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Hi guys,
1985 Trans Am 5L with Rochester Quadrajet E4ME carb. Running very rich. No adjustable Fuel-Air-Mixture screws on carb. Intermittent problem: stalls at red lights, stops. Idle doesn't seem overly slow or anything. RPMs just lunge to complete stall. Then for whatever reason, it'll start holding up just fine... Not sure yet if it has to any relationship to actual engine temp or just random behaviour.
The dash gauge indicates temp at zero, all the time. So, probably need a new sensor. Was thinking that maybe ECU isn't getting temp info. Could someone please tell me more about which sensor controls the dash gauge and which one informs the ECU about engine temp for choke variation?
Thanks.
Last edited by Iroc_Them_All; 06-03-2021 at 02:36 PM.
It is common for these carburetors to cause rough running conditions when the Carb needs to be cleaned or rebuilt.
Also the Carb does actually have Idle Mixture Screws... but they are hidden.
The Carb needs to be removed from the Intake-Manifold and flipped Upside-Down to locate the Idle Mixture Screws.
They are in the front of the carb just above the throttle-plate... but are covered by the main-body casting.
The two images below show the locations of the Screws if they were not hidden:
When the Carb is flipped Upside-Down... you will see two spots where you can chip-away some of the casting with a punch and hammer.
Then you can make adjustments with the two Screws.
I do strongly recommend that the Carb gets cleaned and rebuilt.
if you're truly interested in diagnosis and repair of the feedback system for your vehicle, there are a few basic checks we can do before we need to acquire scanner of some sort to read the data 'live'
although starting with a scanner is preferable.
if you plan to hack away at your idle mixture screws first though, disregard.
the ecm temp sensor is in the water neck and has a two-wire connector. the dash sender is between #1 and #3 spark plugs and has a one-wire connector. They are unrelated-not interconnected-the function of one has no effect on the function of the other.
It is common for these carburetors to cause rough running conditions when the Carb needs to be cleaned or rebuilt.
Also the Carb does actually have Idle Mixture Screws... but they are hidden.
The Carb needs to be removed from the Intake-Manifold and flipped Upside-Down to locate the Idle Mixture Screws.
They are in the front of the carb just above the throttle-plate... but are covered by the main-body casting.
The two images below show the locations of the Screws if they were not hidden:
When the Carb is flipped Upside-Down... you will see two spots where you can chip-away some of the casting with a punch and hammer.
Then you can make adjustments with the two Screws.
I do strongly recommend that the Carb gets cleaned and rebuilt.
Good luck and have fun!
Ok, That really Rocks! Thanks for that post. I have an extra carb that comes from same generation Camaro. I compared your pix with it and it really looks sealed off (you'd never even think there MAY be screws in there). But, on the carb body there is a round nipple-type top seal where you would usually adjust the screw(s) (one on each side). And when looking into the chamber, there is a small hole (where the needle must sit) in both chambers. Also, when viewed from underneath there isn't the open view into the area with the screw, just the same finish as the rest of the carb. Are we 100% sure there are adjusment screws in there? I'm itchin' to punch through there now.
if you're truly interested in diagnosis and repair of the feedback system for your vehicle, there are a few basic checks we can do before we need to acquire scanner of some sort to read the data 'live'
although starting with a scanner is preferable.
if you plan to hack away at your idle mixture screws first though, disregard.
the ecm temp sensor is in the water neck and has a two-wire connector. the dash sender is between #1 and #3 spark plugs and has a one-wire connector. They are unrelated-not interconnected-the function of one has no effect on the function of the other.
Thank you for that post. I will be poking around in there soon, be back soon with some findings.
Ok, That really Rocks! Thanks for that post. I have an extra carb that comes from same generation Camaro. I compared your pix with it and it really looks sealed off (you'd never even think there MAY be screws in there). But, on the carb body there is a round nipple-type top seal where you would usually adjust the screw(s) (one on each side). And when looking into the chamber, there is a small hole (where the needle must sit) in both chambers. Also, when viewed from underneath there isn't the open view into the area with the screw, just the same finish as the rest of the carb. Are we 100% sure there are adjusment screws in there? I'm itchin' to punch through there now.
Every F-Body that I have had go through my Shop with a CCC E4ME Quadra-Jet Carburetor has had them...
However I am not an expert in CCC E4ME Quadra-Jet Carburetors.
These were way before my time as an Engineer for GM.
It is possible that things changed and maybe the Idle-Mixture Screws are not there... maybe, I do not know for certain.
Here is a Hyper-Link for the GM/ Delco/ Rochester Manual for the Dual-Jet and Quadra-Jet Carburetors (Page 13, Figure 18 shows how to access the Idle-Mixture Screws): Link
They're called anti-tamper caps and are suppose to keep people from messing with the screws, but over time the screws move out of spec. Anyway, the (idle) mixture screws are behind those caps on the throttle plate. You have to break the casting from the beneath the caps to remove or some people drill holes in the caps and pull them out. Either way you have to remove the carb/throttle plate, it helps if you then separate the throttle plate from the carb to do this.
The small aluminum caps on top of the carb are for the lean mixture and rich mixture stops. The caps do have to be drilled and then pulled up/off to adjust the rich/lean screws. If your pull the airhorn off you can also push said caps out from the underside of the airhorn. However, you need a special tool with a tiny double D socket to adjust them stops. There is also a small height gauge used to adjust the rich/lean stops. Back when i had a carb i just made my own height gauge(stops) DD tool some old copper tubes
Having said that it really helps if you get the FSM or at least the haynes/chilton manuals. they show/tell you how all these need to be adjusted. By this point though you might as well rebuild the carb though.
This is a E2 carb, but the caps/mixture stops are the same on the E4. The idle air bleed (screw) also has an affect on idle quality.
Before you start messing with the adjustments on the carb, you need to check a few things first:
1) this carb has an old fashioned thermostatic choke coil supplied with +12v. Is it connected and functioning properly?
"Choke" is not controlled by the ECM. You are thinking fuel injection.
2) those small black vacuum lines get very brittle and easily break over time. Check those for vacuum leaks.
3) the gauge sensor is between #1 and #3 on the cylinder head. The ECM coolant temp sensor is in the water neck where the thermostat is.
It was a common problem for an intermittent connection at that connector because a hose ran right over the top of it. GM's remedy was a new sensor and pigtail with a different style connector.
4) look around carefully. This might not be a carb problem at all.
Also, does the dash "check engine" warning light work? Any codes? Does your carb make a "ticking" noise?
Last edited by NoEmissions84TA; 06-04-2021 at 09:21 PM.
Before you start messing with the adjustments on the carb, you need to check a few things first:
1) this carb has an old fashioned thermostatic choke coil supplied with +12v. Is it connected and functioning properly?
"Choke" is not controlled by the ECM. You are thinking fuel injection.
2) those small black vacuum lines get very brittle and easily break over time. Check those for vacuum leaks.
3) the gauge sensor is between #1 and #3 on the cylinder head. The ECM coolant temp sensor is in the water neck where the thermostat is.
It was a common problem for an intermittent connection at that connector because a hose ran right over the top of it. GM's remedy was a new sensor and pigtail with a different style connector.
4) look around carefully. This might not be a carb problem at all.
Also, does the dash "check engine" warning light work? Any codes? Does your carb make a "ticking" noise?
Thanks for the great post. I will look through your check list before I mess around with the carb.
Tell me, how does the thermostatic choke coil work? Is it similar to the clutch fan, when it reaches a certain temperature around the engine it kicks on? Or in this case, off.
Tell me, how does the thermostatic choke coil work?
It's a bi-metallic coil that heats up when +12 volts is applied to it. As it gets hotter the coil relaxes and the top choke plate is then allowed to open.
There is also a linkage connected to this setup that speeds up your idle when the choke is ON, and your engine speed steps down as the coil heats up and the choke plate opens, finally landing you at curb idle when the plate is fully open. By then the engine should be warmed up enough to keep running without the choke. A cold engine/cold air requires the mixture to be richer.
If yours is not working, either you do not have 12 volts at the choke coil, or the coil is dead and you need to replace it.
06-03-2021, 02:33 PM
