Low Oil Pressure

[JeepGirl1013]

When I cold start my tj it beeps and the check gauges light comes on. I took it in to a jeep shop to diagnose some other issues and was told that it is because my oil pressure is low. The gauge on the dash is slow to increase from a cold start. But as the car idles it always sits around 40psi. However at the shop, I was told even though The gauge said 40psi, the computer was reading around 10psi. He told me to change out the oil pressure sender. So I did. Now, I get the beep and check gauges light about half the time I cold start.

I’m not sure where to start diagnosing. Also, would low oil pressure explain why she doesn’t want to cold start on the first crank? Fuel filter, spark plugs, fuel injectors, and vacuum lines have been replaced. And after I changed each of those it would start right up for a week or so and then be back to not wanting to start again

 

[macleanflood]

Probably time to roll in new bearings at the very least... possibly a full rebuild.

Engines need spark, fuel, compression and timing to fire and run.

If you've got low oil pressure, and are confident of your fuel pressure and spark, then I'd be doing a compression test, and possibly a leakdown test.

Oil analysis and possibly a compression gas test on the coolant would also help give you a bigger picture upon which to make decisions.

-Mac

 

[JeepGirl1013]

Probably time to roll in new bearings at the very least... possibly a full rebuild.

Engines need spark, fuel, compression and timing to fire and run.

If you've got low oil pressure, and are confident of your fuel pressure and spark, then I'd be doing a compression test, and possibly a leakdown test.

Oil analysis and possibly a compression gas test on the coolant would also help give you a bigger picture upon which to make decisions.

-Mac

My engine was rebuilt within the last 60k miles

I haven’t done a compression test. But my oil has been clean, not frothy or milkshakey.

 

[macleanflood]

Hopefully you've got some warranty left.

Who built the engine?

-Mac

 

[JeepGirl1013]

Hopefully you've got some warranty left.

Who built the engine?

-Mac

It was the previous owner. They had it done at a machine shop somewhere in AR. I’m not too hopeful. But I’ll try what you mentioned and dig up that paperwork.

 

[macleanflood]

Hopefully it was a rebuild it to keep it job and not a rebuild it to sell it job...

-Mac

 

[BlueC]

My engine was rebuilt within the last 60k miles

I haven’t done a compression test. But my oil has been clean, not frothy or milkshakey.

KISS - simple stuff first. 1- is your oil at the correct level? 2- what oil weight are you running? 3- have you verified the oil pressure?

After all of that is fine, then move on to other diagnostics. Do you have receipt proof of the "rebuild"? I've seen the 'ol craigslist rebuild way too often to believe anyone without documentation.

 

[AndyG]

Sending unit failure??

 

[macleanflood]

Sending unit failure??

Sounds like from the original post that a shop put a mechanical gauge on and tested 10 psi.

Might be worth investing in your own mechanical gauge. I got one from YSTool on Amazon and liked it enough to buy their smoke machine.

-Mac

 

[JeepGirl1013]

Sending unit failure??

I just replaced the sending unit

 

[hear]

My 97 did the same thing. Replaced the sender, same thing. Eventually replaced the oil pump, and never had another problem. In hindsight I should have first checked it with a mechanical gauge, which is what I'm going to do on my daughter's 97 which is currently doing the same thing.

Probably time to roll in new bearings at the very least...

Never done that, but it's not as simple as you just made it sound....is it??

 

[JeepGirl1013]

My 97 did the same thing. Replaced the sender, same thing. Eventually replaced the oil pump, and never had another problem. In hindsight I should have first checked it with a mechanical gauge, which is what I'm going to do on my daughter's 97 which is currently doing the same thing.



Never done that, but it's not as simple as you just made it sound....is it??

Sounds like that’s what I need to do! Thanks for this input

 

[JeepGirl1013]

Sounds like from the original post that a shop put a mechanical gauge on and tested 10 psi.

Might be worth investing in your own mechanical gauge. I got one from YSTool on Amazon and liked it enough to buy their smoke machine.

-Mac

Thanks for that I will pick one up

 

[BlueC]

Eventually replaced the oil pump

That reminded me of an engine a friend pulled apart. Someone had "rebuilt" it and used way too much gasket maker, which clogged the oil pump screen. He cleaned that off and sent it. I know he drove that one for a year after that with no issues.

 

[JeepGirl1013]

KISS - simple stuff first. 1- is your oil at the correct level? 2- what oil weight are you running? 3- have you verified the oil pressure?

After all of that is fine, then move on to other diagnostics. Do you have receipt proof of the "rebuild"? I've seen the 'ol craigslist rebuild way too often to believe anyone without documentation.

Oil level is good. No oil leaks. 5W-30. I have not verified the oil pressure. That’s what I need to do next it seems like. Thank you

 

[macleanflood]

Never done that, but it's not as simple as you just made it sound....is it??

If you've already got the pan down for an oil pump...and maybe a rear main seal...all it really takes is removing the main caps... Junkyard Digs did one on a WJ 4.0.

-Mac

 

[Mike_H]

regarding the hard to start, I didn't see a fuel pump replacement. Try to cycle the key a couple times before starting. Turn the key on, wait for 5 or so seconds until the fuel pump turns off, then turn the key back on and listen for the pump to run and turn off. Then try to start it. TJ's are pretty notorious for having the check valve go out and they won't maintain pressure in the fuel line like they are supposed to. Cycling the key "primes" the fuel system and helps diagnose the issue without having to go buy a fuel pressure gage.

 

[JeepGirl1013]

Sounds like from the original post that a shop put a mechanical gauge on and tested 10 psi.

Might be worth investing in your own mechanical gauge. I got one from YSTool on Amazon and liked it enough to buy their smoke machine.

-Mac

regarding the hard to start, I didn't see a fuel pump replacement. Try to cycle the key a couple times before starting. Turn the key on, wait for 5 or so seconds until the fuel pump turns off, then turn the key back on and listen for the pump to run and turn off. Then try to start it. TJ's are pretty notorious for having the check valve go out and they won't maintain pressure in the fuel line like they are supposed to. Cycling the key "primes" the fuel system and helps diagnose the issue without having to go buy a fuel pressure gage.

Yes, I did a fuel pump replacement. Priming the pump doesn’t make a difference. It still only starts on the second turn. It’s so weird because with each update the hard start goes away for a week or so.

 

[Rickyd]

When I cold start my tj it beeps and the check gauges light comes on. I took it in to a jeep shop to diagnose some other issues and was told that it is because my oil pressure is low. The gauge on the dash is slow to increase from a cold start. But as the car idles it always sits around 40psi. However at the shop, I was told even though The gauge said 40psi, the computer was reading around 10psi. He told me to change out the oil pressure sender. So I did. Now, I get the beep and check gauges light about half the time I cold start.

I’m not sure where to start diagnosing. Also, would low oil pressure explain why she doesn’t want to cold start on the first crank? Fuel filter, spark plugs, fuel injectors, and vacuum lines have been replaced. And after I changed each of those it would start right up for a week or so and then be back to not wanting to start again

Install one of these temporarily. If you use a tee fitting you can use both and see what the pressure is compared to the electrical circuit

 

[tr21triton]

Oil level is good. No oil leaks. 5W-30. I have not verified the oil pressure. That’s what I need to do next it seems like. Thank you

There's your problem. 5w30 my 97 hates it. The check guage light would come on if I idled at a red light or stop. Changed the sending unit still did. Noticed wally world was putting 5w30 in it even though the cap said 10w30. Next change I told them if they put 5w30 in it we were going out back and they were getting a ass whoppin ! Hasn't done it since. Try 10w30 like it says.