oil pressure sending unit
Printed From: TheAMCForum.com
Category: The Garage
Forum Name: Electrical - non engine
Forum Description: Charging systems, lights, non-ignition system, it goes here.
URL: https://theamcforum.com/forum/forum_posts.asp?TID=90177
Printed Date: Apr/23/2024 at 5:05pm
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Topic: oil pressure sending unit
Posted By: mstrcrftr
Subject: oil pressure sending unit
Date Posted: Oct/07/2017 at 8:44am
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something funky is going on with my oil pressure gauge. this is a new install on a new engine. i have a tee fitting on the block for the sending unit. one side of it goes to a mechanical gauge on the engine and that works fine. the other side goes to an electrical sending unit for the dash gauge and its not working. when i jump the sending unit wire to ground, the gauge works. i tried replacing the sending unit and it still does not work. any suggestions on what to do? thanks Barney |
Replies:
Posted By: 6768rogues
Date Posted: Oct/07/2017 at 9:36am
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Did you use some type of thread sealant or teflon tape on the threads of the sending unit or Tee? If so, it might electrically isolate the sending unit from the block. That won't matter for the mechanical gauge. Otherwise, I would guess that both sending units are bad or wrong for the gauge. ------------- Content intended for mature audiences. If you experience nausea or diarrhea, stop reading and seek medical attention. Located usually near Rochester, NY and sometimes central FL. |
Posted By: mstrcrftr
Date Posted: Oct/07/2017 at 10:33am
| i thought of that and tried grounding the case of the sending unit to the block, no change. do you think its possible that i have two new bad units? both were ordered for 80 psi gauge. i was wondering if the unit was different for an 80 psi, but you would think that the gauge would at least move if it was for a 40 psi gauge. |
Posted By: Airdrie AMX
Date Posted: Oct/07/2017 at 10:54am
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Do you have a good ground strap from the engine to chassis? ------------- 72 amx javelin 401 4spd |
Posted By: rockAMX
Date Posted: Oct/07/2017 at 1:15pm
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By the dash gauge, do you mean the oil light or a gauge?
------------- DWR 1968 AMX  |
Posted By: mstrcrftr
Date Posted: Oct/08/2017 at 9:53am
| battery cable goes directly to the block and yes the dash has an actual 80 psi gauge. |
Posted By: rocklandrambler
Date Posted: Oct/08/2017 at 11:27am
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Could it be the mechanical pressure line is siphoning off enough pressure that the electrical sending unit can't sense any pressure? Does the electrical gauge work OK when hooked up by itself?
------------- Past AMC's 1974 Hornet X (new) 1975 Gremlin X (new) 1964 Classic 660 Cross Country 1965 American 440-H |
Posted By: mstrcrftr
Date Posted: Oct/08/2017 at 7:28pm
| mechanical gauge reads 60 at idle. not a pressure bleed thing.. its gotta be two bad sending units. everything else works.. |
Posted By: mstrcrftr
Date Posted: Oct/11/2017 at 1:12pm
 still having issues with this. can someone look at the drawing below and confirm that this is how the circuit actually works? |
Posted By: 304-dude
Date Posted: Oct/11/2017 at 1:23pm
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It is possible that the instrument panel circuit is damaged. You can test with the engine running, by ohming the output on the switch directly. You may need someone to increase the engine RPM to show resistance change from idle to 2500 RPM. If you see the resistance change, it is possible the one of contacts where the oil pressure gauge has a broken trace or wire. ------------- 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 |
Posted By: mstrcrftr
Date Posted: Oct/11/2017 at 2:49pm
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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. |
Posted By: 304-dude
Date Posted: Oct/11/2017 at 3:12pm
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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 |
Posted By: mstrcrftr
Date Posted: Oct/11/2017 at 4:04pm
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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 |
Posted By: 304-dude
Date Posted: Oct/11/2017 at 4:42pm
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 |
mstrcrftr wrote:Posted By: tomj
Date Posted: Oct/13/2017 at 12:25am
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. ------------- 1960 Rambler Super two-door wagon, OHV auto 1961 Roadster American, 195.6 OHV, T5 http://www.ramblerLore.com |
Posted By: mstrcrftr
Date Posted: Oct/13/2017 at 9:59am
| tomj, the block is grounded to the chassis. |
Posted By: mstrcrftr
Date Posted: Mar/04/2018 at 9:48am
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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. |
Posted By: 401MATCOUPE
Date Posted: Mar/04/2018 at 10:11am
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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 |
Posted By: mstrcrftr
Date 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. |
Posted By: 304-dude
Date Posted: Mar/04/2018 at 1:07pm
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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 |
Posted By: billd
Date Posted: Mar/04/2018 at 1:24pm
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Be watchful in that I ordered a sending unit for my SX4 gauge and it read wrong so I ordered another one from another source it also read wrong. I tried one I had here and the dumb thing pegged the gauge when it has pressure because it worked backwards of the other (likely it was from a later Jeep or something) I have had trouble with sending units from parts stores - they may "fit" but aren't always the correct resistance range. (impedance is not the same as resistance- for the record  )(Also, just a tip for lurkers - sending units are for gauges, oil pressure switches are for lights. Sending units vary resistance with pressure where switches are on or off with nothing in between) -------------  http://theamcpages.com" rel="nofollow - http://theamcpages.com http://antique-engines.com" rel="nofollow - http://antique-engines.com |
Posted By: bigbad69
Date Posted: Mar/04/2018 at 7:48pm
------------- 69 Javelin SST BBO 390 T10 |
Posted By: billd
Date Posted: Mar/04/2018 at 8:12pm
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You just said it - "is used in AC circuits". I've never seen it used in DC - it's sure not in any book I have used in reference to DC. (some of those being from the 1960s and 70s) So I consider it misused as applied to pure DC circuits where we measure resistance - and the specs we compare to and measure for are in ohms resistance, a straight measurement and part of "ohm's law" formula. ( I know some folks like to repeat what they read and use it as an attempt to show knowledge - so you see it used or misused in such cases as well) ------------- http://theamcpages.com" rel="nofollow - http://theamcpages.com http://antique-engines.com" rel="nofollow - http://antique-engines.com |
Posted By: mstrcrftr
Date Posted: Mar/05/2018 at 10:28am
| so, you are thinking i have the wrong sending unit? the one i have is domed. |
Posted By: mstrcrftr
Date Posted: Mar/05/2018 at 9:59pm
| is there a certain part number for the correct one? |
Posted By: mstrcrftr
Date Posted: Mar/08/2018 at 9:48am
| Does anybody have a sending unit for the rally pak they would be willing to part with? |
Posted By: 6PakBee
Date Posted: Mar/08/2018 at 10:14am
This is some info on the Miller tool to check the Mopar gauge senders. ------------- Roger Gazur 1969 'B' Scheme SC/Rambler 1970 RWB 4-spd Machine 1970 Sonic Silver auto AMX All project cars. Forum Cockroach |
Posted By: FSJunkie
Date Posted: Mar/08/2018 at 12:43pm
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The new sending units are junk and never seem to work right. ------------- 1955 Packard 1966 Marlin 1972 Wagoneer 1973 Ambassador 1977 Hornet 1982 Concord D/L 1984 Eagle Limited |
Posted By: mstrcrftr
Date Posted: Mar/12/2018 at 7:24am
i have tried 3 new ones and cant get one to work. still looking for a workiing one. |
Posted By: 6PakBee
Date Posted: Mar/12/2018 at 7:44am
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Have you done any more resistance checks? I'm guessing you should have about 55 ohms at idle (15 psig) and 25 ohms at 2500 rpm (40 psig), or thereabouts. This is based on what I THINK a Javelin oil pressure gauge is scaled at, 0-80 psig.
------------- Roger Gazur 1969 'B' Scheme SC/Rambler 1970 RWB 4-spd Machine 1970 Sonic Silver auto AMX All project cars. Forum Cockroach |
Posted By: mstrcrftr
Date Posted: Mar/12/2018 at 9:38am
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. |
Posted By: 6PakBee
Date Posted: Mar/12/2018 at 6:36pm
Hmm. Two thoughts. You have 60 psig at idle? Are you sure the mechanical gauge is accurate? Secondly, I would order a Mopar sender for a '70 Charger and try it. The gauge range is the same and the instrument voltage regulator should be the same voltage, so..... ------------- Roger Gazur 1969 'B' Scheme SC/Rambler 1970 RWB 4-spd Machine 1970 Sonic Silver auto AMX All project cars. Forum Cockroach |
Posted By: mstrcrftr
Date Posted: Mar/13/2018 at 9:19am
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Yes the gauge is accurate, it is reading the same as when it was on the dyno and when it was on the dyno we used a different mechanical gauge. once the engine warms up, it goes down a little bit.. do you know if you can still buy a mopar sending unit from chrysler for the 70 charger? |
Posted By: 6PakBee
Date Posted: Mar/13/2018 at 10:42am
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The gauge sending units are readily available from RockAuto. http://www.rockauto.com/en/moreinfo.php?pk=44334&cc=1496003" rel="nofollow - https://www.rockauto.com/en/moreinfo.php?pk=44334&cc=1496003 The oil pressure still puzzles me. What you are saying is that it's relatively constant from idle to higher engine speed, both hot and cold? This flies in the face of everything I've ever seen. ------------- Roger Gazur 1969 'B' Scheme SC/Rambler 1970 RWB 4-spd Machine 1970 Sonic Silver auto AMX All project cars. Forum Cockroach |
Posted By: mstrcrftr
Date Posted: Mar/13/2018 at 10:57am
| when its cold it will be right at 60 at idle. when it warms up it comes down to about 30 at idle. when the engine is revved up, it goes up to about 80 when cold and about 60 when warm. |
Posted By: mstrcrftr
Date Posted: Mar/13/2018 at 11:00am
| Thanks 6PakBee, i ordered that sending unit. |
Posted By: Scene One
Date Posted: Jul/02/2018 at 7:16pm
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mstrcrftr, I am having the same problem with oil pressure gauge. I also tee'd and added a mechanical gauge and glad I did but would like to get my other gauge working. What was your resolve? Thanks in advance B.P. |
Posted By: mstrcrftr
Date Posted: Jul/02/2018 at 7:28pm
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actually it was using the correct ohm sending unit. i tried all of the ones you can buy in an autoparts store and none worked. Then Roger helped me out with a part number of a unit that will work correctly. "A BIG THANKS AGAIN TO ROGER". Also known on the forum as 6PakBee. |
Posted By: Scene One
Date Posted: Jul/02/2018 at 7:49pm
| Thanks I will give it a try and see.. |