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Please explain carb on 84 Blazer

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blazer88

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I have an 84 blazer with starting issues, but that should be resolved tomorrow morning. The choke pull off was bad, that is getting replaced. I have worked with motorcycle carbs a lot, big and small, have rebuilt them and jetted them, I have also worked on a dirt old chrysler 383 with a 600 cfm Edelbrock standard card.

I know the 84 is a computer controlled carb, can somebody please explain how a computer controlled carb works. The mechanic said the computer is running at full lean. My question is how does a computer controlled carb run too rich when it is controlled by a computer? Is this a sensor that is dead or reading improperly. But back to my original question, how does a computer control carb work? I am unlearned when it comes to these. :confused: I know on a motorcycle if you are to rich or too lean you adjust air/fuel ratio and jet size. Besides on motorcycles I just run everything rich.
 
I have no idea. I have an 84 K5 also. My quadrajet went bad on me, I just replaced it with a Holley 570 street avenger (shoulda got the truck avenger though) but I did have to change the distributer cuz of the "computer" control or something like that. Otherwise I have no idea, I always wondered this my self since a carb is MECHANICAL and there are no O2 sensors, etc.
 
I found some information on it.

http://www.bc4x4.com/faqs/yj.cfm?cat=5&faqid=33

This site explains it a little bit, it almost sounds like an adjustable jet of a sort, but I could have gotten that wrong completely, hopefully somebody here will know how it works. Here is another question if anybody knows it, should I rebuild, replace with OEM rebuild, or replace with name brand Edelbrock, Holley, Etc?
 
If you figure out exactly which carb you have then you can determine the extensivity of the computer control system. It could be as basic as one function or it could have TPS, micture control, etc.....

I'm hating Q-jet's more and more.....they seem to work great when dialed in but really crap out when they get out of whack.

I'm not sure if my 86 is stock but it has electronic choke and vacuum advance distributor indictating no computer control. Are you sure yours is electronic? I thought those were only put on corvettes and higher end cars from the factory.
 
electronic

I have not looked at the stupid thing much, but i am pretty sure it does have some electronic mumbo jumbo on it. The computer said it was at "full lean", which indicates that there is some control on it. From what I have found this should have some "mixture control solenoid"

I will get it back tomorrow, with one problem fixed, and take it to another mechanic next week to get another problem looked at. I dont care if it runs at "full lean" as long as it runs.:doah:
 
mwwebmstr said:
If you figure out exactly which carb you have then you can determine the extensivity of the computer control system. It could be as basic as one function or it could have TPS, micture control, etc.....

I'm hating Q-jet's more and more.....they seem to work great when dialed in but really crap out when they get out of whack.

I'm not sure if my 86 is stock but it has electronic choke and vacuum advance distributor indictating no computer control. Are you sure yours is electronic? I thought those were only put on corvettes and higher end cars from the factory.
Click to expand...

I've also got an '86. Mine is all stock at the moment. All of the carb'd engines have vacuum advance on the distributor from the factory. If you do some research on the history of the Quadrajet, you'll find that the electronic controls were added to the Quadrajet beginning in 1980. (see the link in my previous post) From that point on, the electronic Quadrajet (or Dualjet for smaller engines) appeared on just about every GM vehicle until they were phased-out and replaced by fuel injection. The switch to fuel injection took place at different times on different makes and models. For GM trucks, 1986 was the last year for the carburator.
 
rpinkstn said:
I've also got an '86. Mine is all stock at the moment. All of the carb'd engines have vacuum advance on the distributor from the factory. If you do some research on the history of the Quadrajet, you'll find that the electronic controls were added to the Quadrajet beginning in 1980. (see the link in my previous post) From that point on, the electronic Quadrajet (or Dualjet for smaller engines) appeared on just about every GM vehicle until they were phased-out and replaced by fuel injection. The switch to fuel injection took place at different times on different makes and models. For GM trucks, 1986 was the last year for the carburator.
Click to expand...


Close, but no cigar. There is no vac. advance on my 85. The distributor is computer controlled advance. K5 are different than the trucks. And Ca. K5's are a bit differentt than K5's for other states

OP, does your carb have the 3 prong plug coming out of the top of the carb? Forward center of the body? If it does, then you have the true CCC. If you find someone here in Ca. that will work on them please let me know. Mine needs some help. Everyone I've talked to won't deal with it, and I'm not good with carbs.
 
rockink5 said:
Close, but no cigar. There is no vac. advance on my 85. The distributor is computer controlled advance. K5 are different than the trucks. And Ca. K5's are a bit differentt than K5's for other states

OP, does your carb have the 3 prong plug coming out of the top of the carb? Forward center of the body? If it does, then you have the true CCC. If you find someone here in Ca. that will work on them please let me know. Mine needs some help. Everyone I've talked to won't deal with it, and I'm not good with carbs.
Click to expand...

there still should have been a vacuum advance on the distributor...when mine was stock, it also had the computer controlled advance on the distributor, but also had vacuum advance too...the computer advance just advances or retards the distributor using feedback from the knock sensor
i also just looked at my manual, and it shows all years through 86, and all makes having vacuum advance
 
pictures coming soon

When I get it back from the mechanic and a dry day, or moment, I will snap a picture of the carb, and the distributor. I was also going to try replacing some smaller things on my own. I just need to figure out how to post pictures. I will probably just put them on photobucket or whatever. thanks.
 
djtejas said:
there still should have been a vacuum advance on the distributor...when mine was stock, it also had the computer controlled advance on the distributor, but also had vacuum advance too...the computer advance just advances or retards the distributor using feedback from the knock sensor
i also just looked at my manual, and it shows all years through 86, and all makes having vacuum advance
Click to expand...


No vac. advance on Ca. models of 1985 on K5's. If you look up the UJH (Ca.) routing schematic of the the hoses, you will notice no vaccum line to the distributor. I went through this when I ordered this one through Performance Distributors. Also, I physically just went out and check it, just to make sure i'm not loosing it.. No v/a. I'd post a pic of it but its to dark in the hangar.
 
Ya'll wait till you have to work on a variable venturi ford POS carb, those suck donkey balls!
 
The CCC (E4M series) uses a TPS (in the carb) MAP sensor and O2 sensor to determine what adjustment the mixture needs. The control module controls mixture by varying the pulse-width to the mixture control solenoid. This solenoid is acting on the primary metering rods in the carb, moving them up and down, sort of like varying the rod size in real time. The much-hated CCC was not used on 49-state trucks, only California.

By "full lean", does he mean that the measured O2 is lean or that the pulsewidth to the MCS is at a minimum? With a digital multimeter you can measure the output of the O2 sensor and see if it is grossly lean or rich. Troubleshooting the sensors is the same as for a FI vehicle.

If your only problem is with starting, I would focus on that instead of a general problem with the control system. Working on the choke, pull-off, etc. is probably in the right direction.
 
rockink5 said:
No vac. advance on Ca. models of 1985 on K5's. If you look up the UJH (Ca.) routing schematic of the the hoses, you will notice no vaccum line to the distributor. I went through this when I ordered this one through Performance Distributors. Also, I physically just went out and check it, just to make sure i'm not loosing it.. No v/a. I'd post a pic of it but its to dark in the hangar.
Click to expand...


i looked up the hose schematic again...you are right, everything EXCEPT California has vacuum advance...that must be have been a PITA finding parts the first time you had to deal with the distributor...i would have never thought there was no vacuum advance...of course, ive never had to deal with a Cali vehicle
 
djtejas said:
i looked up the hose schematic again...you are right, everything EXCEPT California has vacuum advance...that must be have been a PITA finding parts the first time you had to deal with the distributor...i would have never thought there was no vacuum advance...of course, ive never had to deal with a Cali vehicle
Click to expand...

ok, I stand corrected. I don't have any personal experience with Calif. emission vehicles, but I do know there's a lengthy history of them having a different configuration than cars produced for the other 49 states. still, knowing how an HEI distributor works, I'm curious to know how the Calif. version is capable of getting enough total advance without a vacuum advance system.
 
Fixed and running

The choke pull off was bad, that is replaced and he adjusted it this morning, he also replaced the coolant temperature sensor, because it was badly falling apart. The mechanic kept the pieces to show them to me, I liked that, most mechanics I have encountered do not do that. It was running at full lean yesterday, dwell was 55, now dwell is 40. It is a California vehicle, we are all cursed here with smog. I used to live in Humboldt County(Northern California) and you smogged your vehicle once, and one time only, as long as you did not sell it. I am in Fresno County now, and you have to smog every two years. It passed when I bought it, I have two years to see if it will pass again.
 
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