Maiden Voyage, Fuel MPG and what I observed/learned

[jeffyork40]

I did a rough calculation of the fuel mpg and I was surprised that my mileage may not be as bad as I thought. My calculations are not exact as I didn't fill the tank to a complete stop and I did not refill it after the trip to see what was the actual consumed fuel.



However, I did this rough calculation. My engine is a GM 454 with not yet 2000 miles on a rebuild. TH400 transmission new, and the motor is bored .30 over, with what the shop called a performance grind cam, dual exhaust and other performance mods, to many to list. My tank is 50 US gallons. I used what appears on the gauge to be exactly a half a tank of gas to go on a round trip of 204 miles. So, that would calculate out to about 8.1 miles per gallon. However, I did not top off the tank when I filled it before the trip. I am curious as to how close to full it was.



If I take into consideration that I ran the generator for just over 2 hours on each leg of the trip, that's about 4 hours of generator and my last generator of the same size and brand was said to burn 1/2 gallon per hour. This would mean that I used 2 gallons of gas in the generator while driving. Then we ran the generator for an additional 4 hours while hiking. So, I estimate we used an additional 2 more gallons of gas in the generator for a total of 4 gallons generator usage.



Taking the 4 gallons of generator usage burn off my 25 gallon usage estimate would result in 21 gallons used for 204 miles. This would calculate to a MPG of about 9.7 mpg.



I realize my calculations are not exact and may be a bit wishful. I will also state that I kept the speed on the highway to a maximum of 60 mph with an occasional run up to 65 when I was going down hill and let it build a little speed. I monitored my speed very consistently. I have always made a point of trying to play a bit of hyper miler when traveling. My toad is a 95 Saturn SL2 automatic and I have achieved 44 mpg many times but 40-41 is more typical. ( The Saturn was used with my previous Fleetwood and as yet not towed behind our Airstream Argosy 28.


I am experiencing the carb float bowl draining down after the rig sits for a few days. I am looking into the fix for that because I had to prime the carb last night to get it to start. More reasons why I want to put in a Fast EZI or Edelbrock EFI TBI fuel injection kit. I am convinced that EFI will increase fuel efficiency by as much as 20% as well as dramatically increase the life of a motor by efficient AF ratio balancing. That is a subject of its own.



I know that a EFI TBI kit will run about 2500 - 3000 and the ROI is not there but, if you look at how much longer an engine will last between rebuilds when you add EFI, the ROI is well worth the cost considering an engine rebuild can easily reach 8 grand or more. Also, TBI EFI is a turn the switch and go system unlike a carb where reliable starts can be difficult. So, dependability is a big plus on TBI EFI.



I am also looking into hard starting issues when the motor is warm. Barely turns over. Looking at heat soak to the starter possibly causing it to pull to many amps ( had that issue in the previous Fleetwood because the heat shield was taken off when the Banks power pack headers where installed) the engine to frame ground will be inspected for corrosion and i will pull the batteries and load test them and probably pull the starter and have it load tested too. I do all this myself so I can keep those kind of costs low.



I would like to hear your feedback and thoughts.



Jeff York
1977 Airstream Argosy 28 motor coach

[Kevininwa]

Please keep us posted if you decide to go EFI. I'm still on the fence, but a good read at this forum (and some other P30-based RV forums) convinced me to stay put for the time being. There are several professional mechanics that have been less than thrilled with the results. My conclusion was that there are other budget priorities, but if money were no object...
There is such a fine line between a legitimate restoration project and a labor of Sisyphus. I'm putting money and sweat a little at a time, and for every mile we go without an engine fire (or similar catastrophe), I feel a little better about it.

[mprokop87]

I average about 6-7mpg with my 1976 Argosy 24'. I do not have the original Quadrajet on it, instead there is an Edlebrock Performer 1902. Both are good options for fuel efficiency. The PO had the Edlebrock on and it was messed up in the process. Ever since I bought the Argosy it would run very rich, even with carb tinkering, but I never worried much about it because I was just trying to get it to a usable state. A few weeks ago my father was visiting and he wanted to mess with the engine, so I let him (free mechanic work!). He found that the install in the Edlebrock was messed up because the rod for the secondarys was hitting the mounting block for the choke thermostat. This cause some extra air to get in, which allows more gas in. As soon as that was fixed it made a world of difference. I havent taken a trip with the new setup yet, hopefully in the next few weeks and I can report back as far as fuel efficiency.

[jeffyork40]

Well, you are making me wonder about my carb so I will be looking at it tomorrow. But, I think its ok but I think I have engine heat boiling off the fuel in the bowl or its leaking down. I may wait until late winter to spring to try the TBI EFI conversion because I am having fun using mine every weekend.

Last night while looking at the carb I noticed that when the re builder put the engine back in, they pulled off the vac tube to the cruise control and plugged the T tap. I wonder why ? I will test the cruise tomorrow.

This weekend, just as I pulled into my campsite I blew a AC hose. I looked at it real close and see the hose was chaffing on the engine cover and it chaffed it until it was thin enough to blow. I hope I didn't destroy the AC compressor.

[J. Morgan]

Edelbrocks Pro Flo II MPEFI is an excellent system and easy to tune.

It is a little pricey, but it is a complete kit including ignition.

Oh, on the half tank thing , I am betting that according to the gage, the top half of your tank is bigger than the bottom half.

That has been my consistent experience.

[mprokop87]

Jeffyork40, those old cruise control units stopped working after a while, which is why they probably disconnected it. Mine was removed at some point and replaced with an electronic unit, however, it was also disconnected.

I doubt you ruined your compressor. Don't worry if you did because they are very common and you can buy them for around $200. I thought mine was shot but it ended up being a bad condenser, which I still need to replace.

[jeffyork40]

Originally Posted by mprokop87

I average about 6-7mpg with my 1976 Argosy 24'. I do not have the original Quadrajet on it, instead there is an Edlebrock Performer 1902. Both are good options for fuel efficiency. The PO had the Edlebrock on and it was messed up in the process. Ever since I bought the Argosy it would run very rich, even with carb tinkering, but I never worried much about it because I was just trying to get it to a usable state. A few weeks ago my father was visiting and he wanted to mess with the engine, so I let him (free mechanic work!). He found that the install in the Edlebrock was messed up because the rod for the secondarys was hitting the mounting block for the choke thermostat. This cause some extra air to get in, which allows more gas in. As soon as that was fixed it made a world of difference. I havent taken a trip with the new setup yet, hopefully in the next few weeks and I can report back as far as fuel efficiency.

I was hoping for a follow up on your father n laws carb fix. Have you noticed a performance increase ? Have you calculated your fuel econ since the repair ? What did your mpg come out to ? Do you experience hard starts after your rig has sat for several days ? I think either my fuel is leaking back down out of the carb or its boiling off from the engine heat. I have a friend that works for a Ford dealership who has the same hard stating issue with his old carb based 350 and he says its caused by a vacuum pulling the fuel out of the carb or something like that. (thats a new one to me)

[idroba]

Just some thoughts on MPG.

I had a '78 Argosy 24, 454... got 8 to 10 mpg.

I had a '83 Airstream 310, 454... got 8 to 10 mpg.

I had a '75 GMC motorhome, 455 olds engine... got 8 to 10 mpg.

I had a lot of friends in the GMC motorhome community... They got 8 to 10 mpg.

Those in the GMC community who had switched to EFI... guess what, they reported that they got 8 to 10 mpg, both prior to and after the conversion.

[mprokop87]

I haven't done much with my Argosy since the fix. I have noticed a little more power but nothing significant. I still have hard starts after sitting a few days but if I pump the pedal three times it sends to help abd will fire up quickly. I did replace my fuel pump when I first got it, wasn't sure if the state of the original.

[mprokop87]

The vacuum pulling the fuel makes sense. On my unit the main engine fuel tank sits lower than the engine and the carb so there will naturally be some force pulling back the fuel. I dint have a check valve installed anywhere, just whatever is in the fuel pump.