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New Engine, New Questions

asymptonic

NAXJA Member
NAXJA Member
Location
Austin, Texas
Okay, so I recently (gulp) bit the bullet and had my 4.0 replaced with a Jasper reman due to an increasing rod knock. With the new engine in, it sounds better, but there are a few rough spots. Would love opinions.


#1. Driving it back from the garage in the Texas heat, I was noticing concerning oil pressure numbers on hot idle. Cold start and non idle pressures are 45-50psi, so far so good. But when fully hot and idling, gauge was reading around 11-12psi, just out of spec. I changed the oil at 50mi with PYB 10w30 and changed the Champion filter they installed with a Wix. Sticking with conventional oil until about 5k miles. That seems to have brought hot idle pressure up to ~15psi. Is this good enough for a new engine or do I have other things to worry about?


#2. I had the clutch replaced while the motor was out. With the new motor and clutch, I'm getting more vibration in the clutch pedal than I was on the old motor. And, starting from a stop in 1st, its pretty hard to avoid a shudder in the drivetrain until it gets moving. Doesn't seem to be RPM dependent as it doesn't do it in other gears. What might be causing this?


Other than that, I'm liking the new engine well enough. Feels like the old one but without the knock.



1998 4.0, AX15 btw.
 
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Did they surface or replace the flywheel, when replacing the clutch? If not, it's possible there are hard spots (from heat) on the flywheel, and the new clutch surface material is grabbing on them. It may go away after a while, but may take some time.


If the flywheel was replaced or resurfaced, it might need just a bit of time to break in. Take it easy on it for a few months, and hope it settles down.


I know on my Kevlar clutch, there were some very specific break-in instruction I've not seen on conventional clutch linings. You might ask whether the new clutch came with any break-in recommendations.


David Bricker / SYR
 
You say a new engine , did the shop rebuild the engine or did they send it out and have it rebuilt , because the hot oil pressure is to low for a new motor . my motor has 160,000 miles on it and it still has 15 psi of oil pressure and that's running 10w-30 Mobil 1 oil you should have at least 25 psi for a new motor . I would talk to the shop and find out what they say about the low oil pressure and I'm a mechanic I work on cars all day long and have done a lot of engines and something is not right with your oil pressure .
 
id get a confirmation on the low oil pressure by a known good calibrated pressure gage. If still out of specification low, the engine needs to be returned. Low oil pressure is not going to improve on its own. Low oil pressure will negatively effect the service life on this motor. It NEEDS to be dealt with ASAP.


Good Luck
 
Have your gauge checked it may be wrong. I had a problem with my gauge after I had a new Mopar crate engine installed my gauge actually failed and went to zero. I disconnected the battery and hooked it back up the the gauge worked haven’t had an issue since.
 
Take it back to the shop and have them check it and save the paper work to show that you were having oil pressure problems so that when your oil pressure drops to almost nothing they will have to fix it . jasper should replace that motor , the oil pressure is to low for a new motor .
 
Okay, I've been working with the shop on this problem. They were unable to reproduce low pressure with a mechanical gauge. They read 20psi at hot idle. So they replaced the sender. On a road trip I was reading 9psi on the dash gauge, so I took it back.


They claim they drove it and got the dash gauge to show <10psi and then hooked up a mechanical gauge and got ~20psi again. Now they think the instrument cluster gauge is defective. Does this make sense? I thought those needles were actuated by the computer.
 
You are correct about how the gauges function. Could be a problem with the cluster gauge or with the ECU. Resistance figures in here too. You can try to clean and lubricate all the ECU/harness/gauge cluster connections. If you can get ahold of a ECU to try also. You also could try another cluster, but remember the mileage is in the cluster!
 
Yeah, that makes sense. I'll see what the shop can do with it and then chase those down myself. I don't feel the gauge is the issue, as it does travel well. I may also try that startup cluster diagnostic mode if I can remember how to trigger it. It tests all the instruments and sweeps their needles from 0-100%. That should rule out or indicate a problem with how the ECU is driving it>
 
BTW; you need to put a mech gauge on it and check it for "yourself" !!!
 
I have a titan crate motor and the oil pressure always drops down low at idle and comes right back up during driving to 40-50. my old motor done the same but im running 10w30 royal purple HPS in this one.
see if you can get an accurate reading and if its running good, I wouldn't worry too much about it. or call jasper directly
 
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