Crank and camshaft sensor diagnosis - Hyundai Forums : Hyundai Forum
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post #1 of 83 (permalink) Old 05-25-2019, 06:18 AM Thread Starter
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Crank and camshaft sensor diagnosis

Hi Folks. My '98 Accent was running fine until about 3 weeks ago. The first symptoms were stumbling badly on startup (sounded like it was only running on 1 or 2 cylinders) then would catch after about 3 seconds and run fine. It did this intermittently for 3 times then quit altogether and won't start at all. The timing belt is good and all the cranking leaves a strong fuel smell up front so I think the pump is okay. I'm suspecting either the crank or camshaft position sensors. My question - is there a way to test these sensors to see if they are functioning ok? I don't want to just start replacing parts without some indication that one is faulty. Thank you.
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post #2 of 83 (permalink) Old 05-25-2019, 09:31 AM
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You can go on youtube to get the answer about how to test cam and/or crank sensors.

I believe that Hyundai uses the cam sensor
(in correlation with the crank sensor) to determine the position of the piston
and the cycle that the cylinder is in
all to be able to set up spark timing..start up
After that it just uses the crank sensor, the cam is not used but still monitored
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post #3 of 83 (permalink) Old 05-25-2019, 01:27 PM Thread Starter
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Thanks for the input and link.
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post #4 of 83 (permalink) Old 05-25-2019, 01:47 PM Thread Starter
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Ok, I took off the crank and camshaft sensors and did some resistance probing. The crankshaft sensor measures 0.85 K Ohm between the center pin and one of the end pins. The camshaft sensor measures 3.04 M Ohms between the center pin and one of the end pins on the 4M scale of my multimeter with the black lead on the center pin. However when I switch to the 40M setting the reading jumps to 22 M Ohms, which doesn't make sense to me. Also when I switch the red and black leads (i.e., red lead now on the center pin) I intermittently get readings that cycle between 2M Ohms and 36 M Ohms then the meter goes to 0.L after a while (on the 40M scale). So I'm suspecting a bad camshaft sensor. Does anyone know if the 0.85 K Ohm reading for the crank sensor is within spec? Thanks all for any input.
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post #5 of 83 (permalink) Old 05-25-2019, 02:27 PM
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Your crank sensor resistance sounds about right, and measuring the resistance of a cam sensor isn't a valid test. That's why the guy in the video never attempted it.

You didn't need to remove the crank sensor to test it. The easiest way to test it is to monitor the fuel pump power supply then just crank the engine. If the PCM switches the pump power on DURING CRANK the crank sensor must be working. The pump wouldn't switch on otherwise.
The cam sensor is tested by monitoring the voltage on the signal wire, then move a ferrous metal past the face of the sensor. The signal voltage should switch between 5/12V and 0V when the metal is moved past the face of the sensor.
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post #6 of 83 (permalink) Old 05-25-2019, 07:06 PM Thread Starter
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I did the cam sensor test as per the video. I first disconnected the sensor from the connector and checked the output from 3 terminals with the ignition switch on. One outer terminal was ground, the other outer terminal had 12 volts on it. Then I plugged the cam sensor back in with some paper clips in-between so I could attach the voltmeter leads. With the ignition on the center signal terminal has 5 volts on it. When I wave a wrench by it it goes close to 0 volts however I have to be within about 1/16" to get the signal voltage to change. Does 1/16" sound correct? I also notice that the sensor probe was covered in oil when I removed it. Would the oil affect any results?

Now on go the crank sensor. I disconnected the connector to see what was on each of the 3 terminals. One outer terminal and the center terminal both have 1.5V on them. The other outer terminal is ground. I'm puzzled by the 1.5V on both of these input terminals with the sensor disconnected. Does that sound right? I did not continue to test the crank sensor plugged back in pending an opinion on that 1.5V result. Thanks once again.
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post #7 of 83 (permalink) Old 05-25-2019, 07:54 PM
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Does 1/16" sound correct?
Yeah, sounds OK to me. I also notice that the sensor probe was covered in oil when I removed it.

Quote:
Originally Posted by rreitz
Would the oil affect any results?
No.

Quote:
Originally Posted by rreitz
I'm puzzled by the 1.5V on both of these input terminals with the sensor disconnected. Does that sound right?
Who knows. I've never seen published figures for what the open circuit voltage of a crank sensor circuit should be because it's not normally how the crank sensor is tested.
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post #8 of 83 (permalink) Old 05-25-2019, 09:42 PM Thread Starter
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Ok, back to the crank sensor then based on monitoring the fuel power supply - where is the best place to tap into the fuel pump power supply? I remember that when the car died for good there was a strong fuel smell in the engine compartment after constant cranking and no start. I just assumed it was supplying fuel to the cylinders. I'm not sure where to tap into the fuel power circuit. As always, thanks for all the tips (all the way from the UK!)
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post #9 of 83 (permalink) Old 05-26-2019, 12:10 PM
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I don't think your car has a pump check connector, so the easiest place to monitor the pump supply will be right at the fuel tank connector under the rear seat.
On top of the tank module there are 4 wires and a 4 terminal connector. The yellow wire on the tank module is the fuel pump power supply...see below.

The smell of fuel in the engine bay kinda suggests your crank sensor is working. The sensor might not be the cause of your non start. I guess we'll find out soon enough.


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post #10 of 83 (permalink) Old 05-26-2019, 06:49 PM Thread Starter
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That fuel pump top cover looks way to pristine for a 1990's Accent! Mine looks rusty brown and old ... I put both sensors back in and cancelled my order to RockAuto until I can come to a better conclusion. I will see if I can monitor the voltage on the yellow connector if there is a bare spot where I can attach a clip - but I suspect the wire will be totally covered from connector to terminal mount. Another way would be to crank and then pull a couple of the plugs to see if they are wet. I did pull them out this AM to see if there were any clues and they were coated with what smelled like unburnt fuel so I cleaned them and put them back in. However the car has been sitting for 4 days so I will crank and look at them right after if I can't find a convenient tap into the fuel tank connector. Thanks again for the interest.
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