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Anti Diesel Solenoid and starting (1/12)
 9/11/18 2:19am
NJAus
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, - Australia

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Currently own a white 1969 427 Big Block Coupe C3 Corvette


Joined: 6/6/2018
Posts: 30

Hi All,
 
After sorting through my issues on my 69 bb including sorting out choke issues and getting the dizzy rebuilt, the last issue was the occasional dieseling/ run on issue. This would occur 1 in 10 drives and would annoy me. Adjusting the timing and idle speed helped but it didn't eliminate the issue completely. I had to run the idle too low and explains why when I purchased the car is idle  was low as the previous owner was dealing with the same issue.
 
The easy solution was to install the anti dieseling solenoid which is wired to constant ignition source. When the solenoid retracts the throttle blades close fully without ignition.
 
On a warm start I just rest my foot on the accelerator and crank, and it fires up no issues. Resting my foot is enough to allow the solenoid to extend.
 
This might be a silly question....on a cold start will I have to rest my foot on the accelerator while cranking (to actuate the solenoid)? Or can I pump a couple of times, take my foot away and crank resulting in fast idle? I am thinking my foot has to always be resting on the accelerator regardless of cold or warm start.
 
I might be overthinking this.
 
Thankyou
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Re: Anti Diesel Solenoid and starting (2/12)
 9/11/18 9:28am
73shark
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Overland Park, KS - USA

Vette(s):
1973 Orange Metallic Coupe (orig owner), L82, 4 spd (WR), PS, (A/C & PW (I installed from wrecked 73)), leather, AM/FM Stereo, ran with '65 FI unit earlier & will again some day.


Joined: 7/9/2003
Posts: 554

I think the solenoid is supposed to extend as soon as you turn the key to the Run position and open the throttle blades slightly to the idle speed. If the accelerator pump and choke are working properly on the Quadrajet, one pump should be enough for a cold start. At least that's been my experience on the several Quadrajet equipped cars I've owned.

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1973 L-82 4 spd

Re: Anti Diesel Solenoid and starting (3/12)
 9/11/18 11:32am
F4Gary
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Grapevine, TX - USA

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1972 LT-1 convertible with factory air.


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It's been my experience with my anti-dieseling solenoid (which I use as a a/c compressor idle bump up solenoid) that it isn't strong enough to actually move the throttle linkage but is strong enough to hold it open once actuated.
So you turn the key on and pump the throttle to actuate the choke, and that also lets the solenoid pop out to where it should be.



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Re: Anti Diesel Solenoid and starting (4/12)
 9/11/18 12:14pm
73shark
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Overland Park, KS - USA

Vette(s):
1973 Orange Metallic Coupe (orig owner), L82, 4 spd (WR), PS, (A/C & PW (I installed from wrecked 73)), leather, AM/FM Stereo, ran with '65 FI unit earlier & will again some day.


Joined: 7/9/2003
Posts: 554

Good point. I forgot about that. I also use the solenoid as an idle speed increase for the A/C. I should have remembered that since I installed the A/C from a wrecked '73 myself.

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1973 L-82 4 spd

Re: Anti Diesel Solenoid and starting (5/12)
 9/11/18 12:32pm
Adams' AppleLifetime Member
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Duncanville, TX - USA

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#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas


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I agree wid Gary on this one...turn key on, then pump the throttle to set the solenoid(and the choke).
There are actually two different designs on these solenoids, and they both have different functions, design-wise. One is used to kick the throttle up with A/C engagement, and the other is more intended to be the anti-diesel, or throttle stop function. The anti-diesel solenoid's function is to hold open the throttle blades slightly once extended, so the throttle blades do not completely close. This is a result of Gov'ment emissions requirements. Emissions go sky high if/when the throttle is allowed to completely closed on deceleration. Holding the throttle open slightly keeps the emissions within the required limits. Of course...an open throttle tends to promote dieseling on a hot engine when the key is turned off, so it(the solenoid) looses power with the key off, returning the throttle blades to almost completely closed.
The other type solenoid, known as a "kicker", is designed to actually raise the engine rpm as the A/C is engaged, so this requires a solenoid capable of actually moving the throttle linkage....which most are not strong enough to do anymore. Seems the only type of solenoid available today is the weaker, anti-sneezle solenoid....which will require you to hold the throttle open a smidge after the key is turned on for it to hold the linkage at the pre-set rpm range.


While we're at it, if the choke is functioning properly, it should set the throttle on "high idle" the first time you press the pedal anyway. After that, the solenoid will have the idle speed duty.


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Re: Anti Diesel Solenoid and starting (6/12)
 9/11/18 4:59pm
NJAus
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, - Australia

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Currently own a white 1969 427 Big Block Coupe C3 Corvette


Joined: 6/6/2018
Posts: 30

I forgot to mention that I have swapped from the Quadrajet to a new Holley Carburetor with electric choke. There is a generic Holley solenoid being used as the anti dieseling solenoid. The solenoid is actuated via a relay when there is power going to the coil.
 
The Holley Solenoid is not capable of pushing the throttle just holding it from my reading.
 
As long as power is on, then the solenoid tries to actuate, as F4Gary mentioned power on and setting fast idle should actuate the solenoid and I can crank with my foot off the accelerator.
 
With the electric choke, I am guessing that is running off the accessory circuit? i.e. as long as the key is in the ignition it runs current to the electric choke to keep it open.
Re: Anti Diesel Solenoid and starting (7/12)
 9/11/18 11:16pm
F4Gary
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Grapevine, TX - USA

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1972 LT-1 convertible with factory air.


Joined: 8/26/2006
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Make sure you have a full 12 volts going to the electric choke.  I'm actually using the old anti diesel solenoid wire since my solenoid is not powered by the a/c clutch circuit.

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Re: Anti Diesel Solenoid and starting (8/12)
 9/11/18 11:35pm
NJAus
Former Member

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, - Australia

Vette(s):
Currently own a white 1969 427 Big Block Coupe C3 Corvette


Joined: 6/6/2018
Posts: 30

The choke definitely opens fully, so it would be getting the full 12V?
Re: Anti Diesel Solenoid and starting (9/12)
 9/11/18 11:47pm
73shark
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Overland Park, KS - USA

Vette(s):
1973 Orange Metallic Coupe (orig owner), L82, 4 spd (WR), PS, (A/C & PW (I installed from wrecked 73)), leather, AM/FM Stereo, ran with '65 FI unit earlier & will again some day.


Joined: 7/9/2003
Posts: 554

I'd recommend measuring it with a VOM and not take a chance. If you don't have one, Harbor Freight has coupons for them periodically for free with another purchase. No minimum on the other purchase either.

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1973 L-82 4 spd

Re: Anti Diesel Solenoid and starting (10/12)
 9/12/18 12:01am
NJAus
Former Member

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, - Australia

Vette(s):
Currently own a white 1969 427 Big Block Coupe C3 Corvette


Joined: 6/6/2018
Posts: 30

I was also wondering is high idle is totally independent of curb idle? i.e. changing curb idle shouldn't affect how much the blades open for fast idle.