Jeep 4.0 guys, I need advice p1391

shocker998md

Well-Known Member
Joined
Mar 6, 2007
Location
grantsboro nc
Hey guys,
I'm doing some Thanksgiving sit back, think and make a troubleshooting plan and could use some advice. I'm working on a 1997 cherokee 4.0

The original engine had a piston come apart so I found a 98 cherokee and snagged its engine. I freshend the head up, did a leak down, checked bearings, and put a new oil pump and timing chain in. I know for a fact the cam and crank sprocket dots lined up.

I just got everything buttoned up and started it yesterday and it has a horrible miss. High idle most of the time, breaks up when given throttle, is a pain to start and has a 1391 code. Now thinking about it there could be a possibility that the crank sensor got damaged on engine install.

I wouldn't think the distributor would have gotten damaged when the original engine took a dump but who knows. But if these are stabbed one tooth off can everything adjust enough for it to barely run?

I'm thinking check number 1 at tdc and where the rotor is pointing, then make sure grounds are good. Then from there test sensors. I dont really want to just throw parts at it but I'm not experienced with troubleshooting sensors on the 4.0

Anyone have any advice?
 
Give the cam and crank sensor wires and connectors a real good look to make sure they didn't get pinched during the swap.
 
So the distributor side all looks good, swapped another spare distributor off a runner and it fired right up but immediately went to high idle, a miss and then searching for idle.

I'll move to the crank sensor, im thinking it got damaged during r&r, or it went bad before the engine gave up.
 
Bring #1 cylinder to tdc on compression stroke
Looked at balancer notch and it was at 0 on timing cover pointer
Alighned rotor to right before #1 terminal on cap so as gears mesh the rotor is pointed to #1 terminal
Dropped it in
Then wired cap clockwise in correct firing order
 
There's more to it than that.
Remove dizzy, rotate DTC comp stroke #1, align notch on balancer to 0 on the cover.
Use flat screwdriver and turn oil pump to 10 o'clock. Now, remove cap and cam sensor from dizzy. You see a 3/16" hole in the pickup plate and a corresponding hole in the bottom of the dizzy body. Line them up and drop a drill bit or something to lock them together.
Now drop in the dizzy. You may need to rotate the oil pump a little bit.
Reassemble and fire it up.
 
Gave that a rip, it seems to run better but still isn't completely right.

Thanks for the tip about locking it inside the cap. Ive never had to mess with that before. Joint point and drop.

Ive got a new crank sesnor comming, I didnt see Amy wiring damage, when I unplug the crank sensor it dies right away. But its still throwing the 1391 and has a miss. But im making foward progress.
 
Well a new mopar crank sensor didnt fix it. Its the only code being thrown. It will idle most times at 1250 rpm. Drove it down the road and when slowing down to turn around it died.
It started right away with a normal idle. Pulled codes and only 1391 still.

I looked all over for vac leaks and couldnt find any. With it at 1250 idling and a vac guage it pulled 20 inches.

I'm going to take a break from it for a day and look over wiring and figure out what the wires should shoot.
 
I re stabbed the distributor perfect at no 1 tdc. Now ive got some grill and fan assembly. Give it a look over and put some miles on the new engine to work its bugs out.

Thanks for the help guys.
 
Bumping it back up. I'm randomly getting the crank sync code. Sometimes it runs fine, then other times it will miss its ass off.
I have replaced the crank sensor with a mopar one
I did replace the distributor because it was cheaper then just a cap, rotor, and base gasket as silly as that sounds.

The distributor is phased and stabbed correctly.

Ive gone over all grounds to make sure those wont give me a fit. So I'm back to testing an intermittently failing crank or cam sensor. Any input or ideas? Ive got some down time due to a surgury so I'll be reading and digging deep on shooting and testing those sensors.
 
Make sure the wire harness for the CPS is not hanging on the intake manifold. This can cause noise on the buss and will have weird issues with timing and starting. Also on the back of the valve cover check the harness is not seeing vibration or touches the engine at all.
 
Jeff B said:
Make sure the wire harness for the CPS is not hanging on the intake manifold. This can cause noise on the buss and will have weird issues with timing and starting. Also on the back of the valve cover check the harness is not seeing vibration or touches the engine at all.
Click to expand...
X2. I've seen an intermittent short on the CPS harness before. Wire chafing is a real thing.
 
Alright guys, heres some updates. I inspected the crank pos sensor harness and then shot it for continuity. Wiggled everything everywhere and it seemed all good. I then located the ground eyelet that ties in for the sensor ground and figured id make it bullet proof, so I snipped off the eyelet and crimped, solder heat shrinked, and then adhesive heat shrink over the entire repair to some 12 guage wire and ran it straight to the battery negative. It's grounded now. I started it up and still immediatly got the 1391 and 0320 codes again. At this point I thought about it and I replaced the distributor withe one from carquest, so unknow cam sensor, and used the replacement mopar crank sensor.

I tried the cam sensor out of my original engine and the 1391 went away. For the heck of it I figured id gamble on maybe that mopar sensor was bad and ive been going in circles. I ordered another, put it in this morning and its never started up so fast before.

I cleaned up a bunch of loose ends, zip tied some wiring up, finished welding some exhaust and sealing up exhaust leaks and just drove it for 30 min constantally pulling info for codes.

I used a smoke machine to check all the hoses for vacuam leaks and all is good there.

I do need to hook up a fuel pressure guage and drive it because it had an odd miss every so often getting on it around 3000 rpm or so, it would have a cough and a miss and then pick back up. So maybe the pump is on its last leg and sitting didnt do it no good, or old gas, or D all of the above.

Thank you guys for helping me out with this one though. I appreciate it.
 
Well Murphy is back screwing with this thing. I put a new cam sensor in and now I'm consistently getting a cylinder number 5 misfire. I did a visual inspection of the spark plug wire and plug which looked good. I then did a cold cranking compression test and got 110 psi on cylinder 5.

It falls on its face while on the highway and leaning in on it, but if I just ease into it very slowly it seems OK. I'm going to verify spark and disconnect and re contect the injector to see if that makes a change. I'm pulling my hair out with this one, it's so frustrating because for almost 10 years it ran perfect until the old engine ran hot and cracked a piston.
 
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