unclecameron

Okay, got the rebuilt engine back in the rig. It's a '98 GC with the 4.0. It cranks over, has very bright spark, has compression, the rotor looks roughly aligned with cyl 1 TDC, (I think) all the sensors are connected, there is fuel on the plugs, but it won't start, or even threaten to start. I really haven't heard a backfire, burp, hiccup, or anything, just cranks over and over. I double-checked the crank/cam chain alignment (not saying it still couldn't be off a tooth or something), and nothing hits anything when rotating the crank by hand on the harmonic balancer. I've left the fan and fanbelt off until I'm sure the thing will fire (also missing radiator hoses and water). I also have the intake and air cleaner off too, hoping to attach once it threatens to start. I replaced the crank angle sensor with a new one, I matched up the flywheel/ring with the same orientation as the old one (pretty darned sure). I cranked over until the oil pressure needle starts to come up when I crank. I've also scanned for codes, in case the computer is unhappy. When I remove a spark plug, it was wet with fuel, so I guess the injectors are working. The oxygen sensor looks plugged in, along with all the injectors.

Am I missing anything? I figure if there's a sensor/EFI/emissions problem, it would store a code, no? I don't quite understand why an engine could have fuel, spark and compression and not run, any ideas? I couldn't get it to turn over fast enough to check timing with the light. There was a very minor engine compartment fire prior to the rebuild, but it was still running when the fire broke out, and no wires were melted, just the plastic shield covers. Again, if something were truly dead, wouldn't it store a code?

Bustedback

Your base timing might not be close enough, is it back firing through the intake or sounding kind of labored when cranking?

unclecameron

No, that's the strange thing, I would think at least 1 cyl would backfire, burble, puke, or show other signs of ignition. On other engines I've done, even if you're off a tooth on either the camshaft gear/sprocket or distributor gear tooth/positioning, the thing backfires like a big dog, or if you're far enough, the valves contact the piston dome when cranking it over by hand. None of that is true here.

One thing I remember is that I moved the flywheel from the original now defunct block/crank to the new crank, and just aligned the flywheel relative to the 7th hole (non-threaded) on the crank, so I used that as an alignment mark. Is it possible that 7th hole is in a different place on different cranks, and is just used as a balance hole? But I think if the crank angle sensor/ring was many degrees off, the computer would throw a code?

Strange.

Bustedback

The flywheel will only bolt on one way. You sure you have the cam timing right? Maybe do a compression test and what is up.

unclecameron

Yeah, good call, will give it a shot What minimum compression would be needed to make these things run? I honed the cylinders and there are new pistons and rings, so I don't think they'd be seated all the way when it first runs, so I guess they'd be a little low?

I guess the timing can't be that far off or the valves would hit. Would it also be possible that the lifters are collapsed and so the valves aren't really opening?

Bustedback

Around the 150 range should be ok, but if you have zero it means something like valves are hanging open or cam timing is off.

the_big_h

You mentioned the rotor points to #1 at TDC - but is it TDC on the compression stroke, or on the exhaust stroke. They say you can tell if you pull #1 plug, and plug the hole with your finger as you turn it over by hand (I haven't tried it myself - I would imagine it would be much easier with a buddy!).
If you are firing at TDC on the exhaust stroke, you won't get any action at all.

The spark timing isn't critical to get it running, as long as it's kind of in the range. I just finished an engine swap, I bought a brand new flywheel, found out the hard way it was machined wrong. It idled "OK" with 60 degrees of advance! I did the same thing you did - fired it up as soon as I could, before reassembling everything. Since it fired up, I reassembled everything - only then I found it had way too much advance .

Your compression test should tell you if you got the cam timing OK.

jnicewan

Compression specs are low for these engines, the actual spec is 120-150psi. A general rule of thumb is you need at least 80-90PSI for a decent running engine. Setting up cam timing can be a little tricky because the cam gear is offset from the crank, that can make it hard to visualize the dots.

1988cherokee

if they were wet with fuel are you sure they arent fuel fouled and if they were soaked you might have an injector that is bad

unclecameron

yeah, compressions were all in the 120-150 range, but yeah, had the rotor 180 degress out...DOH! Now all the plugs are horribly soaked after all the cranking, but it keeps trying harder and harder to run. It won't quite run, but it's getting better and better the more I crank. I tell myself that if I put the fan/fanbelt on and hook up the radiator, maybe it'll clear up and run okay. Like I said, it's getting better and better, but won't *quite* run yet. I don't know what else to look at. It also didn't help that my old battery sucked, so wouldn't really turn it over fast enough. New battery=much better now.

On the flywheel, I just lined up the 7th hole on the new crank flange with the same position as the old one on the flywheel, is it possible this is still wrong? It looked like you could get it on there a number of different ways, which would suck in large amounts.

the_big_h

The flywheel only will bolt up one way. The bolt holes are not quite evenly spaced, there's only one orientation where they all line up.
If you are really concerned, you can double-check:
The timing notches (for the CPS) are in 3 groups of 4 notches. At TDC, the space between a group of notches lines up at the starter hole.
- rotate engine by hand to TDC, per timing mark.
- remove the starter. Look in the hole - look just behind the ring gear teeth. You should not see any of the timing notches. If you stick your finger in, you should be able to feel one notch, if you reach down. You might be able to reach one by reaching up, I think only if you have long fingers.

OR,

Check your spark timing with a timing light.

jnicewan

If your plugs are fuel fouled you either need to clean/dry them or hold the throttle to the floor when cranking and see if it starts. If drying the plugs you can usually get by with blowing them with air or brake clean and let them dry.

unclecameron

I figured it would eventually run, so hooked up the radiator, fan, fanbelt and filled it up with water. But then the battery was pretty weak from cranking, so I pulled all the plugs out and let them dry all night while the battery is on a trickle-charger. They were soaked again when I pulled them out. How close does the timing have to be to get the thing to run? The gas is probably 6 months old and smells like death, but it ran the motor when it still had a hole in the block, missing a rod and banging like crazy before I started the rebuild. Am I missing something, or should I just keep trying to crank it over until it sorts the gunk out and runs? It basically starts to run when you floor it and then let off a bit and keep cranking, but it doesn't *quite* keep running...grrr. I don't hear any strange noises while cranking and the oil pressure needle moves a tiny bit when cranking, so hopefully I don't have any *real* damage. If it was a stick shift, I'd drag it up the mountain and let us coast start, that would clear it out...if I don't have other problems

Bustedback

Try spraying some starting fluid down the intake, just a little at a time. If it lights off with the starting fluid you know you have spark and the timing is pretty close. Six month old gas that smells bad just might be bad enough to not fire off.

unclecameron

I tried starting fluid a little earlier, it made it fire more, but with the old battery it wasn't enough to make it run. I wonder if I still could be off a tooth on the distributor, making it sputter but not run? I'm going to try to hook the timing light back up after the battery charges and see if I'm close on cylinder 1 spark timing.

I still don't see any computer codes being thrown, so I guess I must be close?

What is the likelihood of a hyd lifter staying compressed and not really allowing the valves to open, keeping it from running?