Exhaust popping

[chicklin]

Originally Posted by LONGHAIR

Popping in the exhaust can also be caused by a leak in the exhaust system. A leak up-stream can allow fresh air to be sucked in, especially during decelleration, which can cause the popping

Cool, I'll look around. The cat and muffler have been replaced, but everything in front of that is original (at least since I bought it). The spitting or popping is mostly on acceleration and under load, but I'll see if I can find any leaks.

[hotrodlover]

Might check your distributor to see if it is tight. I might turn just alittle and throw every thing out we had a 73 suburban that was doing about the same

[Rollie396]

Have you checked your plugs?It may narrow the problem down to one cylinder.I'd be looking for one or more sooty plugs.You could also pull one v.c at a time and run it for a little bit looking for one or more rockers not moving as much as the others to rule out a bad cam.

[chicklin]

Originally Posted by Rollie396

Have you checked your plugs?It may narrow the problem down to one cylinder.I'd be looking for one or more sooty plugs.You could also pull one v.c at a time and run it for a little bit looking for one or more rockers not moving as much as the others to rule out a bad cam.

Checked the plugs twice, but it couldn't hurt to do again. Will probably try watching the valves. That sounds like a good next step.

[pig rig]

if its poping like a back fire through the exhaust its in your valve train like burt valves or your rocker adjustment is to loose witch could be your cam going away

and if you have a plug thats not burning fuel, once the fuel makes its way to the exhaust manifold it ignights the fuel mix and that will give you that poping sound
open up your gap on your plugs and see if it helps you can also use a spray bottle of water and spray your exhaust manifold at the port and see if one is burning colder then the others

food for thought
back fire through the intake likely ignition system
backfire through exhaust likely valves
new spark plugs dont mean their always good

hope this helps with figuring it out

[chicklin]

Thanks. I stuck the EGR back on because I was getting pinging and that seems to have gone away. So, now, I really need to try it out with the valves having been adjusted and with the EGR back on.

[68Timber]

Several others have mentioned the cam, I'm wondering if it's wiped a lobe myself. Just pull the valve covers and remove power to the HEI so it won't start. Have someone turn it over while you watch the rockers and see if you notice a lazy one.

Also, don't rule out the carb just yet. If you know of one you can borrow off a good running truck, bolt it on and try it out.

One other thing you can check by hand or with an infrared thermometer (if you have one or can borrow one/rent one) would be to start the engine dead cold and check the exhaust port temps either by hand or by infrared thermometer and see if you have one not warming up at the same rate of the others.

[chicklin]

Originally Posted by BRUISER

Several others have mentioned the cam, I'm wondering if it's wiped a lobe myself. Just pull the valve covers and remove power to the HEI so it won't start. Have someone turn it over while you watch the rockers and see if you notice a lazy one.

Yeah, I probably shouldv'e thought of that when I had the covers off

Originally Posted by BRUISER

Also, don't rule out the carb just yet. If you know of one you can borrow off a good running truck, bolt it on and try it out.

Also a good idea. I have my old carb still. The choke was fried, but it still ran.

Originally Posted by BRUISER

One other thing you can check by hand or with an infrared thermometer (if you have one or can borrow one/rent one) would be to start the engine dead cold and check the exhaust port temps either by hand or by infrared thermometer and see if you have one not warming up at the same rate of the others.

Good thinking, never thought of that.

[tbirdman88]

Sounds like the same problem i had on a small block 400, Under hard acceleration it would pop through the exhaust. It had a bad cam,3 round off exhaust lobes. A new cam and lifters fixed the problem. I also did what was suggested earlier to verify. Take valve covers off and watch rocker arms while rotating engine, The bad ones will not move as much.

Hope this helps
87shortcrewcab

[shrtbx]

Im not an expert like others on here so i can only speak from experience. I would double check the plugs as mentioned earlier. Thats what solved my issue with the popping like yours.

[jared87350]

try checking the deverter valve diaphram if equiped. if defective, replace it, fixed my popping issue.

[motornut]

had this issue is a older 350 someone put a nylon gear (found in 305s) in there and it had a crack......didn't see if you had an air pump.......no leaks and working?

[chicklin]

Originally Posted by motornut

had this issue is a older 350 someone put a nylon gear (found in 305s) in there and it had a crack......didn't see if you had an air pump.......no leaks and working?

I do have an air pump and as far as I know it's working. Where's the diverter valve and how do I check it? I see a little canister mounted front-left (passenger side) that the AIR system is hooked to, is that it?

[chicklin]

Originally Posted by tbirdman88

Sounds like the same problem i had on a small block 400, Under hard acceleration it would pop through the exhaust. It had a bad cam,3 round off exhaust lobes. A new cam and lifters fixed the problem. I also did what was suggested earlier to verify. Take valve covers off and watch rocker arms while rotating engine, The bad ones will not move as much.

Hope this helps
87shortcrewcab

That's starting to sound more and more likely at this point. A couple questions, though. Would that make the fuel mileage horrible (I'm getting around 8mpg)? And, my issue is only happening under load (like going up a hill), would that be consistent with a worn cam?

[jared87350]

Originally Posted by chicklin

I do have an air pump and as far as I know it's working. Where's the diverter valve and how do I check it? I see a little canister mounted front-left (passenger side) that the AIR system is hooked to, is that it?

the deverter valve is just above the air pump. its job is to divert air flow to your air intake on deceleration and heavy exceleration.and sends air flow to the exaust while at cruse and idle.

you should have three hoses leading from it. one to the exaust,one to the intake and one to the air pump.
checking it is not bad. take a vacume reading at at max apply it to the valve diaphram and see if you are losing
vacume. if you lose vacume you have a bad valve.make sure all other air leakes in the exaust are taken care of before replacing
the valve.

[chicklin]

Originally Posted by jared87350

the deverter valve is just above the air pump. its job is to divert air flow to your air intake on deceleration and heavy exceleration.and sends air flow to the exaust while at cruse and idle.

Okay, yeah, that's the one I'm thinking of. So, is there a test to see if it's good?

[jared87350]

checking it is not bad. take a vacume reading at at max apply it to the valve diaphram and see if you are losing
vacume. if you lose vacume you have a bad valve.make sure all other air leakes in the exaust are taken care of before replacing
the valve.

[chicklin]

Originally Posted by jared87350

checking it is not bad. take a vacume reading at at max apply it to the valve diaphram and see if you are losing
vacume. if you lose vacume you have a bad valve.make sure all other air leakes in the exaust are taken care of before replacing
the valve.

Thanks. Is this the right part if it's bad (non-California):



What about the check valve that's near there? Could it cause similar problems?

[jared87350]

Originally Posted by chicklin

Thanks. Is this the right part if it's bad (non-California):



What about the check valve that's near there? Could it cause similar problems?

looks to be the right part CA is a little diffrent.
its a good idea to change the check valve with the deverter valve
as good practice.

all the check valve dose is to stop emission gases from passing back through the air hose.
if it was bad it would cause a backpressure problem

[3r!c84]

where is that valve located?

[chicklin]

Originally Posted by 3r!c84

where is that valve located?

I'll have to go look, but I believe it's on the front of the motor, kind of between the water pump and air pump. Somewhere in there.

[3r!c84]

i dont got a airpump

[chicklin]

Originally Posted by 3r!c84

i dont got a airpump

Then you don't have that valve Lucky you.

[motornut]

yer lucky with no air pump......two of mine have it 85 from .texas and 87 from .ca both the same with it