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Electrical Tech

 
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chevymad
Master B


Joined: 11 Jan 2004
Posts: 5472


1987 Pontiac Formula

PostPosted: Wed Mar 23, 2016 5:20 pm    Post subject: Electrical Tech Reply with quote

Here's a weird thing that happened today.

There's a ground wire that runs from a cam sensor to a ground stud on the valve cover. I take both ends loose and hook an ohm meter from one end to the other. This shows good continuity. 0 ohms. Then I touch the ground end to the stud. Continuity changes to 500 ohms. Ok that's weird. But it gets better.

Now if I reverse the leads of the ohm meter and do the same thing, I have good continuity either way. 0 ohms.
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Twilightoptics
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Joined: 13 Jan 2004
Posts: 9191
Location: Auburn , WA

1987 Chevrolet Camaro IROC-Z

PostPosted: Wed Mar 23, 2016 7:25 pm    Post subject: Reply with quote

Where are the leads testing from? And is your battery fresh. Sounds like theres a diode in line. Without it there would be some terrible noise on that lead. Who the hell doesnt terminate a cam sensor at the ecm?
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QwkTrip
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Joined: 17 Feb 2004
Posts: 3942
Location: Peoria, IL

1989 Pontiac Firebird

PostPosted: Wed Mar 23, 2016 7:32 pm    Post subject: Reply with quote

I think you're saying the resistance between the ground stud and ring terminal was 500 Ohms? Maybe the nut was not tight on the ring terminal, some corrosion on the place you touched, maybe even a surface coating on the threads that isn't very conductive. Really, the only connection that matters is between the flats of the ring terminal and the surface it mates to.

Twilightoptics wrote:
Who the hell doesnt terminate a cam sensor at the ecm?


Good point
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chevymad
Master B


Joined: 11 Jan 2004
Posts: 5472


1987 Pontiac Formula

PostPosted: Wed Mar 23, 2016 7:40 pm    Post subject: Reply with quote

No.. take both ends of the wire loose. Ring terminal is supposed to ground to a stud on the valve cover, other end is the cam sensor connector. Hook up ohm meter and it shows continuity. So far so good. Now, touch the ring terminal to the stud where it belongs(without changing the meter connections) and it switches to 500ohms. But if you reverse the leads to the ohm meter it's 0 ohms either way.

As you say, sounds like a diode, but its supposed to be a direct connection. This is on an older Infinity. Damn thing has 3 different cam sensors. Two on one head and one on the other.

The other fun bit. I'm getting a cam sensor code for the left head. Today I got the wrong left cam sensor, the only one that is different. So I swap the other 2 sensors. Now I get cam sensor codes for both heads. Swap back and only left head again. So sounding like there's not only something wrong with the left sensor, but probably this wiring issue as well.
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chevymad
Master B


Joined: 11 Jan 2004
Posts: 5472


1987 Pontiac Formula

PostPosted: Wed Mar 23, 2016 7:43 pm    Post subject: Reply with quote

Wiring diagram shows the ground connection going straight from the cam sensor to the grounding stud G10 on the valve cover. However, opening up the harness shows that the signal wire is wrapped by the ground wire all the way to the ecm, then comes back to the valve cover stud which was only 2" away from the sensor.

Upper left sensors.


Last edited by chevymad on Wed Mar 23, 2016 7:49 pm; edited 1 time in total
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QwkTrip
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Joined: 17 Feb 2004
Posts: 3942
Location: Peoria, IL

1989 Pontiac Firebird

PostPosted: Wed Mar 23, 2016 7:49 pm    Post subject: Reply with quote

A good diode would give you resistance on the forward bias and OL on the reverse bias. I don't think you'll get zero Ohms both directions.
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chevymad
Master B


Joined: 11 Jan 2004
Posts: 5472


1987 Pontiac Formula

PostPosted: Wed Mar 23, 2016 7:51 pm    Post subject: Reply with quote

Black/white is power, orange is signal and as you see the black is ground. Just found the readings very strange compared to what should happen.
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QwkTrip
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Joined: 17 Feb 2004
Posts: 3942
Location: Peoria, IL

1989 Pontiac Firebird

PostPosted: Wed Mar 23, 2016 8:06 pm    Post subject: Reply with quote

Maybe you have a fractured wire or crimp that hasn't fully separated yet. I assume one of your test leads is touching the terminal inside the connector that you removed from the sensor. Have you put eyes on that wire crimp and condition of the terminal?
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chevymad
Master B


Joined: 11 Jan 2004
Posts: 5472


1987 Pontiac Formula

PostPosted: Wed Mar 23, 2016 8:21 pm    Post subject: Reply with quote

Try this too. I hooked a test lead from ground and touched it to the ring terminal -500ohms. Touch it to the pin in the connector 0 ohms. Reverse leads and opposite happens. I've actually split the wire and connected and it does the same.

I've allready opened up 3ft of harness today. But thinking I may end up opening up the rest tomorrow.

Thing that got me, is that when I originally tested the ground I had the meter hooked in the direction that it shows good. It wasn't until I retested and had the meter hooked up the other direction that I got these weird results. Test flowchart simply has you test for power on the black/white, then ground on the black. If everythings good change sensor.
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QwkTrip
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Joined: 17 Feb 2004
Posts: 3942
Location: Peoria, IL

1989 Pontiac Firebird

PostPosted: Wed Mar 23, 2016 8:23 pm    Post subject: Reply with quote

Same results with a different multimeter?

By the way, there is no chance of me ever making a living as a mechanic. Really the only reason I am responding is because this is the only active thread tonight.
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chevymad
Master B


Joined: 11 Jan 2004
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1987 Pontiac Formula

PostPosted: Wed Mar 23, 2016 8:39 pm    Post subject: Reply with quote

Might have to see if Tracy has a meter. This one's a spendy year old Mac, so I'd hope it works correctly.
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chevymad
Master B


Joined: 11 Jan 2004
Posts: 5472


1987 Pontiac Formula

PostPosted: Thu Mar 24, 2016 4:23 pm    Post subject: Reply with quote

No idea if a different meter would read differently, but a new sensor cured it.

I have a feeling that the right sensor is marginal too. Because yesterday I swapped the right and left. When I did that I got codes for both sides LOL I swapped them back and only got the code for left again. Anyway, I thought it more an interesting/weird story then anything else.
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Dewey316
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Joined: 08 Jan 2004
Posts: 7295
Location: Bringing the tech

1990 Chevrolet Camaro RS

PostPosted: Fri Mar 25, 2016 6:35 am    Post subject: Reply with quote

Is it a VR sensor, or hall effect? Since VR sensors generate their own power, I would imagine that when one goes bad, you can get some wacky readings.
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chevymad
Master B


Joined: 11 Jan 2004
Posts: 5472


1987 Pontiac Formula

PostPosted: Fri Mar 25, 2016 4:36 pm    Post subject: Reply with quote

Sensors and ground lead all disconnected John. So I should have been just testing an unconnected wire according to the diagram.. Somehow I don't think the diagram is correct.
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