PsnRebel
On My Banshee, In the Dunes !! In SoCal
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So we bought a 2005 Mandalay Presidio 39b about 2 years ago. We are fortunate enough to have a Generac Quietpac 75d installed. Around 800 hours.
Last time driving back east the generator suddenly died. It cranks, actually starts but once you let off the start button it dies. It has fuel. Coolant is filled to specs.
Using the flow chart in the service manual I think it’s the control board. Just one test I can’t do. It requires removing the grey plug harness that goes to the control board. I don’t know how it detaches. I can’t see because of framerail is in the way. Anyone with experience changing out the control board ? It appears to be held in place by 4 white plastic posts that have tabs that need to be pressed in , in order to pull the board. How do I collapse those white pins in order to remove board ?
Is my best bet to loosen generator mounting bolts and pulling it forward about a foot ? Any advice would be appreciated.
Thanks in advance. I’m located near Augusta GA if anyone knows of a competent service place for this amazing piece of equipment (sarcastic).
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TechWriter
Part-Timing Again
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Joined: 12/22/2002
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Fuel pump or hose to RV gas tank could need replacing.
Testing the fuel pump is fairly easy . . . disconnect your gen's fuel hose. Then connect another hose that's inside a gas can. Start your gen. If your it runs, then it's probably the pump.
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JimR 1
Custer South Dakota
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Joined: 08/29/2003
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Section 5
ENGINE DC CONTROL SYSTEM
Page 23
CIRCUIT CONDITION- FAULT SHUTDOWNS:
The engine has mounted to it a HIGH WATER TEMPERATURE
SWITCH (HWT) and a LOW OIL PRESSURE
SWITCH (LOS). While running, ENGINE
CONTROL circuit board action keeps Terminal 12
Wire 85 energized with battery voltage. Connected in
parallel to (Wire 85) are the LOW OIL PRESSURE
SWITCH (LOS) and HIGH WATER TEMP SWITCH
(HWT). The (LOS) has normally closed contacts.
After start-up, engine oil pressure will open the contacts.
The HWT has normally open contacts. High
coolant temperature will close the contacts.
Should engine water temperature exceed a preset
value, the switch contacts will close. Wire 85 from the
circuit board will connect to ground. Circuit board
action will then initiate a shutdown.
Should engine oil pressure drop below a safe pre-set
value, the switch contacts will close.
On contact closure, Wire 85 will be connected to
ground and circuit board action will initiate an engine
shutdown.
The circuit board has a time delay built into it for the
Wire 85 fault shutdowns. At STARTUP ONLY the circuit
board will wait approximately six (6) seconds
before looking at the Wire 85 fault shutdowns. Once
running after the six (6) second time delay, grounding
Wire 85 through either switch will cause an immediate
shutdown.
The ENGINE CONTROL circuit board also has overspeed
protection. The circuit board senses the AC
output from the stators POWER winding at Terminals
5 & 6 via Wires 22 & 44. This AC voltage and frequency
signal is used indirectly to monitor engine
RPM. If the frequency should increase above a preset
"adjustable" limit, the ENGINE CONTROL circuit
board will cause an immediate shutdown.
From page 23 of the manual. My high water temperature switch went bad.
You can check this at the oil pressure switch where the wire for the temperature switch as well as the oil pressure switch is attached. You can remove the wire from the switches and then start if it continues to run it is the switch.
JimR
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PsnRebel
On My Banshee, In the Dunes !! In SoCal
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So then in theory if I disconnect the #85 wire from the circuit board , terminal 12, the generator should start and run ?
I tried that and it still won’t stay running once I release the rocker switch (which I’ve tested per the manual).
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PsnRebel
On My Banshee, In the Dunes !! In SoCal
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TechWriter wrote:Fuel pump or hose to RV gas tank could need replacing.
Testing the fuel pump is fairly easy . . . disconnect your gen's fuel hose. Then connect another hose that's inside a gas can. Start your gen. If your it runs, then it's probably the pump.
I believe i can hear the fuel pump clicking when i depress the pre-heat switch on the front of the generator.
I couldn’t locate it the other day, i believe the pump is behind a removable panel on the bottom of the generator, which I couldn’t get to come off easily.
I’ve been having to dodge rain drops for this project…
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JimR 1
Custer South Dakota
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PsnRebel wrote:So then in theory if I disconnect the #85 wire from the circuit board , terminal 12, the generator should start and run ?
I tried that and it still won’t stay running once I release the rocker switch (which I’ve tested per the manual).
Do not know about theory but if you unhook the wires at the oil pressure switch and the gen starts and runs then one of those switches is bad. I unhooked one at a time the first being the temp switch so I knew it was that switch. I did not test at the board.
Behind the front panel and in the upper right 1/4 is the oil pressure switch on that switch there is two wires, can not remember the color or number, one of the wires is for the oil pressure the other that goes to the right and behind the motor is for the temperature switch.
Also if you are holding down the preheat switch and the gen continues to run then you know the fuel pump is good.
JimR
* This post was
edited 02/10/23 10:59pm by JimR 1 *
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JimR 1
Custer South Dakota
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Got to thinking:
We have different Motor Homes so the generator may be a little different.
Mine is a Quite Pact 75D model 4270 it is installed in the front between the frame rails and behind an access door in the front cap.
The front of the generator I reference is where the oil, air and fuel filter are located.
JimR
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PsnRebel
On My Banshee, In the Dunes !! In SoCal
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Yup same generator here! JimR 1 i wanted to thank you for your time, trying to assist me in this. I can read the manual, which is written pretty well for me to understand, but another outlook or explanation sometimes makes things a little clearer.
I just pulled off the front cover. And it looks as you described. Found the oil pressure switch. Trying to determine where heat temp switch is, im having trouble following the wires.
** on edit ** i removed. Each #85 wire (blue) from the oil pressure switch. No luck keeping it running with either wire disconnected.
Before pulling off the cover i held down the pre-heat switch while starting, i then kept it pressed after i let off the start/stop switch. It kept running, until i let off the pre-heat switch, then it startled to die. Pressed it again and it went back to running.
When i tested my pre-heat circuit the other day i didnt test the “pre-heat contactor” i have no idea where thats located and what it looks like. If anyone happens to know.
* This post was
edited 02/11/23 09:21am by PsnRebel *
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JimR 1
Custer South Dakota
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Have you tried to run the generator from the generator start stop switches by unplugging the start stop switches from the dash? Small wire bundle (square plug) from the left side of the generator heading toward the dash just unplugs to test the inside switches. Some times those can short out.
As I remember the temp sensor is almost directly behind the oil pressure on the back side of the motor, other words about 8 to 10 inches away straight back out of sight unless you pull the right side panel or use a mirror.
Should show in the schematics in the manual item 10 page 121 of my manual. Thermo Switch
JimR
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PsnRebel
On My Banshee, In the Dunes !! In SoCal
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JimR 1 wrote:Have you tried to run the generator from the generator start stop switches by unplugging the start stop switches from the dash? Small wire bundle (square plug) from the left side of the generator heading toward the dash just unplugs to test the inside switches. Some times those can short out.
As I remember the temp sensor is almost directly behind the oil pressure on the back side of the motor, other words about 8 to 10 inches away straight back out of sight unless you pull the right side panel or use a mirror.
Should show in the schematics in the manual item 10 page 121 of my manual. Thermo Switch
JimR
I believe i did try starting it with the remote (dash) switch disconnected. I know i unplugged it when running the diagnoses for the start/stop switch. I’ll try it again once the rain stops, since I don’t remember.
I was afraid the temp switch was on the back of the head. I haven’t pulled the top cover off so i wasn’t sure. I guess i should try to access that also just to be certain it’s good. Was hesitant because the way i read and understand it the gen should start and run 5-6 seconds then shut down if either the low oil pressure or temp switch is bad.
I am going to try n add oil (reads 1/2 full on dipstick) also before i test the oil pressure switch with my volt/ohm meter. The manual says to top it off before testing, so i figure that wouldn’t hurt. It doesn’t mention anything about a low oil shutdown, but it wont hurt, especially once i get it started. Lol
Thanks again for your your insight.
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