Home » Public Forums » GMCnet » Gas Mileage 500 Cadillac, 26' coach, 3.42 diffy (Response to Rob Mueller, US Aussie)
| Gas Mileage 500 Cadillac, 26' coach, 3.42 diffy [message #242215] |
Mon, 03 March 2014 17:54  |
cbryan
Messages: 451
Registered: May 2012
Location: Ennis, Texas
Karma: 3
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Senior Member |
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Rob,
Took the liberty of starting a new thread about gas mileage I get with my setup 500 Cadillac, EFI, multiport Accel.
I have a smorgasbord of answers:
1. Not sure because of leaks in lines top of tanks, can't fill it all the way.
2. Even if I could, I don't really "trust" that wondrous setup with the bouncing ball in the drivers side rear wheel well. Liquid gas gets into the line? Then what?
3. I think it is all right, smack in the middle of ERF's predictions. 8 - 10. Just think so, haven't been able to measure it. Having said that, it doesn't smell of gas, and starts quickly and seems dependable so far. I drive about 60 or 65 depending on conditions. It is strong, even with its problems.
4. It is premature to ask, as there is a suspected cam lobe that is flat. Or a cam lobe suspected flat. Or a bent pushrod.
5. As well, there are fuel tank anomalies. Pickups off the floor, nonop tank switching valve (cross connected, so when out of gas, you are out.)
6. It is premature to ask, as I have just discovered the extra squirts that can be programmed just before cranking, the cold start enrichment, that assured half a dozen lean false starts, now fixed, and the acceleration enrichment that has taken care of flat spots. Plan to "balance" the injectors using an IR gun.
7. It's premature to ask because due to KenH's experience and not having looked at all at exhaust temps at or nearing WOT, I want to make sure that the exhaust valves don't overheat, so I will have to look at that for sure, and in the meantime, I won't be putting my foot into it much at all.
8. It's premature and may always be because I will always have a hare brained idea to improve the mileage. This time because I want to investigate lean burn while I am at it.
So, Rob, you have asked something simple that has proven to be complicated for me to do.
With respect to the multiport setup, I think it is potentially a little better than the TBI systems in common use now. I hasten to add that the supposed superiority of the multiport system seems hard to substantiate, or actually there is negligible difference between the two. I think lots of tweaking might add a small amount of efficiency. New aluminum heads with a direct injection setup sounds like a winner by comparison. I have heard of none setup to do this.
Repair is a little iffy. Some of the ignition parts seem to be generic and easily sourced, but that computer box looks long in the tooth and hard to replace. Mercy.
I am as anxious to hear about your setup in your Aussie Coach that will have the 500 rebuilt and all the goodies you plan. You might get a little better mileage with your switch pitch in economy mode with the lower stall speed.
Best,
Carey
Carey from Ennis, Texas
78 Royale, 500 Cadillac, Rance Baxter EFI.
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| Re: Gas Mileage 500 Cadillac, 26' coach, 3.42 diffy [message #242232 is a reply to message #242215] |
Mon, 03 March 2014 20:56  |
Larry
Messages: 2875
Registered: January 2004
Location: Menomonie, WI
Karma: 10
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Senior Member |
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Carey,
I am running a Cad 500 with MPI controled by Dynamic EFI, EBL-P4 software. I hope you are going to the Montgomery Rally, cuz I'd sure like to meet you and talk some about our EFI issues. I'm from Wisconsin and am in the middle of a trip that took us to Yucca Valley CA and now home through Montgomery TX...a totla of about 6K miles. In mid December, we saw the "Polar Vortex" coming and beat it out of the upper midwest as fast as we could. I drove at 65-75mph most of the way just trying to stay ahead of that cold front. I don't even want to know what my actual milage was going ou to CA , because we were really booking it. We are towing a 2200lb car. The coach has a 3.21 FD, but have 245 tires, so our FD ratio is somewhere around 3.03 or so. I'm guessing our average milage to date is somewhere around 8mpg. As you know the EBL keeps track of instant and average milage. Depending on wind direction and speed, actual road speed, and whether we are going up hill or down (going west is mostly up hill) sometimes I saw 7.3mpg and other times I saw up to 9.5mpg on any individual tank full. I'm still working with spark tables and VE learns to tweek it, so may see some changes yet.
Anyway, hope to see you at Montgomery.
Larry 
78 Royale w/500 Caddy
Menomonie, WI.
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| Re: Gas Mileage 500 Cadillac, 26' coach, 3.42 diffy [message #242241 is a reply to message #242232] |
Mon, 03 March 2014 22:23 |
cbryan
Messages: 451
Registered: May 2012
Location: Ennis, Texas
Karma: 3
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Senior Member |
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Larry,
Hope to see you there. We have a non op heater, but can plug in an electric heater and make do with that! Glad to talk about what experience I have been able to come up with.
Some rather poor experiences, some successful. None yielding to anything but help on the EFI forum, and good offices and help on this one.
I can't help but feel that things are still improving for the GMC Motorhome.
Carey
Carey from Ennis, Texas
78 Royale, 500 Cadillac, Rance Baxter EFI.
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