Electronic QuadraJet and factory Electronic Spark Control

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what size is the original carburetor on the 455 and has anyone tried an electronic QuadraJet?

info about them here http://www.early3rdgen.com/forum/viewtopic.php?t=25 these were the carbs just prior to fuel injection that were sort of a hybrid
carburetor/fuel injection that utilized an 02 sensor to modulate part throttle metering electronically on the fly.

I have been digging around the internet for exactly what applications were. so far Ive only seen mentions of them used on any big blocks and havnt
been able to confirm this but it was widely used on the smallblocks in 1985 and 1986

reading more, it seems like it would be a really good system for the GMC that *should* bolt right onto the original intake manifold.

with and OEM ECU, HEI ESC distributor, wiring harness, and O2 sensor this should be able to work well on a GMC but Ive yet to find out what big block
trucks had these if any.

the small block stuff is everywhere and its a 750 cfm spreadbore style carb. Ive also seen mention of Cadillac using it on the 500 but havnt dug into
that deeper yet.

I had a truck that had ESC and a car that had the E.Q-jet and ESC and both of those were 100% reliable in the short time I owned them. drove great
too!

anyone here familiar with or have an interest in this stuff? after reading the link, seems to me it would be a really neat upgrade, if possible (thats
what Im trying to determine)
 
Those feedback Qjets were a stopgap measure until true EFI got sorted out. Other manufactuers were soing much the same starting with the Mopar 'lean
burn' system up 75 until about 85.

I hasd one factory stock on an 84 trans am. Worked well when it was stock, but even mild mods caused the ECU to flip out. Tried some tricks to
modulate it. Eventually gave up and went to a non electronic Q jet and later an Air sensors EFI.

The ECU also controlled the ignition timing and wasnt adjustable or easily tunable. Had to replace the dizzy also.

AFAIK, all those are 750 CFM. 800 CFM Q jets are comparitively rare. They have larger primarys

The feedback system only worked in closed look [idle and cruise] conditions and used a narrow band sensor. open loop [operations were mechanicly
controled as they always had been.

Bottom line is I dont think its worth messing with. If you want to invest the time and money to use an aftermarkert ECU to control it it might work
but you would be far better off with at least a TB type FI or Fitech type self tuning unit
--
76 Glenbrook
 
In an "as left the factory" condition they worked pretty well. I have one on my 84 Riv with Olds 307. The TPS can be problematic and difficult to
adjust. You would also need some serious dyno time and need to write and burn a chip. It worked well in continuous light cruise but in a 12,000 pound
vehicle it might be at max duty cycle most of the time and out of range. Not to mention the needed donor car looms and computer. My stock Qjet/HEI
starts and runs like EFI so I see no reason to add multiple issues.
--
John Lebetski
Woodstock, IL
77 Eleganza II
 
is the GMC Q-jet an 800cfm? how often do the secondaries open up on the interstates?

what about just the ESC, these were HEI type distributors with ECU and O2 sensors, pretty basic but seems like it would be useful on such a loaded
engine. I wonder if any of those might be 'plug and play'
 
The secondaries open up when your foot pushes too hard on the pedal next to
the foot brake. If you do not like that flushing sound of your hard earned
dollars being forced through the intake tract, lighten up on the pressure a
bit. Those secondaries make a holley four barrel double pumper seem like a
fuel saver by comparison. At road speed on flat country, they normally do
not open, but, anytime the vacuum dips below about 7" of water column, the
metering rods lift and the upper plate opens. Dumps fuel right out of the
float bowl through the main jets. $$$$$.
Jim Hupy

> is the GMC Q-jet an 800cfm? how often do the secondaries open up on the
> interstates?
>
> what about just the ESC, these were HEI type distributors with ECU and O2
> sensors, pretty basic but seems like it would be useful on such a loaded
> engine. I wonder if any of those might be 'plug and play'
>
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
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Reactions: eserv
I am not sure what the cfm of the quadrajet is that is on our coaches...

I just made a trip about 600 miles out to Mt. Rushmore and 600 miles back home.

The trip out there, I do not believe my secondaries were opening. My carb was rebuilt back in 2012. I usually drive on flat roads, but going out to
South Dakota, I was heavy on the throttle, and pretty disappointed in it's performance pulling my 99 CRV up the hills. on the flat my vacuum was
normally at 10, but hitting the hills and pressing on the throttle quickly dropped it down to about nothing.

I looked at it before I headed back East, and found the secondary plate seemed a little sticky, and squeaked when I pressed on it. After putting
some oil on the spring that held it closed, it opened up with very little effort.(pushing on with finger). I also verified that when pushing the
foot pedal down the lower flaps would open fully.

On the way east, the hills were not as bad as going west, and the GMC performed significantly better and you could hear the change in the carb when I
hit a hill and had to push down the peddle a bit more. My vacuum going home was up a couple notches to probably 12 on the gauge on the flats, and
pressing on the pedal, it still dropped down to nothing, but there was much more power. 6.5 MPG coming home, running hard on the only tank I
checked. (never put much into that as I think there is large decrepency as to how full I get my tanks each time I fill up).

So from my experience Saturday/Sunday, the secondaries normally only open on harder acceleration, and hill climbing. They are not open or needed at
flat cruising speed, even at south dakota freeway speeds. I think Jim is Correct it is about the 5-7 on the vacuum gauge when you start to hear
them open up.


--
Jon Roche
75 palm beach
St. Cloud, MN
http://lqqkatjon.blogspot.com/
 
> The secondaries open up when your foot pushes too hard on the pedal next to
> the foot brake. If you do not like that flushing sound of your hard earned
> dollars being forced through the intake tract, lighten up on the pressure a
> bit. Those secondaries make a holley four barrel double pumper seem like a
> fuel saver by comparison. At road speed on flat country, they normally do
> not open, but, anytime the vacuum dips below about 7" of water column, the
> metering rods lift and the upper plate opens. Dumps fuel right out of the
> float bowl through the main jets. $$$$$.

thats another thing I was curious about, is the original q-jet a vacuum or linkage activated secondary? your first line indicates it is a linkage but
then you mention 'vacuum dip'.

right now Im looking into the early ESC info. so far it looks like the 1986 calif. versions incorporated ALDL "Assembly Line Diagnostic Link" and the
check engine light functions as a rudimentary diognostic tool when put into dignostic mode which could be usefull.

trying to figure out which vehicles that had ESC and a ALDL port now and then look at the schematics for them to see what all could be done with
those. perhaps a DIY digi panel utilizing the OEM ESC ECU? or some other realtime displays while keeping the carburetor but incorporating the knock
detection etc.
 
The actual secondary throttle plates open progressively via mechanical
linkage partnered with the primaries. But, the fuel is metered by vacuum.
The secondary metering rods are raised by spring pressure held in balance
by high engine vacuum. When that vacuum is reduced as the throttle plates
open, the spring lifts the needles and fuel flows out the main jets. Clear
as mud, right?
Jim Hupy

> > The secondaries open up when your foot pushes too hard on the pedal next
> to
> > the foot brake. If you do not like that flushing sound of your hard
> earned
> > dollars being forced through the intake tract, lighten up on the
> pressure a
> > bit. Those secondaries make a holley four barrel double pumper seem like
> a
> > fuel saver by comparison. At road speed on flat country, they normally do
> > not open, but, anytime the vacuum dips below about 7" of water column,
> the
> > metering rods lift and the upper plate opens. Dumps fuel right out of the
> > float bowl through the main jets. $$$$$.
>
>
> thats another thing I was curious about, is the original q-jet a vacuum or
> linkage activated secondary? your first line indicates it is a linkage but
> then you mention 'vacuum dip'.
>
> right now Im looking into the early ESC info. so far it looks like the
> 1986 calif. versions incorporated ALDL "Assembly Line Diagnostic Link" and
> the
> check engine light functions as a rudimentary diognostic tool when put
> into dignostic mode which could be usefull.
>
> trying to figure out which vehicles that had ESC and a ALDL port now and
> then look at the schematics for them to see what all could be done with
> those. perhaps a DIY digi panel utilizing the OEM ESC ECU? or some other
> realtime displays while keeping the carburetor but incorporating the knock
> detection etc.
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
thanks for clarifying. interesting. I have very little experience with Q-jets, webers are what Im most familiar with and would prefer but the floor is
the limit here. ;)

FI is great but all in all, if youre familiar with carb tuning, the reliability and the amount of spare parts (both in cost and weight) to carry along
and then be able to use effectively, is much less.

the E.Quad-Jet does seem like a perfect compromise between carb or FI for these though but definitely it would take some work to have something better
than just a regular Q-jet.

ESC and a stock Q-jet seems to be a sound logical step up without adding too much unneeded complexity and cost. I'll keep looking into this..

the vapor lock is always tricky but Im sure it can be eliminated while keeping the Q-jet, thats not really directly related to the carb but the fuel
supply system, right?
 
> thanks for clarifying. interesting. I have very little experience with Q-jets, webers are what Im most familiar with and would prefer but the
> floor is the limit here. ;)
>
> FI is great but all in all, if youre familiar with carb tuning, the reliability and the amount of spare parts (both in cost and weight) to carry
> along and then be able to use effectively, is much less.
>
> the E.Quad-Jet does seem like a perfect compromise between carb or FI for these though but definitely it would take some work to have something
> better than just a regular Q-jet.
>
> ESC and a stock Q-jet seems to be a sound logical step up without adding too much unneeded complexity and cost. I'll keep looking into this..
>
> the vapor lock is always tricky but Im sure it can be eliminated while keeping the Q-jet, thats not really directly related to the carb but the
> fuel supply system, right?
>
>
> Edit to add: a GMC site about FI just came up in my 'ESC' searching : http://www.gmcws.org/Tech/efi/efi.html
>
> its from '00 and has this tidbit "Since our distributors do not have the ability to respond to ESC, we can use something like the manual MSD spark
> adjustment and the MSD knock sensor. (MSD devices are used to permit electronic spark advance and retard as a means of providing appropriate timing
> for engine loads, altitude and similar conditions where it is desirable to be able to adjust the timing without manually rotating the
> distributor.)"
>
> is this still the case? and brings me to this question, do the chevy distributors interchange? (fit into the Olds 455)

GMC2k,
To answer your last question, NO, most GM distributors go the other way.

I happen to like real fuel injection systems. This completely eliminates the closed loop carburetors of the mid-70s. Those were just a stop gap that
provided miserable driveability and fuel economy.

With the right setup, popping the hatch and tweaking the distributor is just not a big deal. Now, if I had the time and money to go to a full system
as many have done here with EBL and all, that might be nice, but the real gain here is the engine mapped timing and knock sensing. As it is, my coach
goes all over the place at 9.2MPG (when it has 8 good pistons).

If your coach has HEI, you should carry at least a spare US made module and the correct coil (ours are the rare number) because HEI is not great for
reliability. (That is my personal view based on experience with other's GM products.)

Want to learn more about Q-jets??
http://oldcarmanualproject.com/manuals/Carbs/Rochester/QJet/index.htm

Matt
--
Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan
OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Twixt A2 and Detroit
 
its GMC2000 ...

GM HEI is very reliable from my experience. over 350,000 on one truck with it but a spare ignition module is a good idea on anything.

so if the Olds spins opposite the Chev, then perhaps the dist. drive gear is interchangeable and if not maybe it is with some minor machining or is
there some other reason a chev ESC dist. cant be adapted/modified to work?

it may not have too be, perhaps the ESC components could be used in the Olds HEI dist. I dont have a coach or Olds to compare them (yet) just doing
research until the right one pops up but who knows, maybe someday we will have a 'GMC2000 ESC Ignition conversion kit' available to keep the timing
right on and on the fly automatically.

a Motek or weber-marelli full digital engine management sys would be sweet but to have a complete back up system for that in case who knows what comes
up is a whole lot more pricey than a carb and a hanful of off the shelf GM ignition components. but Id go for it if I was trying to break the land
speed record or something. LOL
 
Sounds like you really want to try 80s electronic controls on your GMC. FYI the Olds V8 continued in 307 cu in displacement through 1990 in some full
size GM cars. These later years all have electronic quadrajets and HEI. I don't know if they had knock sensor control.
For what it is worth I'd stick with the OE quadrajet. They are incredibly tunable and if you are familiar with other carbs you can learn quadrajets
as there are a few good books devoted to the subject such Doug Roe's book. The later years (76-78) have adjustable part throttle (APT) metering.
Between primary jetting, primary rods (the GMCs are a special triple taper), secondary rods, primary power piston springs and the APT the Q-jet can be
dialed in quite satisfactorily. It just takes a linear lambda gauge, an assortment of jets and rods and careful note taking. The only downside
relative to fuel injection is the lack of altitude compensation. I may get some argument over this last point, but there are many here who will agree
that the q-jet is actually pretty darn good in terms of performance and economy.
--
Chris Geils - Twin Cities
1978 26' Kingsley w/ very few mods; Headers, Progressive Dynamics 9040, aux trans cooler, one repaint in stock colors, R134a, Al rad, 50k mi
 
> Sounds like you really want to try 80s electronic controls on your GMC. FYI the Olds V8 continued in 307 cu in displacement through 1990 in some
> full size GM cars. These later years all have electronic quadrajets and HEI. I don't know if they had knock sensor control.
> For what it is worth I'd stick with the OE quadrajet. They are incredibly tunable and if you are familiar with other carbs you can learn
> quadrajets as there are a few good books devoted to the subject such Doug Roe's book. The later years (76-78) have adjustable part throttle (APT)
> metering. Between primary jetting, primary rods (the GMCs are a special triple taper), secondary rods, primary power piston springs and the APT the
> Q-jet can be dialed in quite satisfactorily. It just takes a linear lambda gauge, an assortment of jets and rods and careful note taking. The only
> downside relative to fuel injection is the lack of altitude compensation. I may get some argument over this last point, but there are many here who
> will agree that the q-jet is actually pretty darn good in terms of performance and economy.

thanks for this input. upon searching the internet further about ESC I found another GMC document (pdf) this one a presentation from a club event or
something and mentions one of the forum members or maybe more that Im not familiar with.

http://www.gmceast.com/technical/Swartzendruber_Generic_TBI_SlidesNotes.pdf

it is a great presentation! Im mainly interested in the ESC part of it right now but there is alot of good info on the TBI side and yes it mentions
that in fact there is an ESC HEI dist. for the Olds from a 307 car as you mention here.

this is the first Ive seen about this. Ive read about folks using knock sensors and alert systems for them and MSD manual timing control but not using
the OE ESC to do it all automatically but apparently a few have done this.

the cool thing is, it can be used with an original Q-jet and it would help with altitudes slightly too just through the timing. not better than FI but
better than no, or manual timing control.

but.. the 307 Oldsmobiles that had the ESCs, likely had the E.Q-jet carb too. I'll keep digging..

the pdf also mentions "John Wilsons DIY manual" anyone familiar with it and know where to obtain it?
 
Well, I thought Lean Burn represented the worst of both worlds. No loss at all, and a good way to ruin a Carter carburetor.

--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
 
> Well, I thought Lean Burn represented the worst of both worlds. No loss at all, and a good way to ruin a Carter carburetor.
>
> --johnny

too lean is a good way to ruin pistons, and carbs too I guess, if they are on top off an exhaust crossover. but I think lean, generally, is more
efficient than rich, it also helps keep the ridges that develop in the top of cylinder bores to a minimum.

I wonder if that heat blocker gel stuff for use when welding sensitive parts (remarkable stuff!) would help a non blocked exhaust crossover?
http://www.athea.com/file/0312-web-tech-data-sheet.pdf

or if it could be made into a solid? something like a phenolic spacer.. or if not, if a gel filled spacer with it could be useful? if it doesnt loose
its potency over time.

I bet it could help in some areas for vapor lock issues as it is (gel) too..

Ive found a complete ESC and E.Q-jet system in a Caprice a friend has been parting out, he just wanted the engine and trans from it and says I can
have all the other stuff. also have access to a superflow 901 engine dynomometer.

I think its time to start looking for a 455 Olds power source.. LOL and I love that LeMans Blue they came in too.
 
Jim Hupy-- going back a few responses-- the spring on the secodary air valve trys to CLOSE it. The air flow on the wider side of the air valve wants
to open it wide. The spring combined with the vacuum pot want to close it. The dropping vacuum is timed via an orifice in the vac pot to limit opening
speed. Rod height (enrichment) is a function of mechanical cam action based on air valve degrees rotation. To adjust air valve there is a wind up
spring and locking screw to adjust spring tension. A larger orifice hole will also speed opening. Faster is not better though.
--
John Lebetski
Woodstock, IL
77 Eleganza II
 
gmcmhphotos site member 'rharms' has looked into this and posted some photos of the E.Q-jet and stock Q-jet side by side along with some close ups of
the E.Q-jet parts here http://www.gmcmhphotos.com/photos/g4322-feddback-q-jet.html

and 'weidnerl' has posted some photos and info on the later M4E Q-jet that is not electric but has altitude compensation here:
http://www.gmcmhphotos.com/photos/g4144-altitude-compensating-q-jet.html

also found details on a different OEM E.Q-jet and HEI set-up from 1981-86 trucks/vans with 305s (RPO LB9). this HEI had a 5 pin module and the E.Q-jet
it came with was 800cfm and did not adjust the mixture at all and only had an electronically controlled auxiliary accelerator pump that was only for
cold conditions and worked off a coolant temp sensor.

this one seems to be the best donor for the ESC componenets to make a stand alone ESC to be used with a stock Q-jet carb.
 
Jim Hupy-- going back a few responses-- the spring on the secodary air valve trys to CLOSE it. The air flow on the wider side of the air valve wants
to open it wide. The spring combined with the vacuum pot want to close it. The dropping vacuum is timed via an orifice in the vac pot to limit opening
speed. Rod height (enrichment) is a function of mechanical cam action based on air valve degrees rotation. To adjust air valve there is a wind up
spring and locking screw to adjust spring tension. A larger orifice hole will also speed opening. Faster is not better though.
--
John Lebetski
Woodstock, IL
77 Eleganza II
—————-
 
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.
--
Bob Broadwell
76 Eleganza II-Rebuilt performance engine, Manny trans, Manny 1-ton front end living in Las Vegas
 
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