vegaslightsss

Hi All, Not a Newbie,but starting to feel like one. Working on a 98 4.0 XJ "Crate Motor" from Dealer with 35k on it. Jeep Overheated,Head Gasket blown.Driven for several months like that with Straight Water Only in Cooling System ,Radiator rusted and small leak.Missing the Fan Shroud,Bad Maintenance,Sludge SO thick by valve springs you could pick up a chunk with a screw drive 1/2" thick with No Exaggeration,OH YEAH,Add Vegas Summer Heat to the equation.
OK-Steam Cleaned and degreased head ,took to Machine shop ,head was surfaced by twelve thousands. replaced head with SD Severe Duty Gasket from Felpro ,Surface and rest of motor prep was flawless.Replaced Cap,Rotor,Wires,and Plugs With BOSCH Copper+ Plugs (Also tried Champion 12YC Copper Plugs)Cleaned Injectors,replaced all "O"Rings on Both Ends.Jeep Runs AWESOME,except at IDLE,tried everything I can think of getting 1+3 Multiple Misfire Code. Swapped Injectors from 1+3 with 2+4 to see if Injectors were causing the Issue.Replaced 2 Injector Connector Leads with NEW Ones. Replaced IAC & TPS with Autozone Parts.Radiator was a custom 4 row copper tank,nice unit,had it rodded & repaired. Seafoamed the throttle Body (produced massive white smoke cloud when revved following the application)No Vacuum Leaks. Starting to think there is a crack in the head or something. There is nothing on the plugs like antifreeze. Going to try the Mopar Decarbonizer stuff and clean the cam and crank sensors tomorrow..Anybody ever run across this DTC (Multiple Misfire on 1+3) where it runs perfect except at idle? If its in gear, it idles so roughly that you have to put it in Neutral where it runs perfectly,AS LONG AS THERE IS NO LOAD ON IT, (and its not fuel pressure,this 6 cylinder gets after it).The second you gas it its clean from 1000 RPMs to Wide Open. Its Making me nuts Thanks,Vegas

mikesignal

does temperature affect misfire?

vegaslightsss

No Difference Hot or Cold,A/C on or off. It's 104+ Today. Not sure If I mentioned I checked the ground straps from the Motor to the firewall at the back of the head on drivers side as well as the one on the other side by the sensors. Pulled the plugs on those cylinders they look fine,good color,no sign of coolant,fuel,or oil fouling,this thing is bugging me out out .Compression is good and even across all cylinders. Guess I will pull the valve cover and do the paint marker or scratch thing to make sure the valves are rotating. It about has to be a carbon in those valve seats. I have also seen a few posts about PCM or ECM going bad. I cleaned the IAC which was horrible,I hate spending 70.00 without knowing its bad for sure,I am not getting that error on scasn codes.Thanks for Chiming in,I appreciate it,Vegas

97jeepxj40

I could be way off the mark here but I had those symptoms with a bad o2 sensor. Could that be a possibility? Could be worth unplugging for a quick test

tjwalker

Carbon is a possibility. I'd consider trying a treatment of Mopar Combustion Chamber Cleaner (CCC). It's a creeping foam that really gets into the carbon. Ford and Chevy have basically the same stuff I think. Worth a shot for about fifteen bucks for two cans, which is probably what you'll need. Follow the directions exactly as you read them.

The IAC is absolutely not high on my suspect list; not for specific misfires.

vegaslightsss

Just got off work, on my way to Dealer for 2 cans of De-carbon spray. I will follow instructions. Would it not be better to pull the fuel rail and put it right in the Injector hole. Is Seafoam the same or different? Also I had the Champion Copper Plugs in,the R12NYC or whatever for about 150 miles. I changed them over to the Bosch Copper Core+ because several People on the Forums said that Champion Copper Plugs cause problems like this. I know Platinum are not recommended,

vegaslightsss

Ok,The Stuff is in the throttle body. It's amazing how much of that stuff they can cram into one of those 13 oz. cans. Crossing my Fingers. The only other variable from not throwing the Misfire codes is the Bosch Copper + Plugs.Everything is new with the exception of the actual Injectors. Swapped Injector Positions & replaced the actual Pigtail connectors. New Cap,Rotor,Wires,Plugs,Cleaned out the throttle body and IAC / TPS sensors. New Severe duty Head Gasket (Machine Shop took 12 Thousands to resurface for head warp compensation)
Just to refresh,this motor was driving after head gasket was toast for several months ,I am attempting to attach a pic of the sludge,custom metal 4 row radiator was blown up like a balloon (had it rodded and repaired) its amazing how durable these 4.0 are after this kind of abuse. I just put a new engine in my 3.7 Liberty which is a V-6 Aluminum Heads on Cast Iron Block which are notorious for dropping the #2 Steel Valve seats out of the aluminum Heads and once overheated you are in for more problems that you can imagine...

belvedere

I had the same misfire on my '98 - only missed at idle, on cyl #1. After all other possibilities were eliminated, I ran the Mopar CCC and replaced the valve springs on #1, per the TSB. Problem solved.

vegaslightsss

Ran the CCC through it ,Let is sit 3.5 hours ,did the Low gear "Blow out" it does seem to have more power,blew out quite a cloud of white oil smoke which dissipated and cleared up after 4 or 5 of the low gear runs. Hasn't thrown a Trouble Code yet but I am sure one is coming. I am going to put a few miles on it and check the plugs. If you noticed the pic I posted of the sludge built up,there were no doubt some nasty deposits in the seats. Did you change your springs out with the head on the engine or take it off? Thanks Everyone Again,Vegas

tjwalker

Keep us posted. I'm not a fan of Bosch plugs. Some with the 4.0 can run them with no problems, but I've seen isolated cases of confirmed misfires with them.

For your vintage, I recommend Champion copper plugs, changed every 30k. You'll find many others that will echo this sentiment.

belvedere

I changed springs with the head on the engine. Used the old "rope in the cyl" trick to hold the valves. Maybe you won't need to change yours, though. Try tj's suggestion of Champion (or NGK) coppers.

vegaslightsss

Sorry I havent been back. Did some High RPM runs to blow the CCC stuff out. Changed to Brand New Champion OEM "RC12YC" Copper Plugs from the Bosch Copper+,Cleaned out IAC (pretty dirty after CCC process) .Jeep had more power but still pretty rough idle. Got through the Nevada Smog Check finally,It threw another code while the "PASS" Certificate was printing. I dont know what that code was yet as this is someone elses vehicle. I have owned 11 Cherokees and Currently on my 1st Liberty (Cherokee Worldwide?). Installed a Rebuilt 3.7 VIN "K" motor after valve seat and head gasket Hell at 130k on the way to Vegas from Cal. with it. I have 5k on it now with no complaints other than Gas Mileage. I told the 98 XJ owner to replace the IAC ,as I accidently pulled it apart (2 parts) when I was desludging it. After driving it in Vegas heat with a hole in the radiator and a seriously Blown head gasket for 6 months I am surprised it runs at all. Could have had water in the cat for a while as the 3/4 cylinders did. Thanks,Vegas