Oil pressure flutter

C

Cymadesign

Member
Sep 11, 2021
47
16
18
Niagara, ON
I have an intermittent oil pressure fluctuation. The pressure drops about 5-10 psi at random. In a 4 hour drive, the fluctuation will occur 2 or
three times. I’ll watch the needle move up and down for a few minutes and then it will return to normal and stay there until the next random event.
The fluctuations can occur at either normal highway speed and at idle. 1974 455 with 80,000 miles. The cross-over has not been blocked. New oil
pressure sensor and all the wiring has been checked twice for loose connections. The coach is new to me 4 months ago, but I did not notice this
behaviour when I drove it the 2,500 miles home. Normal oil pressure as speed is just below the halfway marker on the gauge. Idle is at just below the
1/4 marker.
The only explanation I can come up with is something intermittently blocking the oil pump inlet. Could enough carbon from the turkey tray collect in
the sump? From what I have read here, I can’t remove the oil pan with the engine in place.
Any theories or suggestions for things to investigate?
Nk you
--
1974 26’ 455, 90,000 miles, pertronix, aluminum rad, headers
Port Colborne, ON Canada. Southern end of the Welland Canal
 
Before blaming the engine I would replace the oil pressure sender. It sounds like an electrical problem to me.

Emery Stora
77 Kingsley
Frederick CO

>
> I have an intermittent oil pressure fluctuation. The pressure drops about 5-10 psi at random. In a 4 hour drive, the fluctuation will occur 2 or
> three times. I’ll watch the needle move up and down for a few minutes and then it will return to normal and stay there until the next random event.
> The fluctuations can occur at either normal highway speed and at idle. 1974 455 with 80,000 miles. The cross-over has not been blocked. New oil
> pressure sensor and all the wiring has been checked twice for loose connections. The coach is new to me 4 months ago, but I did not notice this
> behaviour when I drove it the 2,500 miles home. Normal oil pressure as speed is just below the halfway marker on the gauge. Idle is at just below the
> 1/4 marker.
> The only explanation I can come up with is something intermittently blocking the oil pump inlet. Could enough carbon from the turkey tray collect in
> the sump? From what I have read here, I can’t remove the oil pan with the engine in place.
> Any theories or suggestions for things to investigate?
> Nk you
> --
> 1974 26’ 455, 90,000 miles, pertronix, aluminum rad, headers
> Port Colborne, ON Canada. Southern end of the Welland Canal
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
 
Checking wiring is a great start, but verifying gauge itself is good is difficult. Get a non electric oil pressure gauge and hook that up. Don’t do
what I do….but I hooked up a harbor freight oil pressure tester (hose directly to block outlet eliminating sender as well) and like the reliability
and the big easy to read gauge and I left it on. That needs a permanent solution. My point is to try a complete alternative.
--
1975 Glenbrook, 1978 Royale rear bath
Raleigh, NC
 
My best guess is still a poor connection at the sender connector. Even replacing the sender, the female connector end can have 40 years of grime and
oxidation. I would suggest “playing” with the connector when it acts up to pinpoint. If that’s not it I would investigate the cluster and
resistor connections. The movements themselves are pretty reliable.
The pump pickup screen has a spring loaded bypass door in the event the screen is loaded with debris, the bypass opens to prevent starvation, so I
don’t think that’s it.
--
John Lebetski
Woodstock, IL
77 Eleganza II
 
The sender and connection gets the blast of air from the fan and dirty air
constantly .
Notice that the female connector tends to get loose and requires some mild
crimping to get firm contact.

On Sat, Sep 25, 2021 at 7:24 AM John R. Lebetski
wrote:

> My best guess is still a poor connection at the sender connector. Even
> replacing the sender, the female connector end can have 40 years of grime
> and
> oxidation. I would suggest “playing” with the connector when it acts up to
> pinpoint. If that’s not it I would investigate the cluster and
> resistor connections. The movements themselves are pretty reliable.
> The pump pickup screen has a spring loaded bypass door in the event the
> screen is loaded with debris, the bypass opens to prevent starvation, so I
> don’t think that’s it.
> --
> John Lebetski
> Woodstock, IL
> 77 Eleganza II
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
>

--
Jim Kanomata ASE
Applied/GMC, Newark,CA
jimk
http://www.gmcrvparts.com
1-800-752-7502
 
This is great. Four opinions, more or less the same. And sensor/wiring issues are fairly easy to troubleshoot compared to my plan to pull the pan.
Will report back. Thank you
--
1974 26’ 455, 90,000 miles, pertronix, aluminum rad, headers
Port Colborne, ON Canada. Southern end of the Welland Canal
 
A bad dash ground caused my gauges to fluctuate alarmingly.
--
Greg Crawford
KM4ZCR
Knoxville, TN

"Ruby Sue"
1977 Royale
Rear Bath
403 Engine
American Eagle Wheels
Early Version Alex Sirum Quad bags
 
Cymadesign,

I have actually seen this in dynoland. I very much doubt that those cases are the same as yours.

Case 1 - A technician (soon after unemployed) left pieces of the cylinder head cover gasket inside the engine and these blocked the lube oil return to
the pan. With half the lube oil sequestered in the over head, the pump was starved.

Case 2 - A technician over filled the lube oil by a lot. With the lube oil level that high, the crank and rods caused it to get whipped into a foam
and this reduced the pressure in the system. Other than the engine had an alarming lube oil consumption, there did not seem to be any harm.

My vote would also be for a poor connection somewhere in the system.

Matt - answering from the Northern Wisconsin State Fairgrounds.
--
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
 
I have watched this thread but did not comment because my two thoughts may not be correct. First I believe, like others here, that your problem is
probably electrical. That said, I thought about the ground path to the gauge cluster failing. I have seen that several times but when I looked at
the possibility of just the oil gauge failing due to an intermittent ground, I do not see how that could happen in a GMC. This is because the ground
I do not see it. I believe that this gauge is grounded through the sender and not the mounting of the gauge to the aluminum plate. I could be wrong
on this, as I do not to have an actual wiring diagram of the internals of the gauge itself. Maybe there is an internal path to engine ground that I
can not see on the diagrams. So assuming that we need a good engine ground other than through the sender itself, how do we prove this is or is not
your the problem?

What I would do is to run a 14 gauge or so wire direct from the aluminum plate where the gauge is mounted to a good engine ground. Also I would
remove the gauge assembly and clean up the mounting of it to the aluminum plate. This added wire will bypass all possible bad connections in the
existing ground path. Another thought could be the +12 volts to the gauge assembly but I also doubt it with only one gauge failing.

On the mechanical side. I have seen this failure on other vehicle engines before caused by overfilling the oil in the engine. The crank and rods hit
the excess oil in the pan and cause the oil to foam. Eventually the oil sump picks up some foamy oil and pumps it to and through the engine.

Are you Absolutely sure that the engine has the correct amount of oil in it?/b] The book says that the engine takes 6 quarts of oil with filter.
While that is true on an EMPTY engine, when you change oil you do not get 1 quart out of it because of the front part of the oil pan can not drain
Also there is some oil legtin the cooler and lines that can not drain.

I would try running the oil level one quart lower and see if the problem still occurs.

Ken B.

--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
 
Thanks Ken and Matt for the high oil level suggestion. I don’t know for certain if I have the correct oil level. The dipstick shows oil up to the
full mark. I changed the oil 2 months ago for the first time and don’t remember the amount it took. How accurate is the dipstick marking?
--
1974 26’ 455, 90,000 miles, pertronix, aluminum rad, headers
Port Colborne, ON Canada. Southern end of the Welland Canal
 
My oil pressure gauge has randomly fluttered around since I purchased the coach in 2008. It's definitely a oil pressure sender (sensor) fault in my
case. I know this because I installed a DigiPanel and for fun I hooked the DigiPanel to the OEM sensor. The LED's on the DigiPanel then jumped
around proving the OEM sensor is faulty.

I believe the DigiPanel is a great upgrade. A quick glance and it an all readings are Green then A-OK. If something falls out of acceptable range,
the Beeper will quickly get your attention.... a gauge, not so much.

Maybe someday I'll get around to replacing the sensor for the gauge.

Not sure why JimK took down the DigiPanel website after buying the business. It had great info on wiring etc. Here is the Item on JimK's website:

https://www.gmcrvparts.com/product-p/gdp1.htm

--
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
 
The ground path for the gauge IS the sender. The sender is grounded to the block. It is a 1 wire sender. The sender changes resistance to ground
with oil pressure change.
--
John Lebetski
Woodstock, IL
77 Eleganza II
 
Bruce,

The test you describe only proves that your oem gauge is not faulty not
that the sensor is bad.

Sully
Bellevue wa

> My oil pressure gauge has randomly fluttered around since I purchased the
> coach in 2008. It's definitely a oil pressure sender (sensor) fault in my
> case. I know this because I installed a DigiPanel and for fun I hooked
> the DigiPanel to the OEM sensor. The LED's on the DigiPanel then jumped
> around proving the OEM sensor is faulty.
>
> I believe the DigiPanel is a great upgrade. A quick glance and it an all
> readings are Green then A-OK. If something falls out of acceptable range,
> the Beeper will quickly get your attention.... a gauge, not so much.
>
> Maybe someday I'll get around to replacing the sensor for the gauge.
>
> Not sure why JimK took down the DigiPanel website after buying the
> business. It had great info on wiring etc. Here is the Item on JimK's
> website:
>
> https://www.gmcrvparts.com/product-p/gdp1.htm
>
> --
> Bruce Hislop
> ON Canada
> 77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
> http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
> My Staff says I never listen to them, or something like that
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
>
 
Our experience on the oil pressor sender is that majority of the time, it
is the connector.
The Digi Panel reads off that connector.
Best to crimp the connectors and see first as it take only a minut to do.
Re. dropping the Digi Panel Info sight, not aware of it but if you can
contact me and describe exactly , I will see what my staff can do.

> Bruce,
>
> The test you describe only proves that your oem gauge is not faulty not
> that the sensor is bad.
>
> Sully
> Bellevue wa
>

>
> > My oil pressure gauge has randomly fluttered around since I purchased the
> > coach in 2008. It's definitely a oil pressure sender (sensor) fault in
> my
> > case. I know this because I installed a DigiPanel and for fun I hooked
> > the DigiPanel to the OEM sensor. The LED's on the DigiPanel then jumped
> > around proving the OEM sensor is faulty.
> >
> > I believe the DigiPanel is a great upgrade. A quick glance and it an all
> > readings are Green then A-OK. If something falls out of acceptable
> range,
> > the Beeper will quickly get your attention.... a gauge, not so much.
> >
> > Maybe someday I'll get around to replacing the sensor for the gauge.
> >
> > Not sure why JimK took down the DigiPanel website after buying the
> > business. It had great info on wiring etc. Here is the Item on JimK's
> > website:
> >
> > https://www.gmcrvparts.com/product-p/gdp1.htm
> >
> > --
> > Bruce Hislop
> > ON Canada
> > 77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
> > http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
> > My Staff says I never listen to them, or something like that
> > _______________________________________________
> > GMCnet mailing list
> > Unsubscribe or Change List Options:
> >
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
>

--
Jim Kanomata ASE
Applied/GMC, Newark,CA
jimk
http://www.gmcrvparts.com
1-800-752-7502
 
That is exactly what I thought but I was not absolutely positive. The intermittent / oxidized ground wire connection to the aluminum plate with the
gauges mounted on it and the other end of that wire on the aluminum plate under the right hood are common problems on GMCs. So I did not want to
discount that possibility. I have never seen it cause his exact problem, but I have seen it cause problems with dash lights and other indicators
(gauges).

Thanks for the information.

Ken B.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
 
My internet keeps dropping out here today.

I should have been a bit clearer on my oil pressure sensor test ... I swapped the wires at the sensors between the OEM sensor and the Digi-Panel
sensor. Then the dash gauge was steady and the Digi-Panel LED indicators for oil pressure flicker up and down the scale. After 45 years of
troubleshoot electronic systems infinitely more complicated than the GMC oil pressure gauge and sensor, I think my conclusion that my OEM gauge oil
pressure sensor is a valid conclusion.

Jim, I know there was a website for the Digi-Panel, but Google did not come up with it. I finally found a reference to it on the GMCWS website as
www.digi-panel.com However the website comes up with some Chinese (or similar) writing. You may have let the website registration lapse in error
and now someone else has claimed it.

Here is a screen shot of what the home page looked like in 2015 from the Wayback Machine internet archive. The archive shows it was still an active
website in March of 2021.
https://web.archive.org/web/20150827050758/http://www.digi-panel.com/

--
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
 
Sometimes, when Teflon tape is used to seal a sending unit, you can end up
with a bad ground. Also, check to see if your engine to frame braided
ground strap between the engine and the frame is there and that it is not
corroded or connectors are loose. Your gage problem sounds like an
intermittent faulty ground to me.
Jim Hupy
Salem, Oregon

> My internet keeps dropping out here today.
>
> I should have been a bit clearer on my oil pressure sensor test ... I
> swapped the wires at the sensors between the OEM sensor and the Digi-Panel
> sensor. Then the dash gauge was steady and the Digi-Panel LED indicators
> for oil pressure flicker up and down the scale. After 45 years of
> troubleshoot electronic systems infinitely more complicated than the GMC
> oil pressure gauge and sensor, I think my conclusion that my OEM gauge oil
> pressure sensor is a valid conclusion.
>
> Jim, I know there was a website for the Digi-Panel, but Google did not
> come up with it. I finally found a reference to it on the GMCWS website as
> www.digi-panel.com However the website comes up with some Chinese (or
> similar) writing. You may have let the website registration lapse in error
> and now someone else has claimed it.
>
> Here is a screen shot of what the home page looked like in 2015 from the
> Wayback Machine internet archive. The archive shows it was still an active
> website in March of 2021.
> https://web.archive.org/web/20150827050758/http://www.digi-panel.com/
>
>
> --
> Bruce Hislop
> ON Canada
> 77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
> http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
> My Staff says I never listen to them, or something like that
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
>
 
Hmm, I did use teflon tape when I installed the new sensor. Well, that’s easy to check.

I recrimped the sensor connection this afternoon while the engine was idling. The fluctuation continued.

If the tape doesn’t fix it, then it’s either time for a new sensor or I’ll learn to live with it.
--
1974 26’ 455, 90,000 miles, pertronix, aluminum rad, headers
Port Colborne, ON Canada. Southern end of the Welland Canal
 
I've had and seen several failures of the sender itself. The Corvette guys at Road Atlanta mount the sender on the radiator housing and feed it with
braided oil hose. Sender or connector, the fix is a tee on the pressure port and a mechanical gauge on one outlet, the sender on the other. Compare.

--johnny
--
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
 
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