KJamesJR

Something happened to old faithful today. Drove it up to the docs with the kids, about 20 miles or so. Parked it, shut it off... Then I decided to start it back up to park in some shade. Was a little warm today. It didn't start. Kept cranking over, but no start.

I noticed a few things on the gauges... Oil pressure before turning her off was at it's lowest; 8psi. The engine was at the hottest I've seen; 210. It would crank over strong, just wouldn't fire up. The cap, rotor, and plugs are new. The battery, starter, and alternator are also new. Just did an oil change using 10w 30 and a Wix.

After coming out of the docs, maybe 45 minutes later, it fires right back up again. Drove it around for a while, shut it off again a few times trying to recreate the issue. Couldn't get it to happen again.

Any thoughts on this?

tjwalker

1. Keep monitoring your oil pressure. The spec for the 4.0 is as follows:

*Not less than 13 psi at hot idle
*between 37-75 psi over 1600 rpms

2. Check coolant reservoir to be sure you are where you need to be and that you are not using coolant.

KJamesJR

At idle it drops to around 10, maybe a sliver lower.

At 1,600+ RPMS it stays at 40 almost exactly.

Coolant is good. Also it's still green.

KJamesJR

I'd also like to add... When I was getting the no start I popped the hood to check the oil fluids... Stick was reading about quart OVER. I did the oil change and only put in 6 quarts. Which I could have sworn was what it took. I don't know what that means... Wouldn't the filter be holding some of this oil?

tjwalker

If you used 6 quarts of oil when you changed the oil and you changed the fluid at that time, you should be right on the full line of the oil dipstick. 6 quarts is correct. I'm guessing you read it incorrectly with some oil residue further up on the dipstick.

Your oil pressure is a bit on the low side. If this were my vehicle, I would use a "mechanical oil pressure gauge to verify it. Many big box parts stores will rent you one of these for a few bucks. You simply install it where the oil pressure sending unit resides. Often times the oil pressure sending unit can be inaccurate when it starts to fail. If the mechanical gauge shows higher oil pressure than what you are seeing on the dash, go to your local Jeep dealer and buy an oil pressure sending unit from them. Don't go aftermarket with this part as the Mopar unit is only a few bucks more and is the best choice for dependability/accuracy/mating with your factory gauge. Or if you want to just roll the dice and skip the testing part of this process, buy a new sending unit and install it.

KJamesJR

Yeah, I'm going to hit Napa/AutoZone on my way home this afternoon and rent one. However this no start thing that occured... A buddy at work said the engine will not start if the oil pressure is too low. So I'm thinking this is more than just a sending unit. Though I could be wrong. I just changed my oil... If I need to do it again, and drop the pan for a new pump... I'm going to facepalm myself into oblivion.

I probably stuck the dip in three or four times checking, could have been residual oil, though there was a clear cut-off line. Definately look liked it was overfilled.

I'm not hearing any knocking or harshness from the engine however. It's still riding smooth so I'm really just playing a guessing game I suppose. I still have that eggtimer - like tick coming from somewhere... I was thinking it's probably one of the many exhaust leaks.

tjwalker

Start with that oil pressure reading. Unless there is coolant in the oil, 6 quarts will not overfill your crankcase.

Marginal oil pressure is not going to keep the engine from starting. It is possible that you have TWO things going on here; the oil pressure question and an intermittent no start which could be a lot of things including the crankshaft position sensor. The next time you have a no start, pull a plug and see if you have spark. That is job #1 with any no-start.

KJamesJR

I've delt with CPS issues before on other vehicles. Usually, or at least in my case, when a CPS kills your vehicle, it's like there's no power at all. Last time I had a CPS go out, it was while driving. I thought it was a bad alternator because it killed all the power in my car and I couldn't start it back up for a while.

This time, it was the Jeep running. Then shut off. Then cranked over and was almost like it wasn't getting fuel.

The Jeep has 171k miles on it, doubt the CPS has been replaced. I'll look into that next. I guess I have more tuning up to do.

P.S.

No engine lights have come on... So, I guess I have that going for me.

KJamesJR

Okay so I've been doing some research... Apparently low oil pressure is mainly due to your main bearings and connection rods being worn out. Which in my book is cheaper then a new oil pump. So if it comes to that, is there a write up on changing these? I looked in the Write Up section, but didn't find anything. I'm new to these kind of advanced mechanics. This is all a learning experience to me.

I know you have to drop the oil pan, which looks difficult to do because it's right on top of the front axle. Also if it does come to this, what else should I look into replacing while I'm in there besides the oil pan gasket?

I honestly don't think it's my pump because I'm getting some oil pressure. Not like it's dropped to zero. Unless sludge is causing it... Then it could be a blocked pump, or filter. I'm also concerned about the sending unit being faulty. The needle on the gauge jumps around a lot. This is making me lean toward the sending unit being bad. I'll be down for a pressure gauge in about an hour or so.

Sorry for double posting, I just have many questions regarding this.

tjwalker

Don't get ahead of yourself. Verify your oil pressure first.

Post the results here.

KJamesJR

Went to Advanced Auto Parts... No oil pressure gauge.

KJamesJR

For future photo reference, and in case anyone else is having this issue.

At hot idle

JeepingDan

Another possibility could be the fuel in the fuel rail vaporized from heat since it is right above the exhaust manifold.
Parking it and engine off the engine bay will reach highest temperature with hood shut in the first five minutes before cool down.

KJamesJR

How does that explain it not starting for the next 30 - 40 minutes? If the fuel is somehow leaving the fuel rail, would not cranking it over release new fuel? Being on the cautious side, I ordered a new CPS trough ebay. $20.00 or so... I've been reading the install is painful. I wonder if I can go through the firewall on a 98 and still be able to access it...

tjwalker

Gotta warn you that buying a crank sensor on ebay is not a good idea. The vast majority of them are junk. What makes it more confusing with the cheap charly sensors is that they may test good electrically, but the "spacing" is such that they don't work. Buy your crank sensors directly from your Jeep dealer for the best reliability and longevity.

Here are some links to installing your crank sensor. No, you can't access it through the firewall.

http://greatlakesxj.activeboard.com/...picID=24211453

http://www.go.jeep-xj.info/HowtoCPSchange.htm