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CarburetorsCarb discussion and questions. Upgrading your Third Gen's carburetor, swapping TBI to carburetor, or TPI to carburetor? Need LG4 or H.O. info? Post it here.
Plugs are showing lean, and I have an 80s scan tool that also confirms a lean condition. I have a mild cam, full exhaust, air cleaner, and that’s about it
Re: 82 LG4 quadrajet running lean even in open loop
My information is from an '85, but the systems ought to be close. If the MCS or its circuit is open or short, you should set a Code 23. Now, if there is no code, the solenoid could possibly be mechanically jammed or stuck, or it's being commanded lean for a reason. First though, you said that you are lean and don't go into closed loop. That may be normal. In open loop, you should be lean under most conditions. You would be rich on start (choke) or WOT power enrichment, but open loop is normally intended to be lean for emissions. Do you have a lean stumble drive quality issue? Does your tool show all the other sensors within normal range? Does your tool show mixture solenoid command? From a diagnostic standpoint, I would start by looking for reasons that the engine might think it is rich (problem with carb fuel leak or charcoal canister loaded with fuel) or not be ready to go into closed loop. Is your O2 sensor good? Is coolant temp normal? Any chance you have misfire on the bank with the O2 sensor? A misfire (one bad plug or plug wire) will send unburned fuel downstream and make the O2 sensor think it is rich and it will pull controls lean. The service manual has a number of pages of trouble trees on how to check mixture solenoid performance using a dwell meter, you likely could do some of this with your tool.
Re: 82 LG4 quadrajet running lean even in open loop
Originally Posted by dan5
My information is from an '85, but the systems ought to be close. If the MCS or its circuit is open or short, you should set a Code 23. Now, if there is no code, the solenoid could possibly be mechanically jammed or stuck, or it's being commanded lean for a reason. First though, you said that you are lean and don't go into closed loop. That may be normal. In open loop, you should be lean under most conditions. You would be rich on start (choke) or WOT power enrichment, but open loop is normally intended to be lean for emissions. Do you have a lean stumble drive quality issue? Does your tool show all the other sensors within normal range? Does your tool show mixture solenoid command? From a diagnostic standpoint, I would start by looking for reasons that the engine might think it is rich (problem with carb fuel leak or charcoal canister loaded with fuel) or not be ready to go into closed loop. Is your O2 sensor good? Is coolant temp normal? Any chance you have misfire on the bank with the O2 sensor? A misfire (one bad plug or plug wire) will send unburned fuel downstream and make the O2 sensor think it is rich and it will pull controls lean. The service manual has a number of pages of trouble trees on how to check mixture solenoid performance using a dwell meter, you likely could do some of this with your tool.
heres the weird thing, when I have the terminals jumpered, the solenoid clicks, but not when the jumper is unplugged and the key is on. The reason I checked the loop status is because my plugs were definitely lean (white flakey stuff on plugs), scan tool told me the MCS dwell (don’t remember off the top of my head), and confirmed that it’s running lean. I tested all the sensors and they put out voltage that changed when the car warms up. Coolant temp sensor is giving me a reading. I’m concerned the computer may be bad since when I turn the key it doesn’t click the solenoid. No check engine light or even any codes
I do not believe I have a misfire either, brand new plugs at the correct gap, brand new accel super stock wires, cap and rotor were in great shape. Car starts ok especially when warm. Took on a 15 min drive and still wouldn’t go into closed loop
Re: 82 LG4 quadrajet running lean even in open loop
specifics
how did you determine it is running lean from the scan? the system won't provide a lean/rich reading: it relies on the narrow band O2.
it can show a lean flag, but if the O2 readings are out of range that's just the last 'known good' data the system had.
the MCS dwell can help determine a lean/rich condition if it's maxed out high or low but again that may be its 'last known good' response
what exactly is the MCS dwell doing? a static reading is useless, how does it respond to changes in throttle? does the dwell change at idle when it is warm? and is the rich/lean flag changing? after warm up does the scan tool indicate open or closed loop?
again if the rich/lean flag is staying constant, that is not an indication that it is necessarily lean or rich now.
a failed MCS will cause a rich condition (all else functioning properly) unless it failed and stuck in the down position or one or both primary needles failed and stuck down.
start by looking at the behavior or the dwell, or duty cycle, for the MCS. post back all you note, take a screen shot of your scan data at different times during the observation.
Re: 82 LG4 quadrajet running lean even in open loop
Originally Posted by naf
specifics
how did you determine it is running lean from the scan? the system won't provide a lean/rich reading: it relies on the narrow band O2.
it can show a lean flag, but if the O2 readings are out of range that's just the last 'known good' data the system had.
the MCS dwell can help determine a lean/rich condition if it's maxed out high or low but again that may be its 'last known good' response
what exactly is the MCS dwell doing? a static reading is useless, how does it respond to changes in throttle? does the dwell change at idle when it is warm? and is the rich/lean flag changing? after warm up does the scan tool indicate open or closed loop?
again if the rich/lean flag is staying constant, that is not an indication that it is necessarily lean or rich now.
a failed MCS will cause a rich condition (all else functioning properly) unless it failed and stuck in the down position or one or both primary needles failed and stuck down.
start by looking at the behavior or the dwell, or duty cycle, for the MCS. post back all you note, take a screen shot of your scan data at different times during the observation.
well originally I checked the spark plugs and they showed a definite lean condition (bare metal w white flaky stuff on it), so I went to the scan tool and it had a setting that showed MCS dwell and lean/rich condition. It would show the dwell in one box and in the other (titled rich/lean) it showed L. You’re right I’m not sure how much L. But plugs and scan tool confirm lean, and it doesn’t like to run in the cold (35F) or so it needs to warm up for a while. But from what I’ve read in open loop engine runs on either a factory preset setting or the setting where the computer through the engine was last running “good”, since my battery’s been unhooked for months I’m sure there’s no saved setting left so it probably would use the factory setting. Since I have all the stuff done to the car I think that could be why it’s running lean. I was thinking if I can get it to go into closed loop it could fix the lean issue. As for your questions, it always shows lean since it won’t leave open loop so the carb settings haven’t been able to adjust at all. The dwell settings appear to change as the car warms up I can record that for you. Will not go into closed loop whatsoever. All sensors give me readings that change as the car warms up or as the accelerator pedal is pressed. It’s just so weird that the MCS would cycle like it’s supposed to with the solenoids jumpered, but normally when I turn the key nothing happens. So it makes me think the solenoid is good if it can do that. The 02 sensor reading also is changing like it’s supposed to, I can record readings as it warms up. In the other threads I have read with similar issues, it ended up being the computer was bad. Sorry for rambling hopefully we can solve this
Re: 82 LG4 quadrajet running lean even in open loop
I don't really know the modifications to your engine, so it's hard to know how they might affect normal operation. I suggest that you look at the system performance trouble tree. This is the main way to verify function of your mixture control system. You can sometimes short cut it and learn some things, but usually it's good to run the full test.
Key items to look at:
Item 2A Full rich command- fixed dwell below 10 caused by a lean engine
Item 2B Open loop condition-fixed dwell 10-50. Looks at oxygen sensor and coolant sensor circuits. Note that in the trouble tree, you can manually choke the engine to see if you can get a response.
Item 2C Full lean is defined as fixed dwell over 50 caused by a rich engine condition
I would not jump to a bad ECM without everything else being ruled out. In my experience that is the last thing to change. Even then, most of the time, the ECM doesn't fix it, the actual fault was a bad connection somewhere that was disturbed when changing the ECM. If your ECM is communicating and responding properly, work the symptoms first.
Re: 82 LG4 quadrajet running lean even in open loop
sounds like it's acting exactly as it's supposed to.
after power disconnect the system will operate on factory presets. it will change dwell based on throttle position and vac readings until it gets an O2 reading that it can make sense out of. if the carb settings are far enough out of adjustment, it may never see an O2 reading that will allow it to go into closed loop, or it may not be able to stay in closed loop (full feedback mode).
could be as simple as adjusting your idle air bleed screw, top of carburetor. if it's there, remove the tamper proof cover.
with the engine fully warm, check the dwell. it should vary some, up and down, as the ecm responds to changes in O2 readings.
if it is constant-steady, try adjusting it
check how many turns out it is now, should be around 3-4ish. start at 2 turns out let it continue to idle for about 30 seconds, note any changes in dwell behavior.
dwell still steady and unchanged, turn 1/4 turn further out. do the same dwell check.
repeat until the dwell begins to respond by changing slightly in response to O2. then fine tune it until the dwell hovers around 50% at idle. it should vary slightly while idling going up and down about 5 or so % while you watch it.
if you get to 7 turns out or so, and no change in dwell behavior, we may need to look at other things.
note that dwell is normally measured in degrees, from the old point style ignition systems. the LG4 has a diagnostic lead that can read the duty cycle as dwell on a six cylinder scale where 30 degrees is equivalent to 50% duty cycle. above consider my use of 'dwell' to be synonymous with 'duty cycle' although it's not technically correct.
Re: 82 LG4 quadrajet running lean even in open loop
Originally Posted by dan5
I don't really know the modifications to your engine, so it's hard to know how they might affect normal operation. I suggest that you look at the system performance trouble tree. This is the main way to verify function of your mixture control system. You can sometimes short cut it and learn some things, but usually it's good to run the full test.
Key items to look at:
Item 2A Full rich command- fixed dwell below 10 caused by a lean engine
Item 2B Open loop condition-fixed dwell 10-50. Looks at oxygen sensor and coolant sensor circuits. Note that in the trouble tree, you can manually choke the engine to see if you can get a response.
Item 2C Full lean is defined as fixed dwell over 50 caused by a rich engine condition
I would not jump to a bad ECM without everything else being ruled out. In my experience that is the last thing to change. Even then, most of the time, the ECM doesn't fix it, the actual fault was a bad connection somewhere that was disturbed when changing the ECM. If your ECM is communicating and responding properly, work the symptoms first.
i can run those tests BUT when I turn the key on the MCS doesn’t cycle... when I jump the Terminals and turn the key on the solenoid clicks
EDIT: could you post that picture again, for some reason it’s kinda hard to read on my end, thanks for doing that though
Last edited by 82Firebird5.0; 05-16-2020 at 01:32 PM.
Re: 82 LG4 quadrajet running lean even in open loop
Originally Posted by naf
sounds like it's acting exactly as it's supposed to.
after power disconnect the system will operate on factory presets. it will change dwell based on throttle position and vac readings until it gets an O2 reading that it can make sense out of. if the carb settings are far enough out of adjustment, it may never see an O2 reading that will allow it to go into closed loop, or it may not be able to stay in closed loop (full feedback mode).
could be as simple as adjusting your idle air bleed screw, top of carburetor. if it's there, remove the tamper proof cover.
with the engine fully warm, check the dwell. it should vary some, up and down, as the ecm responds to changes in O2 readings.
if it is constant-steady, try adjusting it
check how many turns out it is now, should be around 3-4ish. start at 2 turns out let it continue to idle for about 30 seconds, note any changes in dwell behavior.
dwell still steady and unchanged, turn 1/4 turn further out. do the same dwell check.
repeat until the dwell begins to respond by changing slightly in response to O2. then fine tune it until the dwell hovers around 50% at idle. it should vary slightly while idling going up and down about 5 or so % while you watch it.
if you get to 7 turns out or so, and no change in dwell behavior, we may need to look at other things.
note that dwell is normally measured in degrees, from the old point style ignition systems. the LG4 has a diagnostic lead that can read the duty cycle as dwell on a six cylinder scale where 30 degrees is equivalent to 50% duty cycle. above consider my use of 'dwell' to be synonymous with 'duty cycle' although it's not technically correct.
that’s the thing, I am not sure that it’s adjusting the dwell at all, it’s still runnning very lean. So you’re saying that maybe it is running so lean it won’t go to closed loop at all? I am concerned about the MCS not clicking like it’s supposed to. It will click when I have the terminals jumpered and the key in the on position, but not when I have it in the on position normally. I have read of that being a bad computer. I can change the screws but I don’t know if it’s a good idea until I have the MCS issue sorted out
Re: 82 LG4 quadrajet running lean even in open loop
Before I would make any adjustments, I would run the basic system diagnostic to see how the system reacted. The service engineers created those trouble trees to guide you to a solution. There are other diagnostic trees after this one once you get through it and know what branch to work. The adjustments suggested by naf may be completely appropriate, but if you have a different problem, it will only confuse you. Let's prove that you need to make the adjustment, then go for it. I wouldn't try to diagnose based on listening to the solenoid, that may lead you astray. You could have a problem in the ECM, you might have a problem with the driver for the mixture solenoid. The only way to know is to run the test and see what it tells you. I can tell you with that 90%+ of ECM and other controller warranty replacements are NTF (No Trouble Found) when they get back to the manufacturer for analysis.
Re: 82 LG4 quadrajet running lean even in open loop
Originally Posted by dan5
Before I would make any adjustments, I would run the basic system diagnostic to see how the system reacted. The service engineers created those trouble trees to guide you to a solution. There are other diagnostic trees after this one once you get through it and know what branch to work. The adjustments suggested by naf may be completely appropriate, but if you have a different problem, it will only confuse you. Let's prove that you need to make the adjustment, then go for it. I wouldn't try to diagnose based on listening to the solenoid, that may lead you astray. You could have a problem in the ECM, you might have a problem with the driver for the mixture solenoid. The only way to know is to run the test and see what it tells you. I can tell you with that 90%+ of ECM and other controller warranty replacements are NTF (No Trouble Found) when they get back to the manufacturer for analysis.
thank you sooo much! Can’t wait to get this figured out
Re: 82 LG4 quadrajet running lean even in open loop
Originally Posted by dan5
Before I would make any adjustments, I would run the basic system diagnostic to see how the system reacted. The service engineers created those trouble trees to guide you to a solution. There are other diagnostic trees after this one once you get through it and know what branch to work. The adjustments suggested by naf may be completely appropriate, but if you have a different problem, it will only confuse you. Let's prove that you need to make the adjustment, then go for it. I wouldn't try to diagnose based on listening to the solenoid, that may lead you astray. You could have a problem in the ECM, you might have a problem with the driver for the mixture solenoid. The only way to know is to run the test and see what it tells you. I can tell you with that 90%+ of ECM and other controller warranty replacements are NTF (No Trouble Found) when they get back to the manufacturer for analysis.
Sorry I’m completely clueless, I don’t understand even what it means by ground test term
Last edited by 82Firebird5.0; 05-20-2020 at 02:28 PM.
Re: 82 LG4 quadrajet running lean even in open loop
Ok so another (related) issue has come up. When I start the car it starts ok but after it kicks down from fast idle it runs super rough and choppy like it’s got a big cam. It’s 70 degrees out it’s not the carb. Wish I could figure this out it’s sputtering and all choppy
Re: 82 LG4 quadrajet running lean even in open loop
Originally Posted by 82Firebird5.0
Sorry I’m completely clueless, I don’t understand even what it means by ground test term
I expect that means the ALDL test terminal that you jumper to make the check engine light flash codes. That is the connector under the dash. That would put the ECM into field service mode.
Regarding rough running, that's why you're doing this. If the engine is truly running with the mixture too lean (or too rich), it should run rough.
Re: 82 LG4 quadrajet running lean even in open loop
Originally Posted by dan5
I expect that means the ALDL test terminal that you jumper to make the check engine light flash codes. That is the connector under the dash. That would put the ECM into field service mode.
Regarding rough running, that's why you're doing this. If the engine is truly running with the mixture too lean (or too rich), it should run rough.
oh gotcha, can I just plug in my scan tool instead? I got it to go into closed loop today but the MCS still won’t cycle got any ideas?
Re: 82 LG4 quadrajet running lean even in open loop
Originally Posted by 82Firebird5.0
I got it to go into closed loop today but the MCS still won’t cycle got any ideas?
no you didn't. the system can not go into closed loop without the MCS cycling. pick one.
there are probably 100's of threads on here about this system. some of the info may be bogus but I'm sure if you read through many you'll be able to figure out which posters know what they're talking about.
a motor that starts stumbling and running rough while known to be out of proper fuel/air calibration is an expected secondary failure. check your plugs. again if you have to.
you were provided two paths towards initial diagnosis above, pick one.
Re: 82 LG4 quadrajet running lean even in open loop
Originally Posted by naf
no you didn't. the system can not go into closed loop without the MCS cycling. pick one.
there are probably 100's of threads on here about this system. some of the info may be bogus but I'm sure if you read through many you'll be able to figure out which posters know what they're talking about.
a motor that starts stumbling and running rough while known to be out of proper fuel/air calibration is an expected secondary failure. check your plugs. again if you have to.
you were provided two paths towards initial diagnosis above, pick one.
I get what you’re saying, but the scan tool showed it to be in closed loop once it warmed up. The air fuel thing showed it going rich lean rich lean back and forth like it’s supposed to, which is weird because it’s lean... But for whatever reason the MCS doesn’t cycle before startup. I will start those tests tonight if I can figure out how to do them
Re: 82 LG4 quadrajet running lean even in open loop
Originally Posted by naf
no you didn't. the system can not go into closed loop without the MCS cycling. pick one.
there are probably 100's of threads on here about this system. some of the info may be bogus but I'm sure if you read through many you'll be able to figure out which posters know what they're talking about.
a motor that starts stumbling and running rough while known to be out of proper fuel/air calibration is an expected secondary failure. check your plugs. again if you have to.
you were provided two paths towards initial diagnosis above, pick one.
got any idea why it’s not cycling to begin with? Doesn’t make any sound with the key on, but it does if I plug the scan tool in...
Re: 82 LG4 quadrajet running lean even in open loop
Originally Posted by 82Firebird5.0
got any idea why it?€™s not cycling to begin with? Doesn?€™t make any sound with the key on, but it does if I plug the scan tool in...
Sorry, I don't have time to be online much at the moment. Diagnosing by sound is not always reliable, that's why there are specific tests. I don't know what the mixture solenoid should sound like with key on and RPM = 0. If it responds properly when the engine runs or in the test modes, why does it matter?
When you start the car cold, it should go to the rich side, but only briefly - time depends on ambient temperature and cold start and catalyst light off strategy. If it doesn't, perhaps your choke setting is too lean or the choke thermostat is out of spec. On a cold start, if the mixture solenoid moves max rich and the choke is open, you may not be able to get to rich mixture. On cold start, fuel doesn't fully vaporize in the intake, so need more of it to get a proper mixture. Remember that until the O2 sensor warms up, rich lean indication the scan tool doesn't mean anything, so you won't be able to see this.
In open loop, the car will run lean by design for emissions purposes
If it goes to closed loop, then your mixture solenoid is working and your mixture is centered around stoichiometric (14.7:1) so that the 3 way catalyst works efficiently.
Your scan tool in these early cars does not get a high speed update rate, it is quite slow, so it can switch rich / lean / rich and you may not see it.
Last edited by dan5; 05-27-2020 at 09:01 AM.
Reason: add comment
Re: 82 LG4 quadrajet running lean even in open loop
the MCS should cycle at 10 Hz for about 30 seconds, maybe less, when the key is initially turned on.
some models may deviate from this. I've also had discouraging results using the scan tool on some early models, in that they read duty cycle incorrectly and an actual dwell meter had to be used at the factory diagnostic lead. I have never connected to an '82 model, although I've used the autoxray on an '81 with good results. do not recall if the '81 cycled KOEO.
as said above, if it's cycling while the motor is running... it's working.
Re: 82 LG4 quadrajet running lean even in open loop
Originally Posted by dan5
Sorry, I don't have time to be online much at the moment. Diagnosing by sound is not always reliable, that's why there are specific tests. I don't know what the mixture solenoid should sound like with key on and RPM = 0. If it responds properly when the engine runs or in the test modes, why does it matter?
When you start the car cold, it should go to the rich side, but only briefly - time depends on ambient temperature and cold start and catalyst light off strategy. If it doesn't, perhaps your choke setting is too lean or the choke thermostat is out of spec. On a cold start, if the mixture solenoid moves max rich and the choke is open, you may not be able to get to rich mixture. On cold start, fuel doesn't fully vaporize in the intake, so need more of it to get a proper mixture. Remember that until the O2 sensor warms up, rich lean indication the scan tool doesn't mean anything, so you won't be able to see this.
In open loop, the car will run lean by design for emissions purposes
If it goes to closed loop, then your mixture solenoid is working and your mixture is centered around stoichiometric (14.7:1) so that the 3 way catalyst works efficiently.
Your scan tool in these early cars does not get a high speed update rate, it is quite slow, so it can switch rich / lean / rich and you may not see it.
thank you so much!! I think you’re right because it definitely cycles so I’m not going to work maybe it didn’t have that feature in 1982 or something. I am having trouble with getting it to idle and run right when cold. Seems like the choke kicks off faster when the temp
outside is warmer and then it stumbles and wants to die and stuff. The electric choke works correctly and so does the pull off I think. Should I try enriching the idle screws a little? Once it’s warmed up it idles ok. When it was colder since it took longer for the electric choke to turn off it seemed to run better since the engine was warmed up by then
Re: 82 LG4 quadrajet running lean even in open loop
Originally Posted by naf
the MCS should cycle at 10 Hz for about 30 seconds, maybe less, when the key is initially turned on.
some models may deviate from this. I've also had discouraging results using the scan tool on some early models, in that they read duty cycle incorrectly and an actual dwell meter had to be used at the factory diagnostic lead. I have never connected to an '82 model, although I've used the autoxray on an '81 with good results. do not recall if the '81 cycled KOEO.
as said above, if it's cycling while the motor is running... it's working.
it’s definitely cycling so I’m not going to worry about it. I ended up adjusting the MCS travel because it wasn’t allowing it to go rich enough. I got the specs out of a GM service manual and it seemed to help. I am having trouble with cold idle maybe you could check out the previous post if you wouldn’t mind I explained the symptoms. I will add since I have the rv cam, air cleaner, and full exhaust I enriched it 1/2 turn already but will go more if that’s the issue
Re: 82 LG4 quadrajet running lean even in open loop
Originally Posted by 82Firebird5.0
thank you so much!! I think you’re right because it definitely cycles so I’m not going to work maybe it didn’t have that feature in 1982 or something. I am having trouble with getting it to idle and run right when cold. Seems like the choke kicks off faster when the temp
outside is warmer and then it stumbles and wants to die and stuff. The electric choke works correctly and so does the pull off I think. Should I try enriching the idle screws a little? Once it’s warmed up it idles ok. When it was colder since it took longer for the electric choke to turn off it seemed to run better since the engine was warmed up by then
OK, now you're starting to zero in on an operating symptom. The cold start and warm up is influenced by the computer control, but is primarily an old school mechanical carburetor function. Carbs have different functions for different operating modes. Cold start and warm up is mostly choke related. So, don't try to adjust idle mixture cold. It should be set warm. If you set it for warm up, it will be off at normal temperature. The choke should open faster when outside temp is warmer, but it may still be opening too soon. Have you replaced the choke thermostatic element? These are bi-metal springs that end to lose sensitivity as they age and there isn't a good test for them. The typical condition is that they lose range or span so that they don't close enough. (Or people reset them so they work cold and they don't open all the way when hot). Have you verified the measured choke settings against specifications? Have you tried a little richer choke setting? Also, have you checked the float level? If it is low, you will tend to be lean and the choke system will be less effective. Your car ought to have an EFE valve with a temperature switch to force heat into the intake manifold during warm up. Is it working properly?
Re: 82 LG4 quadrajet running lean even in open loop
Originally Posted by dan5
OK, now you're starting to zero in on an operating symptom. The cold start and warm up is influenced by the computer control, but is primarily an old school mechanical carburetor function. Carbs have different functions for different operating modes. Cold start and warm up is mostly choke related. So, don't try to adjust idle mixture cold. It should be set warm. If you set it for warm up, it will be off at normal temperature. The choke should open faster when outside temp is warmer, but it may still be opening too soon. Have you replaced the choke thermostatic element? These are bi-metal springs that end to lose sensitivity as they age and there isn't a good test for them. The typical condition is that they lose range or span so that they don't close enough. (Or people reset them so they work cold and they don't open all the way when hot). Have you verified the measured choke settings against specifications? Have you tried a little richer choke setting? Also, have you checked the float level? If it is low, you will tend to be lean and the choke system will be less effective. Your car ought to have an EFE valve with a temperature switch to force heat into the intake manifold during warm up. Is it working properly?
I have not tried replacing the thermostat element, is it hard? I have a non adjustable choke it has rivets instead of screws. How exactly does that work? Does turning the black part make the choke start out in a more closed position? How does it make it more rich? When I start the car in the summer it doesn’t even go to the highest idle it did in the winter, and takes much less time to kick down to idle. When I pull out of the garage and start to drive away if I give it gas it’ll drop a ton of rpms and I have to rapidly push and release the accelerator to get it not to quit. It actually ran better when it was cold outside because it took longer to kick down and by then the car was warm enough to run good
edit: i have a different air cleaner and headers now so I don’t have the EFE anymore
EDIT #2 once I get to work I park the car for 7 hours or so and when I go to start it again to go home it starts and runs much better and barely tries to quit and stuff but it’s still not perfect
Last edited by 82Firebird5.0; 06-01-2020 at 09:02 PM.
Re: 82 LG4 quadrajet running lean even in open loop
Yes, the rivets... It was much easier when they just had screws. Up until the late 70's, you could loosen the screws and rotate the black thermostat assembly either rich or lean and just tighten the screws. The casting had a several "bumps" as reference marks and the coil had a pointer so you could keep track of the adjustment point. New thermostat assembly is available. It requires drilling the rivets out with a 5/32 drill (gently) to just go through the head of the rivet and no further. Then you need to use a sharp tool or small punch to push out the rest of the rivet. I don't know how the kits come these days, whether they provide new rivets or self tapping screws. I am betting they will have new rivets. Back in the day, I had some kits that provided screws, but to do it right, the design with screws also had small spring clips under the screw heads to hold the cover. In your case, with headers and no EFE, screws might be a help so that you can make an adjustment. I think there is a detent in the housing to prevent rotation, so it still may be difficult to do. I still think it might be worth replacing this part. It is a coiled bimetal spring that rotates as it heats and cools. If it is original, it is going on 40 years old and may be not performing correctly. Hard to say for sure, but I would try it. If a new coil isn't enough, the question would be if you can adjust the thermostat by rotating it, even if it means filing down the detent. If you do that, you would need to make a mark so you know where "zero" is.
One more thought, though. This does depend on how much time elapses from a start. If your engine runs long enough to get the O2 sensor warmed up and into closed loop, then you can work all day on the choke and the closed loop algorithm will just counteract it.
Last edited by dan5; 06-01-2020 at 10:25 PM.
Reason: add comment
Re: 82 LG4 quadrajet running lean even in open loop
before replacing parts, ensure your choke pull off is working correctly. with the small vac line disconnected you should be able to push it in, place your finger over the nipple opening and it should not release back out until you remove your finger. you should also be able to observe it retracting once the engine is started.
this is a common failure part.
choke adjustments are covered in the carb sticky. I would check them all.
the ecm will enrich the mixture while the coolant temp is below a set point. use your scan tool to make sure the CTS is showing consistent values as the engine warms. should be near ambient at start and warm up to 200 degrees or so.
05-12-2020, 03:37 PM
