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  #1  
Old July 18th, 2018, 12:32
asymptonic asymptonic is offline
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Incorrect Oil Pressure Reading

Continuation of my thread about my new Jasper motor. Just got it back from the shop where they had read a hot idle oil pressure of 20psi with a mechanical gauge, while the dash gauge shows 9psi.


The sender has been replaced, and I finally bought my own mechanical gauge to double check their work (don't particularly like this shop, but they were one of two local shops that would work with Jasper and the other was even less reputable).


Lo and behold, it is indeed 20psi on my gauge. What are my next steps. Wiring near the sender looks new. I'll try and check the wiring to the ECU and dash, but I'm new to electrical. What would you do?
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Old July 18th, 2018, 12:41
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Re: Incorrect Oil Pressure Reading

Start by cleaning up all the grounds, mainly the ones on the dipstick mounting bolt first.

Get rid of any Teflon tape on the oil pressure gauge threads.
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Old July 18th, 2018, 12:42
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Re: Incorrect Oil Pressure Reading

Interesting, there is some teflon tape on the new gauge. What would be the effect of that beyond the presumably better seal? Ground issue?
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Old July 18th, 2018, 12:51
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Re: Incorrect Oil Pressure Reading

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Originally Posted by asymptonic View Post
Interesting, there is some teflon tape on the new gauge. What would be the effect of that beyond the presumably better seal? Ground issue?
Yes.
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Old July 18th, 2018, 12:57
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Re: Incorrect Oil Pressure Reading

It can effect the body/core temp readings but grounding is done thru the ECU sensor ground.
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Old July 18th, 2018, 20:04
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Re: Incorrect Oil Pressure Reading

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Originally Posted by RCP Phx View Post
It can effect the body/core temp readings but grounding is done thru the ECU sensor ground.
The teflon? I thought the temp sensor was near the fuel rail.


In the same engine replacement I sprung for the max cool mopar radiator. After a ~1500 mile roadtrip which had had trouble in the last, hot, uphill segments on previous trips, temps looked remarkably stable at about 195 by the gauge with no overheats (two minor ones on previous trips). So the temp readings at least feel and seem right.
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Old July 20th, 2018, 18:52
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Re: Incorrect Oil Pressure Reading

Spent yesterday cleaning up the grounds near the dipstick (G101) and the alternator which was the bigger problem (G103). Went from 1.4 ohms from the dipstick to battery to 0.6. But the gauge is still reading low. Will look at the block to firewall ground this weekend, but barring that, what should my next move be?
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Old July 20th, 2018, 19:11
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Re: Incorrect Oil Pressure Reading

Since the sensor is grounded through the ECU, you could check that the ECU itself has good contact with the body. I use electrical grease on all my connections.
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Old July 21st, 2018, 06:46
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Re: Incorrect Oil Pressure Reading

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Originally Posted by RCP Phx View Post
Since the sensor is grounded through the ECU, you could check that the ECU itself has good contact with the body. I use electrical grease on all my connections.

Will do. I also want to check the resistance at the sender and compare it to the resistance at the pin to the ecu connector. BTW, isn't dialectric grease non-conductive? Or is this some other electrical grease?
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Old July 21st, 2018, 08:08
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Re: Incorrect Oil Pressure Reading

Story so far:


Sender Connector to ECU pin: 0.1ohm
ECU ground to battery neg: 0.2ohm
Power on voltage across sender: 5.1v
Still need to figure out how to test the sender ground itself, since its the 2 wire 98 style that grounds through the connection to the oil filter adapter.
Instrument cluster sweep test looks correct.

Nothing looking bad so far. Is there a way to test the sender itself?
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Last edited by asymptonic; July 21st, 2018 at 08:31.
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  #11  
Old July 21st, 2018, 10:22
RCP Phx RCP Phx is offline
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Re: Incorrect Oil Pressure Reading

Nope, it needs to be "conductive" grease(anti-ox)!
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Old July 21st, 2018, 16:22
lawsoncl lawsoncl is offline
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Re: Incorrect Oil Pressure Reading

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Originally Posted by RCP Phx View Post
Nope, it needs to be "conductive" grease(anti-ox)!

Depends what you're greasing. I wouldn't use conductive grease in a in connector as it can short the pins. The purpose of the grease is to keep the air off the metal so it doesn't oxidize.
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Old July 29th, 2018, 08:55
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Re: Incorrect Oil Pressure Reading

Just for closure, the issue did turn out to be the sender. I suspect that though they *said* they put a genuine Mopar sender in, it wasn't. I ordered my own and the Mopar one uses different thread sealant and has the part number stamped into it. The one from this shop didn't.


New sender accurately reflects the mechanical gauge.
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