348 Crank Angle Sensor Resistance

I've been running the Kia sensors in my 348 for around four years now with no issues.

 

its fine.. i actually ran one KIA and one OEM at the same time with no bad effects what so ever..

 

Check the Kia part no against the part no here

http://www.ferrarichat.com/forum/143765234-post13.html

 

Ive just ordered 2 of the above so when i swap them over Ill measure the originals and the new ones if thats any help.

Does it make a difference which tab you use on the plug to measure the circuit (or does it not work like that???)

 

No, but i think you are trying to over think the issue.. its a motor, 90's at that..pistons go up and down like any ole 350.. Its just a magnet turning on and off.. the cables an inch or so longer..but like i said, no issues at all and I drive at 7500rpm all the time!! haha

 

No worries - they are supposed to be delivered tomorrow so Ill post the measurements with some pics

 

I dug through my shop manual and it has no resistance value listed. The only thing shown was the gapping between the tip of the crank sensor and the teeth on the pulley, 0.35 - 0.90. I'm assuming that is mm because it doesn't specify.

 

This is actually very interesting. Warning: blatant speculation peppered with facts ahead:

Similar era Motronic systems had CAS resistances ranging from 500 to 1600, which makes me think 300 isn't a dangerous variation from a hardware perspective, especially since it would lower the voltage returning to the ECU.

Also, the Ferrari diagnostic range for this sensor (on 2.7 systems) is from 500 to 690 based on engine temperature (cold or hot), meaning that it is still within expected ranges at 690, and that the system can compensate by at least 200 Ohms already. This may be a native tolerance in a baseline, or an acceptable range only relative to other temp sensors.

Curiously, while tracking down a bad MAF on my car, I checked the resistance on mine (Kia) and didn't make any notes that they were reading outside of the expected Ferrari range. Either I overlooked it, twice, or the Kia sensors I have are lower resistance.

Anecdotal experiences aside, the increased resistance would logically have an impact on closed loop ignition.

My Bosch manual indicates that this era sensor provides an AC signal to indicate speed of crank rotation in addition to signaling for TDC. Indeed, the Ferrari manual even refers to them as "engine speed and TDC sensors." If they use the AC signal, then they provide an analog voltage value for rotational velocity, and the gaps in this signal are converted to a digital signal to identify TDC. If not, they measure the frequency of the gap after it is converted to a digital signal.

Higher resistance would reduce the peak to peak voltage returned to the ECU, which logically would seem to indicate that the crank would be spinning a relative factor more slowly (AC). Likewise, the TDC detection, which is done be detecting a break in the signal (or impulse), would be slightly affected, crossing the threshold for TDC a bit sooner or later. The center of the signal would remain unshifted.

I suppose the real question is whether or not this variation would cause a shift in the maps, or would be negligible so that the same mappings are used, or just slightly shifted.

I think it would be fair to say it would matter. These values vary across manufacturers for a reason, and engineers are smart guys. The math would also support this, but to what degree it impacts the tolerances of the components and the ECU ranges/maps, and ultimately whether it produces a real world effect, is left for the pros to answer.

 

Just for a bit of info here's my research into the matter. Both Maranelo and eurospares both list the part no as 130975 which is superceded to 130975/A (I believe the 'A' just means approved aftermarket item).

Click on item no. 21 (yes I know ts for a 512M but theres no exploded parts diagram for a 348)

https://www.ferrariparts.co.uk/PagesExternal/ViewExploded.aspx?PageID=3290

It says there that it is suitable for 348 GTB/GTS/GTC/Spider, 348 tb/ts, 512 TR, F512 M, Mondial t Coupe & Cabriolet

And at eurospares click on item 40

http://www.eurospares.co.uk/searchResult_one.asp?S=130975&TM=1&TMo=693&TA=1&TB=41159

This says its suitable for

348 (2.7 Motronic)
348 TB/TS
512 M
512 TR
Mondial 3.4 t


so assimilating the list its suitable for:

Any 348, 512 TR or M or any mondial with the 3.4T engine.

Ferrari part no is 130975 hence below is correct aftermarket sensor...
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The shop manual does say that the gapping can have an affect on timing.

"A phasing error on the sensor leads results in a delay ranging from 3 to 5 degrees in the advance of the bank of cylinders in question."

But again, it say NOTHING regarding what the range the resistance reading should be.

 

Well they arrived Tell me if I'm doing it wrong but he only ohm reading I can get is beteen pins 1 & 2 and thats 935.

However, I'm beginning to think that you cant get a sensible reading off the car. Check out the extracts from workshop manual below.
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It's a variable reluctance sensor. Pin 3 should just be a shield that connects through the harness to vehicle ground. I don't believe resistance is a significant issue as both speed and gap affect the magnitude of the output voltage. It would not make sense to sense crank speed from magnitude when frequency is much more accurate and stable. Also notice that the WSM say gap affects phase, and mentions nothing about amplitude. Gap affects phase because it changes the geometrical relationship between the sensor and the toothed wheel which will affect the wave form of the output.

 

The reluctance sensor will change signal amplitude according to the speed of the rotating mass. The signal of interest is the zero crossing, which is detectable at pretty small amplitude, so the amplitude of the signal is not that important. The SNR is.

 

Voltage does (or should) change with speed of rotation. The voltage is proportional to the rate of change of the magnetic flux seen by the coil in the sensor. As the speed changes the rate of change of the flux increases hence the voltage amplitude changes (or should change).

 

I don't know that I can answer that because it depends on how the resistance comes about. All other things equal, the voltage generated depends on the length of the wire in the coil of the sensor. If two coils have the same length wire they would generate the same voltage. But if one sensor had thinner wire it would have higher resistance. This would mean lower current in the circuit, but the voltage generated by the sensor should be the same. On the other hand, two different sensors could have the same thickness wire but one have a longer wire due to more wraps of the coil. In such a case the sensor with longer wire would have higher resistance but at the same time generate a high amplitude voltage signal. Hope that helps.

 

Just removed the old (original Bosch) ones and made some measurements for you...
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