Hi
wondering if you can help.
I have measured the signal from my flywheel sensor with a scope and have got a very good reading at the ecu connector plug,
now here is the strange thing when i plug the connector back in to the ecu, the signal dissapears.
Reading taken at the back of the ecu plug.
Also the ecu has been tested twice , once at a specialist and once in a friends car.
Any ideas , faulty sensor maybe ?
Thanks
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Mentioning what car it is might help.
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Dave
would it make any difference, i would of thought it would be the same principle in all cars ?
{As you can see from Peter's reply - apparently so. Anyway, now added to subject header should any Porsche experts be looking in. DD}
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Yes it does. Some simple use the induced waveform to detect the crossovers and the missing pulse for TDC and some terminate this signal as the detection cct ir current not voltage sensitive. The latter is often chosen to avoid interference problems. However if you choose to be so secretive about your car then so be it. Regards Peter
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I am not being secretive, the car is a 911 (964) 1990 carrera 4, I just thought it didnt matter.
I just wanted to know how the signal can dissapear by plugging it back into the ecu
Can you hep me ?
dave
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What year and what ECU. Is this a jetronic LH2.4 or LH3.1. From memory these are both voltage devices. I'll go the garage and check. Regards Peter
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dave
If I can correctly recall the details of an uncommon vehicle; the crank sensor attaches to the Bosch ignition amplifier module residing on an alloy plate in the left side of the engine bay. Yes?
I have known, over the years, several of those amplifiers replaced for both internal shorts and internal loss of earthing. [Sometimes, providing an additional casing earth gives a temporary repair.] They are reputed to sometimes have a very short lifespan - just a few years.
I can only recall one solid detail about them - the last one, 5 years ago, cost the staggering sum of £2,242...
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The car is a 1990 and the sensor is self generating so does not need a voltage supply , but generates approx 4.2 volts down the wire to the ecu.
There is no ignition output signal at all from the ecu, it needs the fltwheel signal before it can generate the ignition signal,
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When you probe it with the scope (disconnected from ECU) then you are presenting it with a very high impedance - in other words you are not asking it to supply any current since the 'scope's input impedance will be nearly infinite - in simple terms it is not being 'loaded'.
When you connect it to the ECU, the ECU has a much lower input impedance and will therefore present a load to the sensor. If the sensor is internally faulty (internal high resistance) then it could cause the signal to collapse. If your ECu works on your friends car then it is probably OK.
These sensors consist of many turns of fine copper wire around a permanent magnet - there could be a fault in the winding - could you measure the RESISTANCE of your sensor (when not connected to ECU, obviously) and compare it with that on your friend's car?
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I might also add that you should check for low resistance between the sensor and vehicle earth (should be infinite R with sensor disconnected from ECU). This may not be of significance when you are probing with a scope because the scope is simply measuring the differential voltage across the sensor. It WOULD be significant when plugged into the ECU though..
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Aprilla
I think you have just answered my question , that is what i was thinking.
I will just have to bite the bullet and buy a sensor , i think they are about £130 and an hours work.
I tested the ohms and it was 524 which is just out of range (550-600 i think ?)
Trouble is with testing on my friends car is he is over 300 miles away.
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I tested the ohms and it was 524 which is just out of range (550-600 i think ?)
Well, that doesn't sound to bad. These things vary a bit with temperature and obvioulsy your meter may not be spot on calibration.
Have you checked resistance to earth (chassis)?
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I have returned only to realise I was thinking 928 not 911. Shame I have one here and the sensor and EZ ignition unit. Regards Peter
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The car is a 1990 and the sensor is self generating so does not need a voltage supply but generates approx 4.2 volts down the wire to the ecu. There is no ignition output signal at all from the ecu it needs the fltwheel signal before it can generate the ignition signal
Err; after 30+ years of working on such things, I did actually know that...
Now; are you going to answer the question as to what it connects to - or is this purely an abstract problem?
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So is this a 0261 200 450 ECU M3.1. When you measure the waveform did you see the TDC spike and missing peak. No TDC detection nothing fires, no fuel no spark. Aprilia's ideal of a shot to ground is a good one so probe the senor with reference to an earth. Regards Peter
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Screwloose
i have already stated what the car is, it is in the title and the 4 th post
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The peak was there it shown up the missing tooth on the waveform.
The biggest problem is the dissapearing waveform when the connector is plugged in.
I have since found out the signal should be at pin 47 and not 48 where i am actually getting the reading. I am actually getting the signal coming down the sensor earth 48 and nothing from the actual signal wire 47.
47 and 48 are the 2 wires from the sensor , 47 should be the signal and 48 should be the earth.
Dave
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Is this with the ECU Connected. I have a similair sensor here part number 0 261 210 003 and it has a 3 pin connector. One pin is earth/scene and two pins are the signal wires. The outer sleeve had hardened and as a reult cracked at the moulding and one signal wire has shorted to earth and it just so happens the short is to the wire that actually requires the signal. Probe the sensor wrt to earth and come back with the results. Regards Peter
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The outer sleeve had hardened and as a reult cracked at the moulding and one signal wire has shorted to earth and it just so happens the short is to the wire that actually requires the signal. Probe the sensor wrt to earth and come back with the results. Regards Peter
Yes, this is the thing I am thinking. Check sensor resistance and also resistance to ground ('shield' if there is one and sensor body if its metallic) with the sensor in-situ and not connected to the ECU.
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The peak was there it shown up the missing tooth on the waveform. The biggest problem is the dissapearing waveform when the connector is plugged in. I have since found out the signal should be at pin 47 and not 48 where i am actually getting the reading. I am actually getting the signal coming down the sensor earth 48 and nothing from the actual signal wire 47. 47 and 48 are the 2 wires from the sensor 47 should be the signal and 48 should be the earth. Dave
I think this is just a measurement issue. The sensor outputs an AC signal and output is effectively 'symmetrical' - 'earth' is whichever of the two conductors you want it to be (i.e. whichever the manufacturer connects to ground inside the ECU). So long as when you put your scope across the two wires from the sensor you get an appropriate AC signal then you should be OK.
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ohms test
pin 47 to earth 000
48 to earth 529
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Looking at your last couple of posts ref. p47 and p48 - does this mean that somehow you have got the sensor connections reversed? Has this car run OK with this sensor in the past and just packed up, or is this a new or s/hand sensor that you have sourced?
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this is the same sensor since i have had the car 4 years, and no connectors have been reversed.
The previous theory about the polarity sounds good to me.
I had rough running for a year or so before it finally stalled and died.
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apparantly all you need for a spark situation at pin 1 is voltage at 18 & 37
ground at 2 & 19
and flywheel sensor reading at 47 & 48
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it sounds like the sensor has developed a short to ground on one of its pins. Time for a new one, or possibly just a new cable form the sensor to the ECU depending on where the short is.
--
I read often, only post occasionally
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