1999 Gen VI EFI to Q Jet 4L80E

[92Raiderburban]

Ok here’s a question. On the 93 6.5 diesel trucks that had an automatic with a 4l80e and mechanical injection (no engine computer) did it have a stand alone computer for the transmission or was it mechanically controlled? Mine is dead so not sure if it does or not. Swapping a 350 in it as well.

Yes it is a stand alone controller. if u find one itll work. just need to modify the shift points

 

[Supercharged111]

This is just not true.

98-2001 black box and 0411 DO revert to full line pressure on the stock OS's if you don't change the settings like is described in my previous posts' linked thread on the HP tuners forum. It is not because the data isn't there for it to function, but because the OS is set up to do that when the MAF is failed. There are options in the OS to turn that off. A 2002 0411 OS will not default to full line pressure if the MAF is failed properly. There ARE custom SD OS's, but those are usually only to allow the 2 and 3 bar MAP sensors so that you can run boost. It is standard to fail the MAF sensor in the OS to revert the system to SD so that you can dial in the VE tables. Most people just let it go to full line pressure while doing this, since it doesn't really hurt anything. It just makes the shifting much harsher at low throttle conditions. I'm running an '02 OS, so I don't have this issue at all.

If you fail the MAF in the tune and then just hook up a line pressure gauge to the trans, you can tune the normal and abuse mode tables to set them properly based on what the PCM thinks the engine is doing.

Since this thread floated to the top I took the time to peruse the blackbox tutorials and in EFILive there are no provisions to turn off max line pressure fault enablers as there are in the 411. It's been forever since I ran that PCM and couldn't be too sure I hadn't missed it, but it's not there for EFILive as it is with the 411 so I stand by what I said as it pertains to EFILive. If it's there for HPT, great.

 

[Road Trip]

First and foremost, I am old! Yes back when they invented the wheel old! My diagnostic skills are FAR better on 4 barrels and some hand tools and a vacuum gauge than trying to diagnose a computer. No I don't still carry a beeper. I quit working on my old muscle cars back about 94. Since then it has just been maintenance on my daily drivers.

Greetings,

Really enjoyed reading both your project proposal as well as all of the follow-on
discussion by the ECU subject matter experts -- I've actually wondered about the
pros & cons & real-world feasibility of fabbing up a Q-Jet / 4L80-E hybrid that's good
enough to be a 'get to drive' instead of a 'have to sell' machine. Amazing
how many of my implementation questions were answered...even ones I hadn't
thought of yet on my own. :0)

Anyway, I'm not going to try to persuade you to convert the truck to
carburetion. Or, for that matter, attempt to persuade you to try to
grok EFI. Instead, I'd ask you to simply figure out which of the
2 different approaches will make you actually look forward to opening
the hood (hopefully in preparation for a bucket list road trip) ...and that
is the way to go.

****

Having said that, hypothetically speaking let's assume that you decide
to go ahead and return to Venturi-land. And that all the remaining
ECU <> 4L80-E details are properly sorted out.

So now we're down to choosing a carburetor that isn't just good enough
for a trailer queen or dedicated 1/4 mile racer. Instead, the carburetion is
good enough in the real world to be used for daily driving / carefree
cross-country touring.

Although I may be in the minority, IMHO the absolute best combination
of driveability, efficiency, and full-throttle operation is the Quadrajet.

More specifically, a Quadrajet that is carefully dialed in to your powerplant
according to Doe Roe's book from the mid-'70s titled "Rochester Carburetors":

You must be registered for see images attach

I just checked, and even though this book has been out of print for ages,
there are currently copies of this book for sale, from rough to NOS condition,
for ~$12 & up. IF you decide to run a Q-Jet and don't already have this in your
shop library, do yourself a favor & pick up a copy.

FWIW, Doug Roe worked at GM's AZ proving grounds, and was also a
motorsports competitor, especially in hillclimbs. His knowledge of how to tune
these carbs to the specific needs of a particular build is encyclopedic.

NOTE: Many people don't realize that the part-throttle driveability of a carb
is determined mainly by the strength of the venturi signal obtained from the
air being ingested into the engine. In the case of the Q-Jet, not only are
the primaries small (high velocity airflow) but they are also stuffed with a triple
venturi setup. Jetted up properly, this design quickly responds to the slightest
change in throttle position. (near-zero lag)

NOTE: The only other carb I can think of that comes close to the throttle
response of a modern EFI setup is the Holley 4180 4-bbl that was used
on the '83-'85 Ford 5.0 HO motors. The biggest difference between this
carb vs it's 4160 ancestor was the use of the large annular discharge venturi
in the primaries. The main justification was more precise metering for
lower emissions (again, due to a much stronger venturi signal) ...but the
side effect was improved throttle response/driveability. As a matter of fact,
my first new car was a '84.5 Mustang GT with the 5.0/5-spd, and it drove
EFI good -- made for an entertaining daily driver!

Last but not least, the sound of a Quadrajet at WOT on top of a sharp
350 or 454 (preferably with air cleaner lid flipped) *still* gives me
goosebumps. If everything else technically came up even, the siren song of
the old Q-Jet at full throat would tip the scales for yours truly in favor
of the old school solution.

Good thing we aren't neighbors...I got a feeling that some dumb stuff
would commence in short order. :0)

From one old dude to another best of luck with whatever you brew up!

 

[Schurkey]

The other "must-have" book for Q-jets was authored by Cliff Ruggles. It's immensely easier to read than the Roe book, has color photos, and like every SA Design book ever published, too few pages all sourced from Communist China.

www.amazon.com/Rebuild-Modify-Rochester-Quadrajet-Carburetors/dp/1932494189/ref=sr_1_1?crid=3FXQF8KXIRH8S

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[Road Trip]

Greetings Schurkey,

Have read many of your replies in this forum over the past year while researching repair
strategies for my (new to me) '99 C2500. Good stuff, solid troubleshooting approach!

I've seen this book referred to elsewhere on the interwebs over the years, but at the time
I decided to wait until someone savvy recommended it. Happy to report that your post
tipped me over the edge & I just successfully set this in motion:

You must be registered for see images attach

(Side note: Followed your link for a new copy...but elected to purchase a used
copy from 'GoodwillBooks'. Net cost the same as a new copy due to the small
additional shipping charge...but I'm just hoping this choice puts a small but much-needed
deposit into my karma account. :0)

Thanks again - the deeper the shop library, the more unfair advantage that it becomes. (!)

 

[Scooterwrench]

I've got Ruggles book or should I say Q-jet bible. After studying and putting what I learned to use I was able to get 19mpg in my 355 with cam,porting and headers. It will smoke the tires in first and second and chirp them going into high with a 270 rear gear.

 

[Road Trip]

The other "must-have" book for Q-jets was authored by Cliff Ruggles. It's immensely easier to read than the Roe book, has color photos, and like every SA Design book ever published, too few pages all sourced from Communist China.

Just wanted to close the loop on this. The info in this book neatly dovetails
with the book I already use. Wanted to share a big thumbs up for your
recommendation:

You must be registered for see images attach

One thing that definitely impressed me was that on p. 105 was the first time I've
ever read in print about a trick setup (courtesy of Pontiac) that we used to unfair advantage
back in the early '80s. We used what's shown in the book on a 355ci SBC that we
built/patterned after the '70 LT-1. (Note: We swapped this into a '75 Chevy Monza
that originally came with a sad, asthmatic 262ci/2bbl SBC. At least it had the 4-speed.)

No dyno sheets, but the 355 with the parts we pieced together promised
~3x the suds of the original smogger 262. After we found/destroyed/upgraded all the
associated too-weak drivetrain & suspension bits, the car eventually
became a genuine sleeper.

Pontiac used the Q-Jet on all of their hottest single 4-bbl offerings that actually
made it to showroom floor -- unlike Chevy, which put out plenty of stout engines
equipped with the Q-Jet, but outsourced (insourced?) the Holley 4-bbl for use on
their top of the line 'halo' motors.

...but back to Mr. Ruggles book. After rebuilding/dialing in scores of Q-Jets,
I found that you could really set those Pontiac secondary air valves to open up
quicker than all the other ones. (Chevy, Olds, Buick, Caddy, etc)

The secret was the slotted openings (and associated larger holes supplying
the 'secondary accelerator pump shot' on the leading edges of those huge
air valves. So, instead of the air valve having to open a few degrees
(while pulling against the vacuum break & preload spring) before
the 'accelerator pump' discharge holes would be exposed to air flow, the
Pontiac version started with the accelerator pump delivery just as soon
as the 2 1/4" secondary throttles were opened up by the driver.

The difference in responsiveness was not subtle. You could really throw
your buddy back in the seat with a crisp downshift if they weren't paying
attention. :0)

Of course the Pontiac Q-Jet would not fit on the SBC due to the
forward-facing fuel inlet forcing the fuel line directly into the SBC's thermostat
housing, so we were forced to use the Pontiac top on a modified Chevy Q-Jet
body (with it's side-facing fuel inlet).

It was well worth the aggravation -- thanks to the advantageous power/weight ratio,
the right centrifugal advance weights in the distributor, etc., downshifting &
snapping the throttles wide open gave the same sensation as a Holley double-pumper
...for a lot less money, for we were sourcing all our go-faster carburetor
bits at the local Treasure Yards.

****

Up 'til now, despite visiting more than a few rabbit-holes, I have seen
zero discussion about this Pontiac Q-Jet feature...and nobody I've ever
talked to knew what I was describing. I'm impressed with the whole
book...but I was jazzed when I came across the discussion starting
on p. 105.

Again, big thumbs up for your recommendation. And who knows,
maybe some GMT400/Q-Jet enthusiast will do something similar
and make the tranny behind their engine really work for a living.

Cheers --

 

[Schurkey]

Pontiac's big claims to Q-Jet fame:
1. Removing the second booster venturi on a very few carb applications, for increased primary airflow. Some guys saw the booster ring off, then have trouble getting the calibration right. Pontiac did that for you--IF (big IF) you can find one of those carbs.
2. The secondary air-flap/"accelerator pump" as you described.
3. The externally-adjustable fuel metering on quite a few Pontiac-specific carbs (unlike the booster ring change on very few carbs)
4. Some Pontiac applications had a bigass inconvenient float-bowl vent that requires a hole in the air cleaner housing. The float bowl vents directly into the air cleaner, trapping the fumes for later burning.

Buick's big claim to Q-Jet fame
Starting in...'71 or '72, Buick was the first to use the larger primary venturis. Instead of losing the outer ring on the booster venturi like Pontiac, they made the venturi larger. This transferred to many other Q-Jet applications across the GM brands, especially after the "Mod-Quad" in '75. LOTSA applications had the bigger primary venturis.

Olds big claim to Q-Jet fame. (Well, I've seen it on Olds carbs, but I don't know that it was ever an exclusive feature.)
"Pull-Over Enrichment". There was a pair of holes in the choke tower over the primary venturies, each with a brass tube leading to the float bowl. At heavy throttle, high RPM, there was enough vacuum along side those holes to draw additional fuel from the float bowl to provide heavy-throttle enrichment. This meant that the jetting/air bleeds could be leaner for better economy at low throttle settings.

I can't think of any Chevy or Caddy Q-Jet exclusives.

 

[L31MaxExpress]

Pontiac's big claims to Q-Jet fame:
1. Removing the second booster venturi on a very few carb applications, for increased primary airflow. Some guys saw the booster ring off, then have trouble getting the calibration right. Pontiac did that for you--IF (big IF) you can find one of those carbs.
2. The secondary air-flap/"accelerator pump" as you described.
3. The externally-adjustable fuel metering on quite a few Pontiac-specific carbs (unlike the booster ring change on very few carbs)
4. Some Pontiac applications had a bigass inconvenient float-bowl vent that requires a hole in the air cleaner housing. The float bowl vents directly into the air cleaner, trapping the fumes for later burning.

Buick's big claim to Q-Jet fame
Starting in...'71 or '72, Buick was the first to use the larger primary venturis. Instead of losing the outer ring on the booster venturi like Pontiac, they made the venturi larger. This transferred to many other Q-Jet applications across the GM brands, especially after the "Mod-Quad" in '75. LOTSA applications had the bigger primary venturis.

Olds big claim to Q-Jet fame. (Well, I've seen it on Olds carbs, but I don't know that it was ever an exclusive feature.)
"Pull-Over Enrichment". There was a pair of holes in the choke tower over the primary venturies, each with a brass tube leading to the float bowl. At heavy throttle, high RPM, there was enough vacuum along side those holes to draw additional fuel from the float bowl to provide heavy-throttle enrichment. This meant that the jetting/air bleeds could be leaner for better economy at low throttle settings.

I can't think of any Chevy or Caddy Q-Jet exclusives.

Caddy had the altitude compensating bellows and 3rd jet.

Chevy had the dual capacity accelerator pump.

I have added transition eyebrows, opened up those ports, added primary pull over enrichment, cut down the booster rings on large bore mod quads as well as deleted the power piston and primary metering rods. Tow vehicles, RVs and Boats really enjoy the down leg booster ring delete combined with the primary rod delete. Really helps them get some additional part-throttle power without having to go into the secondaries. Running a little richer helps reduce the tendency for manifolds to crack as well on hard working engines like the P30 454.

 

[Schurkey]

Caddy had the altitude compensating bellows and 3rd jet.

Was that "only" Caddy? I thought several of GMs divisions had that...in '75 only, first year of Mod Quad. I think it was gotten-rid-of for '76.

I haven't seen one in ages. Everything I've taken apart has the black plastic "shot glass" where the bellows was.

Chevy had the dual capacity accelerator pump.

Good point. Saw a lot of those on early-80s pickups. Lotsa folks thought it was a mixture-control solenoid, but the visible plastic part was a different color from a MC Solenoid.