Volvo 240 SE 1993 B200F LH2.4 Jetronic. Yes that one but bear with me here. I am still in trouble with my Volvo but I have made some progress. I thought the Knock sensor was not working and removed same to test off the block only to discover the scope lead was faulty. However this caused me to dig out my timing strobe only to discover the engine at tick over appears to be well retarded but does advance once the throttle switch comes in and the revs pick up it advances a lot.
As I has a spare ignition ecu I tried that but it made no difference to the tick over timing but now assume the high idle is being caused by the well retarded engine.
Any ideas as to what may be causing this. The ignition LT pulses are spot on and stable but just late. No Fuel or Ign ECU error codes and engine now cycling the O2 at Tickover and at 2500 rpm. Any help appreciated. Regards Peter
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Hi Peter,
Sorry to hear that you are still having bother.
Does your ignition ECU have a vacuum connection as well as the electrical one. The reason I ask, is that it isn't unknown for the little pipe inside linking the port on the casing to the vacuum sensor to come adrift.
Is it an EZ61 type of ignition, with a toothed wheel as a pickup, or does your car have a hall sensor as an engine position sensor? Sometimes, there is also an oil temperature sensor for the ignition instead of coolant temp as for the injection.
Number_Cruncher
Number_Cruncher
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This model has the EZ116K so no vacuum only throttle switch and coolant temp and load sense signal form the Fuel ECU. I even swopped Ign ECU but timing still lagging at tick over. Regards Peter
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AFAIK
the knock sensor activity can be tested in situ - with the timing light attached and the engine running at tick-over, gently tap the engine block close to number 1 cylinder.
The timing should be seen to retard.
If not, is it on maximum retard as it considers that pinking is occuring?
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Yes it is on maximum retard with or with out the knock sensor connected. No error codes, very strange. Thanks Peter
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AFAIK
the knock sensor is a piezo-ceramic device which produces an oscillating voltage in the 6 to 15Khz range when the engine knocks.
Is there continuity of signal and earth from the sensor to the ECU?
You could probably 'scope its output and simulate a knock with gentle(!) application of hammer to the block, and see if the KS functions.
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The KS is functioning and produces 3 volt spikes it tapped gentle, however it does not ring as I thought it might and some data books suggest. The signal is present whether connected to or not to connected to the ECU which looks like a 1m ohm impedance. If disconnected the ECU does not report an error or though there is a code for No KS Signal detected. I'm rained off today but keep the ideas coming. Does anyone know what information is send via the 'Load Signal' between the Fuel ECU and the Ignition ECU. Regards Peter
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The knock sensor should, when mounted on the block, have a (self)natural frequency at about 4kHz, although I would be surprised to see it ringing significantly because the energy you put in by tapping the sensor is rapily dissipated elsewhere in the block. (The disconinuities formed by the graphite in the structure of cast iron make the material a good dissipator of vibrational energy when compared to more homogeneous materials).
This natural frquency of the sensor can be tweaked by how tight the knock sensor is tightened down - too tight, and the natural frequency becomes too high.
I agree with the testing method suggested by another John H, with the engine running fast, a few taps* near the sensor should see the timing back off noticably.
* Taps with a lighter, harder tipped, hammer mean that the hammer tip is in contact with the block for a shorter time period, and increase the high frequency content of the pulses picked up by the sensor. The sensor would probably not detect a heavy hit by a rubber faced sledge hammer, because there would be little high frequency content in the pulse, while it would pick up a tap from a much smaller steel tipped hammer.
Although I don't think it is a problem in your case, I have come across a case where the knock sensor was picking up excess mechanical noise from a very worn engine. By removing the sensor from the block, but keeping it electrically connected, a car which initially was completely gutless was (temporarily) transformed. Once we realised that it was the worn valve train rather than any combustion fault that we had to fix, the job was plain sailing.
As another example, Mongos of this vintage were also prone to picking up a high frequency exhaust resonance, mistaking it for knock, and retarding the ignition!
I don't know what the load signal will look like. I would guess either a serial bit stream, or, like the IAC signal, a mark/space ratio modulation.
Number_Cruncher
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Still raining I'm afraid so no more action on the car front. Several tests yesterday only produced a non resonant respose both when fitted to and not fitted to the block. I got a good amplitude signal but quite unipolar in anture. I'm wondering if the KS is faultly. Regards Peter
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Are you sure the KS has a good earth connection back to the ECU?
(Either via the block, or second wire from KS)
If it is floating, there is at least one source of electrical noise the wiring may pick up which could be mistaken for the pinking waveform: ignition HT pulses - they ring a bit too.
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Yes the signal wire is a coax and carries it's own earth up to the KS. I hope to identify the signals at the Igniton ECU today, weather and time permitting. The only one I do not know what form it takes is the Load Signal from the Fueling ECU. I looked up some KS waveforms last night and mine are not like them I definately have an unipolar type pulse from the KS non resonant and mostly a positive pulses very few negative. Regards Peter
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I have finally got my Volvo fixed. It turns out that even a Bosch specialist had trouble finding the cause but eventual after having the Injectors cleaned 3 times but failed to meet the flow rate they where replaced but although this solved the leaness issue and car sat at 1300 rpm, no faults and everything seemed to test out ok. However a tap on the AMM and the engine note chances but the ECU has still gone into default mode and no ICV singal, so a replacement AMM and instant return to smooth running.
Total bill £540 inc Ouuuch Regards Peter
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I'm glad you have finally got it sorted out Peter - I have watched your posts here and at the Volvo site.
If the fault was actually the AMM in the end, why do you think it didn't show up as a OBD code?
When mine failed some years ago the engine ran rough for a few minutes, then it sorted itself out (presumably in default mode) but the Lambda light stayed on until someone read the code, which pinpointed the AMM. I was in a panic at the time, never having encountered modern electronics before, but in retrospect and knowing much more about it, it seemed pretty straightforward.
Did yours have multiple faults, or did the diagnostic system fail to pick up the AMM fault?
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The Bosch specialist guy recons the AMM fails during ECU self test when faults are not logged, thus no error, even stranger is that when back probing the AMM the static voltage, idle rpm voltage and the ramp up cuve when opening the throttle all looked OK thus neither of us though it was the AMM. It was only during tapping the AMM that the engine note changed and the realisation that thew AMM was not well internally. Why cleaning the injectors did not redeem their performance we don't know, so new ones fixed the problem and she's running sweetly lambda of 1 CO 0.03 and HC of 13. If any gets an ecu problem with a LH3.1 system and wants to borrow the spare ECU's and all the Pin out data then for postage and a security deposit I'm sure something can be arrange. I also have an Ignition amp and Knock sensors. The ignition timing also returned to normal once the AMM was changed as the ECU was not going into Default mode. This esplains why during my testing if esstablished a stable state albeit with an idle of 1050 or so and I shut it down removed power then reconnected and started it again the engine ran differently. We assume this was the AMM doing strange things at power up. I had found an AMM at a local scappy but I was convinced it was not the problem as everytime I measured the outputs ther appeared to be right to 3 decimal places and ramped up as expected and often quoted was the fact that a faulty AMM causes difficult starting and my car started every time on the first turn of the crank. Going to put the trim and panels back today and wash it. Regards Peter
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My mistake I meant LH 2.4 Regards Peter
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