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oil pressure sending unit

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mstrcrftr View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mstrcrftr Quote  Post ReplyReply Direct Link To This Post Posted: Oct/11/2017 at 2:49pm
304-dude,  i can jump the output wire from the sending unit to ground and the gauge works.  cluster is out of the car so to speak and i did not find any broken traces.  everything on the circuit board checks out.
i am trying to diagnose this and need to know if my drawing is accurate for proper operation or if i am missing something here.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 304-dude Quote  Post ReplyReply Direct Link To This Post Posted: Oct/11/2017 at 3:12pm
Your drawing is pretty much the way it works, but it is never open like a switch. That is why I wanted to see the ohm readings.

Mopar sending units look a similar yet have a higher ohm reading, thus the needle never seems to move with the AMC gauge.

71 Javelin SST body
390 69 crank, 70 block & heads
NASCAR SB2 rods & pistons
78 Jeep TH400 w/ 2.76 Low
50/50 Ford-AMC Suspension
79 F150 rear & 8.8 axles
Ford Racing 3.25 gears & 9" /w Detroit locker
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mstrcrftr Quote  Post ReplyReply Direct Link To This Post Posted: Oct/11/2017 at 4:04pm
i will test it when my wife gets home to rev the engine for me.   what range of ohms am i looking for?

thanks
Barney
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 304-dude Quote  Post ReplyReply Direct Link To This Post Posted: Oct/11/2017 at 4:42pm
Originally posted by mstrcrftr mstrcrftr wrote:

i will test it when my wife gets home to rev the engine for me.   what range of ohms am i looking for?

thanks
Barney


About 82 ohms down to 10 ohms at 80 psi within a 10% tolerance give or take.

Mopar starts somewhere above 100 ohms, not sure exactly as the info was from long ago about such issues with oil sending units. I can guess about 130 ohms. Maybe 440sixpac or Moparguy can say from knowledge.
71 Javelin SST body
390 69 crank, 70 block & heads
NASCAR SB2 rods & pistons
78 Jeep TH400 w/ 2.76 Low
50/50 Ford-AMC Suspension
79 F150 rear & 8.8 axles
Ford Racing 3.25 gears & 9" /w Detroit locker
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tomj Quote  Post ReplyReply Direct Link To This Post Posted: Oct/13/2017 at 12:25am
Originally posted by mstrcrftr mstrcrftr wrote:

battery cable goes directly to the block and yes the dash has an actual 80 psi gauge.

that is good, but you also need a solid electrical connection from block to chassis. AMC used an uninsulated braided ground strap, in various locations, usually near/around a motor mount. battery-negative+engine+chassis need to be electrically one.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote mstrcrftr Quote  Post ReplyReply Direct Link To This Post Posted: Oct/13/2017 at 9:59am
tomj,  the block is grounded to the chassis.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mstrcrftr Quote  Post ReplyReply Direct Link To This Post Posted: Mar/04/2018 at 9:48am
i finally got my tach back and had a chance to check the sending unit.  i am getting 72 ohms at idle and it goes down to 60 ohms at about 2500 rpm.  this is with the wire disconnected from the sending unit.

i am wondering if my cvr is bad.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 401MATCOUPE Quote  Post ReplyReply Direct Link To This Post Posted: Mar/04/2018 at 10:11am
What are you working on??  Model and year....there are 3 different specific sending units for dash gauges.

1. 68-70 AMX/Javelin Rallye Pac
2. 71-74 AMX/Javelin Rally Pac
3. All AMC's with gauge package, in center console, like Pacer, Hornet, Gremlin, Concord, etc.

Neither will electrically interchange or read properly when swapped around, they all have the same 1/8" NPT thread.  The first and third one look exactly the same, Stewart Warner Units with a square looking top.  The second unit is domed on top. 
Ross K. Peterson
68X,GoPac,343,AT,52A(1stCar)
68X,GoPac,390,4sp,52A
69X,GoPac,390,4sp,64A
70X,GoPac,390,4sp,87A,8
70X,GoPac,390,4sp,BBO,8
70 Jav SST,390,AT,BSO
74MatX,401,AT,Prototype
74MatX,401,AT
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mstrcrftr Quote  Post ReplyReply Direct Link To This Post Posted: Mar/04/2018 at 12:34pm
the car is a 74 amx but the dash came out of a different car.  so not sure on that. it is the rally pac with the oil, fuel, temp and amps on the left, speedo in the center and tack and clock on the right.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 304-dude Quote  Post ReplyReply Direct Link To This Post Posted: Mar/04/2018 at 1:07pm
Your gauges are for the 71 to 74 Javelin bodies.

What is explained is there are three oil pressure sending units. The domed top on the sending unit is what yours should look like.

I have one that looks very close to the AMC unit, but its a MOPAR part. I may need to add a resistor the lead to make up for the impedance difference.

71 Javelin SST body
390 69 crank, 70 block & heads
NASCAR SB2 rods & pistons
78 Jeep TH400 w/ 2.76 Low
50/50 Ford-AMC Suspension
79 F150 rear & 8.8 axles
Ford Racing 3.25 gears & 9" /w Detroit locker
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