vjz

Hello!

So, my 98 4.0L is experiencing something, to me, that is weird.

I have a one year old "life time warranty" oil pressure sending unit from Advance. I broke the OEM one last year while getting the oil filter out.

Anyway, I have had zero trouble with the Jeep, really, until recently.

What happens is that, say you want to pass someone on a two-lane road, you punch the gas, and on my gauge, the needle dips all the way down to the 10psi-ish mark on the gauge. Then after it shifts or you let off the gas, it goes back to 40-45.

40 is usually where it stays while running. Some days it moves around from 20-40 sporadically

Might the sending unit just be bad?

My last oil change in June, I used Lucas as one quart substitute. Too thick of oil for the summer? Since the sending unit is under warranty, I'll probably just go replace it anyway and do an oil change.

I did use 10-40 with a quart of Lucas, so perhaps that's why.

RTorrez1

You need to verify the pressure with a mechanical pressure gauge. After market sending units are not very accurate to begin with. An oem will give you a little better reading.

mentalbreakdown00

prolly a crap sensor

bigbadon

Falling pressure on acceleration means clogged pickup screen if gauge is working correctly.

JBimmolate

How's the oil level? Low oil level can do this under hard acceleration. The pump starves for oil and pressure drops. I would guess bad sensor as well but level is easy to check.

Miles

s346k

what happens if you slam on the brakes or take a corner fast?

cruiser54

What brand of oil filter are you currently using?

vjz

No change in pressure on hard braking or fast cornering. I don't tend to take fast corners in an SUV though, but I did take a fast one to test.

The worst issue is on hard acceleration. Say, I have to pass a semi or farmer that doesn't care about speed limits on highways. Then, it it will drop to the first hash mark and after I shift or let of the gas, it goes back to 40-45. Occasionally it just bounces around from 10-45. However, most of the time is sits right at 40 with minimal fluctuation.

I've always used Castrol oil in every car I have owned.

The filter currently on the Jeep is the Purolator Pure One, which is their yellow filter that is textured for grip. It was rated as one of the better filters on the market.

I usually use a Mopar filter from Advance.

I'll probably replace the sensor this weekend since it's a lifetime warranty. Might as well do it whenever I feel like since it has a lifetime warranty.

I'm surprised if it were any major issues. It runs so smoothly. It doesn't even have the typical 4.0L lifter tick that most of my other Jeeps have had. And it's approaching 200,000 miles!

True diamond in the rough. No rust, no tick, pristine interior, and has 196k on the clock. Of course, I bought it from the original owner last September 10th with 172k on the odometer, and, for the most part, they took excellent care of it.

Everything else on the Jeep is fine. Miscellaneous suspension noises (front shocks creak in cold weather and will be replaced soon).

Hopefully I don't have to replace the oil pump. Seems like a PITA.

vjz

Update.

Oil level is fine, and the oil is very clean with about 2,500 miles on it.

I didn't get a chance to change the oil or the sensor this weekend.

I just hope it isn't anything major.

Last night it ran around the 10 PSI mark while driving at 60MPH.

RTorrez1

Without verifying what the actual pressure is you can just be throwing money at it and never figure out what the real problem is. You can rent a mechanical pressure gauge at any auto parts store.

vjz

Finally got around to fixing it the other day.

Wound up that the sending unit was bad. It's a lifetime warranty part, so it looks like I'll just replace it anytime I get a bad reading.

Pressure is fine, oil is clean.

I changed the oil again at 2,500 miles just because I wanted to ($25, who cares).

Next up is the valve cover gasket and drive shaft re-grease.

BassMasterCHS

Rubber valve cover gasket ftw.

C H E R O K E E 98XJ

X2, Fel-pro