Back Firing after Oil Change

[UNL1MTD]

I'm thinking I did a big opps. I haven't had an 'old' engine yet. There was a bunch of ticking from what I thought were lifters from the engine.So I decided to treat it to Castrol High Mileage and also some Slick 50 additive. Anyways before the oil change I never noticed a backfire, not to say it didn't happen, but I never noticed it. I only got 1 mile on the truck, maybe 25 minutes of run time.

 

Today I changed the Oil, added the Slick 50, and changed the Oil filter. I fired her up after the oil change and let it idle for 5 minutes, nothing new. Got on th gas and she back fired. Just went out after an hour and now the MJ will start fine, but even at idle it will back fire occassionally. When I get on the gas it will do it just about every time. Additionally the Orange Up pointed arrow lights up on the dash. Not sure if this is signaling a misfire or a sensor going bad, but it flashes (then goes out) right after the back fire.

 

Any help is appreciated, I'm thinking I could either replace the plugs, wires, cap, rotor tomorrow (since I was going to do it anyway) or just change the oil again back to 10 w 30, sans the Slick 50 additive. My guess is the Additive isn't playing well with a sensor, but who knows it could just be the plugs/wires/cap/rotor. The exhaust on this truck is stock to the cat, then it's a glass pack with a turn down before the axle. The cat doesn't rattle, not sure if this exhaust is contributing to the problem or not.

 

Any ideas?

[JeepcoMJ]

the orange "up" light is generally the Up-shift light if i'm not mistaken. and general rule of thumb, if it worked fine before you did something to it, you did something to it wrong. now, i'm not sure what it would be though...is it idling very high (more than 1100 RPM at idle...should be about 900 to 950). that may be why the upshift is coming on if it's high. other than that, i can't think why it would backfire

[UNL1MTD]

I don't have a tach, so no idea what the exact idle is. But it did idle really high this last time out and immediately back fired after it did that. It only did that once, generally its idling fine. Well that would make sense about the up shift light coming on if I had ti in neutral and starting reving it.

[Eagle]

How's your gas? If the stuff in the tank is old, it can cause backfiring.

 

By the way, I hope you didn't put Slik 50 in with the new oil. That stuff is DEATH IN A CAN. All it does is clog up the oil passages.

[UNL1MTD]

How's your gas? If the stuff in the tank is old, it can cause backfiring.

 

By the way, I hope you didn't put Slik 50 in with the new oil. That stuff is DEATH IN A CAN. All it does is clog up the oil passages.

 

The gas is low, in the red, and the PO never mentioned filling the tank while he owned it, so I'm guessing the gas is 1.5 years old. Interesting opinion on the slik 50, it is in with the new oil. I followed their directions and just used it as a 1 quart replacement. Basically a guy at work was telling me about it and how it would quiet everything down, i bite on it and bought it, rough to swallow at 15 bucks, but ohwell. Live and learn. New oil filter too you think?

[Stumpy]

all/everything an engine needs is clean oil. additives are just a way to make money, some manufactures will void the warranty if additives are found in a bad engine.

[UNL1MTD]

so is there anyway that the additive or changing the oil could cause the backfire? The old gas is a valid suggestion. What are some other typical reasons engines backfire?

[Eagle]

so is there anyway that the additive or changing the oil could cause the backfire? The old gas is a valid suggestion. What are some other typical reasons engines backfire?

Typically, an oil change should not induce a backfire. Old gas could. If you disturbed a spark plug wire or two when changing the oil that might affect it. Firing order could affect it ... the correct order should be 1-5-3-6-2-4. A cracked distributor cap can cause a backfire, so if you slipped and clobbered the cap with a wrench that might be something to check.

[UNL1MTD]

Well, i put in 2 gallons of new gas. Idled a lot better, but still backfired at high rpms. I changed out the plugs, wires, cap, rotor, using di-electric grease on the connections. It seemed to help out, drove it around the neighbor a bunch and only backfired 3 times, each when letting off of first gear at a higher rpm. I think she might just need to be driven a while and it might stop when she passes all the old gas. :D I haven't changed the oil again. I plan to run this for 500 -750 miles or until 2 months pass.

 

On a side note, my plugs and wires weren't in the best shape. Alls plugs had carbon deposits and the gapping was worn down to .45 on most. I was expecting this. Plugs 4 and 5 had oil on them. Each plug was barely finger tight in the block. Normally I got to muscle up on a 3/8s to break a plug, but all of these easily spun out of the block. There also was oil in the distributor. I cleaned it out with WD40. I have a valve cover leak, which is pretty much 360 degrees around. Could oil leaking from the valve cover possible get into the distributor and onto the plugs? or am I looking at a bigger problem?

 

I went out and got a cork gasket for the valve cover, but haven't pulled it yet. This will be my first time, any pointers. I know I'm going to see some sludge on things under the cover, what can I do to clean it without dissembling the engine?

[JeepcoMJ]

put a fuel addative in it...injector cleaner or anything really. then run it basically dry and add new fuel, preferably high octane. it sounds like you've buttoned up the mechanical issues and now you simply need to get that old gunky gas outta the thing.