Does 85 GMC 305 have O2 sensor ?
 

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:lol:.

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

Any help is appriciated.
Zac

Re: Does 85 GMC 305 have O2 sensor ?
 

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..

Re: Does 85 GMC 305 have O2 sensor ?
 

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.

Re: Does 85 GMC 305 have O2 sensor ?
 

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

Re: Does 85 GMC 305 have O2 sensor ?
 

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

Re: Does 85 GMC 305 have O2 sensor ?
 

Re: Does 85 GMC 305 have O2 sensor ?
 

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

Re: Does 85 GMC 305 have O2 sensor ?
 

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

Re: Does 85 GMC 305 have O2 sensor ?
 

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

Re: Does 85 GMC 305 have O2 sensor ?
 

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!!!!

Re: Does 85 GMC 305 have O2 sensor ?
 

What year did they start this computer controlled carb? My 84 don't have this
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Re: Does 85 GMC 305 have O2 sensor ?
 

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.

Re: Does 85 GMC 305 have O2 sensor ?
 

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

Re: Does 85 GMC 305 have O2 sensor ?
 

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...

Re: Does 85 GMC 305 have O2 sensor ?
 

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.

Re: Does 85 GMC 305 have O2 sensor ?
 

Here's my snake pit and E4ME Qjet :waah:
http://img67.imageshack.us/img67/5576/truck010ba9.jpg

Uploaded with ImageShack.us

Re: Does 85 GMC 305 have O2 sensor ?
 

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)


That thing looks brand new!! NICE

Re: Does 85 GMC 305 have O2 sensor ?
 

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?

Re: Does 85 GMC 305 have O2 sensor ?
 

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.

Re: Does 85 GMC 305 have O2 sensor ?
 

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

Re: Does 85 GMC 305 have O2 sensor ?
 

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

Re: Does 85 GMC 305 have O2 sensor ?
 

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)

Re: Does 85 GMC 305 have O2 sensor ?
 

Re: Does 85 GMC 305 have O2 sensor ?
 

Re: Does 85 GMC 305 have O2 sensor ?
 

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?