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Old 08-09-2017, 09:28 PM   #1
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Incredible loss of power at high altitude 10 - 12000 feet

We are travelling from Montreal Quebec to California on a two months trip.

In Colorado we crossed the mountains. Suddently at a certain level my motorhome becomes very very lazy. I go in low gear and it is very difficult to climb.

So I disconnect the Honda Odyssey at the back (with two 12' Kayak on top and 4 bikes at the back), I put my five kids and my wife in it with the many water bottle pack to remove the more weight possible.

Then I continue to climb. After 15 minutes it is too difficult for the engine. I decide to drop all the fresh and gray water (we are always full of water because we are 7). My motorhome climb at 25 mph with the engine working at 4300 rpm at low gear. Very very difficult because I tell myself I will have to go back.

Then I see a sign on the side of the road, we are at nearly 12000 feet at Mount Monarch. I see a ski station. I made it but I feel my motorhome could not have climbed another 1000 feet.

I have solar panels, have added many things so we are a bit overweight. But I never thought it would be so difficult at high altitude.

Here in the mountains the regular fuel is 85 instead of 87. I suppose they know there is less oxygen in the air so they reduce the octane in the fuel. I was full of 85.

I read that we loose 3% of HP power per 1000 feet above sea level. If this is true then at 12000 feet I could have loose 36% of my power. So it is like if my 10 cylinders was now a 6.4 cylinders.

Since then we had to unhook the car three times.

I have the original exhaust manifolds. On the 1999 they were very badly designed and they both merge in a 3.5" pipe.

I have recent spark plugs and recent coils boots. I have enough power at sea level.

Would I get more power putting 87 or 89 octane fuel in those high altitude?

BTW, I met only another motorhome going at Mount Monarch and it was on the side of road at the beginning of the hill.
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Old 08-09-2017, 09:40 PM   #2
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I would guess that you're more than just a little overweight , but that would be only determined by a trip over the scales.
If you didn't hear any pinging during the climb , as I did on my last gas tow vehicle on 85 octane , I doubt that higher octane will help .

BTW. When you head home , avoid having to buy fuel where it has 40% ethanol , that WILL really drop your power . ( Ohio if memory serves ) My 8.0L Dodge V-10 didn't like that fuel at all.
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Old 08-09-2017, 09:42 PM   #3
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Codes P0171 P0174

After Colorado we went in Las Vegas at Oasis Campground. We stayed there three days. After those three days at very high temperature, I started the engine and after a few minutes I got the codes P0171 and P0174 meaning Lean code for Bank 1 and 2.

I reset the codes and drove for three hours and the codes did not come back. Maybe the fuel evaporated in the injectors or in the fuel filters because of the heat? I don't know.

Anyway, we are heading toward Death Valley where the temperatures are the highest on earth.
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Old 08-09-2017, 09:44 PM   #4
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HP Loss = (elevation x 0.03 x horsepower @ sea level)/1000

You have a normally aspirated gas engine? They suck at altitude.

The reason why many aircraft use superchargers or turbos above 10K for best performance.

Here's a handy calculator.

http://www.csgnetwork.com/relhumhpcalc.html
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Old 08-10-2017, 03:43 AM   #5
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Quote:
Originally Posted by Skip426 View Post
I would guess that you're more than just a little overweight , but that would be only determined by a trip over the scales.

......
My GVWR is 20500 on my sticker and on the scale I was 22280 full of water with my family on board.

So I climbed the montain without the kids, the wife and the water and without the car at the back. So I feel I was overweight but not so much.

I had no pinging sounds.

Do you feel my engine is not behaving normally? I keep it in good working order.

Here is a picture I have found on the internet about the ugly exhaust (or similar) that connect to the manifolds for the 1999 F53:



They changed the design later.
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Old 08-10-2017, 05:57 AM   #6
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Carl, I have the same engine and tranny you have. In a 35 ft Southwind.

As you go up in altitude, the air becomes less dense. Below are two charts:

1) Air density in percent vs altitude.

2) Density Altitude calculator (Air density vs temperature).

i.e. your 305 hp V10 will produce 305 hp at sea level. But creeping up to the Eisenhower tunnel on I-70 at 11,000 ft, your 305 hp engine can only produce about 77%, 235hp, of that if its 20 degrees outside (standard temperature for that altitude).

DENSITY ALTITUDE - Air temperature also effects air density, So if I were making my Eisenhower climb in the summer and the outside air temperature was 85 Deg, The warm air is even thinner and is more like an altitude of 15,000 ft. (about 68% of sea level). With air density of only 68%, my 305 hp engine is now down to only 207 hp.

You were at 12,000 ft so your case may have been worst - i.e. engine only putting out 200hp.

Making the climbs - I slow down, downshift to a lower gear and maintain the highest speed that 4000 rpm will produce without the gas pedal constantly on the floor. I don't allow the engine to upshift. I keep it in gear manually. This keeps me from loosing the speed I gained and also keeps the transmission torque converter from unlocking, then slipping, and producing heat.

In the case of the 11,000ft Eisenhower tunnel, I make that climb in 1st gear, 25 mph, at 4,000rpm. I'm fully loaded and towing a toad. not a problem. Keep the rpms between 4000 and 4500.

NOTE - When you get to Death Valley, Its below Sea Level, so you should make more than 305hp depending on air temperature
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Old 08-10-2017, 06:41 AM   #7
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Quote:
Originally Posted by cbilodeau View Post
My GVWR is 20500 on my sticker and on the scale I was 22280 full of water with my family on board.
...
I am really surprised so many are ignoring how overweight this vehicle is. It is unsafe and yet the OP carries the whole family. You need to reduce that weight. You are not just a little over weight. Also note you don't mention what you are towing and what it's weight is. And you are in the mountains where brakes will easily overheat an underweight motorhome never mind a SUBSTANTIALLY overloaded one. And are the tire pressures correct for such loads???
You are endangering your entire family and others on the road.
You can't justify this by saying you are a family of 7 and need full water. There is no logic in this at all! Sorry but this angers me to no end.
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Old 08-10-2017, 06:44 AM   #8
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Exhaust system - On the 365hp V10, the "T" exhaust was probably an issue, and that's why it got changed.

On our 305 hp version, a "Y" would be better, but I don't think its worth the expense of a retrofit.
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Old 08-10-2017, 06:49 AM   #9
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Quote:
Originally Posted by cbilodeau View Post
My GVWR is 20500 on my sticker and on the scale I was 22280 full of water with my family on board.

So I climbed the montain without the kids, the wife and the water and without the car at the back. So I feel I was overweight but not so much.

I had no pinging sounds.

Do you feel my engine is not behaving normally? I keep it in good working order.

Here is a picture I have found on the internet about the ugly exhaust (or similar) that connect to the manifolds for the 1999 F53:



They changed the design later.
My 2006 on a 2004 f53 chassis had the same looking exhaust pipe. The recommendation from 5 star tuning was to go to a muffler and have the right pipe altered to flow straight. When i spoke with the muffler shop he was familiar with that design and had done the mod before. Think it cost about $100. Helped some but not as much seat in the pants improvement as the 5 star tune.

That one crazy U turn. Thought i had an after pic but don't.

The red lines is where they cut and yellow is the flow of the pipe they put in. The T section was replaced with a new bent pipe. Click on picture for a larger view.
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Old 08-10-2017, 07:05 AM   #10
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Weight wise, Mine runs a little less than yours, no kids

However, my DW packs everything as if we are permanently moving

There isn't a lot of difference between the 22k and the 20k chassis, Same brakes, suspension, engine, tranny, etc. The two main differences is frame rail length (wheel base) and the 22k has 22inch tires vs 19.5 inch tires.

Our toad weights about 3k lbs, yours is probably around 4500

LEAN CODES - These may have been set because of the altitude - I suspect they would have self cleared as the engine relearned its altitude.
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Old 08-10-2017, 07:06 AM   #11
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The OP has a first generation, 275 HP, 2 valve V 10.

Not much is going to make it much better. Wind it up to 4500 RPM and climb the mountains.

Wonder where he dumped the gray water ?
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Old 08-10-2017, 07:12 AM   #12
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Yes what you experienced at 12000 feet is normal. There will always be a power drop off as the altitude increases in a normally aspirated engine. As you have now learned that power drop off can be quite dramatic. Next time find a route that doesn't take you that high.
I'm a retired helicopter pilot and aircraft have to pay attention when flying in the mountains to make sure they didn't run out of power at altitude.
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Old 08-10-2017, 07:12 AM   #13
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Bruce;

I hate the exhaust system ---- If I had access to a pipe bender, I'd clean it up. but its not worth doing if I have to pay someone.

If I had the 365 hp, yah, Its moving a lot more volume than our 305.

Next spring I need to replace manifold bolts (rusted and 1 missing). maybe I'll look at the exhaust system at that time. Its hard to justify it on an 18 year old chassi that only gets driven 10k miles a year.
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Old 08-10-2017, 12:44 PM   #14
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Waiter21 wrote.
"In the case of the 11,000ft Eisenhower tunnel, I make that climb in 1st gear, 25 mph, at 4,000rpm. I'm fully loaded and towing a toad. not a problem. Keep the rpms between 4000 and 4500."

WOW! I am surprised at how the V10 falls off at altitude.
My 95 460 with Banks and toad (21,000 lbs. total) run up the west side at 35 MPH in 2nd gear @3200 RPM and I had more, just didn't want to turn the ol 460 any faster.
Even passed a tour buss half way up.

Richard
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