1980 Feedback Qjet help needed

[cv67]

Looking at a 80 E Camino
Guy took out the 305 put a goodwrench 350 in it with a smallish cam betting something a touch more than stock thats it. Did a nice job all the smogs there

Noticed the motor shook some guessing its lean?
Carb is the one off the 305. Solenoid was clicking away on it.

Can this be richened up, are these problem pieces meaning it would never "be right"?

[RednGold86Z]

E4ME carb or something like? I pulled a 305 4bbl out of our 86 El Camino this winter, and I've also got an 86 Z28 with that - not using either.

You can check the voltage on the Oxygen sensor with a voltmeter. It should be switching between <300mV to > 600mV every 1 or 2 seconds. That means it's lambda 1 (14.7).

A shake could be an ignition problem or a vacuum leak - there are a bunch of plastic and rubber vacuum lines that could be cracked.

If I recall correctly think they put some plugs over the idle mixture screws. Easy enough to take off.

Here's a scan of the book on it:
http://www.thirdgen.org/techboard/carbu ... uild.html

[nhrastocker]

The expert on those carbs is Dean Oliver.
http://www.deanoscarbs.com

[Tuner]

If you are handy with electronics an Innovate MTX-L will give you an A/F gauge with the capability of supplying two different (separate, as in with some creative wiring you can switch between two different AFR settings) programmable analog signals to connect to the O2 sensor input to the ECU and provide the voltages the ECU expects to see from the narrow band O2 sensor, but adjust the AFR to whatever you choose (within reason). The ECU will control the carb in feedback like it does now but at the AFR you choose.

It probably will like to be a bit richer a very light load, but at higher cruising speed and intermediate loads you can lean it to the 17/1 AFR range pre-smog engines enjoyed and get better mileage. When you crowd the throttle for moderate acceleration, engines can run very lean to save fuel.

A QJet has the double-booster primary venturi which vaporizes the fuel very effectively and for that reason can usually run most engines in intermediate load conditions more than 1 A/F leaner than other carbs. Some engines are happy as a clam at 18/1 in a moderate acceleration part-throttle load condition, below 12” Hg down to 6” or so, below which you would change to the power A/F. Naturally, the engine wants whatever A/F it wants for best power at WOT, 12.5/1 or ??/1. How lean an engine will run at part-throttle depends a great deal on A/F distribution.

Have you removed the idle mixture screw anti-tampering plugs and tried adjusting them at all? To idle smooth the cam will probably want a little richer A/F than the the original cam, but as you make adjustments the ECU and O2 sensor will be changing the carb solenoid dwell trying to move the A/F back to stoichiometric. Have you read a service manual so you know the procedure to use a dwell meter to set the carb solenoid travel?

The secondary is just a normal QJet. If it has a DH rod it should be OK.

[justahoby]

Tuner , is their any direct way to use that solenoid, in a simple circuit with an 02 sensor? or is that solenoid need to be strictly used pulsating via the control unit? I gots a pile of electronic q jets...

[Tuner]

Easiest way is to use the ECU and all the related sensors so the ECU will be happy. The carbs have a TPS built in and the system needs the Temp Sensor and what ever else. The ECU will follow the O2 voltage and you can feed it the voltage oscillations it expects at any AFR between .5 and 1.5 λ with the Innovate system, the same as I described in a thread about the GM TBI.

I imagine someone who knows their stuff could figure a way to use a 555 timer to control a circuit to run a driver controlling the carb solenoid by itself, but why bother when the factory ECU will do it?

[RednGold86Z]

Tuner , is their any direct way to use that solenoid, in a simple circuit with an 02 sensor? or is that solenoid need to be strictly used pulsating via the control unit? I gots a pile of electronic q jets...

I could make you a control ECU... with wideband and ignition control... But, I think those carbs are pure open loop at full throttle.

[justahoby]

Tuner , is their any direct way to use that solenoid, in a simple circuit with an 02 sensor? or is that solenoid need to be strictly used pulsating via the control unit? I gots a pile of electronic q jets...

I could make you a control ECU... with wideband and ignition control... But, I think those carbs are pure open loop at full throttle.

Yea.. The secondaries are just like the old fashioned ones... No electronics on the secondaries. Just the big ol back barrels dumping fuel

[justahoby]

Easiest way is to use the ECU and all the related sensors so the ECU will be happy. The carbs have a TPS built in and the system needs the Temp Sensor and what ever else. The ECU will follow the O2 voltage and you can feed it the voltage oscillations it expects at any AFR between .5 and 1.5 λ with the Innovate system, the same as I described in a thread about the GM TBI.

I imagine someone who knows their stuff could figure a way to use a 555 timer to control a circuit to run a driver controlling the carb solenoid by itself, but why bother when the factory ECU will do it?

Thank you... I was reading the early TBI was similar on the oscillations frequency.. How reliable was the system for these? People seemed scared and ripped of the electronic Q as fast as they could... Often I wondered if it was simply the solenoid needed changed, or just a simple problem, like they pulled the carb apart, and the float was set wrong.. it seemed the control unit was really closely related to the TBI , and they don't rip them out to go carb..

[barnym17]

If I remember correctly(it has been a long time)the soloniod opens and closes 60 times per second and was checked using a dwell meter. The computer controlled part throttle mixture by varying the closed vs open time .Holley had similar arrangement called 1/4 mile dial if you can find one of these controllers I would imagine it would work well with the Q-jet.With no current applied or disconnected the carb is in the full rich state (metering rods up) with current full lean(rods down).The computer pretty much tried to average between to lean and to rich to end up just right.
You can use these carbs to good advantage without the computer by adjusting the metering rod height to get the mix you want at cruise the adjuster is accessible from the top of the carb just keep lowering the rods a little at a time till it is to lean then back up till it cruises smoothly or use an afr gauge and really dial it in.

[DaveMcLain]

There is a target MC solenoid dwell that you shoot for when the engine is idling in closed loop. I can't remember right off the top of my head what that is but essentially you go down through the top of the carburetor and adjust the position of the primary rods till you are within that target range. It's certainly possible that the carburetor has something in an idle feed restriction that's causing it to be excessively lean. With the ethanol fuels of today the carburetor with the standard calibration will probably be very lean at idle and you probably should remove the idle limiter caps so that you can adjust the screws as part of your rebuild.

There's nothing scary about the electronically controlled Q Jets really.

[cv67]

Havent taken anything apart still belongs to someone else just looked at it.
Wanted to make sure I wasnt potentially buying a problem seems safe enough.

If I did whatever I enounter has to be simpler than OBD2 issues Im having

[novadude]

I always thought that it would be cool to have a adjustable controller available that let's you dial-in cruise AFR with one of these E4M carbs. Seems like it would be a good way to keep tight control on cruise A/F while flowing plenty of air to support a hot street car. Might have to play with metering rods and rich / lean stops a bit, but it seems like it would be a great street / strip carb.

Not surprising that no one has ever released such a gadget given the perception of q-jets in the hot ridding community. Te time to jump on this idea would have been 10 years ago when junkyards were littered with e4m carbs that were almost free.

[Tuner]

The regular QJet with the 3/8” bowl vapor vent nipple on the front is easy to rig with “back-suction” by connecting a hose from the PCV with a valve to control intake vacuum applied to the bowl vent. By reducing bowl pressure you can lean it at a cruise. When you roll in the throttle the vacuum drops so the leaning effect diminishes as load is applied.

[DaveMcLain]

The regular QJet with the 3/8” bowl vapor vent nipple on the front is easy to rig with “back-suction” by connecting a hose from the PCV with a valve to control intake vacuum applied to the bowl vent. By reducing bowl pressure you can lean it at a cruise. When you roll in the throttle the vacuum drops so the leaning effect diminishes as load is applied.

That's sort of what happens when the car has a bad canister purge valve.