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Author Topic: Diagnosing Poor MPG  (Read 1783 times)

Heli_av8tor

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Re: Diagnosing Poor MPG
« Reply #30 on: September 04, 2017, 11:55:55 AM »
Gary, the filter was paper with a K&N type foam bonnet on the front side. Wasn't any evidence of that it had been oiled. I too had read that oil contaminated MAF sensors.
It now has the ACDelco filter with the foam glued in place.

Keeping my fingers crossed that the problem is solved. It may help offset these hurricane gas prices :)
Tom & Theresa
2004 Pace Arrow 37C
Workhorse W22, 8.1 Vortec
2014 Honda CR-V Toad, Roadmaster -5 Base and tow bar
SMI Stay and Play Duo Brake system

Arch Hoagland

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Re: Diagnosing Poor MPG
« Reply #31 on: September 04, 2017, 02:16:43 PM »
Two things I noticed after cleaning my MAF besides the no more CEL.

1. When sitting on level ground with my foot off the brake the coach should creep forward. Wasn't doing that with dirty MAF.

2. When climbing a mountain and transmission shifts down to lower gear you should start gaining speed just a bit with the 8.1. It didn't do that with a dirty MAF.

After cleaning I started gaining speed after a downshift on mountains and started creeping forward again with foot off brake.

Shop that cleaned my MAF said to never use a K&N filter due to over oiling. 
2004 Monaco La Palma 36 DBD
W22, 8.1 gas,  Allison 1000 Transmission
7.1 MPG over 80,000 miles

2000 Lexus RX300, 4020lb
U.S. Gear Braking System

Bill N

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Re: Diagnosing Poor MPG
« Reply #32 on: September 04, 2017, 02:20:02 PM »
Two things I noticed after cleaning my MAF besides the no more CEL.

1. When sitting on level ground with my foot off the brake the coach should creep forward. Wasn't doing that with dirty MAF.

2. When climbing a mountain and transmission shifts down to lower gear you should start gaining speed just a bit with the 8.1. It didn't do that with a dirty MAF.

After cleaning I started gaining speed after a downshift on mountains and started creeping forward again with foot off brake.

Shop that cleaned my MAF said to never use a K&N filter due to over oiling.

Arch, may I ask you for the location of the MAF.  I do not yet have any of the indications you describe but with the same engine I suspect that I may enounter them some day.  Is this a major job or one an older guy with a bad back could possibly do? Thanks.

Bill
Bill & Joan N in Missouri
USAF (Ret)
2002 Winnebago Adventurer 35U
Workhorse W22, 8.1L Chevy V8
2013 Chevy Sonic Toad
Furbearers:  Heidi-17(Forever), Grace-10 & Squeak-4, Winnie - 8 months

WILDEBILL308

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Re: Diagnosing Poor MPG
« Reply #33 on: September 04, 2017, 05:04:20 PM »
Good luck on your trip.
Bill
2003 Bounder 38N
300 HP 5.9 Cummins
Allison 3000MH Trans.
Towing 2014 Honda CRV
Home base Fort Worth, Texas
A man who carries a cat by the tail learns something he can learn in no other way.
-Mark Twain-

Charlie 5320

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Re: Diagnosing Poor MPG
« Reply #34 on: September 04, 2017, 05:49:03 PM »
Arch, may I ask you for the location of the MAF.  I do not yet have any of the indications you describe but with the same engine I suspect that I may enounter them some day.  Is this a major job or one an older guy with a bad back could possibly do? Thanks.

Bill
The MAF sensor is located in the right fender well right by the air filter housing. My coach has some material blocking or directing the airflow so I'll have to cut some zip ties to get mine out. Waiting on the new air filter before doing this. By turning the wheels all the way to the right gives much more room. My coach has a K&N filter that I'm replacing with a WIX.
2003 National Dolphin 5320
496  8.1  Workhorse

98 Damon Daybreak 3130
GM Vortech 454  4L80E
SOLD

Heli_av8tor

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Re: Diagnosing Poor MPG
« Reply #35 on: September 04, 2017, 06:42:32 PM »
Mine didn't have the baffle restricting access. I run the front jacks all the way down along with turning the wheel to the right. This gave plenty of room to sit in the wheel well to get to the MAF. I used blocks under the axle in case of a jack failure.
 Might depend on how bad your back is. It can be stressful as you can't fully stand up.
Tom & Theresa
2004 Pace Arrow 37C
Workhorse W22, 8.1 Vortec
2014 Honda CR-V Toad, Roadmaster -5 Base and tow bar
SMI Stay and Play Duo Brake system

Heli_av8tor

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Re: Diagnosing Poor MPG
« Reply #36 on: September 04, 2017, 08:26:49 PM »
My CEL has not come on nor have there been any pending codes.

Good to hear that my transmission acting better is likely not just my imagination!

Tom
Tom & Theresa
2004 Pace Arrow 37C
Workhorse W22, 8.1 Vortec
2014 Honda CR-V Toad, Roadmaster -5 Base and tow bar
SMI Stay and Play Duo Brake system

Bill N

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Re: Diagnosing Poor MPG
« Reply #37 on: September 04, 2017, 09:13:00 PM »
Thanks for the tips guys.  I'll take a look and see if I can get mine out to clean.  I had the filter changed out the last time it was in the shop and the guy showed me where that was and, like you said, he turned the wheel to the right to get access. Never thought of running up the jacks.


Bill
« Last Edit: September 04, 2017, 09:15:03 PM by Bill N »
Bill & Joan N in Missouri
USAF (Ret)
2002 Winnebago Adventurer 35U
Workhorse W22, 8.1L Chevy V8
2013 Chevy Sonic Toad
Furbearers:  Heidi-17(Forever), Grace-10 & Squeak-4, Winnie - 8 months

Heli_av8tor

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Re: Diagnosing Poor MPG
« Reply #38 on: September 04, 2017, 10:09:09 PM »
Bill,
Just don't bet your life on hydraulics if you use the jacks. Always use jack stands, wood blocks or something that will support the coach if a hose bursts.

Tom
Tom & Theresa
2004 Pace Arrow 37C
Workhorse W22, 8.1 Vortec
2014 Honda CR-V Toad, Roadmaster -5 Base and tow bar
SMI Stay and Play Duo Brake system

WILDEBILL308

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Re: Diagnosing Poor MPG
« Reply #39 on: September 04, 2017, 10:32:24 PM »
On your trip I would try a good gas additive, like Lucas 0r seafoam.
Bill
2003 Bounder 38N
300 HP 5.9 Cummins
Allison 3000MH Trans.
Towing 2014 Honda CRV
Home base Fort Worth, Texas
A man who carries a cat by the tail learns something he can learn in no other way.
-Mark Twain-

John Stephens

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  • Vacations begin when you leave the driveway
Re: Diagnosing Poor MPG
« Reply #40 on: September 04, 2017, 11:28:04 PM »
A couple of thoughts...

The Vortec 8.1 is notorious for melting plug wires on one side because of the way they are routed on the W-24 chassis, so you might have the same problem with the W-22. Unless the original plugs were iridium, they probably will not last longer than 35-45,000 miles, even if your owner's manual says to go longer. You could have an O2 sensor problem, but you might also have a knock sensor problem that will give you the same rich mixture by having the plugs fire at the wrong time. Although, if your knock sensors go bad, your check engine light should be on.

At 34,000 miles, I installed new plugs, wires, fuel filter, air filter and knock sensors (light was on.) Essentially, as complete a tuneup as I could think of. It made a small difference in my mileage, maybe .5 mpg.

What made the biggest difference was not running my cab a/c this vacation. I got better mileage towing my car in mountains (8.4 mpg average) than I used to get going without toad on flat ground (7.5 mpg.) Using the coach a/c and keeping the generator running saved me gas and still gave us plenty of cool air.
John
Cape Coral, Fl.
2005 Winnebago Adventurer 38J
Acme EZ Tow Dolly and 2007 Azera

Arch Hoagland

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  • Clovis CA
Re: Diagnosing Poor MPG
« Reply #41 on: September 05, 2017, 12:12:30 AM »
Arch, may I ask you for the location of the MAF.  I do not yet have any of the indications you describe but with the same engine I suspect that I may enounter them some day.  Is this a major job or one an older guy with a bad back could possibly do? Thanks.

Bill

Bill...I raise the front of my coach up as far as possible. I then place two floor jacks under the front frame. Then I turn the wheels so I can get in the drivers side wheel wheel. The air filter is located there. It has three clips on the top, no others.
Remove the cover to change the air filter. You may have to pry the cover out as the bottom sticks a bit. The MAF is located after the air filter, about one foot. It has several wires coming out of it.

Just before my last trip I didn't remove the MAF to clean it, I just emptied one full can of MAF cleaner into the air line with the air filter removed while the engine was running. I've done it the same way on three other vehicles and it seemed to work good. 
2004 Monaco La Palma 36 DBD
W22, 8.1 gas,  Allison 1000 Transmission
7.1 MPG over 80,000 miles

2000 Lexus RX300, 4020lb
U.S. Gear Braking System

Bill N

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Re: Diagnosing Poor MPG
« Reply #42 on: September 05, 2017, 08:57:07 AM »
Lots of good videos on YouTube on cleaning MAFs. Didn't realize it was that simple.  Will get a can of MAF spray and go to it.  Thanks for all the help.
Bill & Joan N in Missouri
USAF (Ret)
2002 Winnebago Adventurer 35U
Workhorse W22, 8.1L Chevy V8
2013 Chevy Sonic Toad
Furbearers:  Heidi-17(Forever), Grace-10 & Squeak-4, Winnie - 8 months

Heli_av8tor

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Re: Diagnosing Poor MPG
« Reply #43 on: September 07, 2017, 08:04:15 PM »
Here are pictures of the two worse plugs. They are ACDelco 41-983 and have 49K miles.

I decided to also replace the O2 sensors before the trip. They will go in tomorrow.

The first leg of our trip is this Sunday so it won't be long until I know if my efforts have paid off.

Thanks again to everyone who offered their thoughts.

Tom
Tom & Theresa
2004 Pace Arrow 37C
Workhorse W22, 8.1 Vortec
2014 Honda CR-V Toad, Roadmaster -5 Base and tow bar
SMI Stay and Play Duo Brake system

Gary RV_Wizard

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Re: Diagnosing Poor MPG
« Reply #44 on: September 07, 2017, 08:13:22 PM »
Not good looking plus at all. Definitely want to replace them, but the question why are they fouled like that in the first place? Hope your MAF fix eliminates the root cause...
Gary
--------------
Gary Brinck
Summers: Black Mountain, NC
Home: Ocala National Forest, FL

Charlie 5320

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Re: Diagnosing Poor MPG
« Reply #45 on: September 07, 2017, 08:52:38 PM »
I would defiantly replace the 02 sensors with plugs that looked like that. It has been running rich for a very long time. What did the rest of them look like? You may even have a problem with some injectors. Have you ever had a misfire code set? Do you remember what cylinders those plugs came from? If so I'd be checking them again after your trip. If they are darker than the rest, then it could have some bad injectors or coil pacs. Something is telling the ecm to dump a lot more fuel than necessary. When you get this thing figured out you will feel like you have a different coach. 
« Last Edit: September 07, 2017, 08:55:38 PM by Charlie 5320 »
2003 National Dolphin 5320
496  8.1  Workhorse

98 Damon Daybreak 3130
GM Vortech 454  4L80E
SOLD

Heli_av8tor

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Re: Diagnosing Poor MPG
« Reply #46 on: September 07, 2017, 09:35:17 PM »
Here's a shot of all plugs. The picture is lower resolution than I'd like due to forum restrictions.

The foreground is the left (drivers side) bank. The right bank is in the rear. The front is on the left.

There is slightly more deposit buildup on the right bank plugs. Other than that I don't see any significant difference.

There have been no codes generated while I've owned the coach.

Tom
Tom & Theresa
2004 Pace Arrow 37C
Workhorse W22, 8.1 Vortec
2014 Honda CR-V Toad, Roadmaster -5 Base and tow bar
SMI Stay and Play Duo Brake system

Charlie 5320

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Re: Diagnosing Poor MPG
« Reply #47 on: September 08, 2017, 07:59:06 AM »
A couple of those plugs have quite a bit of deposits too, but all are on the rich side. All the plugs have a sooted base. The pic of the first two would alarm me, there is something else going on with those two cylinders, that I would fallow up on. I would use some type of fuel injector cleaner on the next tank of fuel mixed on the strong side. You may have some dirty injectors, that may be leaking when they are supposed to be closed. I like Lucas products, but you run what you want. Seafoam  I hear is good too, but I've never used it.
2003 National Dolphin 5320
496  8.1  Workhorse

98 Damon Daybreak 3130
GM Vortech 454  4L80E
SOLD

Heli_av8tor

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Re: Diagnosing Poor MPG
« Reply #48 on: September 08, 2017, 10:23:11 AM »
I'd wondered about dirty injectors, but hadn't considered them leaking fuel when they are supposed to be closed.

Have you tried the Techron Fuel System treatment? After reading this thread I think I will give it a try.

http://www.irv2.com/forums/f22/8-1-l-vortec-misfire-and-ping-solution-non-plug-wire-issue-114150.html

Tom

Tom & Theresa
2004 Pace Arrow 37C
Workhorse W22, 8.1 Vortec
2014 Honda CR-V Toad, Roadmaster -5 Base and tow bar
SMI Stay and Play Duo Brake system

Charlie 5320

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Re: Diagnosing Poor MPG
« Reply #49 on: September 08, 2017, 02:13:34 PM »
I'd wondered about dirty injectors, but hadn't considered them leaking fuel when they are supposed to be closed.

Have you tried the Techron Fuel System treatment? After reading this thread I think I will give it a try.

http://www.irv2.com/forums/f22/8-1-l-vortec-misfire-and-ping-solution-non-plug-wire-issue-114150.html

Tom
Yes I have, I use it in my Corvette a couple times a year because it sets so much. That's going to get expensive to treat a fuel tank in your MH. But I don't have any idea what a sea foam treatment would cost either.  Guess it don't really matter huh? Got to get it fixed. The injectors can leak quite a bit of fuel running at the pressures we run. Then every time you shut the engine down they will leak until the pressure drops.

My coach runs very well, but I'm going to pull the plugs and change them. I'm sure they are original, and they really don't coast that much. When I had the 7.4 engines in my last 3 coachs, they were hard on dist. caps and rotors. I changed them every other year. Wasn't just the 7.4s either. I had a 93 K Blazer that went thru caps and rotors and it was a 5.7, but the parts were the same.
« Last Edit: September 08, 2017, 02:55:40 PM by Charlie 5320 »
2003 National Dolphin 5320
496  8.1  Workhorse

98 Damon Daybreak 3130
GM Vortech 454  4L80E
SOLD

Gary RV_Wizard

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Re: Diagnosing Poor MPG
« Reply #50 on: September 08, 2017, 03:56:18 PM »
In most gas coaches, it's not the cost of the plugs that is the deterrent. Rather, it is the lack of accessibility.

Unlike days of yore, fouled plugs are a symptom rather than the cause of an issue. An engine with closed loop fuel injection isn't running poorly because the plugs are fouled; rather, the poorly running engine caused the plugs to get full of crud. When the ECM is managing things properly, the only deterioration of the plugs should be a very slow erosion of the electrode tip. No baked on crud, no oily residue, and no burned spots, and the ceramic should be a creamy tan.

By all means check the plugs at 50k or whatever miles, but if you find a plug problem, start looking for the root cause.
Gary
--------------
Gary Brinck
Summers: Black Mountain, NC
Home: Ocala National Forest, FL

Heli_av8tor

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Re: Diagnosing Poor MPG
« Reply #51 on: October 05, 2017, 08:30:03 PM »
Ok, I think my efforts have paid off, but not to the degree I'd hoped. We just got home from our 21 night, 2723 mile trip from Illinois to Colorado and Utah. We ran the 5.5 KW generator 19.7 hours. We used 441.3 gallons of gas computing to 6.17 MPG. If I assume the genny burns .6 gph the MH engine got 6.34 MPG. Not great but better than the 5 to 5-1/2 we got on our trip around Michigan's UP.

I ran the genny in lieu of the dash air for much of the trip across Iowa and Nebraska. The winds on the trip were not kind and almost always had a headwind component. The best we saw was a direct crosswind or very slightly shifted towards a tailwind. I'd hoped we would see a tailwind on the trip home but it wasn't to be. (Kind of my luck flying cross country in Cessna's, too.)

Our route took us over three major passes with long pulls and descents. The first was I-70 going west out of Denver. The second was Monarch Pass, and the third Wolf Creek Pass. The first two had me down to 1st gear running 25 mph (up and down). It really hurt that after burning all that gas to gain altitude I had to waste the stored energy by using low gears to come down safely. There were many other smaller pulls.

I don't have the coach loaded weight but suspect I'm bumping up to max. We pulled our Honda CR-V toad. All things considered I'm likely close to the best I can expect.

The engine ran great. I did have a "Check Transmission Temp" warning 3/4's of the way down Monarch Pass. It went out shortly after getting out of 1st gear. I found one of the two electric cooling fans locked up. I replaced it at Gunnison and haven't seen the warning since.

Thanks to all who made suggestions.

Tom

Tom & Theresa
2004 Pace Arrow 37C
Workhorse W22, 8.1 Vortec
2014 Honda CR-V Toad, Roadmaster -5 Base and tow bar
SMI Stay and Play Duo Brake system

ArdraF

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Re: Diagnosing Poor MPG
« Reply #52 on: October 06, 2017, 06:26:38 PM »
Headwinds really cream your mpg so I'd say between that, using the generator, and where you went over high passes, that's probably not too bad all things considered.

ArdraF
ArdraF
:D :D

RedandSilver

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Re: Diagnosing Poor MPG
« Reply #53 on: October 06, 2017, 08:18:10 PM »
Quote
Ok, I think my efforts have paid off, but not to the degree I'd hoped. We just got home from our 21 night, 2723 mile trip from Illinois to Colorado and Utah. We ran the 5.5 KW generator 19.7 hours. We used 441.3 gallons of gas computing to 6.17 MPG. If I assume the genny burns .6 gph the MH engine got 6.34 MPG. Not great but better than the 5 to 5-1/2 we got on our trip around Michigan's UP.

I read though this thread and never saw you post what the normal MPG where only that you were down to 5 to 5.5.
So did it ever get better mileage and then suddenly it got worse?

Headwinds really cream your mpg so I'd say between that, using the generator, and where you went over high passes, that's probably not too bad all things considered.

ArdraF


I kinda agree with Andra - that's a lot of things going against good MPG's.  So overall not too bad.

2002 Rexhall Rose Air  Cummins 8.3  350hp

Heli_av8tor

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Re: Diagnosing Poor MPG
« Reply #54 on: October 06, 2017, 10:45:45 PM »
I bought the coach in March so I donít have mpg history.

Tom
Tom & Theresa
2004 Pace Arrow 37C
Workhorse W22, 8.1 Vortec
2014 Honda CR-V Toad, Roadmaster -5 Base and tow bar
SMI Stay and Play Duo Brake system

John Stephens

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  • Vacations begin when you leave the driveway
Re: Diagnosing Poor MPG
« Reply #55 on: October 06, 2017, 11:34:49 PM »
Tom - With headwinds and large mountains to climb, I don't think your mileage was out of range of what it should be considering your load, age of vehicle and the miles already on it. We took our three week trip from SW Florida to Asheville, NC to Pigeon Forge, TN and then to Columbus, OH before heading back home. We crossed the Smokies and had some pretty good grades, although nothing like you experienced in Colorado and Utah. I took accurate mileage from both the onboard computer's last 50 mile average and doing it the old fashioned way since auto computer mileage is known for being off. In our case, assuming .5 gal/hour going to the genset running our coach a/c, the computer was pretty accurate, giving me a reading of 7.4 mpg for the overall trip, while my manual calculations showed 6.98 mpg including the gas going to the generator. I kept a pretty steady 62 mph when I could.

My coach is heavier than yours with its W-24 chassis and additional length and my toad weighs in at 4,500 lbs, so I'm not sure how that compares with yours, but I should be getting worse mileage than you since I'm running the same engine. I now have 38,000 miles on the coach and it's a year newer than yours, so I would expect those facts to give me slightly better mileage. I anticipate my mileage getting worse with age and use and plan on extending the life of the engine as best I can by regular oil changes and routine maintenance. If you're like me, you didn't receive any service records on your coach when you bought it, so you may not be aware of the kind of service it received. If the previous owner didn't take care of it and provide timely maintenance, you may have a weaker engine that will never give you optimal mileage.

But if you can get 6+ while towing in mountains and headwinds, you're doing okay.
John
Cape Coral, Fl.
2005 Winnebago Adventurer 38J
Acme EZ Tow Dolly and 2007 Azera

Heli_av8tor

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Re: Diagnosing Poor MPG
« Reply #56 on: October 07, 2017, 09:09:02 AM »
John - Yes, you should be heavier than me. A thousand on the toad alone. I believe you should have the 6 speed Allison whereas I have the 5 speed. Numerous times I thought having that extra gear with closer ratios would have helped. I too drive 61 / 62 mph.

I ended our trip with 52K miles on the coach. I have good records of maintenance from the original owner but they stop 3-4 years ago. I think it set for several years before I got it. Perhaps illness or death of the original owner?

My manual says the AVG MPG computer gives a 50 mile rolling average. I swear it has to be averaging over a much shorter distance, perhaps 5.0. Normal interstate grades, both up and down, across Nebraska and Iowa just have too much effect on the readout. (Yes, I'm sure it's not in INST mode.) I noticed a strange thing with the mileage computer pulling mountain grades. It would start out at 6 something and decrease to 0.0, then to "---". Then it would go to the 80's or 90's and work it's way back down.

I did try to stick with "Top Tier" gas and started this trip with a double concentration of Chevron Techron fuel additive.

Several suggested that I could have fuel injectors leaking when they are supposed to be closed. I'd like to clean the injectors using something like the OTC Tool ( https://www.amazon.com/gp/product/B00GZ0H9VC/ref=ox_sc_act_title_1?smid=ATVPDKIKX0DER&psc=1 ) But it's pretty pricey for a my limited use.

I won't have another trip until January and it will be across flatter ground. I hope to see a little better mpg, but you're probably right that I'm about where I'm going to be.

Tom
Tom & Theresa
2004 Pace Arrow 37C
Workhorse W22, 8.1 Vortec
2014 Honda CR-V Toad, Roadmaster -5 Base and tow bar
SMI Stay and Play Duo Brake system

Arch Hoagland

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  • Clovis CA
Re: Diagnosing Poor MPG
« Reply #57 on: October 07, 2017, 11:45:12 AM »
Tom...I'm at about 25,000 lb with toad and have basically your same RV. The MPG readout on the dash is, let's say, very optimistic.

I calculate my MPG by hand and have recorded every gallon of gas I've ever put in it.  7.1 is the average and I always use the cheapest gas.

I live and travel in the west where every trip involves a mountain of some sort, there's no getting out of the central valley of California without going over a mountain. 

So track your mileage for the next several thousand  miles and you'll get a good feel for it.  I don't think there are any modifications that will improve it.

Let us know what you find out on the next trip.
2004 Monaco La Palma 36 DBD
W22, 8.1 gas,  Allison 1000 Transmission
7.1 MPG over 80,000 miles

2000 Lexus RX300, 4020lb
U.S. Gear Braking System

John Stephens

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  • Vacations begin when you leave the driveway
Re: Diagnosing Poor MPG
« Reply #58 on: October 07, 2017, 12:49:27 PM »
John - Yes, you should be heavier than me. A thousand on the toad alone. I believe you should have the 6 speed Allison whereas I have the 5 speed. Numerous times I thought having that extra gear with closer ratios would have helped. I too drive 61 / 62 mph.

I ended our trip with 52K miles on the coach. I have good records of maintenance from the original owner but they stop 3-4 years ago. I think it set for several years before I got it. Perhaps illness or death of the original owner?

My manual says the AVG MPG computer gives a 50 mile rolling average. I swear it has to be averaging over a much shorter distance, perhaps 5.0. Normal interstate grades, both up and down, across Nebraska and Iowa just have too much effect on the readout. (Yes, I'm sure it's not in INST mode.) I noticed a strange thing with the mileage computer pulling mountain grades. It would start out at 6 something and decrease to 0.0, then to "---". Then it would go to the 80's or 90's and work it's way back down.

I did try to stick with "Top Tier" gas and started this trip with a double concentration of Chevron Techron fuel additive.

Several suggested that I could have fuel injectors leaking when they are supposed to be closed. I'd like to clean the injectors using something like the OTC Tool ( https://www.amazon.com/gp/product/B00GZ0H9VC/ref=ox_sc_act_title_1?smid=ATVPDKIKX0DER&psc=1 ) But it's pretty pricey for a my limited use.

I won't have another trip until January and it will be across flatter ground. I hope to see a little better mpg, but you're probably right that I'm about where I'm going to be.

Tom

We have the same transmission, most likely. I have the Allison 1000, which is a four gear with overdrive, or 5 gears.

You're lucky you got some records. When I bought my coach, it had 23,005 miles on it and I thought it had been fairly well taken care of because it was a one owner that was former military. But I got no records, had no idea when the last oil change had been done, and didn't know if anything else, such as tranny fluid change, tune up, air filter, etc. had ever been performed due to its low mileage. So I had to spend the money to get it all done whether it was needed or not, just to be on the safe side.

I know exactly what you mean about the rolling average seeming to change drastically quicker than you would think if it was taking a 50 mile average. When I coasted down a mountain this last trip, the computer might have read 6.0 from the climb, but after going downhill only one or two miles, the average was now up to 10.5. Of course, if you have ever switched it to "instant" mode, you have found that when coasting, you'll register in the 20's or 30's. That reminds me of a diesel that consumes no fuel when idling. I never experienced what you mentioned about the reading going to zero or blank and wonder if you may have an issue with your computer, or at least the mileage readout.

I have always used the cheapest gas I can find in all my cars and the coach and have (knock on wood) never had any problems as long as I keep the fuel injectors clean by giving the the required service every 30,000 miles. Now that you mention it, I can't remember if that was done on my coach when they did the tuneup. I'm pretty sure they did.

You can read the many posts from a variety of people who want to make everyone think their coach is better than anyone else's by stating they are getting outrageous mileage. But the simple fact is, nearly every gas coach made is going to get between 6 and 8 mpg. Variances will occur with age of coach because many of the newer ones are built lighter and with more efficient power plants, size and weight will make some difference but not much, whether or not you tow, and the highway, traffic and weather conditions of your trip. One leg of our last journey, I got almost 9mpg because I had a strong tailwind, and one leg, I got 5.5 because I was battling headwinds. That, it itself, in my opinion, gives the greatest variance when driving because when you're traveling in the mountains, the downhills are going to neutralize the uphill climbs to some extent. I actually found myself getting better mileage in the mountains than on flat ground. Reason: I turned the cruise control off and anticipated the climbs by going faster than my norm before hitting the grade. If I was coasting downhill and saw a climb coming up, I would speed up to 68-70 mph so I could make the grade all the way up or most of the way before having to downshift. When you leave the cruise control on, it cannot anticipate those grades coming up and will maintain the same speed all the way down the hill you're on, and then downshift almost as soon as you start the climb. It's a trick I learned as an OTR truck driver. My mileage on flat ground, such as the interstates in Florida, was about 7.0-7.5 on the computer readout, while my mileage in the mountains without the cruise on was over 8.0 most of the time.

Good luck with your mileage. The best thing you can do is simply keep it maintained properly and it will give you its best performance.
John
Cape Coral, Fl.
2005 Winnebago Adventurer 38J
Acme EZ Tow Dolly and 2007 Azera

ArdraF

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Re: Diagnosing Poor MPG
« Reply #59 on: October 07, 2017, 05:35:46 PM »
Quote
I noticed a strange thing with the mileage computer pulling mountain grades. It would start out at 6 something and decrease to 0.0, then to "---". Then it would go to the 80's or 90's and work it's way back down.

That's probably an instantaneous reading as opposed to actual gas mileage.  It tells you that you're doing well at 6 and not so well at 85, which is normal on lower and higher hills.  When we had gas engines we always added a vacuum gauge which was a similar way of telling us how much fuel we were expending.  Sometimes if it's really a high number you can lessen your foot pressure on the gas pedal or perhaps drop back on the cruise control.  We usually drop our cruise control back to 55 or maybe less in rolling terrain because the transmission wants to "hunt" (e.g. shift gears frequently) too much.  When going over mountain passes like you did on I-70 up to the tunnel from Denver we disengage the cruise control and drive it ourselves.  Even with our big 500 hp Cummins engine we slow a lot and of course use more fuel at the higher elevations.

ArdraF
ArdraF
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