Robert Campbell

Ok so iv been going around in circles with this, iv got a 1994 jeep cherokee sport 4.0 high output. I just recently put a lift on it, a snorkle then new cap rotor, and plugs. Since i did that it runs really rough, spits and sputters and backfires through the throttle body. And before i did all this, it ran awsome, iv checked timming, has good compression. Iv been told timing chain, but I'd it was a timing chain you would hear it, was also told crank positioning sensor but im sure if that went out, it wouldn't even start. Please help!

cruiser54

Check this:

Robert Campbell

Yup, iv checked to fireing order and timming over and over, everything there is good

fb97xj1

Weak valvespring, perhaps. Or possibly carbon buildup, not letting them seat completely?

Ok, maybe not, after thinking a bit. What are the plugs gapped to? Should be .035". What brand? Wouldnt burt to check the fuel pressure, just because.

Bugout4x4

It's too logical that if it started when the tune up was done it's the tune up. Did you check the cap and rotor to make sure they where the exact same? Is the cap actually seating all the way down on to the housing? Does it look like the rotor tab is actually making contact with the with the coil input contact inside the cap? Did you have the distributer/cam sensor out?

Did this sit a long time while this was all being done and have bad fuel?

BlueRidgeMark

Most likely cause? You goofed. Like all the rest of us have done time and time again, you made a simple mistake and now you can't see it. Double check your work. I don't care how sure you are, you had the cap & wires off, and now you have mixed up wires symptoms. Check your work AGAIN and don't start by assuming you got it right. If you have that assumption in mind you will skip over the mistake like you have already done. A little humility is likely all you need to solve this problem. I'd say it's at least 80%, more likely 90% sure to be a mis-wiring.

Second possible cause - you messed up your cam sensor. Check that.

As to the chain, no, you would not necessarily hear it. If it skipped a tooth you'll be out of time and you will not hear any difference in the chain.

tech

Ok start by finding witch cly, is not firing , I would try unpluging the plug wires one at a time to see if that cly. is working . if you have more than one they may be crosted or may be a bad wire out of the box.

awg

I long ago learned to NEVER throw out used parts, (unless they are destroyed), prior to making sure the new ones work perfectly. Even then I often retain them as "breakdown" spares

ie try re-fitting old cap, rotor, wires etc

Robert Campbell

Ok thank you guys, I'm going to double check everything again. Iv got a buddy with a computer reader that's going to look at my system for me. I also have a feeling i pulled a very big mistake! I welded on the jeep, and im not 100% sure if i unplugged the battery or not.... so i could have fried something.

BlueRidgeMark

Hey, you aren't using a Chilton or a Haynes manual, are you? One or both of them has the wiring pictured incorrectly. It's a very official looking drawing of the distributor, nicely marked, and WRONG. It has tripped up a lot of us. In my case, I went looking on the 'Net for a photo, pulled that one from somewhere, and then spent a few hours pulling out my hair. If I had known the source, I'd have known to ignore it.

When you check your work, use Cruiser's photo, above.

67 GMC

Can you disconnect the snorkel and see if that improves things? Wondering if it's upsetting the MAP / MAF sensor. Most likely something is not quite back to normal as the others posted so if you start removing the things you changed, you should be able to figure it out. Most of my vehicles started in the "non-running or not running very well" condition so you have the advantage that it was running well before you started.

Jeepin'_Aint_EZ

Hopping in to see mixed up firing order.........

Robert Campbell

So kinda figured it out. It was a fuel problem. Injectors were plugged up with gunk. And when i pulled out the sending unit, the filter was tore and plugged, so i got it all unplugged and fixed. It runs better, have 40psi of fuel pressure. But still runs a little rough. Thinking it has something to do with the computer because it throws a code of (positive battery input to pcm was disconnected within last 50 key turns or some **** like that? Not sure what that means.

cruiser54

It means go drive it!!

What did you do with the injectors?

Robert Campbell

i cant drive it because it still idles rough and backfires. I went through the timming again and its dead on from last time i timmed it. And as for the injectors and ports i just sprayed them with carb cleaner really good.