Popping Exhaust/Backfire and stalling while offroading

[chevychic]

Hey all,

Been driving my truck again for the past week. It's got a brand new front-end on it and new tires on the rear.
It's been sitting for about a year now and it definitely needs a tuneup.

Some of you may remember that a little over a year ago, my 2nd tranny blew out so I had the original tranny and t-case rebuilt and the torque converter replaced. After I got the truck back I noticed that I'd get a popping/backfire out the exhaust under acceleration. It was usually under medium to heavy acceleration and would happen the worst just before the tranny shifted. After shift, the sound would go away. I also have what sounds like an exhaust leak under normal driving.
This weekend I plan to take a look at the plugs...the wires are relatively new...maybe 10,000 miles old, as well as the dizzy/caps/rotor/etc....I'll check them anyways since with all this moisture we've been having here in Oregon (surprised we're not underwater by now) and sitting for about a year, I'm thinking it's likely my cap and rotor need to be replaced. I'm also going to check my timing. I really don't see why my idle mix would be off as it was fine before and no one has messed with it that I'm aware of.
Is there anything else I should pay special attention to to locate the cause of the popping?
Is it possible that a different stall torque converter create this problem?
Or could my exhaust leak create this?

About the stalling while offroad....it's usually when I just tear through the bumps and ruts without taking it nice and easy...who wants to go nice and easy when you're playing in the mud anyways??....After going over about 3 - 5 good bumps/ruts, it'll stall out...my guess is the float in my carb is too high so gas is sloshing out the top of the carb...this is indicated by the wetness and gas smell around the carb and manifold when I get out and check it...but will this cause it to stall since there should be enough gas in the bowl to keep the truck going for a little bit further, even if it's not much?
We're still dealing with a Quadrajet rebuilt 2 years or so.

Other than that, it's SO nice to be driving the beast again!!!

[Russell]

Hey! Welcome back! Been a long time since I've seen a post from you

First off, with the popping, I'd be thinking not enough timing in the upper end. Maybe check to make sure that both your vaccum, and mechanical advance are working correctly. A lean condition in the top end could also cause popping when you let off the gas. EGR could also cause issues similar to that. Actually, there are a lot of things that could cause popping, LOL

And as far as the stalling out, I'd say thats typical of a q-jet offroad

[carrzy4]

I had that before with a truck i bought, for me, i found out the sprak plugs were ****ty and some were crossed, itran, but felt underpowered and popped and banged.

[chevychic]

Thanks Russell..how's the truck?

No popping when I let off the gas. Mechanical and vaccum advance were working when I installed the new dist. I'll check those if everything else checks out. No EGR...all emissions crap is gone.

Carrzy4~ If the wires were crossed, wouldn't I be getting a miss at idle and under normal acceleration?...I'll check though just to be sure.

[Russell]

Truck is still not running, just like when you left, lol

Its a tuned port injected 4x4 now though, so I suppose I have gotten at least something done

If you're timing is good, and you've got no emissions systems, then that leaves either a valve out of adjustment, or a fuel system issue. Unless of course that exhaust leak is causing the popping by introducing fresh air into the exhaust stream, mixed with a rich condition, causing the fuel in the leaky pipe to pop when the exhaust is hottest at higher RPMs under heavy load...

[see ten]

I had an old Jeep CJ that would run perfect until you went off road. While off roading and for some time after returning to the pavement she would not idle and backfire and pop when you backed out of the gas. I dropped the gas tank to change the sending unit and found I had 2-3 gallons of muddy water in the tank. It ran fine going down the road but when the tank was sloshed around (off road) the water was being picked up. Once I got all the water out she was good to go.

[swervin ervin]

Hey Heather. Long time no see.

Russell, a Q-jet is a great off road carb and I doubt very seriously it is the cause unless it might be a plugged fuel filter or something. No way the float is off unless someone sneaked and moved it while not being drove. It worked perfectly the last time she drove it and I don't see why it would have changed.

Think of things that would have changed with the truck just sitting. Think strongly of water/moisture since it's been raining a lot. Moisture could have very well gotten into the tank or carb. I wouldn't touch the Q-jet until every thing else has been addressed, well maybe change the filter at most. Most folks will jump on the carb first thing and it's usually not the problem.

[Bishops Trucks]

Heather,
I just had the same popping problem with my truck which drove me crazy. I changed the plugs,cap, rotor,and wires and it was fine for about 10 miles then it started again. After scratching my head for a while wondering why one of my plugs were redish in color I pulled the vacumn line from the trans to the carb off the carb and found tranny fluid in the port. That was fouling a plug. You should check your modulator valve to see if they changed that. It can cause that type of problem. Just a thought.

[chevychic]

Originally Posted by swervin ervin

Hey Heather. Long time no see.

No way the float is off unless someone sneaked and moved it while not being drove. It worked perfectly the last time she drove it and I don't see why it would have changed.

Hey Mike...I've been wondering how you've been doing....

That someone could be yours truly....The last time I wheeled my truck was about a year and a half ago just before life went all wacky. Got seperated, divorced, moved 3 or 4 times and took on the full time care of my daughter, since my ex moved to Seattle with his new family.
When I last wheeled it, it did it then, but with everything going on, I didn't care about fixing it nor did I have the time. I hadn't wheeled it much since the carb rebuild, what with the downtime while the tranny was being rebuilt. So it's very possible that during the carb rebuild, I set my float high. But the only time I see any indication is when I'm wheeling and I hit enough bumps to get the sloshing action going. But what puzzles me is that I wouldn't expect enough to get sloshed out to stall the truck immediately....although I guess it's possible. I'll pull the top of the carb off and check....all my books are packed away still...what is the recommended height?

[crazyred]

Hey could it be that when you are going over all the bumps and ruts, the knock sensor is miss reading and picking up a knock from the crazy vibrations …. That would cause retarded timing and a miss here and there … maybe enough to stall the engine ….just a thought…. correct me if I am wrong

[chevychic]

Originally Posted by Bishops Trucks

Heather,
I just had the same popping problem with my truck which drove me crazy. I changed the plugs,cap, rotor,and wires and it was fine for about 10 miles then it started again. After scratching my head for a while wondering why one of my plugs were redish in color I pulled the vacumn line from the trans to the carb off the carb and found tranny fluid in the port. That was fouling a plug. You should check your modulator valve to see if they changed that. It can cause that type of problem. Just a thought.

I don't think it could be a modulator valve. I have a 700r4 and as far as I know, it's not equipped with a modulator valve. The detent/tv cable tells it when to shift. Please correct me if I'm wrong.

[Russell]

You're correct with the TV cable

Mike, I've never personally wheeled with a q-jet, but lots of guys on CK5 complain about them regularly when you're off camber, or going hard in a bumpy situation (such as through a mud pit, lol)

Well, I guess I can't say I've never wheeled, I did go through a mud pit we created at the school once, and my truck did the same thing, bouncing around like crazy in the middle of the pit, and she stalled out on me,

[Bishops Trucks]

Heather,
I didn't realize what year you were talking about but you are correct. Mine is a '71 K10. Demon and Edelbrock make carbs just for 4X4's that don't loose fuel at steep inclines. Check with Summit Racing. Good Luck with this issue.
Jim.

[chevychic]

Thanks for the help guys.

After reading the title I put on this thread, I thought I should clarify. The popping/backfire isn't while wheeling...well it would be if I had gone lately. The stalling is always while wheeling.

[chops333]

cam?

[79BIG10]

Hey Heather been a long time. I need to do some wheelin like you when I get the Blazer up and going better. On the stalling I'm thinking timing more than anything else. Like Swervin said it's probably not the carb. With the stalling it's got me thinking maybe a vacuum leak? I know it's not all the time but it's the only thing I can think of along with the timing causing the popping/backfiring.

[chevychic]

Originally Posted by 79BIG10

Hey Heather been a long time. I need to do some wheelin like you when I get the Blazer up and going better. On the stalling I'm thinking timing more than anything else. Like Swervin said it's probably not the carb. With the stalling it's got me thinking maybe a vacuum leak? I know it's not all the time but it's the only thing I can think of along with the timing causing the popping/backfiring.

Hey Brandon...how've you been??

That would make sense. But there is strong evidence of gas sloshing out the carb as it get's very wet with gas and has a very strong gas smell when it stalls.
I'll be checking the timing this weekend and will probably be taking it out to play. We'll see if it still stalls after I check the timing. Generally set between 10 - 14 btdc if I remember right?

[79BIG10]

Originally Posted by chevychic

Hey Brandon...how've you been??

That would make sense. But there is strong evidence of gas sloshing out the carb as it get's very wet with gas and has a very strong gas smell when it stalls.
I'll be checking the timing this weekend and will probably be taking it out to play. We'll see if it still stalls after I check the timing. Generally set between 10 - 14 btdc if I remember right?

Been doing good still with the same gf and the weight loss.

Right timing should be about 10-12. 14 would be kinda high. 8 seems a bit low for some but if it pings then lower. If it's sloshing it may be the float it set a bit high for off roading. With the angles that you may be putting it through it may be coming out a bit above the gasket and leaking out. If it leaks all the time like on the street driving then I can almost bet it's a float issue. Same thing happened to my Edelbrock 1406 with the floats set too low.