Backfiring YJ

[Bull]

I bought a 89 YJ 4.2L 5-speed a few months back and am still trying to figure out what the last owner(s) have done to modify it. The problem I am having is similar to that of the question about losing power going uphill. The only difference is that mine doesn't have to be a long hill, a short hill will cause me to have a significant loss of power and on occasion it will backfire. When the engine backfires there is a rich fuel smell in the cab (leaking through the shifter plate). I was wondering if this might be the catalytic converter being clogged or is this more of a timing problem? I have 96k on the engine and there have been some modifications such as a SuperCoil, so I am not sure if the last owner was running some high octane juice in it with an advanced timing or what. Any help would be greatly appreciated.

[LeadFoot]

You need to fix the backfiring ASAP, as it is no good for the carb. When I "modifyed" my exhaust pollution, one of the mods included hacking the return pipe off the cat. Now, it did rumble like a V-8, but did backfire. Either your carb is mis-adjusted, or you have a hole in the exhaust somewhere. What carb do you have? I have the aftermarket Weber. Note how few hoses there are, hardly any.

http://community.webshots.com/photo/61655484/62730821fzmMUJ

[Bull]

Running a remanufactured Carter right now. (pretty much was a replacement for original). I know that it gets worse when the air filter starts getting dirty. Guess I'm gonna have to take it down the street to the shop. Thanx for the help.

[Bull]

BTW... how well does it pull that big trailer? I was going to put a hitch on mine but not sure on towing capacity and handling while towing.

[89wranglin]

Bull, my 89 5spd 4.2L pulls my jon boat, motor and cargo just fine. Total weight around 1000lbs.

Leadfoot, any emissions requirements in Weirton? I'd like to install the Weber, but think it may fail emissions inspections.



:USA:

[Bull]

OK I may have the problem resolved. I was performing my pretrip overhaul (also 100k over haul) and when I pulled the plugs they were fouled out pretty bad on all cylinders except #3. They had a carbon build up covering most, if not all of the gap. I also noticed that the plug wires were different so I changed them out with new ones and got a new cap and rotor also. BTW if you have an 89 258 (4.2L) and the stock rotor and cap don't fit, tell the parts store that you need a 86 Ford F150 4.9L I-6 Cap and rotor, that was what fit mine (another great ALL Motor Company suprise, FOMOCO distributor). Also put a new air filter and changed the oil. I am going to take a road trip down to Florida and the whole drive in on interstate, so I should find out if that took care of the problem or not. I will keep yall informed with the news in case anyone else comes up with this same problem.

[LeadFoot]

Bull: I would NOT tow a 26' camper like I did! It was purely to get it into position for our full size van to hook up to (350 engine). The camper empty weighs around #5000! I used 4-low and first gear, and after moving, the little four banger required no throttle to keep from stalling out! We have a Hidden Hitch on it, bolted to the rear crossmemeber and the frame. If the Jeep can pull it, the hitch can also. The poundage rating is just a safety precaution so people don't try things you shoudlnt even attempt to pull. 2" reciever.


89wranglin - No emission crap in WV. We do however have annual inspections (Headlights, brakes, turn signals, etc). In 4wd's magazine, they specify the Weber carb as off-road only; probably because it dumps the use of the pollution control and the stock compter. Haven't had anything wrong with it, yet. <Knock on wood>

[Bull]

Ok I trhink that I got the problem fixed. I just took a trip down to Florida and I was concerned with only being able to travel at 55 mph (anything faster was causing the backfire). So I did a complete overhaul on the engine. I replaced the plugwires, distributor cap, rotor, plugs and air filter. Over the course of the 1500 miles I traveled, I experienced no engine related problems (only problem I had was a catastropic tire failure). The plug gap on 5 of the 6 plugs was completely covered with carbon and I am pretty sure that the problem was that the carbon was getting hot and leaving hot spots so when the fuel/air mixture came in, the hot spot ignited it. I think this should solve the problem. Thanx for the help.