Home » Public Forums » GMCnet » [GMCnet] 4.8 MPG
| [GMCnet] 4.8 MPG [message #324184] |
Fri, 22 September 2017 09:16  |
glwgmc
Messages: 1014
Registered: June 2004
Karma: 10
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Senior Member |
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Hi Rob,
I'm glad it is working for him as he is a good friend and I respect his ability to diagnose on the fly if something were to go wrong at those lean a/f ratios. I doubt that the majority of our owners, including me, could, so I preferred to run both of our coaches richer for the kind of driving we do/did. I will gladly pay a bit more for fuel to avoid having to replace engines.
Larry's findings about a bad canister causing icing on his set up is also interesting for this conversation. Our coaches show so many variations at this ripe young age of 40 that it I find it hard to diagnose much of anything without being hands on. Guess that is why I approached both our GMCs with such conservatism.
Jerry
Jerry Work
The Dovetail Joint
Fine furniture designed & hand crafted
in the 1907 former Masonic Temple building
in historic Kerby, OR
http://jerrywork.com
.........
Date: Thu, 21 Sep 2017 20:32:00 -0500
From: "Rob Mueller"
To:
Subject: Re: [GMCnet] 4.8 MPG
Message-ID:
Content-Type: text/plain; charset="us-ascii"
Jerry,
Randy Van Winkle gave presentation at the Elkhart GMCMI Convention and noted that he runs his coach with EFI at that range
consistently.
Regards,
Rob M.
The Pedantic Mechanic
Sydney, Australia
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
USA '77 Kingsley - TZE 267V100808
........
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Jerry & Sharon Work
78 Royale
Kerby, OR
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| Re: [GMCnet] 4.8 MPG [message #324186 is a reply to message #324184] |
Fri, 22 September 2017 09:34  |
Justin Brady
Messages: 769
Registered: April 2015
Location: Bell Buckle, TN
Karma: 11
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I'm with you Jerry. I'd much prefer a 1mpg drop (or lack of gain I suppose) to a new engine.
Just not an envelope that's worth pushing to me.
Somewhat related:
When I was running around out west I found that richening up the mixture a tad to about 12.5:1 made a nice difference on hill pulling power. I forgot to reset it and noticed a good dip in mileage once I got back east!
Justin Brady
http://www.thegmcrv.com/
1976 Palm Beach 455
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| Re: [GMCnet] 4.8 MPG [message #324188 is a reply to message #324184] |
Fri, 22 September 2017 09:40 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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Hmmmm. I seem to remember Randy and George replacing cylinder heads
somewhere in the middle of a cross country trip because of a "lean cruise
experiment". I for one, will back the timing down a bit, and go with a rich
fuel mixture on my coach. A couple of miles per gallon is not worth a
beside the road overhaul to me. But, what the heck, America is still a free
country, spend your retirement income any way you choose, before the
Government figures out a way to extract more money from you by taxing that
too.
Jim Hupy, In Canada at Harrison Hot Springs with a bunch of our GMC friends.
On Fri, Sep 22, 2017 at 7:16 AM, Gerald Work wrote:
> Hi Rob,
>
> I'm glad it is working for him as he is a good friend and I respect his
> ability to diagnose on the fly if something were to go wrong at those lean
> a/f ratios. I doubt that the majority of our owners, including me, could,
> so I preferred to run both of our coaches richer for the kind of driving we
> do/did. I will gladly pay a bit more for fuel to avoid having to replace
> engines.
>
> Larry's findings about a bad canister causing icing on his set up is also
> interesting for this conversation. Our coaches show so many variations at
> this ripe young age of 40 that it I find it hard to diagnose much of
> anything without being hands on. Guess that is why I approached both our
> GMCs with such conservatism.
>
> Jerry
>
> Jerry Work
> The Dovetail Joint
> Fine furniture designed & hand crafted
> in the 1907 former Masonic Temple building
> in historic Kerby, OR
> http://jerrywork.com
> .........
> Date: Thu, 21 Sep 2017 20:32:00 -0500
> From: "Rob Mueller"
> To:
> Subject: Re: [GMCnet] 4.8 MPG
> Message-ID:
> Content-Type: text/plain; charset="us-ascii"
>
> Jerry,
>
> Randy Van Winkle gave presentation at the Elkhart GMCMI Convention and
> noted that he runs his coach with EFI at that range
> consistently.
>
> Regards,
> Rob M.
> The Pedantic Mechanic
> Sydney, Australia
> AUS '75 Avion - The Blue Streak TZE365V100428
> USA '75 Avion - Double Trouble TZE365V100426
> USA '77 Kingsley - TZE 267V100808
> ........
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
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| Re: [GMCnet] 4.8 MPG [message #324189 is a reply to message #324184] |
Fri, 22 September 2017 09:47 |
emerystora
Messages: 4442
Registered: January 2004
Karma: 13
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Senior Member |
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Jerry
Apparently you don't know the whole story about this.
Randy has the Howell TBI system with the EBL added on. With the addition of a variable speed sensor one can go into lean cruise mode which allows leaner fuel mixtures. That can only occur at specific conditions such as cruise speed with a high vacuum and a light foot on the gas peddle. As soon as you get a load on the engine the computer enriches the mixture to what you have with a carb.
There is no need to "diagnose on the fly" as the TBI computer does it automatically.
Randy is not the only one doing this. Many, many of us, including me, have been using this system for many years and go to a higher air fuel mixture under certain cruising conditions.
The greater amount of air keeps the engine as cool as a surplus of fuel.
One gets better gas mileage when the system is in cruise mode and no harm is done to the engine. The system includes a screen for your computer display (optional) that shows several things including speed, MPG, vacuum, gallons consumed, and even cylinder temperature if you add a temperature probe. But it goes in and out of lean cruise automatically.
Emery Stora
77 Kingsley
Frederick, CO
> On Sep 22, 2017, at 10:16 AM, Gerald Work wrote:
>
> Hi Rob,
>
> I'm glad it is working for him as he is a good friend and I respect his ability to diagnose on the fly if something were to go wrong at those lean a/f ratios. I doubt that the majority of our owners, including me, could, so I preferred to run both of our coaches richer for the kind of driving we do/did. I will gladly pay a bit more for fuel to avoid having to replace engines.
>
> Larry's findings about a bad canister causing icing on his set up is also interesting for this conversation. Our coaches show so many variations at this ripe young age of 40 that it I find it hard to diagnose much of anything without being hands on. Guess that is why I approached both our GMCs with such conservatism.
>
> Jerry
>
> Jerry Work
> The Dovetail Joint
> Fine furniture designed & hand crafted
> in the 1907 former Masonic Temple building
> in historic Kerby, OR
> http://jerrywork.com
> .........
> Date: Thu, 21 Sep 2017 20:32:00 -0500
> From: "Rob Mueller"
> To:
> Subject: Re: [GMCnet] 4.8 MPG
> Message-ID:
> Content-Type: text/plain; charset="us-ascii"
>
> Jerry,
>
> Randy Van Winkle gave presentation at the Elkhart GMCMI Convention and noted that he runs his coach with EFI at that range
> consistently.
>
> Regards,
> Rob M.
> The Pedantic Mechanic
> Sydney, Australia
> AUS '75 Avion - The Blue Streak TZE365V100428
> USA '75 Avion - Double Trouble TZE365V100426
> USA '77 Kingsley - TZE 267V100808
> ........
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
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| Re: [GMCnet] 4.8 MPG [message #324210 is a reply to message #324188] |
Fri, 22 September 2017 14:17 |
rvanwin
Messages: 325
Registered: April 2007
Location: Battlefield, MO
Karma: 6
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Senior Member |
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James Hupy wrote on Fri, 22 September 2017 09:40Hmmmm. I seem to remember Randy and George replacing cylinder heads
somewhere in the middle of a cross country trip because of a "lean cruise
experiment". I for one, will back the timing down a bit, and go with a rich
fuel mixture on my coach. A couple of miles per gallon is not worth a
beside the road overhaul to me. But, what the heck, America is still a free
country, spend your retirement income any way you choose, before the
Government figures out a way to extract more money from you by taxing that
too.
I'm on my way home from Elkhart and have limited time here but since my name has come up several times I want to clarify a few things.
First, Jim, neither George and I have replace cylinder heads on any trip and neither of us has experienced any issues with running with a lean mixture. I DO NOT want the wrong information to get out or the inference that lean cruise has or is causing issues with our engines. I did pull one head to replace a valve but the final diagnosis of that was a failed spark plug that caused some mis-firing heating the back side of the intake valve causing it to extrude (tulip) then that cylinder went dead. Replaced the valve and now after 25,000 miles not a bit trouble. When the head was open, a close inspection revealed no evidence of excessive heat or even the hint of any damage. I have put over 100,000 miles on this engine running lean cruise most of the time.
Everyone has their opinions on what AFR is best to run. I use the EBL upgrade on the 7747 GM ECM. That provides the ability to run under lean cruise during light cruise conditions. I run as high as 16.5 but the ECM monitors several conditions as Emery stated and will richen the mixture based on load. As load increases, if you don't richen the mixture then temperatures can climb at a rate that is scary. I would not advocate that a carbureted engine go very lean as you do not have a computer that is reacting in nano-seconds to make AFR changes. If you jet a carb to run at 16.2, then based on what George and I have observed, it will start getting really hot (hot enough to melt something) and will do it quickly unless you are on it enough to kick in the secondaries. Once you start dumping in fuel the temps will stabilize. What we learned is that once additional fuel is introduced, temps stop climbing but it will not go back down during the loaded interval. In our case, the computer monitors load and starts riching the mixture as load increases until it gets back to 14.7 AFR. As load continues to increase, the computer goes into Power Enrichment (Secondaries) going to around 13.8 initially, then continues to richen mixture as load continues over time. I have seen the resulting mixture get down to around 12 to 1 and a couple of times in the high 11s. With a carburetor you do not have this kind of control so if you are going to play with AFR, I suggest a WB O2 sensor as well as Exhaust Gas Temperature (EGT) probes. That way you can monitor and possibly avoid engine damage. One other point: When we change to lean cruise we limit the ratio to 16.5 to 1. I would never go this high with a carburetor or some of the aftermarket EFI units. Unless you are also changing Spark Advance (SA) as you go into lean cruise you will start losing the ability to make sufficient power at around 16.2 to 1 in our coaches (might get away will slightly more in a car). By advancing the timing, you can continue to make good power to up around 17 to 1. After that, the mixture is too lean and you cannot keep our heavy coaches moving and the engine starts to struggle. At 16.5 to 1 AFR, I advance the timing by an additional 5 degrees. This EBL computer has the ability to do this. So, as AFR gets leaner, the SA advances more in parallel and goes the other way as load increases. All done automatically - I never have to think about whether a problem is lurking or not.
Bottom line, don't mess with lean cruise unless you have a fuel injection system that is set up with the logic to manage that environment. If you still want to go lean during cruise, be sure to get a WB O2 sensor and EGT gauges so you can monitor the results. I do state in my fuel injections sessions at rallies that I am running lean cruise but try to qualify the fact that it is under computer control and done after a lot of testing.
And, I agree with what Jerry Work has said except that I believe that lean cruise is possible (if done correctly) without damaging our engines. Look at Hal Kading's post. Aviation guys have been doing this for years - even doing it manually but they get a lot of training on how to monitor and adjust properly.
Randy & Margie
'77 Eleganza II '403'
Battlefield, MO
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| Re: [GMCnet] 4.8 MPG [message #324232 is a reply to message #324184] |
Fri, 22 September 2017 17:31 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Senior Member |
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It's way easier in the airplane - it's running at constant RPM and constant load. You're going to lose ~~ an inch of MAP per thousand feet of altitude, the mixture needs to lean to make up for this anyway. Rule of thumb is 50 degrees below max EGT. The auto engine sees constant changes in speed and load, and thus wants a computer to keep up with what's going on in a near instantaneous manner to keep from breaking something. I've seen the result of rejected landings where the pilot didn't do the GUMPP check and cobbed the engine and climbed out with the mixture set for cruise some several thousand feet up. It breaks things.
--johnny
(GUMPP - prelanding check mnemonic - GAS UNDERCARRIAGE MIXTURE PUMPS PROPS)
Foolish Carriage, 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
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