Rochester Quadrajet 4v Solenoid - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Classics Fan · 01-25-2019, 05:55 PM

I have a 1971 Jimmy with original rebuilt 350 and A/C. Questions about the carburetor solenoid: first, is this an idle stop to prevent dieseling, or an idle increase for the A/C to prevent low idle stall?

When I start the engine, the solenoid plunger extends (sometimes, not every time) for a few moments then retracts. This action seems to happen irregardless of whether the A/C is in the or off position. The A/C belt was removed by the PO and I have never replaced it so I’m not certain whether the air works or not.

Where does the solenoid get its power, and what possible causes are there for it to only work momentarily, intermittently? I have the idle speed set using the designated screw. If the solenoid is for idle stop, then why is there also an idle speed screw?? Thanks in advance for any insight to help clear up my confusion.
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Classics Fan · 02-04-2019, 09:36 PM

Bump. Any Rochester gurus around? TIA!
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jaros44sr · 02-05-2019, 09:10 AM

I would call cliff rugles, googled it and all kind of info

Classics Fan · 02-06-2019, 07:00 PM

Quote:

Originally Posted by jaros44sr

I would call cliff rugles, googled it and all kind of info

I did my Google research before posting here and did again, but haven’t seen anything that answers my questions. Thanks for the Cliff Ruffles lead.
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jaros44sr · 02-06-2019, 08:10 PM

Quote:

Originally Posted by Classics Fan

I did my Google research before posting here and did again, but haven’t seen anything that answers my questions. Thanks for the Cliff Ruffles lead.
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sorry you misunderstood me , I was only referring to get the addy for Rugles. You might PM green monster, when I was working his truck we were discussing that solinoid, we didn't get very far

**pound41** · 02-07-2019, 10:01 AM

If you are talking about the plunger type solenoid that hooks on the carb with a bracket. I don't think that is the anti dieseling for the AC. I say that because I have 2 1971 Blazers. #1 doesn't have AC and it has the carb based solenoid but who knows.

Blazer #2 has AC. I will have to look and see if it has the carb based solenoid.
the fan switch and blower motor would only work on med.Which drives me crazy I checked all the grounds. Didn't fix the problem so I started replacing everything Heat and AC related. On my blazer down near the Cig lighter behind the dash it has a what I will describe as a relay mounted. The relay is very similar to the relay for the blower motor. The wires are different though. Anyway I found in my research that was a anti dieseling relay that was supposed to engage/disengage the clutch under load etc. This was a few years ago when I worked on it

Classics Fan · 02-07-2019, 02:01 PM

From everything I’ve been able to find and read on this subject, the solenoid is EITHER an anti- dieseling device (always activated with ignition “on” and deactivates with ignition “off”) or is only activated when AC is on. As an anti-diesel it allows the butterflies to fully close when the ignition is turned off. As an AC function it activates only when AC is turned on to increase idle speed to prevent low RPM stalling. This understanding and erratic behavior on my truck tleads me to the questions in my original post. If your non-AC Blazer has the solenoid as original equipment it must act as an anti-diesel. If you have the solenoid on both vehicles and are inclined to investigate further, let me know what you find! Anti- diesel on both, or only the non-AC and anti-stall on the other, or ....? My Jimmy runs great but my curiosity is piqued.
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JackB · 02-13-2019, 11:51 PM

The solenoid is 1971 only and its called a Combination Emissions Control (C.E.C) valve. It has electrical and vacuum connections. In addition to the valve (solenoid) there should be two relays on the firewall near the master cylinder.

A google search for 1971 CEC should answer any questions about how the system works. Most of the time its just removed.

Classics Fan · 02-14-2019, 11:22 AM

Quote:

Originally Posted by JackB

The solenoid is 1971 only and its called a Combination Emissions Control (C.E.C) valve. It has electrical and vacuum connections. In addition to the valve (solenoid) there should be two relays on the firewall near the master cylinder.

A google search for 1971 CEC should answer any questions about how the system works. Most of the time its just removed.

I think you hit the nail on the head. Thanks for the info!
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02-05-2019, 09:10 AM	#3
jaros44sr Registered User Join Date: May 2006 Location: Philadelphia, Pa. 19454 Posts: 9,421	Re: Rochester Quadrajet 4v Solenoid I would call cliff rugles, googled it and all kind of info __________________ Semper Fi...Uncle Sam, you da man All parts offered to help are free, unless otherwise noted Dont try this stuff in my build thread, unless you have 55 years of mechanical OTJ training SAFETY FIRST AS usual, off topic They say your mind goes second, can't remember the first Jim

02-07-2019, 10:01 AM	#6
pound41 Registered User Join Date: Dec 2002 Location: Northern Virginia Posts: 1,267	Re: Rochester Quadrajet 4v Solenoid If you are talking about the plunger type solenoid that hooks on the carb with a bracket. I don't think that is the anti dieseling for the AC. I say that because I have 2 1971 Blazers. #1 doesn't have AC and it has the carb based solenoid but who knows. Blazer #2 has AC. I will have to look and see if it has the carb based solenoid. the fan switch and blower motor would only work on med.Which drives me crazy I checked all the grounds. Didn't fix the problem so I started replacing everything Heat and AC related. On my blazer down near the Cig lighter behind the dash it has a what I will describe as a relay mounted. The relay is very similar to the relay for the blower motor. The wires are different though. Anyway I found in my research that was a anti dieseling relay that was supposed to engage/disengage the clutch under load etc. This was a few years ago when I worked on it

02-07-2019, 02:01 PM	#7
Classics Fan Registered User Join Date: Jan 2018 Location: Anacortes. WA Posts: 118	Re: Rochester Quadrajet 4v Solenoid From everything I’ve been able to find and read on this subject, the solenoid is EITHER an anti- dieseling device (always activated with ignition “on” and deactivates with ignition “off”) or is only activated when AC is on. As an anti-diesel it allows the butterflies to fully close when the ignition is turned off. As an AC function it activates only when AC is turned on to increase idle speed to prevent low RPM stalling. This understanding and erratic behavior on my truck tleads me to the questions in my original post. If your non-AC Blazer has the solenoid as original equipment it must act as an anti-diesel. If you have the solenoid on both vehicles and are inclined to investigate further, let me know what you find! Anti- diesel on both, or only the non-AC and anti-stall on the other, or ....? My Jimmy runs great but my curiosity is piqued. Posted via Mobile Device

02-13-2019, 11:51 PM	#8
JackB Registered User Join Date: May 2015 Location: Prescott AZ Posts: 199	Re: Rochester Quadrajet 4v Solenoid The solenoid is 1971 only and its called a Combination Emissions Control (C.E.C) valve. It has electrical and vacuum connections. In addition to the valve (solenoid) there should be two relays on the firewall near the master cylinder. A google search for 1971 CEC should answer any questions about how the system works. Most of the time its just removed. Attached Images

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01-25-2019, 05:55 PM	#1
Classics Fan Registered User Join Date: Jan 2018 Location: Anacortes. WA Posts: 118	Rochester Quadrajet 4v Solenoid I have a 1971 Jimmy with original rebuilt 350 and A/C. Questions about the carburetor solenoid: first, is this an idle stop to prevent dieseling, or an idle increase for the A/C to prevent low idle stall? When I start the engine, the solenoid plunger extends (sometimes, not every time) for a few moments then retracts. This action seems to happen irregardless of whether the A/C is in the or off position. The A/C belt was removed by the PO and I have never replaced it so I’m not certain whether the air works or not. Where does the solenoid get its power, and what possible causes are there for it to only work momentarily, intermittently? I have the idle speed set using the designated screw. If the solenoid is for idle stop, then why is there also an idle speed screw?? Thanks in advance for any insight to help clear up my confusion. Posted via Mobile Device

02-04-2019, 09:36 PM	#2
Classics Fan Registered User Join Date: Jan 2018 Location: Anacortes. WA Posts: 118	Re: Rochester Quadrajet 4v Solenoid Bump. Any Rochester gurus around? TIA! Posted via Mobile Device



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