Marine XJ

Ok so I just rebuilt my 90 4.0 and slid it in the other night. It ran perfect before the rebuild except for it started knocking. After bolting it in I cranked it up for the first time and it started right up and idled great! I go to rev it up a little and it starts to fall on its face and starts backfiring. Let the throttle go and returns back to its regular idle. Now when its idling it cycles up and down randomly like when the a/c cycles on and off. I "think" I have checked over all the vacuum and it all looks fine except for the hose that goes to the (carbon canister?) from the fuel tank but I wouldn't think this would make it back fire right? When I go to start it now it seems to take too long before it starts to stumble to life. Once on it idles good besides the cycling up and down randomly. So what do you guys think? I had to have hooked something up wrong or a vacuum line is not hooked up maybe? Any help will be greatly appreciated. Thanks guys.

mike37

are you sure you have the right firing order

a1racer

check your timing

Marine XJ

Yes, That what I first suspected. I have the right firing order and have set the timing twice to top dead center on the compression stroke on #1. If the timing was off it wouldn't idle good right?

Marine XJ

Correct me if I'm wrong but you can even adjust the timing on these. You can even turn the dist. It could be off a tooth but would it idle right?

OverlandZJ

Correct, timing is computer controled. Did you check that the marks on timing cover and harmonic balancer were correct when you dropped the dist in? If it's off a tad it could give you these symptoms.

I dropped a motor in an 88 years back and did just what i explained. Let me grab my FSM real quick.

Marine XJ

OK first thing tomorrow I'm going back out there and check the timing once again since everyone including myself seems to lean towards the timing. By the way of all the xjs I see on all the forums I like your overland the best. I keep the pict of yours on my desk top as inspiration for mine. Thanks guys for your help it is really appreciated. I'll keep you guys posted if this worked. I hope so I want to break it in!!!!!

OverlandZJ

Since it's a new engine you'll need to start from scratch.

Pull the dist out.

Rotate the crank till the timing mark on the harmonic balancer is aligned to the "0" on the timing cover scale on compression stroke. Tip: using chalk or white finger nail polish on the timing mark makes it easier to see.

Take a long reg tip screwdriver and insert it into where the distributor sits, turn the oil pump shaft till the flat edge points to the 11 o'clock position.

Drop the dist in and tighten down.

Install rotor button, it should be pointing to #1 cylinder on cap. Install cap and double check the firing order. 1-5-3-6-2-4 clockwise rotation.

See if she runs better. If not you may want to remove the dist again and rotate the crank one revolution (180*) aligning the timing marks again. Reinstall dist.

If you have a second hand you can easily find the compression stroke by removing the #1 spark plug and putting a finger over the hole. When air blows finger off thats the compression stroke.

Since you rebuilt an engine i'm sure your aware of this, but it doesnt hurt to post for future reference.

Also, are you 100% certain the marks were lined up on the cam and crank gears? They need to face each other exactly.

ColoradoJeepXJ

It sounds like you may be off one tooth on the timing.

Marine XJ

IT WORKED!!!!!!!!! Thank goodness! I drover her today for the first time with the rebuild. Everything went fine at first. As I was driving oil pressure slowly started dropping until it held at about 20 psi. It was running at 60 and 80 at first. So I bring it home and go to change the oil. It came out a blueish greenish black color and really thin. I called my buddy and he said it was from the all the assembly lube makes it lose viscosity. Thats about the color it was and I did use ALOT of it when I assembled it. It never knocked or chattered at all. What do you guys think? Sound right?

OverlandZJ

Change the oil again in 500 miles. What oil and filter do you plan to run?

Yeah, as oil heats and thins you'll lose pressure as well.Not exactly sure the techical behind that. Factory specs are 10lbs for every 1000RPM's. You look good.

Any oil leaks? Dont forget to retighten bolts like intake/exhaust, valve cover etc. Just dont overtorque.

Marine XJ

OK that makes me feel better. The last thing I want to do is pull it back out AGAIN. LOL I was planning to use a WIX filter and castrol 10w 40. What do you think good oil? I haven't done it yet I figure I let it all drip out over night plus for some reason the filter I got was the wrong one. By the way I wanted to say thanks for all the support!!!!! You guys are a good bunch of guys. If I would have posted this on Pirate4x4 they probably would have made me walk the plank. Thanks again and I will post picts of the jeep and engine in the next few days. I just bought this thing for $600. It came with rusty's 8.5 long arm kit, ford 8.8 rear with a detroit locker, the whole front end is heim jointed with some really thick bars, bushwcker flairs, custom rear bumper with swing out with tire mount, hella lights, and alot more. I lucked out big time with this thing thats for sure.

OverlandZJ

Hell Yeah lets see those pics. Pirate...Plank! They can be rough over there at times, good people here and a few other sites.

And yes, good choice on oil/filter. After break in switch to a synthetic (Mobil1, Castrol) and K&N filter.

Marine XJ

Forgot to mention no leaks at all so far. When putting it together I printed out a complete torque spec chart and torqued everything to factory specs. I would let it set for a while and then came back and torqued it again before moving on. So far it seemed to have worked good. Lets see how long that lasts.

CoffeeCommando

I'm trying to do the same thing with the timing right now because I just got a stroker, but the damn cam gear won't move and the only way to get the distributor to seat puts the distributor house almost an incho off from how it's supposed to bolt on to the engine. How the hell do you turn that thing? I have an allen wrench in the holes holding it in place and no matter how much I try to turn it the bastard won't move... so I can't seat it in the oil pump at 11 unless the whole distributor is turned where I can't bolt it down.


((cam gear))