I just had a new engine put into my 2003 jeep liberty. Sparatically the car engine light starts blinking the motor runs really rough and mis fires. I shut it off wait awahile turn it on and it works fine . I brought it back to the mechanic can't figure it out. Hsppens like every other day. HELP>

yeah its definately a misfire. If the place your taking it now cant figure it out try elsewhere. But whoever put the motor in should be able to figure out why it is misfiring.

@tom-perhaps the place they are taking it has cleaned the battery to chassis ground multiple times and is left wondering how this problem could posibly still exist.

I have the same problem with my 05 Lib and I was told to change the ASD relay (under the hood on the right, in the front), I did this and it stopped acting up for about 100 miles and then it started to misfire again, I pulled over and shut it off and restarted it and it ran fine again, so, my guess is that it has something to do with the ASD relay ($14.69 at Napa)

An extremly lean condition can cause missfires. trash in injectors,water in fuel,low fuel pressure, broke valve spring, upstream 02 sensor not reading right, Ive seen where carbon buildup in tip of injector has created issues. Where some vehicals have one hole in tip of injector, these have four. More prone to partially plug. Now the ASD relay powers up all injectors,fuel pump relay, alt. field, ign.coils and some other things. If this were going bad, vehical would want to shutdown. Like someone turned it off. Another thing you should never do, Is to put as much fuel in tank as poss.(force it in) When fuel pump clicks off, thats usually enough. If you overfill, raw fuel can get into charcoal canister. When this happens, the evap. system basically floods system. 02 sensors say.....fuel system is running too rich. They start cutting back fuel to try to reach their happy zone and this causes eng. to missfire due to lean condition. Hope this all helps.....

Thanks Jeep Doctor, actually my Jeep started acting up when I filled up my gas tank at an Irving station. What you said about the evap makes perfect sense, because it only misfires when I put any type of load on the system (accelerate or A/C) and the more fuel you put in the system with the vapor canister flooded would cause it to lean out. I will check the injectors also. how do you resolve a flooded vapor canister? replace it? Or will it clear up over time?

yes you replace it. What I would do before I condem it, is to unplug evap sys. from the engine and see how it runs. As far as how much fuel is in tank, this will make no diff. Once canister is flooded it will run rough. There is a hose that connects to intake behind throttle body on driver side. Disconnect hose by pulling it off, then plug off port on intake. Start eng. and see if missfire goes away.

the hose that you unplug goes to the duty purge solenoid. Just sayin this so you pull the right hose off.

could also be water in fuel. gotta use a release tool to take off fuel line. Then have someone hold a clean, clear plastic bottle to end of fuel line. Then just turn key to run position, wait a few seconds and do it again. Then allow fuel to sit for a short time. If you see bubbles in bottom of bottle, there is water in tank.

Thanks!

Update**** It turns out the Valve cover gasket seal was bad. Oil was leaking down onto the spark plug wires and grounding out the spark causing it to misfire. Appherently, this is a problem with both the four cylinder and the six cylinder engines.