Author Topic: Air compress, fuel guage question...  (Read 1746 times)

Offline travelingfools

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Air compress, fuel guage question...
« on: July 23, 2008, 09:03:42 AM »
Things are moving ahead for us here..Just picked up a sedan door last weekend to replace the bi-folds. Cant wait to get some free time to install it !!!!

So on to my questions..The first is about the air compressor...My air kicks/cycles off at around 122 and on at around 90ish. Is that correct or do I need to adjust the govenor ? it seems like I run out of air fast, like when im doing a 5 point turn getting into a campsite. Sometimes Ill have to stop and rebuild air...i dont remember ever having that problem with other vehicles Ive driven.

Secondly (is that even a word ??), I got a fuel guage and sending unit. Im guessing that the guage gets straight 24v to the hot side and the ground runs through the sending unit ?? is that correct..?

Thanks in advance for all the help...
John P, Lewiston NY   1987 MC 9 ...ex NJT

Offline TomC

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Re: Air compress, fuel guage question...
« Reply #1 on: July 23, 2008, 09:20:17 AM »
The air compressor is putting out correctly.  Some go a little higher to around 125lb, but not worth the effort.  Do you have air assist steering?  If not, don't be pressing so much on the brakes-I know it sounds cool, but obviously you're running out of air too soon.
Typically the way a fuel gauge works is you put the power to the gauge, then the wire from the gauge to the sending unit where the sending unit controls the amount of ground.  Having a proper ground on both the tank and sending unit is key to having a accurate running fuel gauge.  At least on mine, no ground is empty, complete ground is full.  Good Luck, TomC
Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.

Offline JackConrad

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Re: Air compress, fuel guage question...
« Reply #2 on: July 23, 2008, 04:52:01 PM »
Need to know if your gauge was designed for 12 or 24 volt. Wrong voltage will let the snkoe out or not read correctly.  Jack
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Offline Lin

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Re: Air compress, fuel guage question...
« Reply #3 on: July 23, 2008, 05:17:48 PM »
What gauge and sending unit did you get?
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Offline fraser8

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Re: Air compress, fuel guage question...
« Reply #4 on: July 23, 2008, 05:40:55 PM »
Your cut in and cut out is well with in limits. Our DOT requires the compressor to build from 50lbs to 90lbs within 3 minutes at a fast idle. 1,000 to 1,200 rpm. Run your air down to 50 and time it to 90 anything more than 3 minutes should be of concern. This part of our pre trip...
Fraser Field
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Where the milk cows out number the people, but they can't vote
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Offline NJT 5573

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Re: Air compress, fuel guage question...
« Reply #5 on: July 23, 2008, 07:52:12 PM »
It sounds like you have a blown brake service diaphram and are loosing air under application. If you blow the one on the other side (emergency) it can burn your bus.
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Offline buswarrior

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Re: Air compress, fuel guage question...
« Reply #6 on: July 23, 2008, 08:02:01 PM »

For the air system:

Build up the air pressure, release the parking brake while you are waiting, when the compressor cuts out, shut off the engine. Press the brake pedal to the floor and see what the air gauge does.

It would be really excellent if it doesn't move at all for a minute.

If the gauge is moving at any noticeable rate, you need to find the leaks, and repair them. Trouble here is if the leaks are in a bunch of auxiliary items. Makes identifying honest brake related leaks a whole lot harder.

When using air brakes, the goal is to use as little brake pedal as necessary for what you are trying to do, and no more. The more pedal you press, the more air you use, and waste.

A good air system should be able to withstand even a novice making a number of turning and backing moves before showing a low air warning.

When did you drain your air tanks last? Water takes up space that was meant to store air...
This only makes a difference if you have a water level in the tanks that can be measured by the cup fulls, not a little spray.

let us know, please!

happy coaching!
Frozen North, Greater Toronto Area

Offline NJT5047

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Re: Air compress, fuel guage question...
« Reply #7 on: July 23, 2008, 09:13:03 PM »
Yep.  You got leaks in the air system, or the compressor is failing.  As already stated, drain your tanks and see what comes out.  If no oil, leaks are the likely culprit.   The NJT dryer should keep the tanks dry...if it's working properly.   
I've got an identical coach to yours and when the compressor kicks in on mine, it just climbs right up.   Never have to wait for air unless starting cold.  And I got leaks too. 
Get a bored child (or young babe!  ;D) to listen for leaks. They can hear them surprisingly well. 
A 24V fuel gauge will be hooked up with 24V to "ignition" terminal on the guage, ground to about any part of the guage body, and the 'sender' terminal lead to the sender center terminal.  Your NJT has the fuel guage wiring appropriated for the fuel primer pump.   I'd recommend restoring the fuel sender lead by disconnecting it in the ACJB (upper LH front bay) and reataching it to the fuel guage wiring...which is in your bus.   
The sender for an MC9 tank is proprietary and nothing else that I know of will interchange. 
The water temp guage and voltmeter both have 24V that can be jumped off the stud.  There's a ground bus (stud) right next to the fuel guage mounting hole (RH dash).   
The sender ground wire is taped up just to the right side of the fuel tank.  The ground wire should be attached to one of the 5 sender mounting screws.   
Once electrically out of the system, the primer pump can be used directly from the batteries with a 4' jumper if you need it.  I'd definitely keep the primer pump servicable, just rewire as necessary.  And the momentary primer switch should be tossed.  That's a PITA to use.  Just use an alligator clip on a wire.  You won't leave it on overnight if you cannot close the fuel and battery compartment doors!   ;)
If you wish to run a new lead for the fuel guage, the best route is thru the battery box, into the front bay, across to the small tunnel which will route the wire right behind the drivers seat area, and then thru the bottom of the side switch panel and into the dash.   Pretty easy to do. 
May I suggest you buy a good quality fuel gauge sending unit.  The cheapos will fail due to terminal rust when sitting.  I bought an cheapo and it failed after one year of use.   Bought the second unit from US Coach and it has been in the coach, and working, for 2 years now. 
The sender is always above the fuel it's ripe for rust. 
And I keep my fuel tank full. 
Good luck on that door!  I had to pull the RH upper SS panel to facilitate welding the hinge in place.   Breck was able to weld his from the dash?  The dash will have to be cut out for the limit arm anyway...cut it out first and you'll have a good deal more room to visualize your work area.
Install the air lock too.  The box is already there.  The air solenoid for the bi-folds can be used to control the air lock.  Check the solenoid for air leaks.  Most leak. 
The door is too heavy to latch into the middle of the door jamb when under way. The door isn't designed to be latched from the middle anyway.   
The center door frame is OK for a campground latch. 
Note that the upper door hinge bolt is threaded thru the uppe hinge.  This allows vertical adjustment for the door.  BE SURE THAT THE LOCATION OF THE UPPER HINGE PLATES ALLOW FOR THIS ADJUSTMENT.   The lower hinge allows 'tilt' on two planes. 
Check the dimensions of the door v the frame before hanging the door.  Any RF damage will have to be corrected before the door will close. 
Don't forget to leave room for the weatherstripping.  That's a bummer when the door is hung, but the weatherstrip won't go in due to lack of clearance.
Sedan doors are really tight fitting.  About 1/8" + - is it.
Don't attempt to 'buck' the upper door section with the glass installed. 
VERY IMPORTANT:  leave a window or hatch open when working on the door.  If you get locked out, you want a way to get inside to remedy the situation.   ???

My dos centavos, JR

JR Lynch , Charlotte, NC
87 MC9, 6V92TA DDEC, HT748R ATEC

"Every government interference in the economy consists of giving an unearned benefit, extorted by force, to some men at the expense of others.”

Ayn Rand

Offline travelingfools

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Re: Air compress, fuel guage question...
« Reply #8 on: July 24, 2008, 11:57:07 AM »
Just got back into town..thanks for all the Ive got to sit down and sort through. The guage and sending unit came of an '83 MC9..
John P, Lewiston NY   1987 MC 9 ...ex NJT