Electronic QuadraJet and factory Electronic Spark Control

[gmc2000]

> I got one of those carbs-they call it a dual capacity accelerator pump that the shop I bought my 76 GMC from
> put on when they built the engine. The builder left out the solenoid and has a pug in the top where the wiring
> would go. These carbs had no (MC) mixture control solenoid or (TPS) throttle position sensor. From what
> I have been able to find out so far is they were on 85-86 non computer controlled trucks 305 on up. I am looking
> for the jets and rods that were used on this carb to have some place to start tuning.

cool! yes, one of the two electronic q-jet carbs.

Ive been looking for a complete engine wiring harness diagram for this one so I can learn more about it. please let me know if you run across anything
while digging for info. I havnt found any concrete info on exactly what trucks came with it and kinda need that to find the diagram. I will be sure to
post back if/when I find more details about it too.

best I can tell from searching the internet is that it had a coolant temp sensor to activate the electronically controlled aux pump but it would seem
to me that that would have to have some sort of ECU on its own, but also as far as I have been able to determine, the trucks that came with this carb
also had the ESC HEI system and thats really why Im most interested in the wiring diagram for one, so I can tell exactly what is involved with the ESC
since it would be the only OEM ESC that was not controller by the engine ECU like on the other electronic q-jet and all the TBI stuff afterwards.

 

[gmc2000]

from your link Quote:
> On E4MED models, ... The idle speed solenoid, used primarily on air conditioned vehicles, maintains correct curb idle speed whenever the
> compressor clutch is engaged.

there was recently a topic about adding an idle controller for when the A/C compressor kicks in on here, it was interesting to read some of the
suggestions. looks like this carb would do that without any backyard engineering.

the wiring diagram on that page shows an ECU and O2 sensor etc. still nothing concrete as far as exactly which trucks came with this though but there
is some codes on the diagram

V8=LS9
K100(06) & LS9 & NB2
K100 (03) (06) & LS9

I know what LS9 is but whish I could figure out what the other codes mean, that seems like it would translate into something I could use to get all
the right components.

I am getting the other CCC components I mentioned from that caprice but dont have anything to experiment on with them yet. on the look out for 455s
now too and might end up with an engine before a coach. lol I have a lead on an early toranado thats been in a barn for decades. guy says it was
wrecked and has some front end damage but not real bad just got to go look at it. its not a for sale deal, but he said he was sure they would sell it.

 

[johnny]

Fred, 'lean burn' was the Mopar way of meeting emissions with a controlled carburetor. It did as lousy a job as everyone else's of the time, FI cured
the problems. I had not any great problems with my carbureted coach - as long as it ate non alcohol gas. Summertime plus ethanol plus traffic adds
up to potential problems in a GMC. I got the coach to survive with a new fan clutch, recored radiator, and dropping the engine driven fuel pump in
lieu of a pair of electric pumps. It would then - by actual unfortunate test - survive thirty or forty minutes of downtown Atlanta Friday afternoon
traffic without complaint.

--johnny
--
76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
"I forgive them all, save those who hurt the dogs. They must answer to me in hell" - ol Andy, paraphrased

 

[gmc2000]

the ESC is what Im most interested in but I also think that both of the GM electroQjets are worth more investigation and could be very useful.

Ive been meaning to ask about the popular e. fuel pumps that seem to be most recommended for these. the big carter ones, does anyone know if they can
be doubled on the same line? specifically, if one can push fuel through another that is inline but turned off and also could they pull through another
in line that is off?

I found some wiring diagrams that I think have what I need to run stand alone ESC. this is the best one so far:
http://www.73-87chevytrucks.com/techinfo/7387CKMans//Wiring/ST_352_86_1986_Chevrolet_GMC_Light_Truc_Wiring_Manual_CK_10_30_Only.pdf

 

[johnny]

The Mr. Gasket pumps have backflow valves but presumably you could pull gas through one, although one has to ask why. Sucking the current stuff
called gasoline in the summer is a prescription for vapor lock. All I can see cascading them would gain is one more point of failure. If you want to
go to electric pumps for a carbureted system, here's how:

http://www.gmcmhphotos.com/photos/g6198-cane-9-creek-rv-park-heflin-2c-al.html

--johnny

DOS Tip: Don't use the supplied input filters. Pick up a pair of the Wix replacements. The originals will develop air leaks.
--
76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
"I forgive them all, save those who hurt the dogs. They must answer to me in hell" - ol Andy, paraphrased

 

[jim kanomata1]

You will not gain anything by going to 800 CFM carb as you will not rev up
enough to get there.
If you drag race, then you'll Need to address that.
I feel you guys can come up with an improvement with your trials.
I'll be following your progress

On Sun, Jul 1, 2018 at 8:02 AM Johnny Bridges via Gmclist <

> The Mr. Gasket pumps have backflow valves but presumably you could pull
> gas through one, although one has to ask why. Sucking the current stuff
> called gasoline in the summer is a prescription for vapor lock. All I can
> see cascading them would gain is one more point of failure. If you want to
> go to electric pumps for a carbureted system, here's how:
>
>
> http://www.gmcmhphotos.com/photos/g6198-cane-9-creek-rv-park-heflin-2c-al.html
>
> --johnny
>
> DOS Tip: Don't use the supplied input filters. Pick up a pair of the Wix
> replacements. The originals will develop air leaks.
> --
> 76 26' Eleganza(?) with beaucoup mods and add - ons.
> Braselton, Ga.
> "I forgive them all, save those who hurt the dogs. They must answer to me
> in hell" - ol Andy, paraphrased
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
--
Jim Kanomata
Applied/GMC, Newark,CA
jimk
http://www.appliedgmc.com
1-800-752-7502

 

[johnny]

Nor did I say anything about huge carbs, Jim

--johnnny
--
76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
"I forgive them all, save those who hurt the dogs. They must answer to me in hell" - ol Andy, paraphrased

 

[BoboBob]

I have to disagree when you say "You will not gain anything by going to 800 CFM carb".

Yes it is true we don't need the 800 CFM on the top end but what you are really gaining
with a 800 CFM carb is an increase in airflow that is due to a larger primary venturi.
1 7/32 inch venturi = 800 CFM
1 3/32 inch venturi = 750 CFM

As we run around on the primary venturis 80% of the time this would help us out and also
maybe stay out of the secondaries as much.

--
Bob Broadwell
76 Eleganza II-Rebuilt performance engine, Manny trans, Manny 1-ton front end living in Las Vegas

 

[BoboBob]

Best setup I have found so far for vapor lock is do away with the factory pump.

Install a good electric pump back by the fuel tanks-can use 2 pumps or a switching valve.
No fuel filter between the pumps and the tanks. Up front where the old pump used
to be install a 3 port fuel filter-3/8 inlet/outlet with a 1/4 return-they are a bit
hard to find. Then run a new line off the 1/4 side of the fuel filter all the way back to
the gas tanks and dump into the tanks.

Works well and this is where I got the idea from.

http://www.gmcmhphotos.com/photos/3-port-fuel-pump-2c-filter-2c-and-hot-fuel/p57439-3-port-fuel-filter.html
--
Bob Broadwell
76 Eleganza II-Rebuilt performance engine, Manny trans, Manny 1-ton front end living in Las Vegas

 

[Jim Hupy]

If you really want poor throttle response on the bottom end, on vehicles
with tall final drive ratios, ( like 3:07 - 1 ) then just bolt on a big 'ol
Holley double pumper. It will fall right on it's nose. Same thing with a
big Quadrajet, or Carter AFB.
What you ARE after, is velocity in the inlet tract. This will promote
throttle response. This requires smaller, not larger primaries.
It was the reason for tri-power instead of one great big carb.
Don't have enough room on the net to explain further, but trust me on
this one. If you want a more in-depth explanation, catch me at a rally
sometime and we will add it to the bull session.
Bigger ain't better, no matter what your car guy buddies say.
Jim Hupy
Salem, Or
78 GMC ROYALE 403

On Sun, Jul 1, 2018, 1:19 PM Robert Edwin Broadwell
wrote:

> I have to disagree when you say "You will not gain anything by going to
> 800 CFM carb".
>
> Yes it is true we don't need the 800 CFM on the top end but what you are
> really gaining
> with a 800 CFM carb is an increase in airflow that is due to a larger
> primary venturi.
> 1 7/32 inch venturi = 800 CFM
> 1 3/32 inch venturi = 750 CFM
>
> As we run around on the primary venturis 80% of the time this would help
> us out and also
> maybe stay out of the secondaries as much.
>
> --
> Bob Broadwell
> 76 Eleganza II-Rebuilt performance engine, Manny trans, Manny 1-ton front
> end living in Las Vegas
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

 

[johnny]

The pumps I referenced need filters in front of them and the filters ship with the pumps. Any vane pump should have a filter in front of it. The
pumps listed will deadhead without problems, there's no need for a return line. It doesn't show, but I capped the selector vale openings with push -
on caps. The pumps are fed by the original lines to the selector, and the same switch picks up the relay for AUX. In this way you can revert to OEM
for bolting a mechanical pump on and replacing the three hoses... no cutting necessary. Cured vapor lock in Georgia in July - August. Also, if you
turn the ignition on for ten or fifteen seconds before cranking, it primes the carb for a quick start.
Go down to the Men's Mall and find an '05 or so Ranger pickup with a 3 liter Vulcan motor. Look on the firewall in the cab just above the passenger
toeboard under the carpet. Under a guard bolted to the firewall is the turnover switch. The Ford one also shuts down on a certain G-force so if you
hit something but the wreck stays upright and running it'll still kill the pumps. Use it in lieu of an oil pressure switch. I say Vulcan motor
because mine had one, but i suspect the four cylinder and four liter ones use the same setup.

--johnny
--
76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
"I forgive them all, save those who hurt the dogs. They must answer to me in hell" - ol Andy, paraphrased

 

[gmc2000]

I prefer a return line but Im not sure the best way to do it on a Q-jet.

you can also do the safety kill by taping into the low oil pres sender or light itself without a special sender, run that to a relay then out of it
onto the e.pump so it removes power when the light comes on. then use the ignition switch to starter solenoid for start up, some ignition switches
even have a primer circuit built in just ahead of the regular starting position and also spring loaded and you can prime before going into the start
position.

 

[johnny]

well, what benefit will you gain by having a return line on a float bowl carb?

--johnny

--
76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
"I forgive them all, save those who hurt the dogs. They must answer to me in hell" - ol Andy, paraphrased

 

[gmc2000]

some carbs (some webers anyway) have recirculating float bowls, not sure exactly why, maybe consistent pressure, but keeping the fuel flowing seems
like a good idea for keeping it cool too but also cleaning it for stuff that doesnt get used as frequently.

I use modular glass filters, for visibility reasons mostly and I route them safely and in some cases cover them for protection.

 

[jim kanomata1]

My comments are backed by trial and error. Like JimH said you'll not gain
much unles you rev in 4,000

On Sun, Jul 1, 2018 at 5:12 PM Johnny Bridges via Gmclist <

> well, what benefit will you gain by having a return line on a float bowl
> carb?
>
> --johnny
>
> --
> 76 26' Eleganza(?) with beaucoup mods and add - ons.
> Braselton, Ga.
> "I forgive them all, save those who hurt the dogs. They must answer to me
> in hell" - ol Andy, paraphrased
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
--
Jim Kanomata
Applied/GMC, Newark,CA
jimk
http://www.appliedgmc.com
1-800-752-7502

 

[johnny]

I agree, jim. I just wondered why you quoted my post and then mentioned high flow carbs. No matter. I think Hupy is correct, after I took the big
one off my truck and put a Holley clone on it steams along much better.

--johnny

--
76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
"I forgive them all, save those who hurt the dogs. They must answer to me in hell" - ol Andy, paraphrased

 

[gmc2000]

Ive found more good stuff..

this is a fairly easy and inexpensive repair for worn throttle shaft bores with teflon bushings: http://rmcavoy.freeshell.org/Q_Jet_bushings.html

FWIW it does look like there is room in the throttle casting for small sealed ball bearings as those found on some weber carbs.

a link to the latest Q-jet manuals for all the spreadbore carbs. includes the two electronic ones:
http://www.oldcarmanualproject.com/manuals/Carbs/Rochester/QJet/index.htm

and the best Ive found so far: http://truckroadservice.com/barth_attachments/7993991167_86_P30_service_part3.pdf this has both the E.Q-jet specs, All
the ESC timing advance specs including the HEI module specs.

BoboBob13, here is the wiring diagram for the E4MED:

its a direct circuit with no ECU control like I thought it would have to be.

 

[johnny]

If you want to use oil pressure to run a relay you'll have to add it. The GMC oil sender runs a gauge - it's a rheostat, not a switch. I'd rather
not add stuff to the oil system with another porential leak. I'll use the Ford one.
If you hang a relay across a low oil light switch, you need a steering diode, otherwise the oil light is going to glow slightly.

--johnny
--
76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
"I forgive them all, save those who hurt the dogs. They must answer to me in hell" - ol Andy, paraphrased

 

[BoboBob]

2K

My 4M4ED only has mixture adjustment screws on the primary side-never seen or heard of mixture screws on secondary side.

The stock carbs on the GMC MH were 750 CFM with a 1 3/32 inch primary bore.
The carb I'm setting up is an 800CFM with 1 7/32 inch primary bore.
Why am I using this carb? It's what they put on the motor when they rebuilt it.

Waiting for some new primary rods to go with the jet set I bought along with a set of
drill bits from 0.3 to 3.0 mm so I can do some modifications. Using Cliff Ruggles First
Recipe as a start point and installing a AEM wide band Air/Fuel Ratio gauge so I can see where
I'm at and fine tune things.

Thanks for the wiring diagram-not sure if I will ever hook it up. As of now I don't have the solenoid
that goes in the carb. The temp switch is the ground and 39 is power but I don't see where they are
pulling power from. Would be easy enough to hook it up if there is a cold drivability problem.

Bob B
--
Bob Broadwell
76 Eleganza II-Rebuilt performance engine, Manny trans, Manny 1-ton front end living in Las Vegas

 

[gmc2000]

I'll try to get my hands on one of those Ford safety tilt/impact switches to play around with. thats a good idea. at least for normal operations and
adding a direct prime with it should take care of the rest.

the adjustable a/f screws would be great for anything that spends and extended amount of time @WOT. I use an A/F indicator for tuning too and also
cylinder head temp senders and exhaust temp probes, with gauges still sometimes but the reading the O2 of the GMC at least I would consider a must
have on something as stressed loaded as the GMC engine.

that best so far link really does have some good info! shows all the variances in the HEI distributors too.

but I wouldnt throw out a good mechanical ignition distributor either, I'd keep it handy as a just in case back up for who know what the future holds.
I guess thats another reason in the back of my mind that I have such a thing for old school carbs etc.

https://i.imgur.com/9xZiEc2.jpg

that and the old boy scout motto just stuck with me I guess.