4.9 in 02 big problems need help electrical

[scott_87]

This is my first post, im completely new to this, so you will have to bare with me.... I have an 02 wrangler with the stock 5 speed man behind it. I have put a 4.2 crank in my 4.0 and also had the block bored .030. Seems very common. All machine work was done at local machine shop very reputable guys there. Engine went in very well, no problems, until i tried startin it. The motor turns over very hard, i know there is a lot of compression, but still. With the plugs out it turns over very easy by hand and with starter so i know its not mechanical. I was told to retime my distributor or camshaft sensor. I put the motor at TDC on compression on #1. Set the timing in the camshaft sensor with a toothpick in the alignment holes like told to by chrylser dealer. Reinstalled the oil pump drive in the block with the sensor facing 0 degrees towards the back of the block. Still nothing. Call my brother inlaw over, he has a snapon modis, we hook it up and as the motor tries to turn over, im only showing 32 crank revs and sometimes 64 crank revs. I know it spinning faster than that. Like i said it turns over very hard, sometimes a backfire. I take the crank sensor out of the belhousing and try cranking it over to make sure that im not getting any crank revs. Just like i thought its showing 0 for crank revs, however the motor spins over very well, but no fire, which i understand, that all controls the spark and fuel, with no revs, no spark or fuel. I clean it, inspect it for damage, and there is nothing, so i put it back in, try turning it over again and same thing, hard to spin over back fire, and either 32 or 64 crank revolutions. Im lost, the Jeep ran when it came in the garage, i find it hard to believe that the sensor went bad in 2 weeks while the motor was being built. If someone could help i really would appreciate it, if you need more info, tell me, i might have left out something important. I will get you whatever information you need.


PS. only the bore, crank and rods were changed. Everything else is stock, well at least on the motor

[ibanezjeepguy]

I know you're thinking & hoping its an electrical or sensor error but before you jump to conclusions make sure you have proper compression on each and every single cylinder before you start. Then make sure all the injectors are pulsing fuel in and all your plugs are shooting spark out. From there it has to be a timing issue. Break out the timing gun and make sure your cam sensor is set accurate.

Good luck!

[racing89]

Probably a ground issue. Im sure @ one time or another everyone has negleted to hook-up at least one. Did u remove crank sensor before swap? Can easily be damaged.

[Cheromaniac]

I have put a 4.2 crank in my 4.0 and also had the block bored .030.

Your engine is a 4.6, not a 4.9. Displacement is 4587cc.

Like i said it turns over very hard, sometimes a backfire.

Usually a sign that the timing's off so you might want to recheck the cam position sensor. It seems that you do have air/spark/fuel but they're not properly synchronized.

Im lost, the Jeep ran when it came in the garage, i find it hard to believe that the sensor went bad in 2 weeks while the motor was being built.

Anything's possible. Shit happens and sensors can be damaged when doing major engine work. Grounds can also be left off or come loose so go over every ground and sensor with a fine toothcomb.

Good luck.

[racing89]

As I said .( before) Crank sensor can easily be damaged when not removed.

[SilverXJ]

I second the sensor. If the Modis is showing less revs that it is actually spinning then it would point to a faulty crank sensor considering that is hows the engine determines the RPM. That is also assuming that is what is being read of the modis. I ran into this problem as well. Engine would turn over and occasionally back fire. Crank sensor was faulty and it was fine two weeks prior. Also, if you feel it is cranking too slowly check your grounds and battery condition.

[scott_87]

Well, first off i want to thank everyone for the help, whether the diagnosis was right or not. ALL help was appreciated. I just wanted to post a reply and let everyone know what the actual prob. was just in case your in the same boat. I put another crank sensor in it and it didnt help, and i had a few people tell me to recheck timing. It sounds like there is only a few degrees of operating range, so i rechecked everything. I got into and turned the key, and it fired right up. Its been about two and a half months and 3000 miles and no problems. The motor makes good power, way more than stock. I have a small vacuum problem, my heat only blows out defroster, but thats a small issue i will address in the spring since my garage doesnt have the best heat in it. Again i want to thank everyone.