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LG4 ignition timing

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Old 07-09-2017, 07:49 PM   #1
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LG4 ignition timing

Can some explain the timing indicators on thesse cars? Im trying to see if my LG4 has proper timing but the indicator looks alot different then Ford. I have adjusted timing numerous times on my 5.0 Mustang but the indicator was just a pointer pointing to the numbers on harmonic balancer. Is it just reversed on these cars and i just need to line the mark on harmonic balancer with the 6* mark on the indicator? I would like to do this myself and not take it to somebody so positive answers pleasei was a

Lso told i need a timing light with an adjustment dial??
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Old 07-09-2017, 08:34 PM   #2
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Re: LG4 ignition timing

It sounds like you have it right.
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Old 07-09-2017, 09:11 PM   #3
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Re: LG4 ignition timing

+1 sounds like you're on the money
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Old 07-13-2017, 02:25 AM   #4
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Re: LG4 ignition timing

What wire harness do i have to disconnect to disable EST? I was told its the flat 4 conmector, anyome know what colors?
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Old 07-15-2017, 07:04 PM   #5
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Re: LG4 ignition timing

UPDATE: i got the timing set at about 6* but the car is running like s*** pretty much the same way before i adjusted timing. i think she is running rich cause black smoke comes from tailpipes when i rev the engine. she idles real low 500 in park. if i opened a vacuum port and left it open she idles good. and the only way i got her to idle at 800 was to turn the idle stop screw up more. is there some sort of ballpark adjustments i can do to the carburetor to get her to run to a point where i can drive her? i turned the mixture screws in all the way, then 3 turns out what else can i do?
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Old 07-15-2017, 07:43 PM   #6
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Re: LG4 ignition timing

Pictures please. Especially of all the vacuum lines/hoses.
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Old 07-20-2017, 10:55 AM   #7
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Re: LG4 ignition timing

i know it took a while but i finally was able to get back to the car today and took pics all over the carb to show the vacuum hoses i tried to get pics of the idle mixture screws but that is hard

ignore the open tee port where the choke pull off is. thats open cause i took air cleaner off. i plug a line for the IAT sensor in that spot
Attached Thumbnails
LG4 ignition timing-img_5058.jpg   LG4 ignition timing-img_5055.jpg   LG4 ignition timing-img_5054.jpg   LG4 ignition timing-img_5052.jpg   LG4 ignition timing-img_5053.jpg  

LG4 ignition timing-img_5051.jpg  

Last edited by 87tunedport; 07-20-2017 at 11:52 AM.
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Old 07-20-2017, 11:23 AM   #8
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Re: LG4 ignition timing

i also drew up some diagrams of the vacuum routing and the timing i currently have the engine set at 6* BTDC
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LG4 ignition timing-img_5062.jpg   LG4 ignition timing-img_5063.jpg  
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Old 07-20-2017, 11:51 AM   #9
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Re: LG4 ignition timing

ignore this message my stupid computer wants to act up

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Old 07-20-2017, 04:05 PM   #10
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Re: LG4 ignition timing

Did you find the flat 4-wire connector behind/under the distributor to disconnect before setting the timing?
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Old 07-20-2017, 04:16 PM   #11
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Re: LG4 ignition timing

Do you have a vacuum line attached to the sensor circled in the upper left?

That's not the MAP sensor. That's the BAR or barometric pressure sensor. The nipple should be open (originally had a foam square over it, but they typically degrade and fall off).
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Old 07-20-2017, 04:17 PM   #12
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Re: LG4 ignition timing

This is the MAP sensor, circled with an arrow pointing to it in the upper right corner of the pic.

Notice it has a hard plastic line attached to it. The other end is the hard plastic line attached to the back of the carb at the base.
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Old 07-20-2017, 05:20 PM   #13
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Re: LG4 ignition timing

That sensor is connected with a vacuum line so i should remove the line then?

Hows the mixture screws look?

yes i disconnected the 4 wire connector. that triggered SES so i unplugged the power wire for ECM to clear it

Last edited by 87tunedport; 07-20-2017 at 05:26 PM.
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Old 07-20-2017, 07:16 PM   #14
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Re: LG4 ignition timing

Quote:
Originally Posted by 87tunedport View Post
That sensor is connected with a vacuum line so i should remove the line then?
Yes. It should only have the wiring connector attached to it.

Quote:
Originally Posted by 87tunedport View Post
Hows the mixture screws look?
No clue. If you lightly seated them, then turned them each out 3 turns, they should be fine.

Now you need to adjust the IAC dwell.

Quote:
Originally Posted by 87tunedport View Post
yes i disconnected the 4 wire connector. that triggered SES so i unplugged the power wire for ECM to clear it
Good. Timing should be fine at 6 degrees base, then.
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Old 07-20-2017, 08:24 PM   #15
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Re: LG4 ignition timing

Quote:
Originally Posted by 87tunedport View Post
UPDATE: i got the timing set at about 6* but the car is running like s*** pretty much the same way before i adjusted timing. i think she is running rich cause black smoke comes from tailpipes when i rev the engine. she idles real low 500 in park. if i opened a vacuum port and left it open she idles good. and the only way i got her to idle at 800 was to turn the idle stop screw up more. is there some sort of ballpark adjustments i can do to the carburetor to get her to run to a point where i can drive her? i turned the mixture screws in all the way, then 3 turns out what else can i do?
So no codes then? It sounds like the carb is dumping excess fuel, for some reason.
Needle & seat maybe?

I don't (or can't) see an air pump or air injection on the exhaust manifolds. Good for you.

Get your fingers to the EGR valve's diaphragm and move it. It could be sticking open, letting exhaust into the intake.
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Old 07-21-2017, 10:52 AM   #16
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Re: LG4 ignition timing

it may help to acquire an autoxray or similar scan tool to determine what the ECM is seeing and then set dwell.

in the meantime I'd set both the idle mixture and IAB to near 3 turns out and verify that the TPS is set at near 0.40 volts at idle. with an old school dwell meter you can then attempt to get the dwell set properly on the carb.

the excess fuel could be as simple as an improper dwell adjustment, providing all else is functioning correctly. that's why the scan tool really helps troubleshoot.
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Old 07-21-2017, 03:00 PM   #17
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Re: LG4 ignition timing

Quote:
Originally Posted by five7kid View Post

No clue. If you lightly seated them, then turned them each out 3 turns, they should be fine.

Now you need to adjust the IAC dwell.
where is the IAC? my car is carborated so i didnt think i had one
Quote:
Originally Posted by NoEmissions84TA View Post
So no codes then? It sounds like the carb is dumping excess fuel, for some reason.
Needle & seat maybe?

I don't (or can't) see an air pump or air injection on the exhaust manifolds. Good for you.

Get your fingers to the EGR valve's diaphragm and move it. It could be sticking open, letting exhaust into the intake.
no codes, i did have a code 23 when i first got the car but i replaced the MCS and counted the number of turns for the lean stop screw, so im pretty sure i put it back in the same spot. the car ran great for a while after i did that then this. no before i got the car the AIR system was removed all i have now is a jagged chopped pipe that runs from exhaust into the engine bay. ill give that a shot with the EGR
Quote:
Originally Posted by naf View Post
it may help to acquire an autoxray or similar scan tool to determine what the ECM is seeing and then set dwell.

in the meantime I'd set both the idle mixture and IAB to near 3 turns out and verify that the TPS is set at near 0.40 volts at idle. with an old school dwell meter you can then attempt to get the dwell set properly on the carb.

the excess fuel could be as simple as an improper dwell adjustment, providing all else is functioning correctly. that's why the scan tool really helps troubleshoot.
where is the IAB screw? its not the stop screw on the throttle bracket.
which wire on the TPS is the signal?
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Old 07-21-2017, 06:27 PM   #18
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Re: LG4 ignition timing

You are correct - carbs do not use IAC.

TPS - is a potentiometer.
Measure from the bottom wire (ground) to the center wire (wiper). I use common
pins pushed into the wires. I believe you are looking for .48v at idle.

See attached. Circled in red is where you adjust the TPS.

MCS - use an old school dwell meter set to 6 cyl. Connect the same way as TPS. You are looking for 30 degrees (50%) at idle.

I see that your carb is missing the throttle kicker solenoid. This is where you would have set your idle speed. Now you will have to set it with the stop screw for the throttle linkage arm.
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LG4 ignition timing-qjet.jpg  

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Old 07-22-2017, 06:59 AM   #19
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Re: LG4 ignition timing

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You are correct - carbs do not use IAC.

TPS - is a potentiometer.
Measure from the bottom wire (ground) to the center wire (wiper). I use common
pins pushed into the wires. I believe you are looking for .48v at idle.

See attached. Circled in red is where you adjust the TPS.

MCS - use an old school dwell meter set to 6 cyl. Connect the same way as TPS. You are looking for 30 degrees (50%) at idle.

I see that your carb is missing the throttle kicker solenoid. This is where you would have set your idle speed. Now you will have to set it with the stop screw for the throttle linkage arm.
i thought the throttle kicker solenoid was for the AC? when you switch it on it increases idle speed to accommodate for the extra drag on engine. i am trying to track one down because i fixed all the AC components on my car but those damn things are 100+
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Old 07-22-2017, 12:35 PM   #20
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Re: LG4 ignition timing

ok so i got the vacuum line removed from the baro sensor and rejoined the EGR vacuum supply line.

also removed the EGR valve and saw it was not sticking open, but it also does not work so ill be replacing that soon. ill put that on the back burner for now since that should not be contributing to my problem. the solenoid also feels like its closed so it should not be allowing vacuum through
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Old 07-22-2017, 06:00 PM   #21
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Re: LG4 ignition timing

Quote:
Originally Posted by 87tunedport View Post
i thought the throttle kicker solenoid was for the AC? when you switch it on it increases idle speed to accommodate for the extra drag on engine. i am trying to track one down because i fixed all the AC components on my car but those damn things are 100+
A/C idle bump up is one function of that solenoid.
The stop screw gets set to a very low idle speed.
Your normal idle speed it set at that solenoid.
That way when you turn the engine off, the solenoid retracts and helps
prevent run-on if the car was very hot and otherwise wished to do so.
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Old 07-22-2017, 06:07 PM   #22
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Re: LG4 ignition timing

Rock Auto has your solenoid.

Get your new EGR valve there also.
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Old 07-22-2017, 06:16 PM   #23
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Re: LG4 ignition timing

Quote:
Originally Posted by 87tunedport View Post
ok so i got the vacuum line removed from the baro sensor and rejoined the EGR vacuum supply line.

also removed the EGR valve and saw it was not sticking open, but it also does not work so ill be replacing that soon. ill put that on the back burner for now since that should not be contributing to my problem. the solenoid also feels like its closed so it should not be allowing vacuum through
I personally do not use EGR. In the past I have kept the valve in place, looking functional, but I had a BB in the vacuum line to prevent operation. I would just remove the BB for emissions testing. I believe your ECM cannot tell whether the valve actually opened, or not.

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Old 07-23-2017, 10:10 PM   #24
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Re: LG4 ignition timing

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Originally Posted by NoEmissions84TA View Post
A/C idle bump up is one function of that solenoid.
The stop screw gets set to a very low idle speed.
Your normal idle speed it set at that solenoid.
That way when you turn the engine off, the solenoid retracts and helps
prevent run-on if the car was very hot and otherwise wished to do so.
any idea what wire color goes to this? all my wires are chopped
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Old 07-23-2017, 10:36 PM   #25
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Re: LG4 ignition timing

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Old 07-24-2017, 07:04 AM   #26
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Re: LG4 ignition timing

The idle solenoid is engaged under certain conditions, none related to normal curb idle speed.

AC on
ECM command during decel
Power steering low pressure switch

Later models had the low pressure switch in the power steering line but it was not connected when AC was installed.

If your solenoid stays engaged at idle with AC off it could point to a faulty TPS-confusing the ECM into thinking it's still decelerating.
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Old 07-27-2017, 06:30 PM   #27
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Re: LG4 ignition timing

I was wondering would the choke have an effect on the cars idle if it was not adjusted right? The car fast idles fine at like 1100-1300 until i tap the gas then goes to normal idle
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Old 07-28-2017, 08:08 AM   #28
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Re: LG4 ignition timing

yes. the choke's fast idle may stay engaged. easy to check, just ensure that the throttle is completely set against the curb idle stop. you can fiddle with the choke linkage and ensure that its cam drops and releases the fast idle.
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Old 07-28-2017, 04:18 PM   #29
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Re: LG4 ignition timing

ok i watched and while tapping the throttle the fast idle releases fine

the TPS is .38 at idle. someone mentioned i may have a blocked air passage inside the carburetor causing a rich mixture cause i remove a vacuum cap and introduce more air the car runs better
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Old 07-28-2017, 06:24 PM   #30
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Re: LG4 ignition timing

Take a can of carb cleaner with the straw attached. You might want to epoxy one to the spray button so it does not get lost down the carb. I hate that. In the air horn, you will see a bunch of drilled holes, especially near the primary boosters. Shoot some carb cleaner in each of those passages with the engine off. Let it sit a few minutes for it to work. Start the engine and do it again. If you can relatively easily get to them, remove and clean the idle mixture screws and their passages also.
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Old 07-29-2017, 12:46 PM   #31
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Re: LG4 ignition timing

Well i just spent the entire morning taking the carb apart and cleaning it. It wasnt really that bad, but considering its only a year old i didnt expect much in rhe first place but im desperate. Put it back together, reset the mixture screws 3 turns out, i put another TPS in (like i said im desperate) turned the lean stop screw 1 more turn, put it all back together, and put on the car. Still idled at 500 in park and rough. The only way i can get to run at 900 is by removing the vacuum cap that goes to the air cleaner. I didnt touch the IAB
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Old 07-29-2017, 01:26 PM   #32
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Re: LG4 ignition timing

while i had the carb off i took some pics of the position of the mixture screws, idle stop screw, and the IAB. i also took a pic of the model numbers and canister vapor hose looks like there is a filter in there.
Attached Thumbnails
LG4 ignition timing-img_5074.jpg   LG4 ignition timing-img_5075.jpg   LG4 ignition timing-img_5076.jpg   LG4 ignition timing-img_5077.jpg   LG4 ignition timing-img_5078.jpg  

LG4 ignition timing-img_5079.jpg   LG4 ignition timing-img_5080.jpg   LG4 ignition timing-img_5081.jpg  
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Old 07-29-2017, 04:51 PM   #33
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Re: LG4 ignition timing

im gonna go out and get a vacuum gauge and adjust the mixture screws properly. if i turn them in will the vacuum increase or decrease?

update dwell meter and vacuum tested ordered and on the way any ideas about IAB? should i do anything with?

Last edited by 87tunedport; 07-29-2017 at 05:46 PM.
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Old 07-29-2017, 09:41 PM   #34
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Re: LG4 ignition timing

Question - does the carb make the MCS "ticking" sounds?
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Old 07-30-2017, 07:46 AM   #35
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Re: LG4 ignition timing

Quote:
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Question - does the carb make the MCS "ticking" sounds?
Yes, it does. It didnt when i first got the car and i had a code 23 for MCS. I replaced the solenoid and counted the number of turns when i took the lean stop screw out. So im pretty sure its back in the same spot. Now it clicks when i turn ignition on
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Old 07-30-2017, 06:08 PM   #36
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Re: LG4 ignition timing

How do the mixture screws work? If i turn them out does that allow more air? What do i use to adjust the MCS lean stop screw with out taking carb apart again?
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Old 07-30-2017, 06:57 PM   #37
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Re: LG4 ignition timing

WOW. We are going way back here.
OK. Good that the MCS is working.
Mixture screws - CW (IN) is leaner, therefore CCW (OUT) is richer.
They control an emulsified air and fuel mixture, not just air.
I have a bunch of special tools to adjust a CCC carb, some bought, some home-made.
I'm going to have to do a little research to get those old brain cells working again regarding the MCS lean stop.
Maybe someone else will chime in - with pictures.
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Old 07-30-2017, 07:35 PM   #38
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Re: LG4 ignition timing

The carb being rebuilt bothers me because you never know what was done to it.

You engine does not have a somewhat radical cam in it, correct?

Please check if your PCV Valve is working correctly.
It is a controlled vacuum leak. If it were totally blocked, that might explain why the idle speed increases and the engine smooths out when you remove a vacuum line, introducing more air.
Beyond that, we need to figure out what the ECM is seeing and therefore trying to control.
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Old 07-30-2017, 07:44 PM   #39
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Re: LG4 ignition timing

Have you determined if both of your mixture screws are working, and evenly?
Does each seem to have the same amount of control?
Start with each one at 5 turns out. Notice how it runs at this setting.
Then start turning one of them in (CW). At some point do things get better, or worse?
Then reset to 5 turns each and repeat for the other side.
Post what happened.
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Old 07-30-2017, 08:05 PM   #40
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Re: LG4 ignition timing



https://www.hemmings.com/magazine/mu...e/3720231.html
















If none of the above solves your problem, then there is a VERY SMALL chance that the well plugs are leaking. I see epoxy on the front of your carb, so I suspect your inner plugs were also done during the rebuild. Many are going to say that your plugs are leaking, but that was a common problem on the OLDER carbs, not the 80s models. But still, anything is possible.

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Old 07-30-2017, 08:20 PM   #41
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Re: LG4 ignition timing

In case you already didn't know this, this carb is just like a manual quadrajet with the addition of the MCS solenoid that leans the mixture at idle and part throttle ONLY. At a certain point of greater throttle opening, the ECM abandons control of the mixture and then the carb relies on its rod & jet calibrations.
So calibrating this carb involves essentially setting the RICH and LEAN stops, providing a window in which the ECM can properly control the mixture for your engine.
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Old 07-30-2017, 11:01 PM   #42
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Re: LG4 ignition timing

Quote:
Originally Posted by NoEmissions84TA View Post
The carb being rebuilt bothers me because you never know what was done to it.

You engine does not have a somewhat radical cam in it, correct?

Please check if your PCV Valve is working correctly.
It is a controlled vacuum leak. If it were totally blocked, that might explain why the idle speed increases and the engine smooths out when you remove a vacuum line, introducing more air.
Beyond that, we need to figure out what the ECM is seeing and therefore trying to control.
Quote:
Originally Posted by NoEmissions84TA View Post
Have you determined if both of your mixture screws are working, and evenly?
Does each seem to have the same amount of control?
Start with each one at 5 turns out. Notice how it runs at this setting.
Then start turning one of them in (CW). At some point do things get better, or worse?
Then reset to 5 turns each and repeat for the other side.
Post what happened.
as far as i know engine is completely stock. as far as PCV, the valve was replaced as well as the hose and connector going into the carb as far as internal passages i do not know.

one time i turned the mixture screws all the way in and the car continued to run and didnt miss a beat. once i tried tuning them by ear listening to the speed of the engine, but as i turned them there was no change in speed/sound or running condition even when they bottomed out

where can i get those tools especially the gauge/wrench for the MCS? i have a dwell meter and vacuum gauge ordered but after looking at the notes i doubt they will have any use for me.

seems more involved tuning the carb then i thought. would it be a better idea to just get another preset carburetor? or maybe take the air horn and throttle plate off the original carburetor since those have the presets and plugs still in place? i dont really have anybody around me that will still tune a carburetor let alone a computer controlled Quadrajet. maybe a Chevy dealer but i know ill get raped to have them do it if they even have the tools to do so

edit: i just drove the car up to storage facility and as i was pulling her in started to idle real low again and stumble, i started to turn the idle stop screw once more to bring idle up so she could stay running and i would turn the screw then WOT i would see drops of gas being thrown from the secondary plates. this car must be running super rich

Last edited by 87tunedport; 07-30-2017 at 11:09 PM.
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Old 07-31-2017, 12:07 AM   #43
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Re: LG4 ignition timing

one time i turned the mixture screws all the way in and the car continued to run and didnt miss a beat. once i tried tuning them by ear listening to the speed of the engine, but as i turned them there was no change in speed/sound or running condition even when they bottomed out

OK. Now we're getting somewhere. This is a problem.

where can i get those tools especially the gauge/wrench for the MCS? i have a dwell meter and vacuum gauge ordered but after looking at the notes i doubt they will have any use for me.


Most are not available anymore. But you can make your own. I will take pictures of mine and tell you how to do it.
The dwell meter you WILL use.

would it be a better idea to just get another preset carburetor?

No. Besides, we have not actually determined that the carb is the problem, yet.
If you wanted a great and updated for modern fuels qjet, see: http://cliffshighperformance.com/
You should have upgraded to a viton accelerator pump (compatible with modern gasoline) while you were in there.

i would see drops of gas being thrown from the secondary plates. this car must be running super rich

Your float level is too high, or you have too much fuel pressure overpowering the needle & seat.
Does your car use a block-mounted mechanical fuel pump? The original? Do you also have the in-tank electric pusher pump?
The block-mounted FP is easy to change (yours is like 32 years old if the original). Look for a Carter M6626 on ebay. Can be had for less than $20. Plus it's a great upgrade.
These cars use a 1/4" return line off that FP. If that line had a blockage (or kink, or crushed), the internal regulator in that FP would be disabled, and this could cause that problem. Look under the car.

Last edited by NoEmissions84TA; 07-31-2017 at 12:11 AM.
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Old 07-31-2017, 12:06 PM   #44
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Re: LG4 ignition timing

i found the J tool used to adjust the lean stop screw but as far as the gauges, have not found any.
Edit: i think its pretty ridiculous these tools are not available anymore, what are we supposed to do if we dont have them? Just screwed? I searched Thexton 370, balkamp 700-1134 and no shred of these tools are for sale used or new. Very frustrating 😠

since the original carburetor has all the plugs and factory adjustments should i try putting the throttle plate and air horn on the new carb? also whats the specified number of turns for the lean stop screw once i bottom it out?

i dont know if i have a pump in the tank but im pretty sure its the original block mounted pump since it looks pretty gritty

i went to put gas in the tank and as i was taking cap off loud hiss could be heard indicating built up pressure.

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Old 07-31-2017, 05:05 PM   #45
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Re: LG4 ignition timing

did you figure out the 4 wire that needs to be disconnected from the distributor? can i get a picture of this possibly?
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Old 07-31-2017, 06:48 PM   #46
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Re: LG4 ignition timing

but as far as the gauges, have not found any.

You use one of the cheap thin cardboard scales included in most carb rebuild kits. Cut it narrower to fit your needs.

i went to put gas in the tank and as i was taking cap off loud hiss could be heard indicating built up pressure.

This indicates that your tank is not properly vented. I assume your charcoal canister is no longer there? A common item to fail is the "UFO" tank vent located behind your driver's side rear wheel above the axle. You can't get a new replacement anymore. For $16.00, you can install this: https://www.summitracing.com/parts/tnk-vvr
There is also a member here working on reproducing those with a laser printer.

since the original carburetor has all the plugs and factory adjustments should i try putting the throttle plate and air horn on the new carb?

I would not start mixing parts from 2 different carbs yet.

also whats the specified number of turns for the lean stop screw once i bottom it out?

I would have to look that up.
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Old 07-31-2017, 06:57 PM   #47
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Re: LG4 ignition timing


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Old 07-31-2017, 09:23 PM   #48
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Re: LG4 ignition timing

Tuning Logic
Since the carburetor is self-correcting to the desired mixture strength, it is critical that all internal adjustments are correct. Once the float level, M/C solenoid travel, idle air bleed and TPS are set, the ideal dwell of 28 to 32 degrees (30 is perfect) is made by adjusting the mixture screws. This is what many mechanics did not understand back when these carburetors came out. They would try to get the dwell in range simply by turning the mixture screws, while all of the internal adjustments were incorrect. That is what gave the feedback carburetor a falsely earned bad reputation. It was not the fault of the carburetor, but the mechanic. The proper procedure is to do all internal settings, then seat the mixture screws gently in their bores. Next, back each out 3.5 complete turns as a base setting. Then install the carburetor and let the engine run and fully warm up so the system is in "closed loop" operation, meaning that the ECM is monitoring the oxygen sensor. It is best to drive the car a few miles before making any adjustment.

From the link I posted above: https://www.hemmings.com/magazine/mu...e/3720231.html
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Old 07-31-2017, 09:57 PM   #49
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Re: LG4 ignition timing

I found this while I was searching for those Thexton tools.
http://www.autozone.com/repairguides...00c152800a80d8
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Old 08-01-2017, 04:20 AM   #50
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Re: LG4 ignition timing

No, actually my canister is still hooked up. I even set it up to vent full time by removing the purge TVS and ran the vacuum line for the tank pressure valve directly to a vacuum source.

Yes i disconnected 4 wire connector. I have no pic but it goes from distributor base toward firewall and into the main wire harness back there. If you reach back tje right next to the oil pressure sender you will feel it

just ordered a rebuild kit that comes with a gauge so hopefully you guys can explain how to use it on the lean/rich mixture screws, and air bleed

Last edited by 87tunedport; 08-01-2017 at 09:42 AM.
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