More Vacuum

[FrankO]

We drive the mountains on most trips since we live in Colorado. I have experienced some issues with low vacuum when climbing the hills as the vent air reduces significantly when in climbing mode. I also have read on this and other forums where others have experienced similar problems so I am not alone. Has anyone added an additional vacuum pump to help with this issue? Is there another approach that I could take?
Thanks -- Frank O.

[DriVer]

Quote:

Originally Posted by FrankO We drive the mountains on most trips since we live in Colorado. I have experienced some issues with low vacuum when climbing the hills as the vent air reduces significantly when in climbing mode. I also have read on this and other forums where others have experienced similar problems so I am not alone. Has anyone added an additional vacuum pump to help with this issue? Is there another approach that I could take?

Frank O, That's weird. On the Winnebago there's a vacuum reservoir. Looks like a softball. I'd check to see if there's a leak in the attached hoses going to the HVAC controls.

[FrankO]

Driver-
Thanks for the quick response. I have had this MH since almost new (2007) and it has done this since day 1. When on flats all is ok, I just notice the problem when under power. I will check the connections and insure that there is a reservoir. I also notice that when I am above 9K ft in elevation and pulling hard that my tranny will not downshift and hold in the lower gear. It seems to want to upshift 1st to 2nd even thought he rpms are below 4K. This only happens at the very top of our passes so I just slow down (25 mph) and enjoy the scenery. I thought this behavior might be related to low vacuum.
Frank O.

[jdsr]

I had to rpl my vac lines several years ago. They were very small hairline cracks. Hard to see with naked eye but they where there. My problem was with the blue and green lines but I rpl all because it was easy to do. good luck

[Alan_Hepburn]

I don't think you're describing a vacuum issue. You say the vent air is reduced when under power - when you're climbing hills under power you're probably holding the throttle pretty close to wide open. Most engine computers today will shut down the air conditioning compressor when the engine is working that hard to reduce the heat load on the system. At wide open throttle, the manifold vacuum is at a minimum, but adding more vacuum won't make the AC pump out more air - reducing the load on the engine WILL, though.

[George Z]

Quote:

Originally Posted by Alan_Hepburn I don't think you're describing a vacuum issue. You say the vent air is reduced when under power - when you're climbing hills under power you're probably holding the throttle pretty close to wide open. Most engine computers today will shut down the air conditioning compressor when the engine is working that hard to reduce the heat load on the system. At wide open throttle, the manifold vacuum is at a minimum, but adding more vacuum won't make the AC pump out more air - reducing the load on the engine WILL, though.

Allen on my WH a low vacuum situation will make the dash heating or cooling default to defroster ducts only. This may be what is happening

[FrankO]

My issue is more like what George is experiencing. I rarely run air in the mountains and never run it while pulling the passes.
Thanks -m Frank O.

[DriVer]

I remember back in the day when automatic transmissions had vacuum controls. I do not believe that the Allison has an interface to a direct vacuum source. I'm just sayin'

[FrankO]

Thanks Driver. I guess I am back to the drawing board as to why I can't stay in 1st gear. For now I will just have to be satisfied with the last mile or so running at 25mph. At least the scenery is really nice. Passes that I have experienced this on is Monarch EB, Freemont WB, Eisenhower both EB/WB and Vail EB. When I was in ALaska and pulling their passes at much lower elevations I had no problem pulling at 45 to 55 mph. It seems related to grade and elevation.
I will be visiting my MH in storage this weekend and will check for the Vacuum Reservior but not for leaks until I bring it home to prep for my next trip in January.
Frank O.

[DriVer]

Quote:

Originally Posted by FrankO For now I will just have to be satisfied with the last mile or so running at 25mph. .

Frank O., When we went W. Bound on the Blue Diamond Highway out of Vegas, that grade took me down to 25 MPH instantly. The reason why it did that was because I turned a corner and there it was. I had no time to rev up my energy level but we did climb it although I felt helpless. Eventually wound up at Terrible's in Pahrump.

[max49]

I live in CO and have no idea what vacuum has to do with us having little power out here, bit I'm willing to learn

It sounds to me like u have a shift point problem or you just need to lock it down manually to keep it from upshiftimg

I don't know which is harder on the powertrane, letting the engine rev and breathe, or lugging it up the hill in a higher gear
I always went with rev & breathe but since my first 8,1 blew up, I'm a little gun shy.

[CoastieSCPO]

FrankO, I'm not an expert on this, however it may sound like the problem has a lot to do with altitude, especially since the transmission is acting up at altitude as well. i hope that you solve the problem.

On another note, especially since you mentioned Alaska, I do believe that we were parked next to you at the Hinton, Alberta KOA in 2009 and also near you at the "Mile O" campground at Dawson Creek prior to our journey up the Alaska Highway. Hope you had as good a trip as we did.

Bob

[TrekPR]

Frank O,
A couple of questions: Are you manually shifting to 1st gear and having it shift out? If not, if you ease off the gas at all don't you expect it to shift out of 1st? I've done a little climbing and when I want to hold a gear and maintain a speed or RPM I manually shift to the gear otherwise every time I ease off the gas a little it will shift.

To all, what is magical about 4000 RPM? If you are able to accelerate in a gear are you lugging the engine? At altitude are you not going to lose horsepower and will this not be multiplied with a dirty air cleaner or intake restrictions?

I pulled through Elsenhower pass years ago in a 350 Chev hauling a 30' boat, I pulled the air cleaner and chugged over the top at less than 5 MPH. I have never been in a situation with the 8.1 where I felt I couldn't drop a gear and cruise over a pass, it might not be a 60MPH but easily between 3000-4000 RPM.

[FrankO]

Paul,
I do shift into 1st the las 2 miles to try and keep my RPMs above 3800. It does ok until that last mile when the tranny seems like it does not like the pull and upshifts to 2nd even though I do have it in 1st gear. So something is overriding the manual shift setting.

Driver,
What do you think would cause the tranny shifting out of a gear (1st) it is suppose to be locked in even though I am only running 4000 to 4200 RPMs. I can run in the mid to high 4000s in 2nd and 3rd. Could it be the torque converter?

Bob,
I do remember you. We had a fantastic trip.We were gone 100 days and loved every moment. Met so many great folks including you and your wife. If memory serves me right you had an issue with one of your storage doors at Mile 0 abd then in Hinton you were worried about your brakes. I think you had an appointment to get them looked at or fixed. I hope all went well for you after that. Send me a PM so we don't get this thread thrown off course.
Frank O.