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Author Topic: 1981 Formula Computer controlled carb and ignition problems.  (Read 274 times)

TimBarb

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Hi. I recently purchased a 1981 formula with about 95000 miles on the clock. The car was stored indoors for about 14 years . It was started and moved about every month or so, but was not driven on the road on any trips. It has the 4 speed with the 305 chevy engine. I had it shipped from Oregon to Illinois. I performed all the usual maintenance items--oils, filters, gear lube etc. The car started started and ran, but rough.-I changed  the cap, the rotor, plugs. plug wires, air and fuel filters.-Cleaned the carb. Ran a bit better but still a little rough. Exchanged the carb for a rebuilt unit .Replaced the fuel pump. Had new true dual exhaust installed (deleted the cat). Replaced all the vacuum lines. The car has a backfire through the exhaust (mostly on deceleration and in between shifts) and appears to be running very rich--noted a wet soot actually deposited under the exhaust tips on the concrete floor and could smell the gas vapor. I noted no cracks in the exhaust manifolds and the exhaust is new. The only thing i have not done is check the timing.  The car starts well, and will run ok , but is inconsistent like the computer controlled carb is not receiving proper input signal.--Then the carb will either lack fuel and try to stall or will load up and run rich with the backfire. Really frustrating!!! I'm really considering pulling the computer controlled carb and distributor, installing a standard vacuum advance HEI , and no-computer  carb. Looking for input on best way to go. Im guessing i would need a carb from a 1980 model with 305.If anyone else has had this [problem, please let me know what was your solution, and if it was to delete the computer controlled items, please let me know what part numbers I would need. ALSO--i was unable to locate info on how to use diagnostic read out on check engine. -Everything I found was for OBD II. I know there is a way to"jump across " 2 OBD port terminals to read the code via flashing check engine lights, but i could find no info on which pins to jump. Thanks in advance for any help!!!

firebirdparts

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Re: 1981 Formula Computer controlled carb and ignition problems.
« Reply #1 on: June 23, 2020, 02:44:51 PM »
Welcome to TAC!

I have certainly owned a bunch of OBD "one" stuff over the years, but not anymore.  You can get error codes by blinking, but any sort of sensor testing will have to be brute force method.  They had diagnostic tools back then, and the 301 turbo guys actually may have some that they share, but I don't know.  The 1981 305 is very similar in the controls.  In fact, the system was used GM-wide in 1981 on everything. Be open to finding people who know how it all works.  Even the knock sensor was used on a lot of Chevrolets, but I don't know if that applies to you.

I will just throw this out there:  The distributor advances the timing based on a voltage signal coming from the ECU.  It's an analog bit of information, so it has to be translated on both ends, and so there are plenty of reasons why it might be wrong.  The timing light won't know the difference, so that's good.  Also, you can throw the distributor away and use old-timey advance and you'll be happy with that. So no big deal there.

About 90% of the carburetor is still just a carburetor.  The computer has only modest control over it.  We have a lot of carb problems discussed here.  It's not really all that different from a carburetor in the 1950's, and if the ECU goes totally dead, it's really not affected terribly.  If you bought a carb from an auto parts store, then that would automatically worry me.  A Q-jet has many adjustments and you have to set up all that.  Getting the choke working is critical and we've had 10,000 posts on that.  The choke has godlike power over metering.  When you are troubleshooting, the engine needs to be at normal operating temperature and the choke needs to be fully open.  These old cars wouldn't go into closed loop until 180 degrees F. 

You may need to avoid emissions equipment confusion.  The heat riser valve needs to open; the EGR valve needs to stay shut.  Do they work?   I don't think that is your problem, but I would certainly want to know if they work.  The heat riser valve on a 305 seems a little "overwrought" to me.
« Last Edit: June 23, 2020, 02:51:49 PM by firebirdparts »
I want to be like Paul Kenny when I grow up
Joe Bays
1977 Y82 4-speed (red interior)
1978 Skybird 350
1978 Redbird 305
1979 Redbird 301 4-speed
1992 Lincoln Mark VII LSC/SE (red)
1970 Datsun Pickup
1953 Chevy pickup (converted 4x4)
1988 T-bird Turbo Coupe

Fbird

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Re: 1981 Formula Computer controlled carb and ignition problems.
« Reply #2 on: June 24, 2020, 05:40:46 AM »
start here...
https://nastyz28.com/threads/81-camaro-check-engine-light.232305/

then here

https://studebaker-info.org/Avanti/81Avanti/GMCCCTroubleCodes.htm

the carb is a mess on these things... computer controlled mixture solenoid.....

Just move on remove 20 lbs of wiring bundle.....if it is NOT mandatory for you to have it (probably not anymore) a nice simple q-jet and dizzy are all you need since yours is a clutch car.
67 Firebird
1981 Turbo TA (injected 400 now :) )

TimBarb

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Re: 1981 Formula Computer controlled carb and ignition problems.
« Reply #3 on: June 24, 2020, 01:26:02 PM »
Gentlemen--Thank you for your quick response and the info. F-bird thanks for the 2 links--finally some usable info! So should i be hunting for a specific q-jet (i.E. for a chevy 305 non CCC) or will any chevy  non CCC q-jet work?  Looks like the air pump and and the emissions jungle could go too once its running on old school distributor and carb. I'll post the results regarding the changes.Thanks again!

firebirdparts

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Re: 1981 Formula Computer controlled carb and ignition problems.
« Reply #4 on: June 25, 2020, 07:00:35 AM »
That question gets asked a lot too.  Q-jets are "sort of" all the same size but they are customized by jetting.  GM made carbs for each application unique, but the changes they made were small.  So a 305 carb, which would be plentiful, is certainly a good idea.  Without looking at the jets, I would not turn my nose up at a 350 carb, which would also be plentiful.

That said, on the carb you have, if the computer controls don't work, it just goes mildly rich, which for a 1981 calibration is not all that bad.  It may have a stepper motor controlling the idle, but I never owned a 1981 LG4, so I don't know for sure.  I had a car with that and some without.  Those are absolutely the only 2 things the computer can do.  Main metering is important, of course, but it was designed to vary over a pretty narrow range and I think it fails rich (which was "safe").  I admit I could be proved wrong about that.

With these old Q-jets, condition is very important; getting the choke working is important, expecting it to behave like a carb is important, and then correctly jetting the carb is important.  The jets/rods/calibration/what-it-came-on is just one important factor.
« Last Edit: June 25, 2020, 07:05:49 AM by firebirdparts »
I want to be like Paul Kenny when I grow up
Joe Bays
1977 Y82 4-speed (red interior)
1978 Skybird 350
1978 Redbird 305
1979 Redbird 301 4-speed
1992 Lincoln Mark VII LSC/SE (red)
1970 Datsun Pickup
1953 Chevy pickup (converted 4x4)
1988 T-bird Turbo Coupe

79 Moneypit

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Re: 1981 Formula Computer controlled carb and ignition problems.
« Reply #5 on: June 25, 2020, 09:12:51 AM »
In closed-loop, the computer controls the mixture-solenoid, which controls metering needle position.  Closed-loop operation results at a certain coolant temp, and the o2 sensor is hot enough to start working.  The computer also controls spark timing via the 7-wire (I think) ignition module.  As already mentioned, the changes made to these systems don't really affect things to the point you'll notice, rather you would see the changes on an exhaust gas analyzer if everything was working perfectly.  I can't remember, but it may be possible to remove the solenoid and return the needles to vacuum control, like an old-school Quadrajet.  I wouldn't try to fix any of it, it will never provide the performance increase of computer controlled fuel injection.  Should be easy to find an older carb and distributor for a 305 or 350.   

firebirdparts

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Re: 1981 Formula Computer controlled carb and ignition problems.
« Reply #6 on: June 26, 2020, 08:43:57 AM »
As I started talking about this from very old memory, I got curious and when I googled it, I observed that people put a dwell meter on the mixture solenoid and with the car running, they can tell what the computer is doing to the main metering needles.  I don't have any expectations of what that dwell should be, but I thought that was interesting.

I started wondering now if these carbs didn't have a power piston, and it sounds like they don't.  It would just be too complicated to make the rods controllable by vacuum and the computer too. 
I want to be like Paul Kenny when I grow up
Joe Bays
1977 Y82 4-speed (red interior)
1978 Skybird 350
1978 Redbird 305
1979 Redbird 301 4-speed
1992 Lincoln Mark VII LSC/SE (red)
1970 Datsun Pickup
1953 Chevy pickup (converted 4x4)
1988 T-bird Turbo Coupe

Fbird

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Re: 1981 Formula Computer controlled carb and ignition problems.
« Reply #7 on: June 28, 2020, 05:47:46 AM »
IIRC they do NOT have a power valve/piston...
67 Firebird
1981 Turbo TA (injected 400 now :) )

TimBarb

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Re: 1981 Formula Computer controlled carb and ignition problems.
« Reply #8 on: June 28, 2020, 07:21:31 AM »
Thanks again for all the input. Does anyone have a resource regarding a quality non CCC . — Thanks !

79 Moneypit

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Re: 1981 Formula Computer controlled carb and ignition problems.
« Reply #9 on: June 29, 2020, 12:42:28 PM »
I hate to say it, because I don't like telling people they should spend money, but an EFI retrofit is really more cost-effective than you might think.  Sure, you can find a used carb and distributor.  But, then they both need a rebuild prior to installing.  Then you spend the time to do a good tuneup...And repeat each spring when you get the car out.  EFI is expensive up front, but over the long haul, has some ROI, even saving some gas, engine wear from stuck chokes, and quicker starts for less starter wear.  That's my 2 cents, and I am saying this with all due respect to the fact that I have no idea what your budget is, and don't like telling people how to spend their money.

firebirdparts

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Re: 1981 Formula Computer controlled carb and ignition problems.
« Reply #10 on: June 29, 2020, 12:53:28 PM »
Thanks again for all the input. Does anyone have a resource regarding a quality non CCC . — Thanks !

Send "maryland bandit" a PM on here.  He is definitely a resource for rebuilding;  He may not have a big stockpile of carburetors, but you may not need one.  He could give you an opinion on the carb you've got, maybe.
« Last Edit: June 29, 2020, 12:58:22 PM by firebirdparts »
I want to be like Paul Kenny when I grow up
Joe Bays
1977 Y82 4-speed (red interior)
1978 Skybird 350
1978 Redbird 305
1979 Redbird 301 4-speed
1992 Lincoln Mark VII LSC/SE (red)
1970 Datsun Pickup
1953 Chevy pickup (converted 4x4)
1988 T-bird Turbo Coupe

TimBarb

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Re: 1981 Formula Computer controlled carb and ignition problems.
« Reply #11 on: June 30, 2020, 05:33:28 AM »
Thanks again for all the input . 79 Money Pit— I totally agree with you. I am planning on replacing the 305 with a 350 of ? And using the EFI. Just wanting to make the bird safe and reliable for now so I can drive it!! Thanks!

79 Moneypit

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Re: 1981 Formula Computer controlled carb and ignition problems.
« Reply #12 on: June 30, 2020, 10:33:01 AM »
Sure, no problem...Always easier to spend someone else's money!

Fbird

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Re: 1981 Formula Computer controlled carb and ignition problems.
« Reply #13 on: July 01, 2020, 06:02:43 AM »
not sure what kind of tune-up you do on a HEI OEM stock 4 speed. (NON-Computer controlled)..... maybe raise the hood and check the oil.  In stock form (especially a Q-jet) the darn things run forever.  EFI is "nice" when you start getting tooo far away from simple systems. A daily driver 200 hp stock car.... thats like a maintenance DREAM!...set and forget, do nothing and drives forever...no efi needed to feed that. Trying to get 450 hp drive able thru 50-100 degree weather with rain and snow.....takes a few more adjustments than a carb has.
67 Firebird
1981 Turbo TA (injected 400 now :) )

Maryland Bandit

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Re: 1981 Formula Computer controlled carb and ignition problems.
« Reply #14 on: July 03, 2020, 01:49:04 PM »
I learned all about the Qjet with my 1985 Monte Carlo SS. The O2 sensor has to see 600 degrees to go into closed loop, along with the coolant temp sensor at 180. Then, theres the dwell. The green plug that goes nowhere on the harness controls the dwell, which should be 30 degrees at idle. All that said, without the proper scan tool, it's almost IMPOSSIBLE to get the settings needed to run right. There are 2 sensors in a CCC carb. The big blue one on top controls the primary jets and how they rise and fall due to demand that the ECM sees, The white connector on the side controls the TPS ( throttle position sensor). This tells the ECM how far your foot is in the gas and to send more fuel. more timing. It's very delicate, probably brittle, and you need a LOT of finesse getting the airhorn back down flat, without breaking the darn tip off the sensor, ruining it after a rebuild. Both of these sensors are still available aftermarket. The CCC carb is cast with different internals then a regular Qjet.  I had the SnapON tool that read all the sensors. Sold it to Joe Richter who runs the site on the turbo Trans Am. You can occasionally find them on eBay, but are expensive. Then, you also need the special tools by Thexton to adjust things on carb, such as the TPS, and the dwell. 
 What I would do? Without the scan tool, you are in for a world of frustration. 
Get a vacuum controlled distributor to start. Then, get a Qjet for a Chevrolet motor, because of the side mounted fuel inlet. Any carb starting with 1705xxx will be ok to use. If, you want it rebuilt,get a carb kit from Cliff Ruggles first. PM me here an we can discuss price on labor and what you want done.   
« Last Edit: July 03, 2020, 01:56:34 PM by Maryland Bandit »

Re: 1981 Formula Computer controlled carb and ignition problems.
« Reply #14 on: July 03, 2020, 01:49:04 PM »


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TimBarb

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Re: 1981 Formula Computer controlled carb and ignition problems.
« Reply #15 on: July 03, 2020, 03:05:18 PM »
Maryland Bandit— thanks for your reply and excellent explanation regarding the CCC and the computer controlled distributor . I have a much clearer understanding of how they function and the tools required to dial in the tune on cars with that equipment. I have a vacuum HEI  on the work bench and I’m searching for a suitable non CCC. I appreciate your help and will  check back with you once I procure a non computer carb.

Re: 1981 Formula Computer controlled carb and ignition problems.
« Reply #15 on: July 03, 2020, 03:05:18 PM »
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