Redneck DoD

[Deancr11]

Well seams like you just need to get a 4 banger and drop in. That way your only using only 4 and your happy.

 

[Schurkey]

You assume all my O2 sensors are working (both downstream are not)

Upstream O2 sensors affect fueling. Downstream O2 sensors monitor catalyst efficiency, but don't affect fueling.

 

[JJF20]

Sounds like the original DoD systems.. look up the 1981 Cadillac 6-8-4. Most unplugged it, didn’t work very well. That said, I had a Eldorado in the late 80’s, and it never gave me an issue.

I agree on opening the circuit. Imho, I think you’d end up with a mess on your hands, fouled plugs, rough engine.

It would be an interesting experiment. Not one I’d want to do on a family trip though. Sounds like play time stuff to me.

 

[0xDEADBEEF]

Just drive it. You are going to cause yourself an issue trying to save $100.

 

[RichLo]

Someone stated earlier mentioned "flow-matched injectors". How about a recommendation? I want to replace all 8 before I set out, but I'm nervous about getting crap. 6 to 7 thousand miles for a road-trip, I want to make sure everything is running top-notch before I leave.

Bosch, Power & MPG, 1996-2000, GMC, Chevrolet, 454, 7.4L (J)

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www.fiveomotorsport.com

 

[johnckhall]

Just drive it. You are going to cause yourself an issue trying to save $100.

My son that just graduated with a BBA in Economics would tell you to weigh your "opportunity cost". Does the time and effort (and aggravation in getting it right) outweigh the $100 savings? I agree, just take off and enjoy the trip without the hassle.

 

[Pinger]

My son that just graduated with a BBA in Economics would tell you to weigh your "opportunity cost". Does the time and effort (and aggravation in getting it right) outweigh the $100 savings? I agree, just take off and enjoy the trip without the hassle.

Is the juice worth the squeeze?.

 

[Erik the Awful]

Drive on the highway for a few miles to get your tires up to temp. While they're still hot, air them up to a couple PSI below the max pressure. That'll get you more fuel economy than your redneck DOD.

When you're driving, accelerate like you have a 2x4 stuck under the gas pedal. Once you're up to speed, try and limit your gas pedal changes. If your cruise control works, use it.

If your A/C doesn't work, fix it and use it instead of having your windows down.

 

[Road Trip]

So I'm thinking about going on a road trip, cross-country, and I had this thought about wiring a couple switches. One grounds out Injectors 1, 4, 6, and 7. The other grounds out 8, 3, 5, and 2. (Firing order is 18436572). The goal is to increase my gas mileage on the highway. By having 2, I can switch between them to ensure more even wear.

So besides my computer throwing codes for constant misfires, can anyone see any reason not to do this for those many hours cruising at highway speeds?

It's a 96 Vortex 7400 (454). Just my truck, kids and luggage. Not towing. Nothing on the rack. Constructive responses appreciated. Thanks.

Hello mpyusko,

Great question. When it comes to pushing the MPG envelope with a specific vehicle, a thought
experiment like this can yield additional insight to the engineering tradeoffs built into our vehicles.
Well worth pondering in these times, even if it doesn't immediately yield a demonstrable MPG improvement.**

**** A Brief History of V8 > V4 engine conversions

Back in the '70s during the height of the Arab Oil Embargo, there were a small handful of people who were
experimenting with V8 to V4 conversions. From individual mechanics experimenting all the way to a complete
kit offered by Crower. From the outside looking in, back then a V4 conversion operating 100% of the time
just smelled like 100% of the weight penalty with 50% of the displacement, combined with the coarse feel
of a power stroke every 180° of crank rotation.

Sure, there might be an improvement in MPG, but in terms of the daily driving experience the operator was going to
pay dearly for every drop of fuel saved in the process. :-( (I know the above sounds a bit extreme, but back then
a lot of us were reeling by the tripling of gas prices in a year.)

Q: To put this into perspective, how would a rapid shift to $10-$12/gallon gas today affect your household budget?
So instead of pursuing a V4 conversion, I instead bought a newly released book on Rochester Carburetors and
started experimenting with lean-cruise implemented using brass logic in my '70s-era mechanical computer metering the
precious juice. (Book Full O' Carb Theory)

****

But I digress. Given the above, your idea about a 'part-time V4' under driver control for a GMT400 equipped with a
big block caught my attention. And thanks to the sheer amount of talent in here, the peer review process to date
has been a positive one, especially in the area of implementation details. Here's a prime example:

The computer doesn't supply injector power, rather it grounds the injectors. So manually grounding them will leave them fully open all the time. Would make that #3 misfire less of a priority.

This gentleman's statement is spot on as shown by the '96 FSM wiring diagram for the 454 SFI setup:

You must be registered for see images attach

Studying this wiring diagram, looks like Schurkey's comment is the best way to implement your idea:

I'm thinking that if you HAVE to do this, you want to OPEN the circuit, not ground it.

As engineered by GM, all 8 injectors 'float' at whatever voltage is at fuse ECM 1. Once
the CKP sensor starts sending pulses to the VCM (and we're above ~400 rpm) these
injectors are grounded in the firing order by the VCM, creating the necessary current flow
to open the injector and deliver the fuel shot to the cylinder.

Installing 2 NC (Normally Closed) switches in the dash, one opening the 1-4-6-7 injector path,
with the other opening the 8-3-5-2 injector path looks like a feasible implementation that
wouldn't outright injure any electronics involved? And if the driver uses the 'V4 via fuel cut'
function only during cruise conditions, will this give us both big block cake when working, and
also improved MPG during cruise conditions?

Possible Pros:

* Potential improvement in pumping losses during highway cruise? (ie: lower intake manifold
vacuum when 3.7L displacement V4 is maintaining same necessary cruise HP as 7.4L V8?)

Possible Cons:

#1) Guaranteed disruption of O2 sensor feedback from shut down cylinders distorting Closed Loop
operation as noted by several. Work-around: Force Open-Loop operation in V4 operation.
(Note that Open Loop operation routinely occurs both during warmup and also during WOT operation.)

Also, in discussions elsewhere it's been stated that when the stored tables in the VCM are closely
matched to the engine, the resulting Open Loop operation can be very close to optimal operation.
(Just no realtime tuning around parameters that are drifting from the default values.)
Work-around possible? Yes.

#2) Bringing excess RFI into cab from engine bay using normal unshielded wiring. Big potential
issue for drivers still using their AM radio. Not so much for FM listeners. Not an issue for
drivers using their smart phones as their tunes source. Potential impact on other in-cab circuits
unknown. With shielded wire, proper bypassing where the wire enters the cab, etc., if this RFI
issue surfaced it could be mitigated. Work-around possible? Yes.

#3) Weak/unmetered Air/Fuel mixture in intake manifold (from reversion pulses created by the events
surrounding the closing of intake valves) gets drawn into 'dead' cylinders. Too weak to ignite, these
unburned HCs exit the cylinder and heat up the cats?

We have all seen the training videos showing the feature of SFI, where the intake valve opens, and
a shot of fuel is neatly injected into the air being sucked past the open valve & into the cylinder.

But what a lot of people don't realize is that this is the behavior only when the properly sized injectors are
running at low HP/low duty cycle conditions. When the HP demand goes up, the injectors can and do
end up running at 80-90% duty cycle. In English, the injectors are on 80-90+% of the time...whether
the intake valve is open -or- closed. (!) So I don't think of the intake manifold in the 7.4 SFI setup
as being a perfectly 'dry' intake. Especially with the tuned-length runners and all the slinky-style
pressure pulses going on. (Not to mention any crankcase blowby introduced into all this by the
PCV valve.)

Work-around possible? Maybe. The right combo of short duration intake valve timing (decreased
reversion pulses) + increased size injectors (to lower amount of time open) + small turbo might
get the intake system to operate much 'drier' than stock?

Or, for the old 2-stroke guys in here, if we were able to somehow figure out how to implement
reed valves in the intake manifold runners upstream of the intake valves, then this reversion issue would
be cured.

Thinking on this, I remembered back to the old 100% V4 motors, and one solution with this intake
mixture control problem was neatly solved by using the stock '180° degree' dual plane intake manifold,
and only using the one side of the carburetor associated with the chosen firing order. For example,
if you had a Quadrajet, you would end up breathing only through 1 small primary + 1 secondary,
while the other side wouldn't meter at all, due to zero airflow past the venturis. (EDIT: Assuming old
school kit where valvetrain deactivation was implemented. An alternative approach would be to
leave the valvetrain intact and physically modify the carburetor to be unable to feed any fuel to the
intake manifold on the deactivated side.)

Check this out, here's a bird's-eye view of a V8 in our beloved firing order running as a V4:

You must be registered for see images attach

(Incredibly, this old Mother Earth News link is still working? Kansas mechanic home-brew V4 during oil crisis)

Note: I really like the OP's idea of balancing the wear by alternating which 4 cylinders are made to
carry the load. The 'only these cylinders always do the extra work' just felt wrong to yours truly.

So given the nearly intractable intake mixture control issues with the '96+ SFI setup, for the purposes
of this thought experiment what if we were to switch to a TBI 454 engine bay? Now we have the ability to run
only 1 injector feeding the side of the intake manifold matching the 4 enabled cylinders, and now the disabled
cylinders (via the dash-switch disabled TBI injector) really do only get dry air fed to them?

****

When I first started this reply, I was thinking that maybe planning on driving on well-tuned Open Loop tables during
V4 mode might actually allow the V4 operation that the OP was asking about. But due to the inability to control what the
disabled cylinders are ingesting, the '96+ SFI isn't an ideal candidate for this DoD experiment on a GMT400 machine.

But if you were to combine a TBI 454 with a savvy tuner using a EBL Flash-II setup, I think a good test case
could be put together. V8 454 running Closed Loop vs V4 227 running Open Loop on optimized tables?
This test case would also minimize all the other variables having to do with MPG measurements. (Wt, Cd, gearing,
state of tune, different driver habits, etc)

Sure, we're back to the 100% weight with 50% displacement drawback, but at the same time the driver can
choose to use the V4 mode only when the benefits outweigh the drawbacks. (Steady cruise) I'll bet that if you are running
a steady-state cruise down Kansas Rt. 36 I think you might be able to observe a noticeable difference.

And be able to do so without incurring a large 'Opportunity Cost' to find this out. Probably a negative ROI for 98%
of the people reading this...but for someone with the curiosity shown by the OP maybe the experiment pays for
itself while at the same time becoming a valuable source of new knowledge?

Thanks for the opportunity to think about the old V4 stuff I used to read about back in the day with great interest.
I remember thinking that the new DoD offerings based on the 'lost motion' lifter technology was interesting, but at
the same too many owners seem to have noisy/spendy failures in this area, so I never felt the urge to scratch that itch.

But this dead simple V4 cruise mode based on a tunable (TBI) EBL Flash-II setup may actually allow an old GMT400 to learn
new Redneck DoD tricks. :0)

Food for thought...

****

**Disclaimer: I lived through the early '70s Arab Oil Embargo. The year before this old midwestern boy started driving,
gas was ~33¢/gal...and when I got my license gas was a cool 99.9¢/gal. Including lots of discussion about how to modify
old gas pumps to display triple-digit gas prices? From my perspective, this meant that for every hour I pushed a Lawnboy at
the apt. complex after school I could now buy *2* whole gallons of gas...before taxes, of course. :0)

This may help to explain why I've always been interested in any possible method to maximize MPG, especially on unloaded
milk-run/ferrying portions of 'go retrieve a rust-free vehicle from down south' road trip.

 

[Pinger]

There is another way to reduce throttling losses at part load. It requires a blower with a variable speed drive between it and the crankshaft. Set up with a high (numerically low ratio) as it would be in a normal forced induction set-up it boosts. Change the ratio and there is a ratio that permits full volumetric air delivery but without boosting. At that ratio the blower is invisible to the engine. Lower the ratio further and the effect is as if it were throttled - but instead of the turbulent irrecoverable throttling losses at the throttle plate there is vacuum applied beneath the blower and positive atmospheric pressure above which results in the blower delivering work to the crankshaft in part load running.

The variable speed drive in essence becomes the throttle (reacting to pedal inputs) but it would have to have a further control mechanism to compensate for the lack of intrinsic 'torque back-up' eg, constant pedal opening but vehicle slowing on a gradient.
I doubt that it will ever be implemented on a production vehicle but the theory is sound and the patent already issued.