4.0L oil pressure drops to 0 on hard deceleration

Yea, I understand that the oil all sloshes to the front of the pan on deceleration, but the OP dropping to 0 and throwing a CEL, is new.
Started a few days ago.
OP is a bit low when warm (around 35 usually), but I've never seen it drop to 0 till this past week.

Engine is old and tired. 350,000km on it. It may have a microscopic crack in the #6 cylinder (slow, unexplained coolant loss), it's been progressively making less power for years, occasionally hesitates a few times on acceleration for the first five minutes after starting up, etc.

I'm just wondering if the OP issue (being new) might indicate something I haven't thought of.
I've been wanting to replace the 4.0 for years, but it seems silly to put another 4.0 in there instead of just swapping in a 5.3 or something, but I've never done a SBC into an XJ, and despite mountains of research on the subject, I'm still not 100% comfortable tackling it myself as this is my DD.

Oil was changed a few months ago, level is good, not seeing any evidence of water in the crank case, viscosity seems normal. What are the odds I've got a bad filter or a bunch of gunk in the pickup?

You didn't state your model year but if it's a 2000+ XJ, an "unexplained" coolant loss is usually a sign of a cracked cylinder head. As for the oil pressure, if it were mine, I would replace the sending unit just to rule that out.

kalali said:

As for the oil pressure, if it were mine, I would replace the sending unit just to rule that out.

Click to expand...

Do it. I had a similar issue. I replaced the sensor with a new BWD, but the issue persisted. I swore up and down that my "new" oil pressure sensor was not to blame for two months. I finally replaced the sensor again after replacing the pigtail and redoing all of the block grounds with no change. It started showing the correct pressure on sensor #3 and now I don't panic in traffic anymore. Remember - aftermarket sensors seem to be junk in general these days...

As usual you could check the OP with a mechanical gauge at the sensor port. Replaced mine with a Autometer sensor and gauge. It's worked well so far.

Yes, check with mechanical gauge. For 2000-2001 XJ, I have had good luck with a NAPA Echlin sensor, but my 1997 XJ did not like the NAPA Echlin for that model year (different connector) and after 2, NAPA took it back and I am using a dealer sensor. With wholesale dealer pricing there isn't much difference in price; in fact the dealer unit may be cheaper.

NAPA sensors are reboxed... typically the exact sensors that O'Reilly or Advance sells: BWD.

If you want to ensure that you only need to replace it once, buy OEM from the dealer.