1984 GMC Computer brain
 

Hi all!
I have a 1984 GMC with a 305/700R4 factory an the truck has the brain unit controlling the emissions and such.
What is known about the computers on these and will I need to consider ever needing a back up unit if this one ever fails!
What should I know about these computers on these trucks?
Thanx!
:help:

AFAIK, there is no computer on these trucks through '86. The closest thing to one is the ESC (electronic spark control) on the distributor to stop it from pinging. Most folks just replace it with a standard HEI, which is what I plan to do.

Slonaker

Ahh, so that is what this thing is! It is above my glove box, hooks into the HEI with a 4 plug lead, but I am in california, I am unsure I can pass smog if I change this!
Suggestion?
Thoughts???
:confused:

Sent you a PM

If it starts acting up it will keep you from passing smog. GM's fix for it was to eliminate it when it when bad.

I dont think that I can eliminate it from the Calif smog check out here...Thoughts???

Only the trucks sold in Cali have the Computers, I have an 83 with the same 305/700R4 setup with the Computer and NO it won't pass a smog check without it, I have the 4 wire plug to the HEI and also the E4ME electronic Q jet :(
John

My 85 has the "retarded" computer. From what I understand it has a knock sensor in the block, when it detects pinging it retards the timing by delaying spark pulses somewhere along the line in the distributor. I bought my truck with the computer jumped out so the pulses are never delayed. My truck pings sometimes though.

Mike

malo, no... trucks sold outside of Cali have the computers too... my 82 has it and it was a Texas truck...

I stand corrected, was going off the Chevy truck factory repair manual which states that only trucks sold in Cali have the Computer emissions package :crazy:
John
83 Silverado
KN
HYPERTECH
FLOWMASTER

Malo, you will learn that chevy did alot of weird things with these trucks.. i could be wrong as well... but i see alot of ESC trucks for them all to have been sold in cali...

I don't consider the ESC to be a computer. It is just a knock sensor and a way to retard the timing. Computer controlled vehicles do much more than that.

I think that is where the confusion comes from.

Slonaker

i dont consider the ESC to be a "computer or ECM" either... but as far as i know its the only "computer" that was on these trucks until like you said... 87..

Okay guys to clear this up i,m taking all this info right out of the GM Light Duty Truck 10-30 Series Shop Manual...

COMPUTER COMMAND CONTROL SYSTEM
CALIFORNIA ONLY
The (SYSTEM) in California is an electronically emission system that controls:
Fuel delivery(E4ME electronic Qjet)
Air Injection Reactor(AIR)
Evaporative Emission Control(EEC)
Electronic Spark Timing(EST)
Torque Converter Clutch(TCC)
This system monitors various engine/vehicle operating conditions and using this information can control engine related systems thereby making constant adjustments to maintain good vehicle performance under all driving conditions while allowing the catalytic converter to effectively control exhaust emissions.
ELECTRONIC Control Module(ECM)
The ECM located in the passenger compartment, is the control center of the Computer Command Control System.
The ability of the ECM to recognize and adjust for vehicle variations(engine transmission,vehicle weight,axle ratio,etc) is provided by a removable Calibration Unit(PROM) that is programmed to tailor the ECM for the particular vehicle. There are specific ECM/PROM combinations for each specific vehicle and they are not interchangeable.
The ECM also performs the diagnostic function of the system, recognizing operational problems, alerting the driver through the "CHECK ENGINE" light and storing a code or codes which identify the problem areas to aid the technician in making repairs. :crazy:
I have this system in my truck and it works, in my 22 years of ownership it hasn't failed a Smog check yet, granted it isn't built for performance but as my everyday driver she runs great but when that time comes, if ever, and she's past having to do smog tests you can bet a lot of this stuff will be gone :metal:
John
83 Silverado
KN
HYPERTECH
FLOWMASTER

To bad you live in the land of Smog pigs. The computer on the 84 trucks is limited on it's abilities, so I eliminated mine completely. My unit was replaced by an earlier style HEI unit and that solved all of my problems. The 700R4 in m y truck has the lock-up convertor eliminated for replacement by a 2400 stall unit. I get good mileage for a vehicle that is pushing over 400 Hp, which is at 15 MPG.

Ok, well my GMC is a 1984 fleet order that has this stuff. It is the rarer version as it is a Federal truck; only having smog on the one side of the exhaust system.
I can feel the variations in my performance from this thing
If I remove the electronics from it by using a non-emissions controlled HEI, will it mess up the stuff that is connected to it in the loop??? :confused:

If you remove the computer controlled distributor on this vehicle, at the age that it is, I believe that the tranny and everything will work. I ran my 84 GMC for quite some time with the tranny as the only thing that was connected to the computer. My carburetor had been changed out early in it's life and the tranny was connected for lockup only. ZIf you still have the computer controlled carb, then it may throw a "code" if it doesn't get a feed to the distributor. My bet is that the computer technology is so antiquated that it would not miss the distributor.

RPO keep us updated on your Mods as to how you get around the Snake pit :metal:
John
CentCal

Ill try the HEI non ECM but I am unsure how the rest will react! :confused:

What he said....

CCC...what a wonderful brain child they had with this early way of getting legal with the epa. The ccc carb is one pricy unit if anything should fail not to mention the maze of vacum lines and vacum operated thermal switches....

Problem is you are from cali and the smog nazi's will catch you if you unhook everything....

I grew up in socal and lived that nightmare....

Your only hope...use an lmc catalog or such to decode your vin and make sure there is nothing pointing to cal emissions...then make the oem emissions decal go by by and install a fed version decal that they sell and buy that a like make model manual from ebay (genuine helm) as they can't argue with the factory and carrying the bible with me stopped an argument every time...

Or scrap it all and install tbi from turbocity.com....orange county i believe....if the swap is complete and they can talk with it they will pass you.

just some ideas..

DW

how many wires go into the carb? if its a federal emissions truck you should have 2 just above the fuel inlet, and one at the choke. this is NOT a CCC carb, it simply runs 12v through a coolant temp sensor to work a dual capacity accelerator pump. with 12v to it, it shoudl work just as an old school QJet would, without the 12v, i believe it richens the mixture to aid in cold start situations. if you have any sort of 4 wire connector on it, its CCC.

Correct, mine is an 83 Texas truck and it had the 305/700r4 and the ECM also

ESC controller, there is no ECM.

The ESC is not the metal cased box behind the glove box, the ESC has a black plastic case and is usually mounted on the back of the ECM, the metal cased box is an ECM, a very early and crude one but it is, it even has a 122XXXX number that all the early original ECMs have (for instance later trucks w/ tbi use 1227747...don't remember the # on mine)

If you have an ESC knock controller you also have an ECM as the ESC always reports knock to th ECM, which in turn registers the knock counts and signals the EST (module in distr) to puyll back timing in 7 deg. steps untill no knock counts are registered. The box used w./ the electronically controlled quadrajet on the 305 IS an ECM, even though it does not directly meter the fuel delivery it does adjust the primary metering rods