Cold running problem

2000 Limited, 4.0, NP242, AW4. This one has the distributorless ignition, which may or may not be relevant.

Here's the problem: chugging on cold starts at idle until it warms up (around 180degF or so). Not so badly that it stalls, but badly enough that if you try to drive it while cold it has the classic symptoms of timing being off: pinging, misfires, foot to the floor and no acceleration or climb in revs (engine bogs down).

Fuel economy and response when warm are about the same as they've ever been - makes sense, given that this is only a cold start problem.

I've run an OBD-II scan on it: no codes are stored.

The 'cylinder #3 misfire' recall common to 2000s has been performed per the VIP report.

Searching suggests the IAC and/or throttle body could do with a cleaning, which sounds like a reasonable first step. Having killed a TPS on a different XJ before this doesn't feel the same, mainly because the problem only happens when cold - dead TPSes are noticeable all the time in my experience, so I'm loath to suspect it.

Is there anything I may have missed? Anyone else who's dealt with this on a 2000 have any words of advice, specifically on the cleaning? I'm getting ready to make a Kragen run to deal with this, so advice would be most appreciated.

Your engine could be running lean during the warm-up phase and I can think of two possible reasons; shorted wiring either to the IAT sensor or to the coolant temp. sensor. In either case, the ECU thinks the engine's already warm (when it hasn't) so it doesn't provide the necessary fuel enrichment during warm-up.

I agree,that's a good place to start!

Okay. As preliminary troubleshooting, I've cleaned out the throttle body (it was black up to the top) and IAC. The idle has smoothed out considerably, and acceleration is back where I'd expect it to be.

Any further testing will have to hold off until the morning when I can cold-start it, but fingers crossed this has solved most of the problem. Some new spark plugs probably wouldn't go amiss either.

Hmm........The cylinder #3 misfire TSB is nothing more then insulating the injector with a spark plug shield off a b-van....I have run into this a couple times........what I have found is high amounts of carbon build up on the valves....a normal decarb does not fix it,but you can try it and see if it helps.....what happens is the valves cant rotate and self clean themselves,to check if this might be happening,remove the valve cover,remove the all the rocker arms and look at the top of the valve stem where the rocker contacts it...the center of the stem should have a circular pattern indicating the valve is ok and rotating,if it is not rotating ,you wll see a straight line pattern across the top of the stem indicating the valve is not turning.....couple choices here if you find a couple valves not rotating on thier own......1: remove the head and sub out for a valve job..or 2: remove the spark plugs,put air to the affected cylinder you are working on,remove the valve spring,have an assistent hold the valve with no spring while you remove the air from the cylinder,then rotate the engine by hand to bring that cylinders piston all the way up,then you can let go off the valve and it wont fall in the cylinder,then real slow turn the engine so the valve follows the piston on its downward stroke,stop when you have about an inch of valvestem still sticking out of the head......then spray MOPAR combustion chamber cleaner in the spark plug hole,fill up the cylinder as best you can....grab the valve and push it down and pull it up like a dunking motion in all that Cleaner you have in the cylinder...so spray and dunk,do it like 10 times.....then let sit 10 minutes....then you grab your cordless,chuckless electric drilln and attach to the valve stem,have an assitent spray cleaner in the spark plug hole as you turn on the drill and do the dunking motion again,but with the drill attached,just on the upward stroke with the drill running pull up with a little force so the valve spins on the valve seat...do this 10 times,then reverse the drill and do it another 10 times with like 3 seconds each time pulling against the seat....here is the tricky part,take off the drill...grab some strong rubber bands or orings,and stretch over the stem of the valve you just did to the valve next to it which still has the spring,pull the valve up,,,this will hold up the valve as you install the air back into the cylinder,once you have compressed air hooked back up into the cylinder, and the valve seated,then reinstall your valve spring..........then repeat on the other cylinders or valves you found the problem.............take your time,and can save yourself a bunch of money if you do it yourself...after you are done,clear the cylinders before you put the sparkplugs in,make sure the coil pack is unplugged then crank over for 5 to 7 seconds,reinstall everything and enjoy the smoke for awhile from the tail pipe :laugh3: ........also another thing to look for is if your cam sensor is out of sync,need a scanner for this,,,but for a quick check to see if the cam sensor drive is seizing up rotating the whole housing and throwing sync off...look at the point where the clamp holds down the cam sensor drive(cam sensor drive is where the distribator used to be on the older XJs above the oil filter) and look for new marks like it has forced against the hold down clamp is rotating.........Hope this helps....

Rags
www.arizonajeepextreme.com
Naxja member #114

casm said:

2000 Limited, 4.0, NP242, AW4. This one has the distributorless ignition, which may or may not be relevant.

Here's the problem: chugging on cold starts at idle until it warms up (around 180degF or so). Not so badly that it stalls, but badly enough that if you try to drive it while cold it has the classic symptoms of timing being off: pinging, misfires, foot to the floor and no acceleration or climb in revs (engine bogs down).

Fuel economy and response when warm are about the same as they've ever been - makes sense, given that this is only a cold start problem.

I've run an OBD-II scan on it: no codes are stored.

The 'cylinder #3 misfire' recall common to 2000s has been performed per the VIP report.

Searching suggests the IAC and/or throttle body could do with a cleaning, which sounds like a reasonable first step. Having killed a TPS on a different XJ before this doesn't feel the same, mainly because the problem only happens when cold - dead TPSes are noticeable all the time in my experience, so I'm loath to suspect it.

Is there anything I may have missed? Anyone else who's dealt with this on a 2000 have any words of advice, specifically on the cleaning? I'm getting ready to make a Kragen run to deal with this, so advice would be most appreciated.

Click to expand...

What I would do is pull the throttle body and give it a good cleaning on the bench, once it is squeaky clean and reassembled back on the motor I'd do a carbon cleaning, either GM top engine cleaner or sea foam, both poured thru the throttle body as per the instructions or thru vacum using one of the plugged vacum lines on the intake manifold and a hose. Once you have done that I'd take it and run the heck out of it on the road, some hard acceleration to get that engine to really fire up, high revs. If the jeep is used constantly in heavy slow traffic and is never rung out you will get carbon build up.