Oil Pressure gauge
Mike Shirley
> A few weeks ago there was a thread regarding the bogus oil
> gauge. It was mentioned that by adding a proper sender and
> removing a 20 ohm resistor it could be converted to a correctly
> reading gauge.
This is in the Bryan Richardson's FAQ but here's the info:
3.2. The oil gauge lie
The oil gauge on the Explorer isn't. Simply put, the indicator on the
dash looks like a gauge, but it is really only a binary indication as to
whether the pressure sensor believes that the engine has sufficient oil
pressure or not. If it thinks there is sufficient pressure, then the gauge
reads in the "Normal" zone, usually pointing to a single place (without
varying based on temperature, RPMs, etc.). If there is not sufficient
pressure, then the gauge reads "low." The first item below describes
how to convert the "indicator" back into a gauge. Discussion on this
topic follows:
Subject: Did the oil pressure modification today; it WORKS!
From: mi...@slic.cts.com (Mike Shirley)
Organization: Muth Valley Ford Oil Pressure Check Station and Bakery
I used an "AutoTune" PT3077B transducer, $15, purchased from Kragen
Auto Parts Store. It appears to be a generic application
transducer. Ford's is: Ford sender E4ZZ 9278A, $20.
I went ahead and installed the transducer today. It was a universal 1/4
pipe threaded sender with the "slip over threaded rod" style of electrical
connection to the top. Plenty of room for the tee, original switch, and
the new transducer. I removed the switch from the 45 degree long-
shafted adapter. Used the end of the tee (not the center port) to the
adapter, mounted the transducer upward and the switch outward (center
port of tee). Was able to plug the original connector into the new
transducer. I added a wire for the switch and ran it through the firewall
and attached it to a small piezo chime via 12V+ from the switched
ignition.
The gauge read just left of the N in Normal prior to disabling the 20 ohm
resistor on the dash cluster. After shorting out the resistor, the gauge
needle points to the A in Normal at 2000 rpm and around the O in
Normal at a warm idle in gear. The needle is heavily dampened (so to
react to changes) but is still a worthwhile modification.
I would say that the dash cluster removal is rather involved and not for
the faint of heart. In fact, living without the resistor modification is
really acceptable when you consider the gauge is dampened. If my wife
would allow it, in retrospect, I'd have just done the tee and added the
chime to the factory gauge but installed a real 270 degree mechanical
gauge. And not touch the dash.
From: r...@netcom.com (Richard Hyde)
And now! What the manual says about the infamous OIL
PRESSURE GAUGE!....
"When the engine oil pressure is normal, the oil pressure switch is closed
(short circuit), allowing current flow through the 20-ohm resistor on the
cluster flexible circuit into the gauge which drives the pointer to a
position slightly above midscale. The switch opens (open circuit) when
oil pressure drops to a critically low level (4.5 - 7.5 psi) causing
movement of the pointer to or below the "L" band."
"NOTE: The pointer of the magnetic gauge will remain in it's last
position when the ignition is turned off. It will move to the correct (or
actual) indication whenever the ignition is turned back on." Looks grim..
However, in the 2.3L Aerostar engine section, there *is* a reference to a
genuine oil pressure sender. Unfortunately, no mention is made about
the compatibility of Aerostar and Explorer gauges. Sigh.
From: r...@netcom.com (Richard Hyde)
> Would you say that they are worth the cost for someone who is
> able to get into backyard mechanics? Now that you have them in
> hand, is it necessary to get the $12 electrical diagrams?
Yes and yes. The manual looks to be over 1000 pages and covers the
vehicle in more detail than I've ever seen before. I'm just a tyro
mechanic, but I know I'll get my moneys worth out of them over the
years. The manual does an excellent job of showing where the wiring
harnesses run, but does not identify specific wires. I'm going to be
installing an alarm this weekend and I doubt I could do the job I'd like
without the wiring diagram.
Interestingly, the wiring diagram shows the infamous oil pressure
sender as a rheostat! :-)
> > "When the engine oil pressure is normal, the oil pressure switch
> > is closed (short circuit), allowing current flow through the 20-ohm
> > resistor on the cluster flexible circuit into the gauge which drives
>
> It figures. At least I know that I need to pull the cluster out
> and short out the 20 ohm resistor before I add the pressure
> transducer that I bought and measured out at around 20 ohms. It
> will work correctly then. Thanks...
>
It looks like the cluster is trivial to remove. You have to remove the "ash
receptacle" :-) first. Open the "ash receptacle" and remove two screws
attaching the "ash receptacle" and instrument cluster trim panel.
Remove the ash receptacle assembly.
(Oops - first remove battery ground cable)
Next, unsnap the cluster trim panel by pulling rearward around the edge
of the panel. Depress the hazard warning switch and remove the cluster
trim panel.
Remove the four screws securing the instrument cluster to the instrument
panel.
Vehicles with automatic transmissions require that the PRNDL indicator
be removed.
Remove the two screws attaching the PRNDL to the cluster and slide the
PRNDL down and out of the cluster. Leave PRNDL connections
undisturbed.
Pull cluster assembly rearward to gain access to speedometer cable. If
there is insufficient access to disconnect the cable at the instrument
cluster, it may be necessary to disconnect at the transmission and pull the
cable out far enough to disconnect at the cluster (!)
Unsnap the two wiring harness connectors and remove the cluster.
-------
reassembly is the reverse of the above except you must:
"Apply approximately 4.8mm (APPROXIMATELY 4.8mm???) or 3/16
inch diameter ball of silicon dielectric compound (D7AZ-19A331-A
(ESE-M1C171-A)) or equivalent in the drive hole of the speedometer
head.
(Whew)
Remember :-) : When the battery is disconnected and reconnected,
some abnormal drive symptoms may occur while the EEC processor
relearns its adaptive strategy. The vehicle may need to be driven
10 miles or more to relearn the strategy.
------
Let me know what part you're using for the sender. I'm interested
in restoring the correct operation of my gauge as well.
Thanks!
Rick
From: mi...@slic.cts.com (Mike Shirley)
Subject: UPDATE: Ford's Bogus Oil Pressure Gauges Confirmed by
Ford
Summary: Sorry state of Ford and it's effort in dealing with customers.
Keywords: ford explorer oil pressure gauge switch hoodwink resistor
Date: Thu, 10 Mar 94 21:49:09 PST
Organization: Muth Valley Ford Customers Rating Group, Ltd.
FORD OWNER'S NOTE: It appears Ford is driving it's oil pressure
gauge artificially across many of it's model lines.
r...@netcom.com (Richard Hyde) writes:
>
> What the Ford '92 Explorer Service Manual says about the Oil
Pressure
> Gauge:
>
>
> "When the engine oil pressure is normal, the oil pressure switch
> is closed (short circuit), allowing current flow through the 20-ohm
> resistor on the cluster flexible circuit into the gauge which drives
> the pointer to a position slightly above midscale. The switch opens
> (open circuit) when oil pressure drops to a critically low level
> (4.5 - 7.5 psi) causing movement of the pointer to or below the "L"
> band."
This very day I was able to confirm this bogus gauge implementation
that Ford has been doing for years. I've been trying to get this question
answered by Ford officially since early February. I have contacted three
dealer service shops and Ford Detroit and have gotten 5 different
answers on this simple question:
Is the oil pressure gauge in a 1993 Ford Explorer driven by a simple on-
off switch (as used for an idiot light) or by a variable transducer (
normally and historically used for a gauge)?
It's taken 5 weeks of phone calls to Ford in Detroit to answer this
question correctly:
Ford uses a simple switch to drive the gauge to a fixed position on the
gauge (approximately 80% deflection via a fixed resistor).
Now this may not mean much to most of the motoring public but as I
stated in my initial posting of this bogus use of an oil pressure gauge, I
feel that Ford is hoodwinking the public. The owner's manual doesn't
make any mention of how this gauge is artificially fixed to only 2
positions. The only way to determine this (other than pestering Ford's
Detroit Customer Assurance line) is to buy the official Ford (Helms)
service manual at the cost of $92.00 plus $4.50 S&H.
I naturally was flamed for making this "outrageous" claim without
foundation. When I finally confronted Ford with the fact that I had
removed the simple oil pressure switch, tested it at 5-90 psi in 5 psi
steps, and tested the gauge with values of resistors which drove the
gauge needle across approximately 80% of the gauge face, did Ford
finally give me the official information. This took about 2 hours of
telephone time spread over 4 weeks.
I now plan to write to Ford to explain to them that I feel this is an
inappropriate way to drive an oil pressure gauge. They should either
delete the gauge and add an idiot light, or drive the gauge correctly with
a variable transducer and add an idiot light/audible chime. Failing to
notify the customer of this crappy switch is wrong. I will request credit
for the cost labor to modify the dashboard located resistor and purchase
the correct transducer. I will be sending a copy to Consumer Reports. I
think that this is an excellent example of bad faith product labeling and
merits space in CR's running section.
One has to wonder why Ford has chosen to do this. No one I spoke to
would officially tell me why but one of the many different persons who I
spoke to in Detroit did allude to the fact the the general public doesn't
understand what the information delivered by gauge actually means. In
other words, the mere fact that oil pressure will vary as a function of
temperature/RPM/viscosity is beyond the understanding of it's customers.
Although not officially confirmed, I was told by a dealer service shop
foreman that Ford has been hit with a high number of warranty service
tickets for customers bringing in their vehicles to have the oil pressure
"fixed" because of the varying readings from the gauge. Further, he said
that this is a common fix across it's model lines. I assume that this is
Ford's answer to this problem. They have chosen to artificially fix the
reading of the gauge rather than to delete the gauge, add an idiot light,
or educate the customer via text in the owner's manual, a hanging
placard or affixing a label to the dash, or delivery person indoctrination.
I think that Ford has clearly taken the wrong road in re-engineering the
oil pressure gauge. Curiously, the water temperature gauge still works
correctly. I wonder why Ford hasn't chosen to correct this gauge in the
same fashion. Maybe then they will fix the gasoline gauge too. Just two
positions on the fuel gauge, empty and normal. And of course, not to tell
you about it. Keep that a secret also. Wonder if the motoring public
would feel better about this correction?
From: mikey (Mike Shirley)
I go the following letter from a net user who owns a Ranger PU. Thought
it might be of interest to the group...mps
-------------------------------------------------
Date: Thu, 17 Mar 1994 09:16:10 -0700
From: Al Jackson <a...@swttools.fc.hp.com>
Subject: Fixing My Ford's Fake Framus
Put the pressure/electrical transducer in last night. Also took the
dash apart (four torx screws) and the instrument cluster (four more
screws). Found the 20 ohm res. in series w/ the gauge, plus
solder pads to short it...which I did, don't ya know.
Before starting the engine, I put a mechanical 0-100 lb gauge on the
tee with the sender, soz to monitor the oil press at diff rpms. Here
are results in psi and the corresponding point on the dash gauge
(pointing to the word "Normal"):
Cold Hot
Idle 60 (m) 45 (o)
2K RPM 70 (a) 55 (m)
3K RPM >70 (a) 60 (m)
The sender res. varies from 21 ohms (80 lb) to 40 ohms (15 lbs). Below
15 lbs, it opens, causing the gauge to drift down below "L" in about
2 seconds. That's much better data than with the stock switch
that simply closed (actually about 3 ohms) above 9 lbs.
Now all I have to do is replace the mechanical gauge with the switch
and connect a panic buzzer to it.
Cost was:
Ford sender, E4ZZ 9278A $20.
Brass tee and nipple 8.
Buzzer (shack) 4.
--
$32.
Should I send a bill to Ford?
Thanks for your research, Mike. I wouldn't have pushed to fix this w/out
your experience. I ended up finding one Ford parts guy who
acknowledged
this problem, said "we sell lots of these senders to fix this
situation" and gave me the part number of the sender used on 302s pre
1987. Went to my local Ford guy, bought that unit, and them dumped
on the service mgr, who finally also admitted to knowing about it...but
not until I had the right part in my hand! He even said that
modifying my truck as described wouldn't void any warranty, except for
the sender, which isn't stock for my truck. Jerks!
-- Mike Shirley mi...@cts.com San Diego, CA USA WB6WUI
Robomail: mikey...@slic.cts.com pgp-...@slic.cts.com