I just bought a 2000 GC and it won't start. When I bought it I knew it wouldn't start but got a great deal on it. The last owner sent it to the dealer and they put a new cam, lifters, timming gears, chain, fuel line, coil pack, plugs and all new gastkets. The guy ran out of money and told them to stop work. Everything inside was put together, all I had to do was bolt the chain cover on and all the exterior components on. If I just crank it thats all it will do, but if I hold the pedal to the floor it will start but backfires like hell. If I let off the gas it stalls. The dealer said they don't know whats wrong with it. It has the 4.0 in it. What could be the problem. Oh, when it backfires it does it through the intake. It will not stay running if you let off the gas. Help me please!
Update. It was the alternator the whole time. The dealer basically rebuilt the motor for nothing.

 

They screwed up somewhere and timing is off. Guarantee it.

 

Timing is off, or possibly extremely restricted exhaust. Free guesses would be to recheck the timing (dist and cam/chain timing) and also maybe loosening the exhaust at the manifold to see if the cat or muffler is stopped up. Also sounds like it could possibly be a fuel pressure problem but that doesnt quite match all your symptoms

Im sure you already checked the distributor timing and firing order right?

 

There is no distributor it's a coil pack and how do I check for firing order?

 

OK peeps, I cleaned all the grounds, charged the battery and changed the TCM relay and now it starts and sounds good. The only problem now is I have to keep my foot in the gas or it stalls. Whats the problem? It does have smoke comming from the exhuast and it smells like gas.

 

One other thing, it has a full tank of gas thats been in it for about a year. Could that be causing it to stall if the gas was bad?

 

thats the first thing i would do is put new gas in it.

 

I was told that since the battery has been dead for almost a year that the computer is basically empty and thats why it dies when I let off the gas. It's not reading the positins properly, and that I should start it and run the rpm's between 2000-2500for 3min to reset the comp for sensor positions. Does this sound right?

 

Theres a white wire on the battery, probably a 14-16 ga. Check that wire and make sure its not broken. I had the same thing happen to mine and thats what it was.

Check the battery cables too. Are they corroded up?

 

Alt is bad. Diconnected wires and it runs fine.

 

I paid $900 for this WJ and it has every possible option known to man for it's year and all that was wrong is the alternator. I now have less than 1k into it and they sell for 4-7k all day long. I think I got a good deal. Kinda makes me wanna rethink ever going to the dealer ever again!

 

Well congrats on finding the problem, and getting a great deal.

 

x2

 

Major progress peep's. I cleaned the IAC really good and the plugs. It now idles around 700-750rpm's. I drove it for a couple miles and it sputters a little but I think it's the old gas. It idles around 550rpm's if your at a stop and it's in gear. Thats a little low but I'll take it for now. It also starts fine without having to touch the gas.

 

That sounds good. Glad you're making progress.