New Engine / First Start (Stumbling, Backfiring, Stalling, P1391)

I recently rebuilt the engine (and mostly every other part) of my '99 XJ. The engine got all new internals, required machining, new head (clearwater), distributor, wires, coil, etc. I believe the build to be on the higher side of quality. Actually, the entire build (lift, tcase, engine, etc.) took me 5 months as I did it in the middle of a move and I was super anal about everything I did.

Anyway, yesterday was start day. I primed the oil pump w/ a long screwdriver that had been cut and have excellent oil pressure. I covered the new distributor gear with cam break-in goop (Comp). The distributor was lined up perfectly on the cyl 1 post while the engine was at TDC on the compression stroke of cyl 1.

My wife was the trigger person as I wanted to check for leaks/etc. The belt slipped a bit as she started it (need to adjust) but it fired right up. It was smooth & sounded perfect. I told her to take it up to 2000rpms to break in the cam & we were going to hold it there for 20 mins (between 1500 and 2000rpms). Well, as soon as she hit the gas it began to stumble, backfire and then eventually quit. It wouldn't restart. I checked my Android (running torque) but I wasn't able to connect to the ECM. I unplugged the CPS and then plugged it in again - was able to connect to the ECM. It had a P1391. I checked terminals b/c on the CPS and had a reading of 200 Ohms. I *believe* this is bad as it should have a reading of infinite, right? This was done while the CPS was still installed on the bellhousing - just unplugged it up top.

I ordered a new CPS from the local Jeep dealer but they won't have it until tomorrow morning. In my troubleshooting, I went through and verified all of the plug wires (new) are connected to the correct spots on the dizzy and plugs, the coil is plugged in tight, etc. Then, I replaced the rotor (which was new) and the distributor sensor (which was also new) - same thing. So, I put the new parts back in and stopped.

How would you proceed from here? I believe (99%) the timing was set perfect and I do not believe I have any ground issues. I replaced all of my mains with new cables from 5-90 and grinded the paint off the mounting points before I installed them. I have pressure at the fuel line although I don't know how much as I don't have a gauge. I guess I need to rent/borrow one. The injectors were cleaned prior to reinstalling and have new o-rings on both ends (no leaks). I did NOT check them for clicking while trying to start.

-NA

Tonight, I came home w/ a fuel pressure tester to verify everything was fine w/ the fuel pump/filter. There was 49lbs @ the rail. I bled it several times & it was consistent. Then, I took the TB off and cleaned the IAC and IAC housing. The IAC was absolutely filthy. I put everything back together & it fired up after the second crank. I took it up to 2000rpms and held it there for approximately 3 minutes before my wife came out & told me fluid was going everywhere. So, I shut it down. Turns out I forgot the radiator cap. I put it on and tried to restart, no dice. I let it sit for 5 minutes or so & it started right up. At idle it had a little 'bump/misfire' but it got bad at 1500rpms. So, I turned it off and am waiting for the new CPS tomorrow.

Any thoughts?

ETA: This time, it threw a P0304 and a P1391

Just thought I'd bump this for the daytime folks to see if anyone has any advice. I picked up the new CPS today and will try to install it at lunch time. If this doesn't work, I'm going to shotgun it & replace the TPS, reindex the distributor (even though I feel very confident as it sits), and may pull out the sledge hammer! ;-)

I think you indexed your distributor incorrectly. When at top dead center the rotor needs to located just before the spark plug post (like .020" before the post if I remember correctly). The engine doesn't fire the spark plug at top dead center more like 14 degrees before top dead center.

Well, the new CPS did NOT work. I went home @ lunch, dropped under the Jeep & had the new CPS installed in 5 minutes. It fired up on the second try - took it up to 1700rpms and then it started to sputter and eventually stalled. No restart.

IH392 - When I indexed my distributor, I had my motor @ TDC per the timing cover/harmonic balancer and CENTERED the rotor on the number 1 pin. I'm thinking you might be right. Wouldn't the computer compensate for this though? I'll have to read a bit about indexing the dizzy & see what happens. Either way, tonight I'll be double checking it.

-NA

So, I should move the rotor counter-clockwise maybe 1 tooth when the motor is at TDC? Should the leading edge of the rotor (copper part) be touching the edge of the post or the center of the post? Just looking for instructions on the right way.

I think I have it backwards, the rotor needs to be passed the post. So the trailing edge of the copper on the rotor needs to be past the trailing edge of the contact on the post. It actually is supposed to have a gap of .020" between them. If you think about it, in certain circumstances when the timing is advanced 30 degrees, the rotor needs to be at the post way before it reaches top dead center. Thus why you have problems at higher rpms. I can't remember the rotation of the distributor, but if its clockwise, than you should move the rotor one tooth clockwise. Also, is this an aftermarket cam? If so, you might have to grind the ears on the distributer to get the correct position. I guess the aftermarket cams don't necessarily have the gear tooth on the cam in the correct orientation as the factory cams. I had to do this with my renix, I think it still applies to H.O. engines.

IT IS RUNNING! IH392 - You were exactly on with your suggestion of checking the distributor. Basically, I had the distributor a good 20deg off (counter clock wise). I ended up putting a nail through the bottom of the distributor and through the hole in the "white plate" (whatever that is..., the hole for the 4.0) and then aligned it as per the FSM. I cleared the ECM, plugged in my OBD reader (on my Android) and pulled the trigger. It fired up on the first crank and I took it to 2000rpms immediately - smooth as butter. I ran it for 25 minutes, varying it between 1500-2500rpms. No codes, no misfires, etc. It runs PERFECT. All of my sensors check out perfect as per Torque.

I shut it down and am letting it cool right now. I have to drain the cooling system again as I had put in some Prestone flush to flush out the heater core (even through the engine was a new build, it has a new water pump, radiator, etc.

I am SO excited! You guys can't believe how long/hard I've worked on this thing. Odd thing was, if you stood in front of my garage door after I ran it, my Jeep was at the end of a rainbow! ;-) Cool stuff.

IH392 - I owe you something. Ever get to CO? Have a favorite restuarant?

-NA

Glad to hear it runs. I'll have a cold one to celebrate, and we'll call it good. Thanks for the offer though!