Eric,
And to add to what David said about using an o'scope - when I was diagnosing
my wife's Olds I just clipped the 'scope probe to the wire's insulation and
viewed the signal that was inductively coupled to the probe. Since the
injector is nothing but an inductor there's a fair bit of inductive spike on
the signal and that's what the scope picked up.
Worked for me but YMMV - I was just looking for any injector signal since I
was diagnosing an intermittently dying engine - turned out to be the crank
angle sensor was intermittent. I just idled the car and diddled around in
the garage until the engine quit and promptly rushed over to see what the
scope trace looked like.
And to make matters works the special tool the GM claims is needed to adjust
the sensor was about $300. I took it to the local Chevy dealer and had them
replace the sensor at a total of ~$150. I actually **DIDN'T** use this
opportunity to buy a special tool - I must be getting old.
HTH
Mark Watson
1965 Ford Falcon
1956 Daimler Regency Mk II '104' (long term restoration project)
various transportation pods (still including the '92 Olds referenced above)
----- Original Message -----
From: "David Scheidt" <dmscheidt@gmail.com>
To: "Eric J Russell" <ejrussell@mebtel.net>
Cc: "shop-talk" <shop-talk@autox.team.net>
Sent: Tuesday, October 26, 2010 11:32 PM
Subject: Re: [Shop-talk] noid light
> On Tue, Oct 26, 2010 at 10:52 PM, Eric J Russell <ejrussell@mebtel.net>
> wrote:
>> I have a dead cylinder on our Alfa Romeo GTV6. Spark plugs are good
>> (swapping
>> them does not change the location of the dead cylinder), plug wires are
>> good
>> (normal resistance and I can get a good fat spark by holding the end 1/4"
>> from
>> the block)
>>
>> I want to check for electrical signal to the fuel injector. Can I use a
>> digital voltmeter to test? (Start engine, remove connector and put the
>> voltmeter's probes on the two contacts. I have a wire diagram to tell me
>> which
>> wire is + & - )
>>
>> I don't have a noid light. Is that an LED or some special light bulb?
>
> Depends on the kit. It's just a light, though. LED ones blink on and
> off faster, and you can sometimes see something from that. A bulb
> just lights up. They're cheap, though. A vehicle specific kit is
> like 10 or 15 bucks, and I'd rather use one than try with voltmeter.
>
> You can test with a volt meter, but the circuit works in a way you
> might not expect. There's always 12V on one lead, and the other is
> switched ground. You may, or may not, be able to see the ground switch
> on and off. (If you've got an analog meter, dig it out for this.
> Needle jumping is easy to spot.)
>
> You can also measure the resistance across the injector coils, which
> will let you find a shorted or open coil. You may, or may not, be
> able to find a spec, but they should all be close. If you can, test
> hot and cold. I've seen injectors that fail cold, and work hot, and
> vice versa.
>
> If you've an oscilloscope, this is the time to use it. (If you've
> always wanted one, this might be an excuse.) You can watch the
> waveform, compare different injectors, and see the current draw.
> That's very handy for things that aren't quite as dead as yours seems
> to be.
>
>
>
>
>
> --
> David Scheidt
> dmscheidt@gmail.com
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