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MacNeal dash issues [message #369075]

Sat, 12 March 2022 15:34

rjw

Messages: 697
Registered: September 2005

Karma: 4

Senior Member

The first upgrade I made to my GMC back in September 1998 was to install a MacNeal dash from his company:
http://custominstrumentpanels.com/gmc.htm

I have no real complaints but I've had some issues with the dash over the years. The dash is about 20 years out of warranty.

I replaced the speedometer in 2013 because the odometer stopped working. Several of the gauges, including volts, oil pressure, suspension air tank pressure all read a bit off actual values, but I've learned to live with that over the past 20+ years.

However, the fuel pump switch apparently stopped working which is bad with EFI. As part of my initial startup I used to switch the pump off, crank the engine until I saw oil pressure, then turn the pump on to start. I did that to lubricate the engine, as part of my pre-start routine. Otherwise the engine starts immediately with EFI and I've heard much of engine wear occurs during initial startup before oil is being pumped through out the motor. Q-jet carbs do that automatically. Now I can't do that.

Now my gas gauge stopped working properly, as it reads full on both thanks. I know that means an open circuit in the wiring. Since the symptom is the same on both tanks, I’m thinking there is a problem with the actual gas gage or the fuel tank selector switch in my MacNeal dash.

I wonder if others with MacNeal dashes have had similar problems with gauges and switches.

Richard
76 Palm Beach
SE Michigan
www.PalmBeachGMC.com

Roller Cam 455, TBI+EBL, 3.42 FD, 4 Bag, Macerator, Lenzi (brakes, vacuum system, front end stuff), Manny Tranny, vacuum step, Tankless + OEM water heaters.

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[GMCnet] Re: MacNeal dash issues [message #369076 is a reply to message #369075]

Sat, 12 March 2022 16:42

jimk

Messages: 6734
Registered: July 2006
Location: Belmont, CA

Karma: 9

Senior Member

Your going to have issues with any instruments unless you spend high
dollars.
Mac is caught in a place of offering a product that is affordable to most.
We sell his dashes and seen the work for 20-30 years.
Jim Bounds uses Mac's dashes .

On Sat, Mar 12, 2022 at 1:34 PM RJW wrote:

> The first upgrade I made to my GMC back in September 1998 was to install a
> MacNeal dash from his company:
> http://custominstrumentpanels.com/gmc.htm
>
> I have no real complaints but I've had some issues with the dash over the
> years. The dash is about 20 years out of warranty.
>
> I replaced the speedometer in 2013 because the odometer stopped working.
> Several of the gauges, including volts, oil pressure, suspension air tank
> pressure all read a bit off actual values, but I've learned to live with
> that over the past 20+ years.
>
> However, the fuel pump switch apparently stopped working which is bad with
> EFI. As part of my initial startup I used to switch the pump off, crank
> the engine until I saw oil pressure, then turn the pump on to start. I
> did that to lubricate the engine, as part of my pre-start routine. Otherwise
> the engine starts immediately with EFI and I've heard much of engine wear
> occurs during initial startup before oil is being pumped through out the
> motor. Q-jet carbs do that automatically. Now I can't do that.
>
> Now my gas gauge stopped working properly, as it reads full on both
> thanks. I know that means an open circuit in the wiring. Since the
> symptom is
> the same on both tanks, I’m thinking there is a problem with the actual
> gas gage or the fuel tank selector switch in my MacNeal dash.
>
> I wonder if others with MacNeal dashes have had similar problems with
> gauges and switches.
>
>
>
> --
> Richard
> 76 Palm Beach
> SE Michigan
> www.PalmBeachGMC.com
>
>
> Roller Cam 455, TBI+EBL, 3.42 FD, 4 Bag, Macerator, Lenzi (brakes, vacuum
> system, front end stuff), Manny Tranny, vacuum step, Tankless + OEM water
> heaters.
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
>

--
Jim Kanomata ASE
Applied/GMC, Newark,CA
jimk@appliedairfilters.com
http://www.gmcrvparts.com
1-800-752-7502
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Jim Kanomata
Applied/GMC
jimk@appliedairfilters.com
www.appliedgmc.com
1-800-752-7502

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Re: MacNeal dash issues [message #369078 is a reply to message #369075]

Sat, 12 March 2022 18:41

Matt Colie

Messages: 8547
Registered: March 2007
Location: S.E. Michigan

Karma: 7

Senior Member

Richard,

I happen to have a very unfortunate familiarity with this part of the coach.
If both fuel gauges went full at the same time, then there is an extremely high probability that if it is not the instrument, then the problem is between there and the selector switch. Diagnosis should be real easy. Just clip a lead on a good ground a probe the back of the instrument and then the common on the switch. One of those should make it say empty. If the problem is not there, I bet we can nail it down in short order, but it will require getting dirty.

Matt

Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit

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Re: MacNeal dash issues [message #369080 is a reply to message #369078]

Sun, 13 March 2022 11:39

rjw

Messages: 697
Registered: September 2005

Karma: 4

Senior Member

Matt Colie wrote on Sat, 12 March 2022 19:41

Richard,

I happen to have a very unfortunate familiarity with this part of the coach.
If both fuel gauges went full at the same time, then there is an extremely high probability that if it is not the instrument, then the problem is between there and the selector switch. Diagnosis should be real easy. Just clip a lead on a good ground a probe the back of the instrument and then the common on the switch. One of those should make it say empty. If the problem is not there, I bet we can nail it down in short order, but it will require getting dirty.

Matt

Matt,
I'll try that.

Thanks,

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[GMCnet] Re: MacNeal dash issues [message #369083 is a reply to message #369075]

Sun, 13 March 2022 15:42

Rob

Messages: 651
Registered: November 2013
Location: Victoria, BC

Karma: 3

Senior Member

My Mac dash is from the 2005 time frame (before I owned it) and while the gauges are obviously K-Mart quality level - I've really had no issues up to now. I've replaced a few of them - to measure different things and/or remove the air bag line pressure gauge. I've also had at least one switch fail - Boost, if I recall correctly.

I'm sure that now that I'm replying to your query, my next camping season will be one gauge failing after the next...

Rob
76 Royale Twin Beds, Dry Bath
Victoria, BC

> On Mar 12, 2022, at 1:34 PM, RJW wrote:
>
> The first upgrade I made to my GMC back in September 1998 was to install a MacNeal dash from his company:
> http://custominstrumentpanels.com/gmc.htm
>
> I have no real complaints but I've had some issues with the dash over the years. The dash is about 20 years out of warranty.
>
> I replaced the speedometer in 2013 because the odometer stopped working. Several of the gauges, including volts, oil pressure, suspension air tank
> pressure all read a bit off actual values, but I've learned to live with that over the past 20+ years.
>
> However, the fuel pump switch apparently stopped working which is bad with EFI. As part of my initial startup I used to switch the pump off, crank
> the engine until I saw oil pressure, then turn the pump on to start. I did that to lubricate the engine, as part of my pre-start routine. Otherwise
> the engine starts immediately with EFI and I've heard much of engine wear occurs during initial startup before oil is being pumped through out the
> motor. Q-jet carbs do that automatically. Now I can't do that.
>
> Now my gas gauge stopped working properly, as it reads full on both thanks. I know that means an open circuit in the wiring. Since the symptom is
> the same on both tanks, I’m thinking there is a problem with the actual gas gage or the fuel tank selector switch in my MacNeal dash.
>
> I wonder if others with MacNeal dashes have had similar problems with gauges and switches.
>
>
>
> --
> Richard
> 76 Palm Beach
> SE Michigan
> www.PalmBeachGMC.com
>
>
> Roller Cam 455, TBI+EBL, 3.42 FD, 4 Bag, Macerator, Lenzi (brakes, vacuum system, front end stuff), Manny Tranny, vacuum step, Tankless + OEM water
> heaters.
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:

Rob - Victoria, BC - 76 Royale - Rear Twins/Dry Bath

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Re: MacNeal dash issues [message #369549 is a reply to message #369075]

Sat, 23 April 2022 10:49

rjw

Messages: 697
Registered: September 2005

Karma: 4

Senior Member

rjw wrote on Sat, 12 March 2022 16:34

The first upgrade I made to my GMC back in September 1998 was to install a MacNeal dash from his company:
http://custominstrumentpanels.com/gmc.htm

Now my gas gauge stopped working properly, as it reads full on both thanks. I know that means an open circuit in the wiring. Since the symptom is the same on both tanks, I’m thinking there is a problem with the actual gas gage or the fuel tank selector switch in my MacNeal dash.

I wonder if others with MacNeal dashes have had similar problems with gauges and switches.

I am still fooling with my gas gauge not working. I have ruled out the fuel tank selector switch as being the problem.

First of all I unplugged the 2 pin connector by the fuel selector solenoid and found that there was a lot of corrosion. I thought that might be the problem so I cleaned it up and also cleaned up the ground wire at that location. I reconnected and it still shows over full. If the connector is not plugged together the gauge registers more over fill then if connected. If I short the pins to ground it shows empty on either tank.

If I connect a known good fuel level sensor or a number of resistors in the 30 to 50 OHM range to either of the pins that go to the front and the fuel level gauge I can get the gauge to register properly. i.e. 50 OHM shows up as ~ 1/2 full and that is regardless of which pin I connect them to at that connector.

I checked the resistance of the pins going back to the senders and found them to read 108.9 and 107.2 ohms. By the way the tanks are approximately 1/2 full as far as I know.

I would have thought that over 100 ohms resistance would show more to the empty side than over full as the gauge is 90 ohms.

If it was only one tank not working properly I might think it was a sender issue. But with both senders showing the same I have no clue. I also could not find any damage to the wiring going up to the top of either tank.

I am baffled and really don't want to drop the tanks to look at the senders.

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Re: MacNeal dash issues [message #369550 is a reply to message #369549]

Sat, 23 April 2022 14:51

Bill Van Vlack

Messages: 419
Registered: September 2015
Location: Guemes Island, Washington

Karma: 14

Senior Member

It seems to me that if you're measuring 100+ ohms into the sensor circuits that are supposed to have 90 ohms MAX and 45 ohms at half full, then something is adding resistance to the sensor circuits.

The only connection those two sensors share is ground or the selector switch. You've tested that the gauge response to correct resistance at the connector pin is correct, so that leaves the ground connection(s).

There are two wires from each sensor to a point near the selector solenoid. The 'hot' side goes to the solenoid and the grounds are connected to the frame somewhere near or behind the selector solenoid. If you lift the grounds and then measure the resistance between the hot and ground connections with the connector unplugged, you should see 45(ish) ohms. If they still read over 100 ohms, then each sensor has increased resistance somewhere between hot and ground connection which means you have to drop the tanks and inspect them.

Bill Van Vlack '76 Royale; Guemes Island, Washington; Twin bed, full (DS) side bath, Brazilian Redwood counter and settee tops,455, 6KW generator; new owner a/o mid November 2015.

[Updated on: Sun, 24 April 2022 12:10]

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Re: MacNeal dash issues [message #369552 is a reply to message #369549]

Sat, 23 April 2022 18:45

Matt Colie

Messages: 8547
Registered: March 2007
Location: S.E. Michigan

Karma: 7

Senior Member

rjw wrote on Sat, 23 April 2022 11:49

I am still fooling with my gas gauge not working. I have ruled out the fuel tank selector switch as being the problem.
First of all I unplugged the 2 pin connector by the fuel selector solenoid and found that there was a lot of corrosion. I thought that might be the problem so I cleaned it up and also cleaned up the ground wire at that location. I reconnected and it still shows over full. If the connector is not plugged together the gauge registers more over fill then if connected. If I short the pins to ground it shows empty on either tank.
If I connect a known good fuel level sensor or a number of resistors in the 30 to 50 OHM range to either of the pins that go to the front and the fuel level gauge I can get the gauge to register properly. i.e. 50 OHM shows up as ~ 1/2 full and that is regardless of which pin I connect them to at that connector.
I checked the resistance of the pins going back to the senders and found them to read 108.9 and 107.2 ohms. By the way the tanks are approximately 1/2 full as far as I know.
I would have thought that over 100 ohms resistance would show more to the empty side than over full as the gauge is 90 ohms.
If it was only one tank not working properly I might think it was a sender issue. But with both senders showing the same I have no clue. I also could not find any damage to the wiring going up to the top of either tank.
I am baffled and really don't want to drop the tanks to look at the senders.

Richard,
You just happened to dive into a pool that I know very well......
Unless Mac changed out the instruments, they are what the industry called "Air Core" gauges. They are no longer in vogue. Each instrument has two windings, both receive line power one is grounded through a resistor and the other thought the sender - Be it fuel level, engine temperature or lube oil pressure. The fields are balanced at half scale. They are configured so that an open sensor reads full scale. Full scale for most is ~90 ohms. So, your test was real good.
When you measured the senders from the connector, you should have found something like 50 Ohms.....
Did you measure that between the connector and the tank?
Or did you measure to the frame??? If it was to the frame, go back under there and now measure to the tank body.
If that comes back good (~50Ω), then drill a hole in the flange of the tank (outside the weld) and run a ground to the frame. You have just dodged a bullet.
Next, I get to tell you that the senders don't like crapahol very much.
You can (must) take the tanks down to do any meaningful repair.
You may be able to clean the connectors at the tops of the the tanks and get the sensor back.
The bad connection can also be at the bottom of that connector through-bolt. Remember that has been swimming in gasahol for 20 odd years.
You can take the senders out and polish the wipers and hit the rivets so they tighten up and it may get you by for a while. You have to do this for both tanks.
I actually took the senders out (the fourth time I had the tanks down) and found other sending units to build in there. There is a reason I didn't write about this. It is not a suggested repair and hardly cost effective.
If you can get the sending unit back with external efforts, that is great, but I would suggest that you purchase replacements and the tank o-rings as well.
When I got the replace senders working, that is when the rubber lined on top of the tanks went bad. (I had replaced them years earlier, but not with barrier hose.) So, when you have the tanks down, think about the rubber lines as well.

Did you read my bit about managing the tanks when working alone? You really should.

Was this all worth the effort? In the five trips up and down:
All the rubber fuel and vent lines, even the couplers in the fill pipe. Early coaches have more of these.
Most of the rubber has been replaced with Polyarmor line that is connected to the tank with a brass compression union.
All the remaining rubber is accessible without dropping the tanks (again)...
As said, I replaced the sending units in the original fuel pick ups.
The fill vents got the High T mod.
The little taps for the vapor vent system got resoldered with 50-50 solder and a heat gun (no flame).
The vapor vent lines were replaced with Polyarmor.
The supply line for the APU was replaced with a mix of barrier and Polyarmor.

Was it worth the effort?
The last time I worked on the fuel system was 2012. Until the vapor lock caused by old gas (it sat for nearly two years), I have had no problems.
With the High T mod, I can take on nearly 50 gallons of fuel in less than 10 minutes.
With the good senders, I frequently take on in excess of 45 gallons.

So, I think it was worth the effort.

In the works (was supposed to be a winter project (don't ask) is a rework of install two Carter 4070 pumps down at the tanks.

Matt

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Re: MacNeal dash issues [message #369563 is a reply to message #369552]

Tue, 26 April 2022 12:34

rjw

Messages: 697
Registered: September 2005

Karma: 4

Senior Member

Matt Colie wrote on Sat, 23 April 2022 19:45

rjw wrote on Sat, 23 April 2022 11:49
I am still fooling with my gas gauge not working. I have ruled out the fuel tank selector switch as being the problem.
Richard,

Did you measure that between the connector and the tank?
Or did you measure to the frame???

If it was to the frame, go back under there and now measure to the tank body.
If that comes back good (~50Ω), then drill a hole in the flange of the tank (outside the weld) and run a ground to the frame. You have just dodged a bullet.

Did you read my bit about managing the tanks when working alone? You really should.

In the works (was supposed to be a winter project (don't ask) is a rework of install two Carter 4070 pumps down at the tanks.

Matt

Matt,
Thanks for the extensive write up in response to my situation.

We are currently on a trip to Kentucky with our GMC to visit our son's house to check things out while he is away living in the UK.

So far my additional testing revealed an open ground to one of the senders. I refurbished the connection for both ground wires at a different location on the frame. The open ground persisted. I was able to get "main" only to register ~ correctly for the trip down here. The "aux" stayed over full as expected. We stopped for gas every ~ 150 miles to make sure we didn't run out.

I measured between the individual sender wires and the frame. I'll recheck at the tanks when I get home and see what they read that way. Previously I had measured them with both ground wires tied together.

My plan is to eliminate the selector solenoid and go with dual pumps (as a backup for pump failure since I have TBI).

I am also very interested in getting rid of the fan clutch and go with something like you have.

I need to reread your adventures in dropping fuel tanks as that looks like a big next step for me. I last had them down during a Hamilton Work Rally more than 10 years ago.

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Re: MacNeal dash issues [message #369564 is a reply to message #369550]

Tue, 26 April 2022 12:37

rjw

Messages: 697
Registered: September 2005

Karma: 4

Senior Member

Bill Van Vlack wrote on Sat, 23 April 2022 15:51

It seems to me that if you're measuring 100+ ohms into the sensor circuits that are supposed to have 90 ohms MAX and 45 ohms at half full, then something is adding resistance to the sensor circuits.

The only connection those two sensors share is ground or the selector switch. You've tested that the gauge response to correct resistance at the connector pin is correct, so that leaves the ground connection(s).

There are two wires from each sensor to a point near the selector solenoid. The 'hot' side goes to the solenoid and the grounds are connected to the frame somewhere near or behind the selector solenoid. If you lift the grounds and then measure the resistance between the hot and ground connections with the connector unplugged, you should see 45(ish) ohms. If they still read over 100 ohms, then each sensor has increased resistance somewhere between hot and ground connection which means you have to drop the tanks and inspect them.

Bill,
Thanks for the tutorial on how the fuel gauge works and the suggestion the issue is probably caused by bad grounds. Between you and Matt I have specific thing to check out.

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