4.0 oil issue

[Bride of Frankenstein]

I have a '97 Jeep Wrangler with the 4.0L. Over winter, my hubs and I tore it down and replaced the pistons, rings, and bearing due to having broken skirting on pistons 2 and 5. While testing it out, I ran it out of gas. After that, I started having a lot of issues trying to get it started. We replaced Fuel pump and sending unit, filter, all fuel lines from the tank to the fuel rail, and also the injectors. We also replaced every sensor we could think of. In the midst of trying to get this fixed, we pulled the valve cover off and there was absolutely no oil in the top end. Push rods and rocker arms were dry. There is no leak. No fluid mixing as if there were something cracked or leaking. We have pulled the motor back out to try and find the oiling issue. Pulled the engine all the way down to the block, soaked it with degreaser, and pressure washed it. There was a straw, like a wd-40 straw in the oil gally near cylinder 3, which tells us someone has already tried digging into this motor before we got it. We had the cam and lifters checked while we had them out and were told they were fine. Just to be safe, we put in new cam bearings then re installed the camshaft and the end freeze plug and replaced the oil pump too. Reassemble the engine and torqued everything to spec. Tried priming the pump manually with a drill and long screw driver. Everything is oiling except no oil is getting to the head through the push rods. I don't get it and we are driving ourselves crazy trying to figure it out. I feel like we are missing something simple. If anyone has any input to help me get Frank back on the road, I'd greatly appreciate it.

 

[Chris]

I have a '97 Jeep Wrangler with the 4.0L. Over winter, my hubs and I tore it down and replaced the pistons, rings, and bearing due to having broken skirting on pistons 2 and 5. While testing it out, I ran it out of gas. After that, I started having a lot of issues trying to get it started. We replaced Fuel pump and sending unit, filter, all fuel lines from the tank to the fuel rail, and also the injectors. We also replaced every sensor we could think of. In the midst of trying to get this fixed, we pulled the valve cover off and there was absolutely no oil in the top end. Push rods and rocker arms were dry. There is no leak. No fluid mixing as if there were something cracked or leaking. We have pulled the motor back out to try and find the oiling issue. Pulled the engine all the way down to the block, soaked it with degreaser, and pressure washed it. There was a straw, like a wd-40 straw in the oil gally near cylinder 3, which tells us someone has already tried digging into this motor before we got it. We had the cam and lifters checked while we had them out and were told they were fine. Just to be safe, we put in new cam bearings then re installed the camshaft and the end freeze plug and replaced the oil pump too. Reassemble the engine and torqued everything to spec. Tried priming the pump manually with a drill and long screw driver. Everything is oiling except no oil is getting to the head through the push rods. I don't get it and we are driving ourselves crazy trying to figure it out. I feel like we are missing something simple. If anyone has any input to help me get Frank back on the road, I'd greatly appreciate it.

The fact that you found the straw in the oil galley is definitely a red flag and likely suggests previous attempts at addressing oiling issues.

Here are a few things you might want to check when troubleshooting the lack of oil reaching the top end:

• Check Oil Gallies Thoroughly: Ensure there are no blockages in the oil galleys. Given the previous issues, it’s worth double-checking all passages for debris or damage.
• Verify Oil Pump Installation: Make sure that the oil pump is properly aligned and seated. Sometimes the pump may not be fully engaged with the pick up tube, leading to low oil pressure.
• Inspect the Oil Pickup Tube: Ensure that the oil pickup tube is not cracked or blocked. If it has holes or is damaged, it could be sucking air instead of oil.
• Camshaft and Lifters: Even if they checked out okay, ensure that the camshaft isn’t preventing oil flow, particularly around the cam bearings. Sometimes the installation can be slightly off.
• Push Rods and Rocker Arms: Check the push rods themselves for any obstructions, and ensure that the rocker arms are not out of position.
• Oil Pressure: Use a manual oil pressure gauge to confirm that the oil pump is generating the specified pressure. If you're not seeing pressure, it could indicate a problem with the pump or oil paths.
• Revisit the Seals and Gaskets: If any seals or gaskets are improperly installed, this could lead to oil bypassing where it shouldn’t.
• Oil Type and Viscosity: Ensure you are using the correct oil type and viscosity for your engine—sometimes the wrong oil can result in poor flow.

Since you've replaced so many components already, that to me suggests you may have simply overlooked something.

Sometimes a simple oversight can lead to issues like this. Remember, Occam's Razor is a real thing

 

[Bride of Frankenstein]

Update: It was bad lifters. Every single one of them was stuck. We put new ones in and it is oiling perfectly!

 

[KennethS]

I’ve read on other old car forums about new lifters that didn’t have holes in the metering plate, so no oil to the push rods. Sounds as if that may have been your issue, too.

 

[Duck Doctor]

Update: It was bad lifters. Every single one of them was stuck. We put new ones in and it is oiling perfectly!

Cam lobes weren't damaged? The 4.0 in my XJ had a stuck lifter and the respective lobe was trashed.