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Help with recent engine swap


NAXJA Forum User
Hello all

Blew up engine back in March. Due to the current unpleasantness, the build and swap took a little longer than I had planned. The engine has been in the jeep for over a month at this point and it will not run correctly. It will crank and run after some extended cranking. Once running, it idles perfectly. It will NOT rev past 1800. Any attempt to rev causes stumbling, popping etc..

It moves fine in

1996 Jeep XJ. AW4 Auto.
4.6L Stroker.
After thorough inspection re-used the crank and cam from the previous engine - Using same combination of parts from previous engine. Only carried over crank and cam. I have only managed to get one CEL code. One stumble and die resulted in an intermittent cam/crank missmatch. Will not repeat the code.

1. late model 258 crank
2. Crane Camshaft that does not seem to be made anymore. Apologies. Don't have the number, but it was their "tourquey" cam from 2008.
3. Stock 258 rods
4. New Sealed Power 802 pistons .030 over
5. Stock '98 head
6. Renix era engine block, bored to match new pistons

What I have done/checked
1. Rechecked cam timing. Verified by second set of eyes.
2. Rechecked ignition timing. Verified by second set of eyes.
3. Swapped ignition coil from running jeep
4. Swapped distributor from running jeep
5. Swapped Crank sensor from running jeep
6. Swapped Cam sensor/ignition pickup from running jeep
7. Swapped Throttle position sensor from running jeep
8. New cap/rotor/wires/plugs.
9. Checked fuel pressure at idle. 48 psi. Need second set of hands. Have not checked while trying to throttle. Will do ASAP
10. Unhooked exhaust at collector to check for plugged cat.

So far nothing seems to make any changes.

I am open to any ideas. I have several other XJs, so some quick swaps can be made

I am stumped, any help is appreciated.
You said you checked the cam timing, by what process? Did you actually degree the cam?
No. I am not that sophisticated. I have pulled valve and timing cover to verify that the timing marks line up and that the intake/exhaust valves are moving as expected.

It honestly "feels" like timing, but I cannot see any obvious issues.
Some of the cams require timing other than "straight up", are you sure it's a fuel injection cam and not one their carb models?
The Cam and Crank have been in 3 separate fuel injected jeeps. I built it for a 98 Wrangler, it lived in a Renix (88) for a couple of years and moved it to this exact jeep several years ago. I have timed this camshaft the same way twice before. Its never given me an issue in a fuel injected jeep.

When the engine failed (Broken Piston) I had the cam and crank checked at the machine shop. Replaced all rods and new pistons and as the block was gouged, decided to use another I had on hand.

Not trying to argue. Just want you to understand what was done. Seen your work before, and I could absolutely use your expertise
Well my next thought would be a vacumm leak but it would be pretty large, have you checked all that? What about the injector firing order?
It also sounds like it might be in "limp" mode, have you put a scanner on it?
Yes sir. Didn't think to mention

Sprayed brake cleaner around all potential vacuum spots, and the idle isn't running up like I would normally expect. No change with spray.

My scanner is basic, but i have only had the one code. I've never had an XJ in limp. Would it show a code?

CEL functions (comes on at start up, then goes out) but does not come on when running, except the one time I mentioned.
I did check injectors. The harness lays out correctly and wouldn't easily fit any other way. Plugs read as too much fuel. I should have mentioned, they are 24 lb ford injectors.
I don't really know much about your '96 PCM, have you done a compression test? Have you done a leak-down test? My next thought leads to either sensors or a PCM itself.
Trying to run a compression/leak down check later if a buddy can come by. We also are going to check fuel pressure at open throttle. Just need more hands for those.

PCM is a concern a friend of mine raised. Is there a way to check it?

As far as sensors, are there any that are critical to running I haven't swapped?
PCM is a concern a friend of mine raised. Is there a way to check it?

As far as sensors, are there any that are critical to running I haven't swapped?

Not that "I" know of other than a "in use" check with really expensive equipment.

All the sensors are fairly critical with some of the cheap auto store ones not performing well. But by your description about the only thing that you could do is "data logging" to look for something "unusual" that the PCM thinks is still w/i it's limits.
I really appreciate the input. Might need to scout the local yards for a 96 pcm. Be worth the $40. $200 for a new/reman one is a bit steep for a gamble.

Really hate blindly throwing parts at a problem...
Pcm was working when the engine blew up.

Sent from my SM-G960U using Tapatalk

Yep. It drove all the way till it stopped. Problem was purely Mechanical.

I, personally have never had a Jeep have a PCM go bad (17 Jeeps over the years, 14 XJs, yes I have a problem) so it was not my first instinct. At this point, I have run out of ideas. Battery was out of the car for 3 months, hood closed and engine removed. Could one go bad in that situation? Murphy says yes.
Murphy says yes but unlikely

I've done heads on a few over head cam cars. Seems im always off one tooth on first start well almost always.

I'd bump it a tooth one way or the other

Always turn a motor over by hand before attempting to fire it up for the first.

Something you have done is off or heck crank sensor fubared n assembly tooth chipped on flywheel was dropped i dunno im just guessing.
Don't make it hard on yourself by thinking working parts went bad just sitting there.

Im sure its something stupid simple.
KISS keep it stupid simple

Good luck

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Something you have done is off or heck crank sensor fubared n assembly tooth chipped on flywheel was dropped i dunno im just guessing.

He doesn't have a flywheel and the starter ring is no where near the CPS. The CPS function doesn't use any "teeth" in it's performance.

BigDaddy I would also do a really thorough inspection of the engine wire harness as you may have chafed a wire on installation.
I agree PCM failures are very uncommon, but not unheard of - the original one in my '92 failed years ago, after I had been offroad and noticed that if I went through enough water to get tossed around the engine bay the tachometer would drop out for a bit. That went on for a couple weeks, then the truck quit working altogether and I had to have it towed to a shop and that was the problem. My guess is that the "potting" material that they filled the thing with had degraded somewhat, and there were gaps/cracks where water, if splashed right, could get to and damage the actual circuitry.

If you can really score a PCM for $40 at the yard, it's relatively cheap insurance and you can always sell it on later if you don't need it or keep it as a core/spare, since I'm sure finding one of those in a yard is getting less and less common.
Sorry. Work got busy today. Thanks for further input.

PCM is $40 if they have it. XJs have gotten thin the last could if years.

Cam timing on the same timing set that was running is dead on. Pulled the timing cover twice in the car and had a second mechanic take a look. Took pictures to validate

Install went as easy as I've had. Close look at the flexplate during torque converter and didn't see anything. Eat to look so may do again.

Crank and cam sensors changed from running XJ. No change. Moved sensors from 96 into running jeep. Still runs.

Chafed wire makes a lot of sense. I'll get a look over the next couple of days. Work may interfere today/tomorrow.

Thanks again