Idle-stop (Anti-diesel) Solenoid

[Lynn S.]

Page195 of the most recent TIMJG covers the Idle stop solenoid. It states "When the applications use an idle-stop solenoid, it is mounted to the carb base...". The included phots focus on a, 1975 - L 82, 1976 - L 48 and 1977 - L 48. My 1975 is an L-48 with C-60 and 4 speed. Does my application call for the solenoid to be mounted, or not mounted to the carb assembly. Thanks in advance for everyone's assistance. Lynn Skipper

[Mark E.]

Re: Idle-stop (Anti-diesel) Solenoid

Lynn,

Perhaps other designs are out there, but every idle solenoid I've noticed of this vintage is mounted to the body (fuel bowl) of the Q-jet.
There should be a mounting post and threaded screw hole on the front facia above the left idle screw.

[Russ S.]

Re: Idle-stop (Anti-diesel) Solenoid

You are correct Mark. The 73-74 guide should not use the word base on page 194.

[Jimmy P.]

Re: Idle-stop (Anti-diesel) Solenoid

Page195 of the most recent TIMJG covers the Idle stop solenoid. It states "When the applications use an idle-stop solenoid, it is mounted to the carb base...". The included phots focus on a, 1975 - L 82, 1976 - L 48 and 1977 - L 48. My 1975 is an L-48 with C-60 and 4 speed. Does my application call for the solenoid to be mounted, or not mounted to the carb assembly. Thanks in advance for everyone's assistance. Lynn Skipper

Hi Lynn,
You won't need to worry about where to mount the solenoid on your 75L48. It didn't come from the factory with one. Don't ask me why, thought it might have something to do with HEI ignition staring in '75, but don't think we ever answered this while working on the revision. You mentioned the photos ( page 194) we used in the manual... the 75 L82- note there isn't an anti diesel solenoid on that engine. Also none on the 76 L48, but it shows up again on the '77 L48 on page 195. It is also used on the 76 L82's. We tossed around the theory that perhaps after '75 when it was used again... it's purpose was different. Instead of preventing dieseling it was now used to set curb idle speed, as directed on the Emission Labels of the cars with it! The footnote on page 195 was added for this very reason, I'm pretty sure! Sorry for any confusion here.. made a note to be more specific that it wasn't used in 75
Heres a photo of an original 75 L48 without the solenoid.
Hope this helps!

[Tom R.]

Re: Idle-stop (Anti-diesel) Solenoid

Jimmy does a nice job of summarizing the applications for the idle-stop solenoid. We show typical but stopped at accounting for all applications.

Understand that during this period, Chevrolet (and for that fact all manufacturers), were, experimenting with emission controls, racing to meet emission control requirements. Our work was to figure this out as we wrote the revision and why we incorporated footnotes for the curious reader. Dave McLellan notes this in his book while another book on the subject Cleaner Cars: The History and Technology of Emission Control Since the 1960s by Robert Mondt is another source that details the march toward emission control. The case in point is the delayed production of the 75 L82 option (we do not see L82s before 1975) due to it not meeting emission control requirements.

[Lynn S.]

Re: Idle-stop (Anti-diesel) Solenoid

Thank you all, Mark, Russ, Jimmy and Tom. This makes moving forward a lot simpler. I have a correct solenoid, but we were wondering if it should be mounted. The boss on my correct carb is not threaded and the TIMJG did not have a photo of a '75 L48. Thanks again for everyone's help and explanations.

[Duke W.]

Re: Idle-stop (Anti-diesel) Solenoid

Higher idle speeds lower idle emissions, but may cause "run-on" when the ignition is switched off. My '72 Vega GT had an idle stop solenoid, and the recommended solenoid idle speed was 1200. Well, that didn't last long with me.

With the advent of catalysts, beginning in 1975, relatively low idle speeds could be achieved and still meet emission standards. High overlap cam engines like the L-82 require higher idle speeds for acceptable idle quality compared to low overlap cams making them more susceptible to run-on, so that's probably the reason why in some years the L-82 had one, but not the base L-48.

Dave McClellan discusses in his book that it was a constant struggle in the seventies to meet ever tightening emission standards, which is the primarily reason for all the detail configuration changes on what were basically the same engines through most of that decade.

Duke

[Lynn S.]

Re: Idle-stop (Anti-diesel) Solenoid

Thank you for your reply Duke. I appreciate your explanation regarding the idle speed issues and emissions. Have a great week. Lynn

[Brad Hillhouse (37766)]

Re: Idle-stop (Anti-diesel) Solenoid

Lynn -

Here is a photo of my "crappy" 1975 L48 M40 C60 with 643 original miles.

Happy to help with photos of anything else you may need.

20221212_103719.jpg

Brad

[Lynn S.]

Re: Idle-stop (Anti-diesel) Solenoid

Thanks Brad for the pic. Have a great week. Lynn

[Mark E.]

Re: Idle-stop (Anti-diesel) Solenoid

Brad,

643 miles on your '75! I'd like to hear its story.

Others,

Go to Brad's website and click on "Waffle House" for an inspiring story.

[Tom R.]

Re: Idle-stop (Anti-diesel) Solenoid

Here is a photo of my "crappy" 1975 L48 M40 C60 with 643 original miles.

Is that an original factory present idle-mixture screw cap? (The black thingy)

[Brad Hillhouse (37766)]

Re: Idle-stop (Anti-diesel) Solenoid

Is that an original factory present idle-mixture screw cap? (The black thingy)

Yes, it has both of the black plastic idle screw caps still factory installed.

Brad

[Paul B.]

Re: Idle-stop (Anti-diesel) Solenoid

...nice to see a '75 L-48 automatic with an A.I.R. pump as over the years have been in a few arguments that someone else said otherwise.

Brad, is your car a "California Emissions" car or Federal that you can tell? Should say on emission sticker?

[Brad Hillhouse (37766)]

Re: Idle-stop (Anti-diesel) Solenoid

...nice to see a '75 L-48 automatic with an A.I.R. pump as over the years have been in a few arguments that someone else said otherwise.

Brad, is your car a "California Emissions" car or Federal that you can tell? Should say on emission sticker?

Paul -

It was ordered new in Iowa for the dealer to keep as his personal Corvette.

It sat in his showroom from June 1975 until the great GM shutdown of 2008 closed all the small town dealers.

Emission label AS Code standard Federal emissions not California.

20221213_174933.jpg

Brad