'74 instrument panel trouble
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'74 instrument panel trouble
I'm working on my 74 F250 its been sitting awhile waiting on a engine replacement. Finally got the 390 installed and now its on the road, the gauges all seem to either read low or not at all.
Gauges seemed to work ok befored i pulled the engine 4 months back.
Fuel gauge--full tank only reads a little past 1/2 on gauge
temp gauge--worked at first, but only read to first mark on gauge(180*tstat)
oil pressure--shows low.
I've swapped the IVR with a known good one, no help
Ive swapped the wiring harness from the firewall to the sending units no help
replaced water temp sender no help
haven't replaced oil pressure sender yet.
I do have a ground strap from the engine to the firewall.
Any ideas are appreciated.
Gauges seemed to work ok befored i pulled the engine 4 months back.
Fuel gauge--full tank only reads a little past 1/2 on gauge
temp gauge--worked at first, but only read to first mark on gauge(180*tstat)
oil pressure--shows low.
I've swapped the IVR with a known good one, no help
Ive swapped the wiring harness from the firewall to the sending units no help
replaced water temp sender no help
haven't replaced oil pressure sender yet.
I do have a ground strap from the engine to the firewall.
Any ideas are appreciated.
Ford Parts Specialist
Joined: Nov 2006
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From: Simi Valley, CA
A bad CVR...Constant Voltage Regulator will cause the gauges to move back and forth on their own...try lightly tapping the back of the CVR with a piece of wood...the CVR plugs into the board.....but if that's not the issue...it's prolly a wiring glitch.
Last edited by NumberDummy; Dec 11, 2006 at 11:28 AM.
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Cvr
Do you know of a proceedure for testing the CVR, as well as the gauges and
sending units??
I have another truck and I may swap it's instrument panel into the troubled truck to try to isolate the probs.
Howard
sending units??
I have another truck and I may swap it's instrument panel into the troubled truck to try to isolate the probs.
Howard
Ford Parts Specialist
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From: Simi Valley, CA
There may not be anything wrong...on a 3 row radiator...even with a 180 stat...that gauge location is normal or a fraction low. The gas gauge may have a bad float...it is made in two halves soldered together...it might need a new one...the soldering goes bad...gas seeps in...change the gasket too. Since the truck has sat for a while, the tank sender may be stuck in the half position.
Have the correct oil sender installed? The one for an oil light is different than the one for a guage...or the sender may be the wrong one...or something other than for a Ford.
The oil senders get plugged up with oil, too...another possible cause.
Have the correct oil sender installed? The one for an oil light is different than the one for a guage...or the sender may be the wrong one...or something other than for a Ford.
The oil senders get plugged up with oil, too...another possible cause.
Last edited by NumberDummy; Dec 11, 2006 at 11:38 AM.
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Good idea on checking the resistance on the grounds.
on the temp gauge--it worked initially and read at about the first mark, then at some point it died--doesn't register at all.
I do have the correct sending unit for a gauge--the big round domed unit.
on the temp gauge--it worked initially and read at about the first mark, then at some point it died--doesn't register at all.
I do have the correct sending unit for a gauge--the big round domed unit.
Ford Parts Specialist
Joined: Nov 2006
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From: Simi Valley, CA
Originally Posted by jd730d
I do have the correct sending unit for a gauge--the big round domed unit.
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Just Go to the Temp sending unit and use a test light to check the pulses.
a ICVR pulsing "too slow" with cause this problem.
Next You can check the amount of power with a multimeter attached to the connector.
It should read about 5 volts
and be a steady: Pulse....pulse....pulse....pulse....pulse
If it goes: Pulse...........Pulse..........pulse ,etc
it is too slow and needs to be adjusted faster.
There is a little nub on the back that gets turned clockwise to speed the pulse.
Shown here:
http://www.clubfte.com/users/mil1ion/ICVRadjustment.jpg
This is the ICVR
a ICVR pulsing "too slow" with cause this problem.
Next You can check the amount of power with a multimeter attached to the connector.
It should read about 5 volts
and be a steady: Pulse....pulse....pulse....pulse....pulse
If it goes: Pulse...........Pulse..........pulse ,etc
it is too slow and needs to be adjusted faster.
There is a little nub on the back that gets turned clockwise to speed the pulse.
Shown here:
http://www.clubfte.com/users/mil1ion/ICVRadjustment.jpg
This is the ICVR
Last edited by Mil1ion; Dec 11, 2006 at 06:11 PM.
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sending unit
well i got home tonite and swapped instrument panels--no change. Got my manual out and found there was a test proceedure to verify the ckt and to verify the IVR--test with a ohm meter to show the pulsing 5v of the IVR. Both
IVRs are fine. Even checked the pulse rate per advise, good rapid steady rate.
Replaced the oil sending unit with a new one and this appears to have fixed the low oil pressure issue. will see tomorrow when I get on the hiway
already replaced the temp sending unit, but not with a new one. I'll pickup a new one and install tomorrow.
one point--the manual says to use electrically conductive sealer on the threads (and gives a ford part#) I just used some teflon tape. I checked for continuity from the sending unit body to the engine--all ok, so the threads must have cut through the tape when threaded into the holes.
thanks to all for the help--will post results of temp unit install tomorrow.
Howard
IVRs are fine. Even checked the pulse rate per advise, good rapid steady rate.
Replaced the oil sending unit with a new one and this appears to have fixed the low oil pressure issue. will see tomorrow when I get on the hiway
already replaced the temp sending unit, but not with a new one. I'll pickup a new one and install tomorrow.
one point--the manual says to use electrically conductive sealer on the threads (and gives a ford part#) I just used some teflon tape. I checked for continuity from the sending unit body to the engine--all ok, so the threads must have cut through the tape when threaded into the holes.
thanks to all for the help--will post results of temp unit install tomorrow.
Howard
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Never use Teflon tape on the sending units. It may make contact when cold and not later. Use a liquid or paste type thread sealant available at any hardware store.
To really check out the IVR you need an oscilloscope to calculate the average voltage. The IVR just pulses the system voltage 12-14VDC to average out to 5VDC. It is just a thermal flasher like those Christmas tree flasher bulbs or a turn signal flasher but of the HD 3-terminal type.
To really check out the IVR you need an oscilloscope to calculate the average voltage. The IVR just pulses the system voltage 12-14VDC to average out to 5VDC. It is just a thermal flasher like those Christmas tree flasher bulbs or a turn signal flasher but of the HD 3-terminal type.
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I always tell people to not use teflon tape and get sruck down for soing so.
They make a special conductive sealer for sending unit application ...I supose just like Ford says....only it is an aftermarket product.
See this page for the Fuel sending unit info.
I linked to it on a nother thread I guess.
http://www.clubfte.com/users/mil1ion...strations.html
They make a special conductive sealer for sending unit application ...I supose just like Ford says....only it is an aftermarket product.
See this page for the Fuel sending unit info.
I linked to it on a nother thread I guess.
http://www.clubfte.com/users/mil1ion...strations.html
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I know what you mean about the Teflon tape. Everyone thinks it is great stuff. 
GOOD repair manuals will tell people not to use it. Even some sender units come with instructions that say not to use Teflon tape. Regular pipe dope works well but if you really want some conductivity mix it with Loctite copper anti-seize.
GOOD repair manuals will tell people not to use it. Even some sender units come with instructions that say not to use Teflon tape. Regular pipe dope works well but if you really want some conductivity mix it with Loctite copper anti-seize.
Last edited by Torque1st; Dec 12, 2006 at 06:18 AM.
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Yeah, on these old beasts grounding is a major source of headaches. Everyone forgets that there must be a COMPLETE circuit for those electrons to flow and they will flow in strange ways if an alternate path is available..