View Full Version : New engine, same knock?

April 14th, 2012, 10:00
I put a used engine in my 2000 cherokee with 4.0/aw4, and it is still doing the same exact thing as the old engine. I bought the jeep with a blown engine, didn't even try to start it until I had it home and off the trailer. I started it up and drove 100 feet and it sputtered, died, then started knocking when I started it back up. I got it back inside and pulled the motor. It did have bad scoring on cylinder #2.
Fast forward to the new used engine. Fired it up, ran perfect, great oil pressure, held temperature, so I put it in drive and drove 100 feet. It sputtered and died. When restarted it started knocking. deja vu. When it knocks it runs really rough. Then the knock goes away. It's bad enough that I don't want to run it any more until I figure it out.
Here's what I know:
-New crank sensor
-cam sensor is aligned properly
-wiring harness looks good
-fuel pressure and spray pattern is good
-oil pressure is perfect
-torque converter bolts are tight and flexplate was inspected for cracks(it is the flexplate from the 2000 motor)
-put new plugs in after knocking, old ones all looked good
Anybody have suggestions?

April 14th, 2012, 10:13
This may be too simple, are you sure it is an engine knock & not just the noise from the Evap Purge/ Vent Solenoid ? (located on the passenger side of the firewall)
I have had more than one person tell me their XJs engine was knocking when it was Just the solenoid doing it's thing.

PS: Every Jeep 4.0 I have owned sounded like it was going to fall apart.
I purchased a Brand new 1994 GC Laredo 4.0 (Back in 1994) that had terrible piston slap noise from the first day, After 80K miles I sold it to a buddy at work who sold it to another friend @ 170K miles, I still see the Jeep every now & then, it now has over 250K miles on it & still sounds like it did the first day I took it home from the dealer!

April 14th, 2012, 11:42
The little evap solenoid is ticking as well. I traced that one down when I started the jeep up for the first time. This is a much more significant knock when it shows up. The jeep has a misfire now after the knock started. Still no check engine light. It has a constant miss, sounds like one cylinder isn't hitting. My only guess is that I have bad gas. If the engine had a lifter tick or rod knock it should still run OK, and mine isn't. It isn't running well enough to go anywhere.
The jeep started fine this morning, then got worse after the first few minutes. After it died, it was hesitant to start again. Maybe bad gas or water in the gas?

April 16th, 2012, 00:49
Fuel injectors plugged in correctly? I took my intake/Exhaust manifolds off last week and had an injector plugged in backwards. Might be worth checking.

The connectors on my 96 have a bulge on one side and they should all face the drivers side. In my case it was the one that sits under the cruise/throttle/trans cables next to the throttlebody.

April 16th, 2012, 18:24
Compression test. What year engine did you swap in? If its a 2000-2001 it might have a bad head but who knows with a used motor. Do some basic tests: fuel, spark, compression, leak down, recheck everything pretty much: nuts, bolts, connectors.

April 16th, 2012, 18:29
Are you sure the flex plate was not cracked. It only takes hairline cracks to make really horrible noises. Usually only in neutral or park. It will go away if you rev the motor a little unless it really shot.