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88R 12-16V Thermistors

A

aussiblu

The temperature gauge in the NB Fairlane has been over-reading.
After confirming it was not overheating. checking the wiring,
improving ground connection and changing the sender I found that
it was the gauge (i.e. when the sender read 70 ohm the gauge was
over normal near the red when it should have been exactly in
middle of normal - if I read the resistance at the sender or the
plug on the back of the gauge). I have the factory manual that
gives gauge positions and resistance readings.

Some times the gauge reads OK and accurate but when the cabin
temperature gets warm it plays up - annoying as I was usually
working on the car in the evenings and the fault wouldn't show
so I started taking my Multimeter with me and checking the
sender's resistance whenever the gauge said the engine was hot
and tracked it down that way.

I dismantled the VDO digital gauge set tonight have found the
fault. There is a brown linear resistor type component on both
the fuel and temp gauges marked 88R the one on the fuel gauge
has 88 ohm resistance while the one on the temperature gauge
reads 56ohms at a room temp of 22 degrees C. I suspect these
brown linear components are protective thermistors and the one
on the temp gauge is no longer stable. Can anyone confirm they
are thermistors (or advise otherwise) and tell me a source for a
replacement (tried RSComponents, Farnell, Jaycar, Altronics and
Worldwide Electronics sites so far with no luck).

Can I join lower R rated thermistors in series or put a resistor
in series with a suitable lower R rated thermistor? Other than
voltage and ohms I will be sort of guessing the specs for a
thermistor anyway.

If not I suspect I will have to buy a whole new gauge if Ford
still have stocks or more likely go looking for a whole new
gauge set with a working temp gauge.

For car nuts that think they know Ford model series; yes there
is just one NB model Fairlane. see
http://www.trueblueford.com/RossNBfairlane.html It's an ex Ford
prototype so it also had a gauge set and sender unit from a
later model just to confuse things further.
 
A

aussiblu

I'm starting to think it might just be just a 88R wire wound
resistor.
 
F

Franc Zabkar

I'm starting to think it might just be just a 88R wire wound
resistor.
Click to expand...

Some dashboards have a 10V regulator for the instrument cluster while
others use unregulated battery/alternator voltage. Maybe your 10V
regulator fails intermittently and delivers the full 12V or 14V to the
cluster ??? Some gauges incorporate a 5.1V zener. Does yours?

Could you post the "gauge positions and resistance readings" as stated
in your factory manual?

FWIW, I have a Ford Registered Technician Technical Training Bulletin
# 112 which describes the Electronic Instrumentation for the XF Falcon
and Fairmont. This model series used a capacitive fuel sender and a
resistive temperature sender.

The specs for the cross coil moving magnet temperature gauge are:

ohms reading
---------------
220 cold
70 midscale
39 hot

If it helps, I could scan the relevant pages for you.

- Franc Zabkar
 
A

aussiblu

The specs are the same as the XF temp sender.

i.e:
ohms reading
---------------
220 cold
70 midscale
39 hot


"Some dashboards have a 10V regulator for the instrument cluster
while
others use unregulated battery/alternator voltage. Maybe your
10V
regulator fails intermittently and delivers the full 12V or 14V
to the
cluster ??? Some gauges incorporate a 5.1V zener. Does yours?"

Sounds possible although nothing is show in the circuit in the
factory manual - every think seems controlled by a chip in the
gauge set simply called the "electronic control module". I
don't recall seeing any regulator but I I will dismantle it
again when I have a chance and have a look (needed to put it
back together so the missus could drive it).

The fuel sender is resistance based in the NB.

It would be very much appreciated if you could scan the relevant
pages of the XF tech training bulletin for me as it might help
me sort it out. Thanks
 
A

aussiblu

Sorry I should wake up before posting that should read:

"Sounds possible although nothing is shown in the circuit in the
factory manual - everything seems controlled by a chip in the
gauge set simply called the "electronic control module". I
don't recall seeing any regulator but I will dismantle it
again when I have a chance and have a look (needed to put it
back together so the missus could drive it).

The fuel sender is resistance based in the NB.

It would be very much appreciated if you could scan the relevant
pages of the XF tech training bulletin for me as it might help
me sort it out. Thanks"

PS the fuel gauge which is in the same assembly as the temp
gauge works fine as does the tacho and digital speedo.
 
F

Franc Zabkar

The fuel sender is resistance based in the NB.

It would be very much appreciated if you could scan the relevant
pages of the XF tech training bulletin for me as it might help
me sort it out. Thanks
Click to expand...

The gauge incorporates a trimpot. Maybe its wiper is intermittent?

Anyway, here is a scan of the relevant pages:
http://www.users.on.net/~fzabkar/XF_Gauges/

- Franc Zabkar
 
A

aussiblu

Thanks for those scans Frank. While the fuel gauge has a
trimpot the temperature gauge doesn't.. I've replaced and
repaired the fuel sender before and its the old fashioned
resistance based wiping pot type. The pics you sent I think
shows the 68 ohm resistor where the 88R labelled item is. - it
might just be a badly printed "68" that looks like a "88" but
the one on the fuel gauge reads 90 ohms while the one on the
temp gauge reads 57 ohms. In any event I will look for a tenor
diode as well now.
 
A

aussiblu

Thanks again Frank

Re: '' I'd measure the resistances between the V+ terminal and
the ground and
sender terminals." I've done that and essentially confirmed
that the problem is in gauge somewhere. I guess if I remove and
replace the resistors and any zener diode that's as much as I
can try. I hope if there is a zener it's labelled.
 
A

aussiblu

I hope I can get this working as my problem if I can get a new
gauge from Ford or ebay will be which one do I need. I have a
parts manual on CD that shows five different part numbers that
vary by production date. I have already confirmed some years
ago when the gauge was working correctly that the gauge set in
there isn't the one prior to 9/89 (although the car was made in
8/89) which used a different sender (midrange on the gauge for
the earlier one was 56 ohms) .

There are no numbers on gauge set that match part numbers but
the whole cluster is labelled in black felt pen on the white
plastic surround something like "MV-1 Test Inst 68K" which I
assume suggests it was a prototype or new type instrument
cluster fitted at 68 km or perhaps even 68,000 km. I will 1st be
trying the one that goes from 9/89 to 6/91 although Ford New
Products Engineering owned the car to 1992 so it could also be
the 6/91 to 2/92 set or even the 2/92 onwards set. Most things
on the car including the even original plastic centre caps on
the mags are labelled in beige paint or black felt pen "MV-1".

The joys of owning an ex prototype. Though with luck Titan
Ford's parts guys might find an NB annotation on their online
parts catalogue as they occasionally have.

The car is essentially mostly a mix of NA and NC Fairlane parts
with a few bits from other model Oz and US models thrown in.
The original ECU computer (since died and replaced by me) in
self diagnostics mode identified it as a 6 cylinder Thunderbird
so I suspect the multipoint Electronic Fuel Injections was a
modified version of that on the 6 cylinder T bird and they just
copied and modified the ROM software in the ECU. It appears at
one time it had front as well as rear self levelling suspension
(disconnected air lines were still in place running to the top
of the front shockies). The only other odds parts that as I can
remember that aren't NA or NC parts have been tie rods ends,
bypass hose, and some of the auto gearbox internals (some
solenoids in vertical rather than horizontal positions - it
appears to be the first 4 speed auto fitted to an oz made Ford).
When I had to rebuild the motor I also found that although the
head was stamped 3.9 L, the engine bearings and the crankshaft
were different and it apparently was stroked by Ford from 3.9 L
to 4 L. Luckily ACL also knew about it and had several sets of
bearings to fit. In fact many aftermarket makers recognise and
list NB parts (some even list an NB II suggesting there might be
another although more likely the just assumed there was an NB
model equivalent to the EB Series II Falcon). However, Ford
refuse to acknowledge the model exists.

According to Ford despite what's on the compliance plate, I
simply have a mislabelled NA (they have even offered to change
the compliance plate for me - an offer I politely declined) . It
might be because when I asked DOTARS (who issue compliance
plates) that Department advised that it was illegal plate had
never been authorised by them for use on a production vehicle
for sale to the public. I also chased up its rego history and it
was always registered as an NB model by Ford. Ford do
acknowledge the car is one of their ex prototypes and say hat it
should have been scrapped rather than sold. There are two reason
why it might have been sold: a) it appears to have been
abandoned at a Ford dealer in Geraldton while on an around OZ
test drive and the dealer simply got tired of it taking up space
(the evidence is it blew a head gaskets that was replaced just
before it was sold but it also has 1992 upholstery and carpets
fitted so perhaps it got caught in a flood or something) and b)
it was sold at the when Ford were claiming they were at risk of
closing the OZ operations and they were selling off all sorts of
surplus assets.

Titan Ford parts staff have been very supportive though. They
have taken an interest in the car and been very helpful in ID
ing parts as required. As far as they can ascertain my car is
also the only NB, or mislabelled NA, that escaped into the
public domain.
 
F

Franc Zabkar

There are no numbers on gauge set that match part numbers but
the whole cluster is labelled in black felt pen on the white
plastic surround something like "MV-1 Test Inst 68K" which I
assume suggests it was a prototype or new type instrument
cluster fitted at 68 km or perhaps even 68,000 km.
Click to expand...

MV = Motor Vehicle ????

68K = Motorola 68000 CPU ???
The car is essentially mostly a mix of NA and NC Fairlane parts
with a few bits from other model Oz and US models thrown in.
The original ECU computer (since died and replaced by me) in
self diagnostics mode identified it as a 6 cylinder Thunderbird
so I suspect the multipoint Electronic Fuel Injections was a
modified version of that on the 6 cylinder T bird and they just
copied and modified the ROM software in the ECU.
Click to expand...

Is this the EEC-IV ECU? If so, I have lots of info on this box,
including my own reverse engineered hardware info. There is also a US
forum that has reverse engineered the firmware.

- Franc Zabkar
 
A

aussiblu

Re "Is this the EEC-IV ECU? If so, I have lots of info on this
box,
including my own reverse engineered hardware info. There is also
a US
forum that has reverse engineered the firmware."

Yes and I also subscribe to the EECTuner Forum Digest etc but my
time constraints due to work and family commitments no longer
allow me to play as once I would (pre children). Unfortunately
the reason I had to replace this ECU was a corrupted ROM so that
unique bit of history is probably lost forever.

"MV-1" is written in beige paint or black texta on virtually
everything on the car including even the inside of the plastic
hubcaps on the mag wheels. Other frequently cryptic notes,
numbers and dates sometimes accompany it. I suspect "MV-1"
stands for "Motor Vehicle 1" referring either to the 1st (and as
it turns out probably the last) NB model or the first Oz ford
fitted with a BTR 4 speed automatic.
 
A

aussiblu

PS it's the zener and I am patiently waiting for RS Components
to mail me some suitable replacements I have ordered. While 4
of the 6 cars in this household that I look after are Fords I'm
not sure if I am a Ford fan either. It's just that they are
generally cheaper than Holdens (I do have and EH Van I inherited
from my father as well) and I have built an inventory of special
tools and knowledge on how Fords work or more to the point
sometimes don't work so I am encouraged to stay with the known
technology. Thanks again for your help.
 
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