bigbadon

You have already determined you have low oil pressure with the mechanical gauge so why are you fighting with sending units?

BiplaneGuy

Because the sending unit reads zero, and the mechanical gauge does not.

extrashaky

While it's probably just condensation, any sign of water or coolant in the oil in a 2000 should be taken very seriously because of the potential for the 0331 head to crack. That's especially true for crud on the bottom of the oil filler cap, because that's the exact spot where coolant comes up if you have a crack. Sometimes you can even look down in there with a flashlight and see it. If I were you, I would send off an oil sample for analysis, just to be on the safe side. I use Blackstone, and they charge $28 for the test and send you the sample collection kit for free upon request. It's cheap insurance.

The code you posted above is for the leak detection pump circuit, which is part of your evap emissions system. You have the California emissions, right? (Three catalytic converters, four O2 sensors.) If so, you have an extra pump in the evap system over near the evap solenoid that is acting up for some reason. You might have a vacuum leak, or that pump may be going, or it may be shorted. It's not a major issue unless you need to pass and inspection without any emissions CELs on, but you ought to track it down and figure out what's wrong with it. It's a red herring as far as your oil pressure issue is concerned.

BiplaneGuy

I'm going to keep an eye on the oil, and see how things go. No, not California (at least I don't think so). I mentioned the CEL and code (yes, the leak detection system) only because it happened at the same time, and could conceivably be a bad PCM. Yes, I need no CEL to pass emissions (in Connecticut). However, at lunchtime today I reseated the solenoid connector, tightened the gas cap, and played with one vacuum hose connection that although not obviously leaking, looked a bit weak... and it hasn't come back.

This evening I replaced the oil pressure sender with a Mopar unit, and the gauge is again working. Oil pressure is lower than it should be at idle, but comes up when driving. Could be worn bearings, could be a bad oil pump... how to determine?

extrashaky

There should be a sticker on the firewall in the engine compartment in front of the driver. It will say that the emissions system conforms to either EPA or California emissions. You can also visually determine what you have by looking at the downpipe directly under the exhaust manifold. If it has a couple of extra catalytic converters there with 4 O2 sensors around them, it's California. If it's just a dual straight pipe with the upstream O2 sensor further down under the firewall, it's EPA. They sold CA emissions XJs all over the country, so just because you're in the NE doesn't mean you didn't get one.

I figured it was CA because I don't think the EPA version has the leak detection pump.

It's your motor. But I think you probably ought to read up on the 0331 head crack and change your mind. If you're one of the lucky ones with a defective 0331 and you catch the crack early, it's a matter of a head swap on a Saturday afternoon. If you let it go, it's a matter of a complete engine swap after the coolant in the oil eats the bearings.

Source: Me. I lost an engine because I had always heard 4.0Ls were bulletproof and didn't understand what was happening with that stupid 0331. Two experienced professional mechanics missed it also.

When you say it's lower than it should be, is it dropping to zero? Normal at idle is 13 psi, but if you're still getting 5 psi at idle like you said above, you're probably still okay. Low oil pressure is usually caused by bearing damage. My understanding is that coolant in the oil can also cause low oil pressure temporarily, which then comes back up when you change the oil

BiplaneGuy

It's not dropping to zero... between 5 and 10 at idle when the engine is hot. You said you can sometimes see the crack through the fill hole? What should I look for?

I'll look at the sticker. I didn't realize CA versions were sold elsewhere.

bigbadon

Google 0331 cylinder head crack images....plenty of them. Have you been losing coolant? If so how much? Is it knocking? Your low pressure is not unusual for a high mileage engine, especially a 2000-2001 4.0 because there were factory issues with cam bearings. There are plenty of 4.0s with lower pressure than that that have made it past many thousands of miles.....mine is one of them.

extrashaky

Yeah, Chrysler actually marketed the CA version as "50 State Emissions," because they met emissions requirements in all 50 states. The EPA version was sold as "49 State Emissions," as if it were not as good as "50 State Emissions." That way they were able to boost their total sales of the CA vehicles to help them meet some of the sales requirements. When I bought mine, the salesman tried to push 50 State Emissions as a desirable option.

2000 was the only year with two drastically different versions. In 2001 they didn't offer the EPA version at all. Then the XJ was out of production in the US.