i tryed to search and got some of the answers but i am still in the dark on some stuff.


i am looking at buying my friends 84 Z28 with a LG4? (it's a carbed 305) the car runs great at throttle and screams down the road (dare i say it actualy seems to have *****?) but does not like to restart when up to temp and the carb does not like to hold a tune to save it's life.

so i have some parts left over from my old 74 1/4 project (summit stage 1 intake and my uncle has a non feed back q-jet) and was going to remove the feed back system but not sure what to do a bought the trans it's a 700-R4 so it needs lock up any ideas how to go a bought wiring that up with no computer input? any other issues i may run into?


any help would be great

 

Just need a 12V supply through a switch and the original brake pedal switch which gives you manual control of lockup.
Just have to remember to dis engage lockup when coming to a stop because as soon as you take your foot off the brake pedal the convertor will lock up and you might stall engine
Good reading here ( and page 2)
http://purplesagetradingpost.com/sum...o/700R4p1.html

 

Welcome aboard thirdgen.org.

"Does not like to hold a tune"? What do you do to "retune" it?

Going non-computer is rarely a good move. Most likely there is something simple that needs to be fixed, and the feedback system is head & shoulders better than the non-feedback stuff.

 

the idle speed adjustment solenoid? i think is what it is. if you set it to say 800 rpm idle it will be fine but if you shut the car off and restart the car it goes down to 500 rpm or less and has to be brought back up manualy. and i have not done this but he said he took it to a shop and they said it constantly runs rich at idle and if they leaned it out as soon as it was shut off and restarted it would go back to the low RPM speed and rich idle. if you leve it running even after driving it at diffrent throttle positions it is fine

the cruise speed and wot air fuel is dead on and does not change only the idle adjustments.

hey if it's some thing simple i will not complain i actualy like Q-jets

 

The idle speed kicker solenoid is only supposed to be engaged when the air conditioner is on, and during certain deceleration conditions (emissions control). The "curb" idle is set using the idle speed set screw (https://www.thirdgen.org/forums/carb...e-rebuild.html , items 77 & 78 in the exploded view).

The factory spec LG4 idle speed warm in drive is 500 RPMs.

The idle mixture screws are supposed to be set at 3-3/8 turns out, and then the final adjustment made via the idle air bleed to get 50% duty cycle on the MCS at idle (everything else, like timing, idle speed, and TPS already adjusted).

 

hmm i guess i will take another look

 

well messed with it a bit more got it to hold an idle. still runs a bit rich though. i also think it may need a rebuild for the carb the throttle shaft has a bit of play and i think that might be part of the idle issue

 

bah this carb is starting to drive me batty

the car practicly falls on it's face when you get above 3/4 throttle stumbles and trys to stall out if you back of and ease into the throttle it's fine.

the temptaion of just installing the non-CCC parts is starting to become over welliming. also the fact it now gets a wapping 5 MPG


checked vac lines and replaced a almost all of them becuase they where dry rotted. that actualy made it run wourse. checked timing and checked for slack in the timing chain that was fine. for giggles i replaced the o2 sensor that didn't do any thing. any other ideas before i just rip it out?

on another note it idles fine lol

 

You've made progress, don't give up.

Are you opening the secondaries when these problems occur?

 

hmm i don't know. i guess i could put a camara under the hood of the car and film it

 

You should be able to feel it as you open the throttle. There is a step increase in pedal resistance as you start to open the secondaries.

 

huh i will see if i feel it.

 

I'm inferring that he believes your problem may not be related to the computer controlled portion (range of throttle opening) of your ccc-qjet. Once the secondaries open (and the TPS provides a high enough voltage reading to the ECM) the ccc-qjet behaves like any other mechanical q-jet. OH...sometimes a cleverly placed paperclip will disclose later whether the secondary air valves opened under load.

Rich idle and really bad MPG tell me your carb isn't functioning well in feed back mode.

Hot restart issues are usually ignition component related.

Are any service engine codes present?

Does the MCS (inside the carb) click when the ignition is turned to 'Run'?

If the idle mixture screws have been tampered with it's likely enough out of adjustment so that the ECM isn't seeing the O2 readings it needs to begin adjusting duty cycle. Have any other tamper proof plugs been removed?

 

secondaries open

i actualy looked at it at work (slow day) it was kind of funny seeing one rusty GM among a bunch of brand new shiny ford diesels (god i hate the 6.0 and 6.4) and i bet mine ran the best

a fellow tech had a scan tool that could read OBD1 vehiclas he only had a card for 86-93 GMs so we just used that. there are no codes in the computer

the idle mixture screws still have the plugs and look like they where never messed with.

the o2 is reading rich .700mV at idle and cruise .678mV and when you try to gun it it goes a bit leaner .600mV but then pegs out the o2 1.0V this is when it stumbles. when i let off and ease into it it goes to .800mV

this is with a new o2

hot starts seem to be fine never had an issue with that. idniton is fine timing is on and all cyalnders are firing

TPS is ging a signle 1.1v at closed throttle and 4.8v at WOT

the carb "clicks" with the key is put to run

 

ok i think i figured this out.

i took the top of the carb off and it was just full of junk so i took all the gas out and cleaned it as best i could and success

i have full throttle agian. (and the 4" long black mark to proove it) i am going to replace the fuel filter in the carb and the inline one tomarrow.


idle is still a bit rich though and stalls when you put it in drive some times any way to adjust this? i know the ECM is sapose to but mine seems to not be able to..... agian

 

Does your buddy's scan tool provide operational data while the engine is running? You'll want to look at the MCS Dwell (the amount of time, expressed as a percent, that the primary rods are down in the jets) and verify that it is responding to changes in O2 readings at idle while the engine is fully warm. The Scan tool should also tell you whether it is in closed or open loop-you're looking for it to be 'open'.

If none of the adjustments on the carb have been tweaked at all, and the motor's still stock, there's a pretty wide operating range for the feedback system. However if your carb's got some passages gunked up, vacuum issues, etc. the mixture COULD be far enough off so that the ECM can't make heads or tails of the O2 readings.

Your TPS is a little off, should be reading near 0.40 at idle and 4.0 at WOT but it's not so far off to be interfering with open loop operation-unless the voltage readings are unsteady and bouncing around too much in some range so that the ECM doesn't see a steady throttle.

Curb idle is still adjusted by the set screw under the throttle connection. Always check timing before setting curb idle speed.

See the sticky for more information.

 

what sticky? could you please link?

not sure if his scan tool has that function or not didn't really look too far into it i am thinking of taking it too my old high school they had a tech 1 there

 

In the top section of this forum:
https://www.thirdgen.org/forums/carb...e-rebuild.html

 

saw that right after i posted lol

 

well i found the problem. it was actualy something i never would of even looked for. it had nothing to do with the carb or the igintion. The keep alive memory was not getting a 12v signal so it was not storing the information and was like a brand new car every time i would start it (why it did not like to idle) after i would drive a bit it would learn how to idle the car but as soon as the car would be turned off the memory would wipe clean and it would run like poo agian.

my old high school auto teacher actualy sugested this to me he was a GM tech in the 80's. what it seems to have happen with my car is a previuse owner tryed to install an anti theft device (key word try) and failed horribly. after removing the the hack wiring i was able to re-wire it the correct way and now it idles fine and runs fine.


still stumbles when i try to go WOT but at this point i don't care

 

Another new one for me.

On your bog: https://www.thirdgen.org/quadrajet

 

That's a good tech article, but another possibility for bogging, which adjusting the AV will never cure, is a leaking choke pull-off. The only way to test it is with a vacuum pump like a Mityvac, so you can pump up the vacuum and hold, and see if the pull-off releases. A constant vacuum source like the engine can mask a leaking diaphragm, but a leaking diaphragm can allow the pull-off to release too quickly.

 

would a hand vac pump work?


also thanks agian. i am amazed at the throttle respince this old Q-jet still has. must be the small promaries. also has been getting ~17mpg instead of 8mpg

 

That's what a Mityvac is (or at least, what most people have). When you stop pumping, the vacuum should hold until you release it.

 

goth ya.

 

well thought i should update this i was messing with the green car (the z28) and noticed that when i hit the brakes the idle would go up and when i would release the car would try and stall. so i disconnected the brake booster and plugged the line. and did something unsafe lol

drove the car with out power brakes and well fixed the WOT issue and the idle issue but being a parts car it does not matter much just good to know that the carb is good and the booster is shot