Backfiring and stalling coming to a stop

[Timlt1]

Could a vacuum leak cause this? I know my brake booster is sucking air but it was running fine till today. I know a vacuum leak will make it run like shit but could it also cause this? Cap and rotor, wires, and plugs where changed 2 weeks ago and my timing is on point. My booster will be changed tomorrow to get rid of the leak but what lets could it be?

 

[BLUEGRASS Yj]

before you worry about changing out your break booster grab a can of carb cleaner, start your motor and play seek and find with the vac lines to see if when you spray the carb cleaner on them if they are cracked or leaking. If they are then with the carb cleaner you will hear your engine rev. Also check to see if your air filter is clean and you are getting enough. The same thing happened to me after mudding and clogged up my filter

 

[steady.foot]

If your brake booster is leaking, You will see a diference after you get it repaired.

 

[69jeepcj]

what vehichle and engine is this. stalling is usually vac leak, back fire is usually carb out of adjustment, blown power valve in carb or timing I believe.

 

[superj]

and a leaky booster can usually be noticed at idle when you step on the pedal because your idle will raise a bit

 

[Timlt1]

It's a 87 YJ. The booster is leaking so bad that I can hear it in the cab. I'm going to try the carb cleaner trick and see what happened. I will also change the air filter and I'll let you guys know.

Thanks
Tim

 

[Timlt1]

Ok so the carb cleaner did nothing. She will sit at idle as long as the choke is on but if I kill the choke it will stall. Also when the choke is set and I remove the air cleaner it will stall. This thing is driving me nuts.

 

[superj]

check all your intake to block bolts and carb to intake bolts. you have a heck of a vacuum leak somewhere. actually, pull your brake booster line and plug the nipple on the intake while the jeep is off and then start your jeep and see if still stalls when you move the choke or pull the air cleaner. then you can see for sure if its the brake booster doing it or if you have other vacuum issues also

got a vacuum gauge? they are like 20 or 25 bucks at the autoparts place. will help you locate your trouble too

 

[Timlt1]

Bypassed the booster and she still runs like shit.

 

[Timlt1]

It's pretty sad that I've been a diesel mechanic for 15yrs and I don't know **** about these older gas engines.

 

[superj]

so if you pulled hte booster and it still runs bad, its in another vacuum system. pull all vacuum lines and plug the nipples and see if it still runs bad.

also, what carb do you got on that jeep?

 

[Timlt1]

I'm not sure what carb it is but I think it's the stock one from 87 4.2l. Just hoping I can find this prob and fix it before Sunday so I can take my wife out on some trails.

 

[superj]

the stock is a carter with an electrical harness plugged into it on the back side

 

[Timlt1]

Yep that's the one. Are they any good?

 

[Timlt1]

Ok so my 20min ride home from work tonight it didn't stall or backfire once. Wtf?

 

[69jeepcj]

Vac leak somewhere!! You probably sealed the vac leak temporarily while trying to find it, (moved a vac line just right, smeared some grease on a cracked hose..etc.) Finding vac leaks can be a nightmare, I would see what sizes you need and replace ALL vac hoses and see what happens.

 

[Gennybro]

could possibly be that you need a new distribrater, a friend of mine had a ford f150. was haveing problems with it backfireing and running lousey. Ended up being the distribriter, Put a new one in,problem fixed.

 

[69jeepcj]

That is true, but wouldnt his timing wonder around. He said his timing is dead on. Ive been lucky enough to have never delt with a dist with a worn shaft so I couldnt say from experience.

 

[Timlt1]

Yeah I'm going to auto zone after work tomorrow and I'm getting a **** load of vac hose and replacing it all. The ****ty part is that all the vac hose looks somewhat new. I was also thinking maybe the carb was on its way out like something was getting stuck.

 

[Gennybro]

That is true, but wouldnt his timing wonder around. He said his timing is dead on. Ive been lucky enough to have never delt with a dist with a worn shaft so I couldnt say from experience.

What my friend had told me that on his distributor,part of the ignition module is built into the distributor. With that going bad , it would have the same result as the timeing wandering a little. Even though looking at your rotor everything would look as it should, the ignition module screws it up slightly when it has gone bad. Now these are not words from a professional, just something that happened to him with his vechicle.