Does 85 GMC 305 have O2 sensor ?

[Blue71LWB]

I have searched , but have found conflicting answers.
A friend has a 85 GMC that's running super rich all of a sudden. It has the electronic quadrajet , but does this mean it will have an O2 sensor? I'm his mechanic by default since I sold him the ride.

Also what does the ported vacuum swith on top of the thermo housing control ?

Any help is appriciated.
Zac

[CaliDude76]

As far as the O2 sensor goes... is this truck set-up for emmisions.. i.e smog pump.. tubes.. Check Engine light?... If you want to hunt the sensor down,.. look on the exhaust pipes just under the manifold.. thats where they usually are.. mine is anyway..

[irishman999]

I have never herd of anything carburated using an o2 sensor. The fuel should be controlled by the metering rods. The thermal vacuum switch to my knowledge will block vacuum until the engine is warm, on my engine it looks like it blocks vacuum to the choke pull off on the carb and keeps the secondaries from opening.

[nbpro]

Pretty sure the 85’s were CCC <computer control command> which do in fact have a really simple computer, electronic idle mixture, o2 sensor, etc Check your exhaust work for an 02 sensor. If you find one, you have CCC. http://www.rockauto.com/catalog/x,ca...28H%2529%2BOHV

[gchemist]

Yes, some California models had them. My factory 83 manual has wiring for an O2 sensor on some models.

[C-10 simplex]

i would say yes, it has an Oxygen sensor; HP's Rochester Carburetors is a good book to get in general.

If yer too cheap to buy it---which is totally understandable you could utilize googlebooks:

Pls scroll down and refer specifically to pgs 58-59:

http://books.google.com/books?id=DwU...page&q&f=false

Also, here is another link that i think is good concerning CCC, oxygen sensor etc.:
http://www.robertpowersmotorsports.com/CCC.html

[irishman999]

Awesome, i had no idea. What exactly does the computer control on the carb, is there a servo or something?

[MalibuSSwagon]

CCC systems generally have an O2, my 83 Malibu did. Typically in the right head pipe

[Slonaker]

AFAIK, on trucks, it would only have an O2 sensor if it had California emissions. My '86 did not have one. The "computer" on mine is just a knock sensor and a distributor with ESC. Nothing more.

Slonaker

[CaliDude76]

California is really lame about the whole emmisions thing.. What Cali trucks were required to have,. completely restricts the power.. And you really can't do too much else, as far as high performance, that's beyond emmisions to better it,.. they have to remain the way they came from the factory in order to pass.(as far as pump, plumbing, working C.E.L, and so on) if the C.E.L. light doesn't work,.. out you go, and dont come back till it does.. or take out a small loan to have it diganosed and fixed...or if it's stuck on... same deal.. they won't touch it

What else is messed up is a lot of these "Smog" guys dont really know how to, or are willing to tinker with the q-jets to get em to pass.. they're so use to the electronically controlled.. set-ups that are easy to test and send em out... like a Jiffy-Lube.

Last year, it took dude a whole day to test and adjust, and test again to get it to pass..

California Emmisions Laws SUCK!!!!

[3r!c84]

What year did they start this computer controlled carb? My 84 don't have this
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[irishman999]

Originally Posted by Slonaker

AFAIK, on trucks, it would only have an O2 sensor if it had California emissions. My '86 did not have one. The "computer" on mine is just a knock sensor and a distributor with ESC. Nothing more.

Slonaker

Thats what my truck has also, I keep seeing post on here mentioning computer controlled quadrajets. The o2 sensor is going to detect the right mixture of fuel and air and send a signal to whatever it is metering the fuel. So the electronic pulse goes from the o2 sensor to the vacuum operated mechanical carburator and then what happens?

Could someone explain what the unit poking out of the top of the carb is? Its got a plug for a couple wires, it looks like a cylinoid.

[irishman999]

Just hit me, the o2 censor is just there to turn on the "check engine light".

[CaliDude76]

Originally Posted by irishman999

Thats what my truck has also, I keep seeing post on here mentioning computer controlled quadrajets. The o2 sensor is going to detect the right mixture of fuel and air and send a signal to whatever it is metering the fuel. So the electronic pulse goes from the o2 sensor to the vacuum operated mechanical carburator and then what happens?

Could someone explain what the unit poking out of the top of the carb is? Its got a plug for a couple wires, it looks like a cylinoid.

Your carb look like this?

With a rat's nest full of vacuum lines??... (zip-ties have become my new best friend..lol)

BTW.. that automatic cold choke set-up is a pain in the butt!! to get right... either to high, or won't activate...

[irishman999]

Originally Posted by CaliDude76

Your carb look like this?

With a rat's nest full of vacuum lines??... (zip-ties have become my new best friend..lol)

BTW.. that automatic cold choke set-up is a pain in the butt!! to get right... either to high, or won't activate...

Yea, its pretty close to mine. my secondary pull off is on the same vacuum pod as the choke pull off.

My choke is all screwed up too, I never drilled out the rivets to adjust it when i did my rebuild and apparently its not adjusted right. I finally had to remove the idle step up cam from the linkage so it would idle down.

[Malo83]

Here's my snake pit and E4ME Qjet


Uploaded with ImageShack.us

[CaliDude76]

Originally Posted by irishman999

Yea, its pretty close to mine. my secondary pull off is on the same vacuum pod as the choke pull off.

My choke is all screwed up too, I never drilled out the rivets to adjust it when i did my rebuild and apparently its not adjusted right. I finally had to remove the idle step up cam from the linkage so it would idle down.

Yeah, If i even turn the cold choke screw.. like a quarter turn.. not even that, it bumps up the fast idle, and won't come down.. if i go a quarter turn down the other way..too little..( I can never find that happy-medium adjustment spot...)... but somedays it'll idle nice and high in the mornings till i goose it down...sometimes if i'm lucky it'll kick down by itself... and somedays.. it's like pulling teeth to get it to stay on, and have to nurse the throttle a bit... but once it's warmed u good...(and they're adjusted right w/no vacuum leaks).. sucker will fire up all day every time... WOOM!! in like half a starter click...(I love firing it up at gas stations and such,.. heads turn when this' ol Chevy kicks right over)

Originally Posted by Malo83

Here's my snake pit and E4ME Qjet



Uploaded with ImageShack.us

That thing looks brand new!! NICE

[irishman999]

Originally Posted by CaliDude76

Yeah, If i even turn the cold choke screw.. like a quarter turn.. not even that, it bumps up the fast idle, and won't come down.. if i go a quarter turn down the other way..too little..( I can never find that happy-medium adjustment spot...)... but somedays it'll idle nice and high in the mornings till i goose it down...sometimes if i'm lucky it'll kick down by itself... and somedays.. it's like pulling teeth to get it to stay on, and have to nurse the throttle a bit... but once it's warmed u good...(and they're adjusted right w/no vacuum leaks).. sucker will fire up all day every time... WOOM!! in like half a starter click...(I love firing it up at gas stations and such,.. heads turn when this' ol Chevy kicks right over)

Mine is so far off when i would start it the engine would race to about 4k rpm, Then i would have to pop the hood and reach into the choke assembly and manually move it to the lower step so it would idle down. After it was warm everything was fine. After 1000 miles it started sticking on high idle just driving around town and warm.

That Carb does look brand new, does anyone know what the blue electronic plug unit on the top of it is?

[Malo83]

The blue plug goes to the Mixture Control Solenoid, mounted in the float bowl it controls the air and fuel mixture in the Primary bores.

The carb is a 7yr old rebuild, just gave the truck a tune up and sprayed the carb down with Gumout.

[irishman999]

What controls the solenoid? Im getting erratic performance out of my carb and wondering if this solenoid is causing it.

[Slonaker]

Originally Posted by irishman999

Thats what my truck has also, I keep seeing post on here mentioning computer controlled quadrajets. The o2 sensor is going to detect the right mixture of fuel and air and send a signal to whatever it is metering the fuel. So the electronic pulse goes from the o2 sensor to the vacuum operated mechanical carburator and then what happens?

Could someone explain what the unit poking out of the top of the carb is? Its got a plug for a couple wires, it looks like a cylinoid.

I can't say what the plug on yours is because you are so close to CA that you might have a CA emissions truck. On mine the plug is (well. was...) not a computer control. I think it was related to the accelerator pump.

People often assume it is a computer controlled quadrajet because it has a plug, but it is not. Apparently on CA emissions trucks, they are computer controlled and have a check engine light, computer controlled carb, and an O2 sensor. Mine has none of those, and never did.

Slonaker

[CaliDude76]

Originally Posted by Slonaker

Apparently on CA emissions trucks, they are computer controlled and have a check engine light, computer controlled carb, and an O2 sensor. Mine has none of those, and never did.

Slonaker

Yes Mr. Slonaker,.. you are correct.. unfortunately mine has all that emmisions crap,.. and will have to until Cali pushes up the exempt date.. currently , I believe, it sits at 1976 on down, doesn't need smog..

.. and they couldn't put the check engine light in a more conspicous spot??? LOL (smack-dab in the middle of my cluster... talk about a bad afterthought)

[C-10 simplex]

Originally Posted by irishman999

Awesome, i had no idea. What exactly does the computer control on the carb, is there a servo or something?

i think the computer only controls the metering rods on the carb. It also "looks at" where the throttle is at all times.


2) Also, we have to clarify-----just because a truck has an ESC distributor does not mean it definitely has CCC; Yes esc requires a computer, but the esc system alone is a totally different computer system from CCC. However, a CCC truck/car might also have ESC to confuse the issue further..............

[C-10 simplex]

P.S. Right now, i think the blue plug thing is the mixture control solenoid IF the truck has CCC. If the truck is an 85 or 86 model AND DOES NOT have CCC, then it's a dual capacity accelerator pump. But apparently, a truck could be an 85 or 86 model AND have CCC AND dual capacity accelerator pump AND a mixture control solenoid AT THE SAME TIME. Confusing? It's the GM way.

i got the info on pg. 64 of Rochester carburetors by Doug Roe. i think he's a former gm engineer or something.

[irishman999]

Originally Posted by C-10 simplex

P.S. Right now, i think the blue plug thing is the mixture control solenoid IF the truck has CCC. If the truck is an 85 or 86 model AND DOES NOT have CCC, then it's a dual capacity accelerator pump. But apparently, a truck could be an 85 or 86 model AND have CCC AND dual capacity accelerator pump AND a mixture control solenoid AT THE SAME TIME. Confusing? It's the GM way.

i got the info on pg. 64 of Rochester carburetors by Doug Roe. i think he's a former gm engineer or something.

Im going to have to pick up that book, vacuum seems to move the metering rods fine, i wonder why they would make it computer controlled?