Oil pressure gauge intermittently working

[daav544]

Oil pressure gauge has intermittently been working for the past couple days, been working on start up then I'll start driving and it will randomly drop then come back alive. Seems like it likes to drop out more so when I come to a stop and the truck is idling with lower oil pressure. When I'm cruising and have like 40 psi it usually stays alive. If I come to a stop and it does while I'm sitting there idling I can rev and hold it at like 1100 then it magically comes back alive on the dash. Is this most likely the oil pressure sensor? Or could it be a bad ground somewhere? Sitting idling right now and it's jumping back and fourth check gauges light will come on it will drop to zero then come back alive then die again and so on, it's pretty annoying listening to the beeping constantly lol

[Tractorman]

Two things come to mind.  Oil pressure is serious business.  First, I would immediately check engine oil level.  If it not showing on the stick, obviously add more oil and find the source of the leak.  Second, If it is overfull, then check for serious fuel dilution.  Low oil viscosity can result in low oil pressure.

 

If everything checks out okay, then temporarily install a mechanical gauge to verify oil pressure under the same operating conditions.  If the oil pressure is good, then replace the oil pressure sensor.

 

- John

 

 

[daav544]

I checked all my bases, oil is topped off, not diluted and 100 % have pressure. So there's no chance it could be a bad ground somewhere? I know these things are known to have those sensors go bad l, im sure this one is original to 1999. I just would have figured it would either be dead for good or read like 80 psi with the turn of the key and truck not running like I've heard others experience. Cus it works just fine when it is alive then just drop to 0 like it lost connection then comes back alive. Like I said if I'm cruising at 40psi it will usually stay working until I come to an idle and the pressure comes down to like 20 then it will die and a couple seconds later come back alive and then off and so on, didn't know if like it's supplied voltage could be to low or a bad ground or something? Is there a ground that is specifically for that sensor and other electrical components in the same circuit that I could clean?

[Tractorman]

The diagram below is from my 2002 FSM.  I believe that there are 2-wire and 3-wire oil pressure switches used in the 24 valve 2nd gen trucks.

 

As you can see, there are several components that are grounded to the ECM.  The oil pressure sensor, camshaft position sensor and MAP sensor (not shown) receive 5 volt supply from the ECM.  Terminal #11 on ECM (ground) goes to Splice 165.  Terminal #10 on ECM (5 volt supply) goes to Splice 166.

 

Since you don't seem to be having a problem with other sensors, I think you may have an oil pressure sensor problem.

 

- John

 

 

 

Edited December 2 by Tractorman

[Mopar1973Man]

Be careful to be aware that the MAP sensor and oil pressure sensors can be interchanged for positions. The plugs are the same even. I just had a local gent ask me to look at his truck and the sensor he changed was the manifold pressure sensor. After showing the owner where the actual sensor was located he was thankful and was seriously worried that no oil came out of the hole. Yes, this just happened yesterday.

Edited December 1 by Mopar1973Man

[daav544]

Lol thankfully I am very familiar with the location of the map sensor I had to solder a new plug end on because one of the tabs on the pins inside the plug broke off and was making intermittent connection. So I know all too well about where the map sensor is lol. Also does 35-40psi sound about right for oil pressure while cruising at 2100rpm? My gauge has been working until my pressure drops down to like 20psi then the gauge goes dead. When I start driving and oil pressure comes up the gauge comes alive again. The constant beeping of the check gauge light is getting annoying waiting for the new sensor to come in

[Mopar1973Man]

Minimum Specs... Right out of Dodge FSM.

 

10 PSI at idle

30 PSI at 2,000 RPM

 

Grab a test gauge and test the factory oil pressure gauge is software controlled just coolant temperatures can change the pressure on the oil side. Now another issue is old injectors that are popping too early and the advancement goes unnoticed most don't see or feel any changes. For every -10 bar in pressure is roughly a 1-degree advancement in timing. Suppose the injectors are down to 240 to 260 bar which is a 5 to 7 degree gain on timing that the ECM has zero control over. Now you heat soak the engine oil because of improper timing and typically most have engine oil temperature and coolant temperature running close together in value. I'm the odd duck where I run 320 bar (2 degrees retarded) popped injectors (150 HP) but now with the timing correction on the Quadzilla I managed to reduce oil temperatures by 30 to 35 degrees lower with coolant temperature in the 204°F to 210°F realm and engine oil temperatures are 168 to 175°F. As seen below.

 

Transmission is engine oil temp. Be aware I'm running a 200°F 6.7L thermostat. Still run colder oil temps than most here. 

Edited December 2 by Mopar1973Man