve. The designers chose that location principally because temperature Does vary, which may be all well and good for maintaining Man - Cat temperatures. However that is superfluous given Autodelta headers are fitted. Besides, I remain unconvinced as to how effective Cat temperatures are maintained after the cars left the factory. Evidence of front cat overheating gives a clue as to how well it works.

There is no doubt in my mind however, that the 019 element started to perform better once the NTC sensor had been relocated to within the thermostat housing. Ideally, it would have been better fitted before the stat diaphragm, but the devil drives were needs must; given the simplest and cheapest way of relocating it is where I have now placed it. Overall, the engine seems to be a bit silkier to the extent that I have been exploring higher revs more frequently. Again, it seems content in whatever gear I am in, with torque at the bottom end being colossal.

The new position of the NTC sensor, does cause a bit of a delay, before getting a reading but the engine seems comfortable with that. I believe however, there may be an error in the value. the new NTC is 2k2 ohms, but I have a suspicion it should be 2k5 ohms. However, this would result in the ECU sensing the engine at a slightly higher ambient temperature on start - up. This being the case, the initial enrichment period adopted to warm the man - cats would be shorter, which is no bad thing when there are no cats. This in conjunction with the improved temperature stability the new location provides is very pleasing and I believe is reflected in a tangible improvement in sound track and performance.

Having had conversations with some serious software specialists, it appears, the changes I have made would be either very expensive to achieve in software, or impossible, given there are some functions which cannot be modified. So, all in all, although I believe 300HP is possible, without remapping, 291hp, 31hp greater than standard and 41hp greater than the 3.2 GTA engine is testament to just how good this engine can be. Some very quick and inexpensive modifications can be made to standard engines which would improve it's response and enhance it's longevity. One doesn't have to spend a fortune to achieve that. However, I fear, that without such modifications, these engines will be long forgotten, whilst the Busso will continue to be lauded.