Quadrajet question

[oborowsk]

Hi,
Just had my engine and 4bbl quadrajet rebuilt but having issues connecting some of the vacuum hoses (should have labeled them). Truck is a 86 C10 with 305 and CAL. emission. Question: Secondary choke pull-off, where does it get it's vacuum from. Is vacuum connected to some kind of temp. switch? If engine is cold, it shouldn't get vacuum, right? I have the vacuum hose routing diagram but still lost (will attach diagram). There are also a couple of vacuum ports on the back of the carb, one right next to break booster line (metal) on the lower part of carb and the other one up high. What do they connect to? I also have a hard time starting the truck. Once it gets warm, idles good but it seems to be flooding in the beginning. Again, I just had the carb rebuilt and adjusted to factory defaults. Any help is appreciated.

Olaf

[geezer#99]

The one on the back by the booster line is manifold vacuum for the vac modulator on your tranny or for your egr.
The port higher up is an air supply line for your choke.
The choke pull off gets it's manifold vac from the port at the top front passenger side on your carb. As soon as you start it the choke pull off should suction in and open your choke blade about 1/4 inch.

[beamn7]

85 and 86 California emissions are a one off. Our vacuum lines, etc are different from the norm... Only two years that had dual capacity accelerator pumps AND the mixture control solenoid as identified by the second connector coming out of the mixture control solenoid connector. Small port on the back of the carb at the bottom connects to the manifold differential pressure sensor mounted on the firewall. (looks just like a MAP sensor but functions opposite) The connector at the top of the carb on the back is the breather port for the EGR control solenoid. If you blow through the hose that connects there, you should get air out of the hose that connects to the EGR valve. (this was done to ensure there was no residual vacuum to the egr valve. One of those ca emissions things...) The third hose that connects to the EGR valve solenoid connects to the pass side front vacuum port at the bottom of the carb. As for the secondary choke pull off, it does connect to the thermal vacuum switch that is mounted on the pass side of the air cleaner which gets its vacuum from the fitting in the intake manifold behind the carb. Yes, it should have vacuum when the engine is cold. You and I have the same set up so let me know if you need pics or have any questions. Hope this helps.

[K5owner]

As beamn7 correctly stated that one goes to for all intensive purposes the MAP sensor. Or Differential Pressure sensor. It is what tells the computer to reduce timing when under heavy throttle. If it is not connected you will get knocking when going up a hill or accelerating heavily. I just replaced mine not too long ago. It should be a black plastic tube with rubber on the ends that connects to that port. Look on the firewall just above and to the left of the distributor. You should see a small black box with a weather proof connector and a hose coming from it. That hose goes to the red arrowed port.

[oborowsk]

Hi beamn7,
Glad there is someone out there with the same truck. Getting closer to figuring out the emission hose routing.
Question: See picture of TVS that is on the air-filter housing. Port 1 to port 2 is always open. Port 3 closes when I apply heat to body of TVS. What do each one of those connect to? Can you please briefly explain how yours are connected?
Question #2: EGR Solenoid. Port 2 to 3 is open with no voltage applied. If I apply voltage to the solenoid, 2 to 3 closes. I assume 2 goes to a vacuum source and 3 goes to EGR valve. Where does #1 go? #1 doesn't seem to be doing anything. No flow to 2 or 3 with voltage applied or not applied. Seems to be always closed. Other thing is when car is running, after a while solenoid seems to be "pulsing" or in other words makes fast clicking noise. Normal? I have another one from the junkyard, might swap it out and see what happens.
Thanks again for your help.

[beamn7]

No problem bud. On the TVS, the single port points towards the firewall and connects to the thermac valve under the air cleaner. The port marked "2" connects to the intake manifold vacuum source behind the carb and port 3 connects to the secondary vacuum break. On the EGR solenoid, port 1 connects to the top of the carb at the back. Port 2 connects to the pass side front of the carb for it's off idle vacuum source and port 3 connects to the EGR. As for the clicking, yes, that is normal but not at idle. If your TPS sensor is out of adjustment this will happen. With your idle speed set properly, turn the key on, engine off and probe the bottom and middle wire of the throttle position sensor (3 wire sensor on the drivers side front of carb) with a volt meter. (I made a jumper harness so as not to damage the factory wiring) For a 305 you should have .41v and a 350 should have .48 If it is above that, the ECM thinks you have the throttle depressed and begins pulsating the solenoid. This adjustment will also effect your mixture control solenoid. The adjustment is just behind the accelerator pump arm on the top of the carb. It takes a special tool to adjust and is very sensitive. Sometimes you can still get them from Thexton. Hard to find these days. I have a set I bought years ago off the snap on truck. You may be able to improvise something though...
Here is a kit that will work:
http://shop.advanceautoparts.com/p/t...ntent=22983648

Hope this helps.

[K5owner]

Great info right there beamn7.

[beamn7]

Thanks K5! I figure us CA guys stuck with the factory smog stuff need to share as much info on these as we can. Not many smog techs even know about these anymore!
Oborowsk, I stole your pic and added an arrow to show you where the hole is for the TPS adjustment. Hope this helps. By the way, I have family in Roseville and get up that way periodically. If you like, we can meet up next time I'm up there.

[oborowsk]

Wow, I am very impressed by the knowledge that is "still" out there. You are a great resource beamn7. I have come up with my own drawing that reflects what you have stated to make it easier for others running into the same problem. If you could, please verify and bless the PDF files. I did some research on how to adjust the TPS. I am going to order the tool you suggested but I am also ordering an OTC monitor 85 Model #3485 scan tool which should help me adjust the carb (great buy on Ebay for $22). I had the carb professionally rebuild on the East Coast, looks great but doesn't seem to be running perfectly. I assume the fine tuning has to be done on the truck, which I am going to do. I will take the carb apart again and drill out some of the plugs etc. to have access to the adjustment screws. If you have any other recommendation, words of caution, please let me know. I really appreciate your knowledge and willingness to share with the community. If you ever need to borrow the scan tool, let me know and I'll send it your way. The major thing now is to fine tune it and get it to pass SMOG. This is my youngest daughter's first car and I want it to run smoothly and be reliable. Engine has been rebuilt, interior re-done and almost ready to go. She has been patiently waiting for almost a year for it to be ready. Don't want to disappoint by baby if you know what I mean. Starting to love these Quadrajet carbs the more I learn about them.

[beamn7]

Looks good Oborowsk! Good job and good buy on the OTC monitor! As for drilling out the plugs, don't bother. By looking at the pics, your air/fuel plugs have been drilled out already. Our model carb has the plug for a "rich idle stop" adjustment but there is no adjustment screw as it has a built in rich stop limiter on the mixture control solenoid. (85-86 CA only again...) As for drilling out the plug for the "lean idle stop", that is preset with a special tool when rebuilding the carb to 1.304" The idle air bleed valve on top of the carb is preset using a special tool to 1.756" however, you can adjust this using your OTC monitor to a 50% duty cycle with the truck in closed loop at idle. (30 deg of dwell if you use a dwell meter set to the 6 cyl scale connected to the green plug in the engine harness near the distributor) Best way to tell if its in closed loop is the smog pump will be pumping air into the air cleaner rather than the exhaust manifolds. Many times these 'ol trucks will go into open loop at idle though. I have found that it is best to let it idle in open loop, leave the mixture control solenoid and idle air bleed valve at the preset adjustments and fine tune the mixture with the air/fuel adjustments at the front bottom of the carb. I start at 3 full turns out and go from there. Use a vacuum gauge and adjust out until you get your highest vacuum reading and then turn back in approx 1/8 to 1/2 turn.
I would do these steps in this order:
Set the timing to 6 deg (calls for 6 but can go plus or minus 3 deg under ca smog laws) with the 4 wire connector to the dist unplugged. Then plug the dist back in.
Set your idle rpm. (calls for 550 in drive but you can go plus or minus 300 rpm under CA smog laws) I run 650 on mine.
Then set the TPS voltage to .41v
Once this is done, then adjust the air/fuel screws if needed. Take it out for a drive after that and see how she does. Believe it or not, these old ECM's actually had a "learning" capability and would adjust slightly. Nowhere near like the ECM's do today but many times after making the adjustments and driving it 30 miles or so, you may see a difference....
Best of luck and let us know how she does!