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Old 06-30-2018, 03:23 PM   #1
Pete.M
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Default LH2.4 Intermittent Signal From EZK to Ignition Amplifier

This is an LH2.4 swapped 740, using a 940 loom so I may have done something wrong, or just badly...

There seems to be an intermittent signal from the EZK to the ignition amp/power stage. So far I've only seen a single spark after several attempts cranking the engine. I've checked the signal going to the ignition amp, most of the time it doesn't vary, staying at about 180mV which I believe is in the right region for having the ignition on, but it should pulse with a slightly higher voltage when cranking.

I know what the inputs into the EZK are, but I don't know which ones are strictly required for it to send the ignition signal? I checked out the crank sensor, resistance seems ok. I read it's supposed to produce about 0.3V when cranking. I can't measure any voltage, however I must be doing something wrong because I also can't measure any voltage on my running 940.

I'm sure the crank sensor is fine but I guess I should confirm this first, so what's the best method (in detail) of measuring the crank sensor voltage when cranking? Failing that, I can just swap the sensors between my two cars. And what inputs does the EZK strictly need to send the ignition signal? Any other advice appreciated.
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Old 06-30-2018, 07:11 PM   #2
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You can check the signal the best way with a scope. Next is to have a voltmeter on ac settings and on 2 or 20 volt scale you should read some a/c voltage. I usually swap the sensor since they aren't that bad and I've had ones that ohm out ok but still don't work.

The crank sensor is the main trigger for an ezk box. Then the ezk computer in turn triggers the amplifier. If you know you have a good sensor and the wiring is OK. Then you may have a bad ezk computer if there is still no trigger to the amplifier.
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Old 07-01-2018, 12:34 PM   #3
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It's a 5v square wave. Here is my 240 at idle.


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Old 07-01-2018, 03:13 PM   #4
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Thanks.
Today I swapped the crank sensor and ezk from the other car, no luck. Still can't get any voltage on my cheapo voltmeter so a scope is probably the way forward.
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Old 07-01-2018, 03:58 PM   #5
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You may want to check the condition of the tone wheel on the torque converter flexplate and make sure there isn't a problem there. Then I would double check wiring continuity between things since the ezk and sensor are known good. Start at the ezk unit to the amplifier. The wiring on the negative coil terminal is what the amplifier triggers and that also loops to the dash for a tach connection. If I recall correctly it is also providing the ignition signal to the ecu to turn on the fuel pumps with that wire.

Don't forget about the grounds on the intake manifold. One of those open and you can have no ignition.
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Old 07-01-2018, 04:39 PM   #6
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I use a Picoscope at the shop if I need to, but I also use a $80 Hantek scope that works just fine if you can get the software to display English instead of Cantonese.

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Old 07-01-2018, 07:52 PM   #7
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Any fault codes from the EZK, or ECU? When trying to measure CPS voltage, are you using the AC voltage setting on the meter?
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Old 07-02-2018, 02:10 PM   #8
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I removed the wiring for the diagnostic plug when cutting the loom out of the 940

My meter only has what look to be very low settings for ac voltage, 200 and 600mV I think. I tried it on those settings.

Good idea, I'll check continuity from ezk plug to ignition amplifier.

Is there a reason certain grounds should go to the intake rather than the body? I can't remember exactly what I've done but I may have rerouted a ground or two....
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Old 07-02-2018, 05:40 PM   #9
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Another thought, it's probably not the best idea having the ground of the radio suppression relay go to the same ground as the ignition amplifier. I don't think they're normally in the same place so I'll try moving it.
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Old 07-02-2018, 11:12 PM   #10
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There are supposed to be grounds on the intake manifold that provide engine ground reference for ignition and fuel computers. They should not be on the same bolt that's why they used both fuel rail bolts. Sometimes when computers are grounded to the same location physically it can cause noise in the circuit. These particular grounds should not be on the body of the car.
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Old 07-08-2018, 01:47 PM   #11
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I moved the ground for the radio suppression relay. No luck. The ground for the ignition amplifier is in the original location on the inside wing.

I've got good continuity from ignition amp to ezk, and from crank sensor to ezk, and their grounds.

On one attempt I got a spark when turning the key 'off'. This made me wonder if there was too much of a voltage drop when cranking, however I'm measuring over 10v at various positions when cranking which appears to be in spec.

On second thoughts this spark when turning off could be normal, given that the coil sparks when voltage is lost on the secondary side.

I wired up the tacho to see if it bounces when cranking, but much like the coil it only gives a single bounce when turning off.

What's the deal with this blip when turning off?
Any other thoughts?
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Old 07-08-2018, 02:01 PM   #12
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Yes the blip of one spark is normal and does kind of help in knowing that the components are able to make a spark. Since you are proving out things electrically. It may be time to double check the mechanical parts and make sure there isn't something wrong with the tone wheel on the flexplate or flywheel.
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Old 07-08-2018, 02:22 PM   #13
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That was a quick response. I was considering that, however the gearbox and engine have remained as one throughout the transplant so I'd be surprised if something has gone wrong.

I'm looking at engine grounds, I have a couple but not one going back to the battery like original. Maybe if they're not sufficient then the large current through the starter could affect the crank sensor?
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Old 07-08-2018, 02:30 PM   #14
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That is good but it is a known issue. Volvo issued service bulletins back in the day. You can check it easily with an auto by taking off the engine bracket at the bottom of the bell housing. Or the starter hole. So it isn't too bad to get a gander at it.

However, as you mention. Ground really should go from the battery to the engine with another wire going to the inner fender. Yes, a too small cable from the battery to the starter can make it so there isn't enough current to run things. Also a good upgrade is to make the smaller wire the goes to the body from the negative battery terminal a larger cable. There are also important grounds or at least one ground depending on the car model on the back of the valve cover to the body. Don't forget the alternator case ground to the engine block as well.
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