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Old 03-02-2016, 04:18 PM   #1
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Question about Country Coach w/ Cat C9 3mpg & low power

Hello RVers,

I just bought a used 2005 Country Coach Inspire 36' with Cat C9 400hp 1200lb torque. I also have a 99 39' Bounder Diesel with 275hp/550lbft ISB.

I drove the CC home from Miami to Orlando ~270 miles and burnt 90 gallons of diesel! Averaged about 3 mpg @ 55-65mph. I thought the fuel gauge was bad but before I left, I topped it off until I saw the fuel and when I filled up at 1/4 tank about 40 miles from home I put in 80 gallons.

Also it has power but it doesn't seem like much more power than my Bounder. The bounder is a 4 speed and it starts out slow but kicks in well with the Turbo. In 4th gear at full spool it has decent pickup.

With the 6 speed and 400hp C9 I expected it to have some decent pickup. But it doesn't seem any faster, maybe even slower than the Bounder.

Have any suggestions? The coach was sitting for about a year and a half without being driven at all. Not sure how fresh the diesel was.

I installed a scan gauge D and now it says I'm getting 5-7 mpg during cruising but I haven't done anything except put fresh diesel. It says I'm maxxing out at 25lb of boost which seems lower than some people report at 32-33lb. (possible boost leak)

Last thing, the exhaust is rusted out behind the muffler so I probably have extra back pressure.

I'm not sure if I trust the scan gauge mpg or why it would increase from 3 to 5-7mpg by doing nothing.

Any help would be appreciated.

Thanks
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Old 03-02-2016, 04:20 PM   #2
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That's not good. We are getting 7.6 with our CC and it has a much bigger engine and weighs more.
Cruising MPG will be higher than your average, ours gets up to 12-15 under flat conditions.
As to what's wrong I really don't know as the last CAT we had was a 3126. Does sound like a turbo problem though. Was it blowing black smoke?
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Old 03-02-2016, 04:34 PM   #3
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I have a Silverleaf on my 2002 Windsor and it tracks very closely to what I end up getting via the odometer and fuel used. I've come to trust it. We have 350 HP ISC. We average 7.5 mpg for the ~5000 miles we drove it last year pulling a Jeep Grand Cherokee.

The only time I had a problem is when someone siphoned 20 gallons of fuel out of my tank on a trip out west. I had filled up in Albuquerque, we traveled around Northern NM and then filled up again at the same filling station and there was a 20 gallon difference. On trip we were out and about almost everyday so someone took advantage of that.

Can you tell if you were shifting into 6th gear, what are the RPM's.

Can you tell if the motorhome coasts pretty easily, sitting for a year I wonder if the brakes are dragging? Possibly after driving the distance you did it could have freed them up explaining why the mpg improved.
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Old 03-02-2016, 06:12 PM   #4
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Quote:
Originally Posted by 0phantom0 View Post
Hello RVers,



I just bought a used 2005 Country Coach Inspire 36' with Cat C9 400hp 1200lb torque. I also have a 99 39' Bounder Diesel with 275hp/550lbft ISB.



I drove the CC home from Miami to Orlando ~270 miles and burnt 90 gallons of diesel! Averaged about 3 mpg @ 55-65mph. I thought the fuel gauge was bad but before I left, I topped it off until I saw the fuel and when I filled up at 1/4 tank about 40 miles from home I put in 80 gallons.



Also it has power but it doesn't seem like much more power than my Bounder. The bounder is a 4 speed and it starts out slow but kicks in well with the Turbo. In 4th gear at full spool it has decent pickup.



With the 6 speed and 400hp C9 I expected it to have some decent pickup. But it doesn't seem any faster, maybe even slower than the Bounder.



Have any suggestions? The coach was sitting for about a year and a half without being driven at all. Not sure how fresh the diesel was.



I installed a scan gauge D and now it says I'm getting 5-7 mpg during cruising but I haven't done anything except put fresh diesel. It says I'm maxxing out at 25lb of boost which seems lower than some people report at 32-33lb. (possible boost leak)



Last thing, the exhaust is rusted out behind the muffler so I probably have extra back pressure.



I'm not sure if I trust the scan gauge mpg or why it would increase from 3 to 5-7mpg by doing nothing.



Any help would be appreciated.



Thanks

You might have a injector problem mine has no problem pulling 8,000# at 65to 70 mph but only get around 6 mpg. If your exhaust has a hole you should have less back pressure.
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Old 03-02-2016, 06:17 PM   #5
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Suggest you contact CAT with your engine serial number and get the dyno test sheet run on the engine when it was built. My C-10 generated slightly over 26 psi of boost.

Then suggest you go to http://forum.dieselrvclub.org/index.php?action=forum and ask your questions there. There are several ex CAT people on that site that should be able to help.
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Old 03-02-2016, 07:25 PM   #6
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ours gets up to 12-15 under flat conditions.

I think someone's calculator is on drugs.
Scott
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Old 03-02-2016, 07:33 PM   #7
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ours gets up to 12-15 under flat conditions.

I think someone's calculator is on drugs.
Scott
Nope! That's an accurate readout from the VMS 400CL. It's NOT an overall average, that's a rolling average over the last few minutes and only attainable on the flats @ 55 and low or no wind. Under the same conditions our ISC W/Banks in the '02 DSDP would be up over 18, but it also showed 256 mpg on the downgrades.
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Old 03-02-2016, 09:09 PM   #8
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Well mine gets 6.7mpg like clock work every time we head to the coast going over the coast range. My boost runs 30-32lbs on a good pull on my Silverleaf but I have gotten as high as 8.4mpg on I-5 doing 60mph all by hand calculation.
I would change the fuel filters (use only Advanced Efficiency Filters) and the same with oil filters, 1R-1808 oil.
Replace the air filter my is a Donaldson P527682 P, I went through TruckHelp and got Donaldson Blue DN-EAF5069, Best filter out there.
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Old 03-02-2016, 09:52 PM   #9
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I'm getting 7.5 with my C-9. You need to have a Certified CAT dealer take a look. Are you getting smoke from the exhaust and if so what color?
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Old 03-03-2016, 12:00 AM   #10
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Quote:
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Nope! That's an accurate readout from the VMS 400CL. It's NOT an overall average, that's a rolling average over the last few minutes and only attainable on the flats @ 55 and low or no wind. Under the same conditions our ISC W/Banks in the '02 DSDP would be up over 18, but it also showed 256 mpg on the downgrades.
Well,
If you look at it that way, yes, you will see that "momentary" mileage. Our C-7 runs along at an average of 7.1 with a rare, occasional 7.5 or so. But, I too have seen on the Medallion Info Screen, 99 mpg. The wife and I crack up when this is displayed. My wallet paints a considerably different picture when the fill-up comes around, we don't smile so much then.
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Old 03-03-2016, 12:08 AM   #11
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Well,
If you look at it that way, yes, you will see that "momentary" mileage. Our C-7 runs along at an average of 7.1 with a rare, occasional 7.5 or so. But, I too have seen on the Medallion Info Screen, 99 mpg. The wife and I crack up when this is displayed. My wallet paints a considerably different picture when the fill-up comes around, we don't smile so much then.
Scott
Note that I never said it was an average, I said the VMS showed that on the flat and level, no wind conditions.
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Old 03-03-2016, 06:06 AM   #12
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I have it at Nichols Truck & RV in Eustis. They work on trucks and RVs. I'll update what they say, or if they can't find anything I'll drive it more and see if the mpg increase.

The strange thing was that I was shocked I only got 3mpg real world results on my way back from Miami, but driving the 20 miles to the repair shop I was getting 5.5-8mpg on flat ground.

Only thing I did was change the oil, oil filter, and lube.

I'm thinking the suggestion of sticking brakes could contribute or possibly other items that worked itself out like semi clogged injectors or fuel lines?

The good thing is I was scared it was a cracked CAC or bad turbo, but with 25 lbs boost on the Scangauge its unlikely
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Old 03-03-2016, 10:27 AM   #13
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OP - Look forward to hearing what they find out. And if they are not CAT authorized, you still might be better off having a CAT dealer hook up their computers and seeing what is going on.

And DP's are different then gassers. Unless you are pushing a DP with a BIG BLOCK with substantial HP/Torque, you should not expect a 'pocket rocket'!

The analogy of it's like a locomotive is quite accurate. That Inspire while not a real heavy DP, is still probably several thousand pounds more then your gasser. Also the gearing and lower RPM operation of DP, will feel different to you then what you are used to.

Make sure the mechanical is all up to snuff, then take sometime to get used to the differences. Learn your max HP/Torque curve RPM's, and how to drive the coach to maintain those two. (HP for hill climbing, and RPM's for cruising at best MPG potential.)

Enjoy,
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Old 03-04-2016, 11:50 AM   #14
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It will take at least 3 tanks of fuel for your scan gauge to be accurate. Each time you fill your tank you need to input the amount. I have one on my coach and toad. They are very accurate. My friend has a 42' Cheeta with the same engine and complains about the same things.
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