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Oil pressure drops to zero when coming to a stop

ricekrispyota

ricekrispyota

Well-known member
Joined
Mar 7, 2022
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1999 Dodge Ram 1500 4x4 251,000 miles.

Last week when driving the truck, I was coming to a stop and my oil pressure gauge dropped to zero and the check gauges light came on. When I accelerated from the stop it immediately returned to normal. I now happens every time I'm coming to a stop (~900 RPM). I have replaced the oil pressure sender. I did an oil change back in February, but only have about 500 miles on it since then (it's not a daily driver). I may change the oil filter on Saturday. I have heard it could be anything from the throttle body not closing quick enough to some sort of freeze plug type thing that sits below the sender and loosens over time to the pump. Has anyone else dealt with and solved this problem? What else should I be looking for?

Thank you
 
An accumulator might help for short term fix.
 
Drop the oil pan. Inspect the pickup tube. If it's clean, pull the bearing caps to see wear. Then replace the oil pump with a new one. Retest with clean oil.

If that fails, use thicker oil while you source a new engine or put the truck up for sale.
nothing....jpg
 
Is plastigauge still available?

Use to use it to check main and rod bearing clearance.
 
Most likely bearing wear allowing too much oil to escape past the bearings and/or an oil pump failure of some sort. Could be a clogged screen, weak over pressure spring or just a worn pump. To verify, pull the sending unit and screw in a known good mechanical oil pressure gauge and watch it at idle and through the RPM range, in gear and in neutral. You should have at least 10 PSI per 1k RPM. If not, time to pull the pan and see what is going on. With 250k on a V6 or V8, it's likely just worn out from the lifter bores down to the main bearings and you are letting too much oil go flowing into the crankcase. Thicker oil is a band-aid, but with 250k, might be all it's worth.
 
Suddenly started?
Sounds electronic.
Think brake light shorting out the gauge.

2 fiddy onna dodge, might be a message from the factory (buy another, we need your monies) right....
 
Getting factory GM engines these days are next to impossible, hazard a guess getting dodge engines would be the same.
 
Simply call corporate chimerica,
as we saw that chineeze car in the other thread The shameless fukks will source one.:usa:
 
Yep, wasnt thinking about something that old but even something 10 years old is unavailable supposedly due to covid or the artificial inflation.

Elwenil said:
Lol, you aren't getting any kind of "factory" engine for a '99 model from Mopar. That shit was cancelled a decade ago.
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I bought a mechanical gauge this morning and tried that. On startup psi was right at 40. Once it warmed up, it settled around 20 until I started driving it. Once I started driving the RPM's stayed consistent with the pressure i.e. 1800 rpm = 18 psi. I only got it up to 2500 rpm because of the area I drove it in, but it matched.

Now it looks like I get to chase a wiring demon:mad3::flipoff:
 
Keep in mind the 10 PSI per 1k RPM is the minimum. While it is adequate, I wouldn't be kicking it down into passing gear if it can be helped. Most healthy engines will have closer to 30 PSI at 1800 RPM. If the RPMs jump up faster than the oil pump can keep up, you will be doing damage. Considering the mileage, this isn't surprising, but I would be saving my money for a rebuild or a swap in the near future. Again, thicker oil can help, but I would baby it in the meantime.
 
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Elwenil said:
Keep in mind the 10 PSI per 1k RPM is the minimum. While it is adequate, I wouldn't be kicking it down into passing gear if it can be helped. Most healthy engines will have closer to 30 PSI at 1800 RPM. If the RPMs jump up faster than the oil pump can keep up, you will be doing damage. Considering the mileage, this isn't surprising, but I would be saving my money for a rebuild or a swap in the near future. Again, thicker oil can help, but I would baby it in the meantime.
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Thanks for the info. I'll keep that in mind. Ill work a bunch of overtime to save the money which in turn will keep me from driving it since it's not my daily driver. :beer::beer:
 
Outahand said:
So the Mechanical gauge did not go to zero at hot idle like the stock gauge?

Leave the mechanical gauge on and drive it.
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I would do that, but the gauge I bought is more like this one:
IMG_0622.jpeg


I will shop around for a solid mechanical pressure gauge to install while I’m chasing the wiring demon.
 
Found the problem. The factory oil pressure sensor was snapped in half when I pulled it out. I tried 2 O'reilly's brand sensors and 1 Autozone (Duralast) sensor and they did the exact same thing. Today, I pulled the wiring harness, cleaned all of the ground connections, and rewrapped all of the wires for better insulation from the heat. I also spent the $$ for a Mopar oil pressure sensor. Issue is solved. My guess is there was really no wiring issue, but at least I got to check and make sure there was no breaks. Ultimately, for this situation, I would say stick with the Mopar sensor.

Thanks for everyone's help.
 
ricekrispyota said:
Found the problem. The factory oil pressure sensor was snapped in half when I pulled it out. I tried 2 O'reilly's brand sensors and 1 Autozone (Duralast) sensor and they did the exact same thing. Today, I pulled the wiring harness, cleaned all of the ground connections, and rewrapped all of the wires for better insulation from the heat. I also spent the $$ for a Mopar oil pressure sensor. Issue is solved. My guess is there was really no wiring issue, but at least I got to check and make sure there was no breaks. Ultimately, for this situation, I would say stick with the Mopar sensor.

Thanks for everyone's help.
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Glad you found it.

So you replaced the oil pressure sender twice before you found a good one?

I'm having a similar issue with a low mileage 1998 gm 454. Good oil pressure when cold but gauge drops to zero at high idle. I replaced the oil pressure sender once and exact same thing.
 
blakes said:
Glad you found it.

So you replaced the oil pressure sender twice before you found a good one?

I'm having a similar issue with a low mileage 1998 gm 454. Good oil pressure when cold but gauge drops to zero at high idle. I replaced the oil pressure sender once and exact same thing.
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I replaced it twice with parts store senders. I ultimately got the factory Mopar sender and it works fine. It's almost like the parts store senders are set to read a pressure that's too high for what the factory idle will produce which causes the gauge to show zero. If that makes sense. My Dodge oil pressure is supposed to be 6-8 lbs at idle. I think the the parts store senders read anything lower than 10psi as low oil pressure.
 
blakes said:
Glad you found it.

So you replaced the oil pressure sender twice before you found a good one?

I'm having a similar issue with a low mileage 1998 gm 454. Good oil pressure when cold but gauge drops to zero at high idle. I replaced the oil pressure sender once and exact same thing.
Click to expand...
Stick a manual gauge on it to verify the pressure.
 
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