What causes popping! and WHY

[ISX]

I keep reading about people whose trucks pop while they are all screwed up. My truck has never popped. I helped a guy one time who didn't have fuel getting to his injectors and when I finally tracked down the loose connection and it started, he revved it up a little and it popped for a second. I can't figure out why. Then other guys have issues with timing and it pops. What causes the popping! I want to get to the bottom of this in full detail because it seems to sometimes happen and sometimes not. Like I said, mine has never done it, so what causes it?

[Mopar1973Man]

Retarded timing?

[ISX]

Thats supposedly one thing that causes it. But I want to know what makes it pop. Mine didn't pop at 0* timing. Something causes these things to pop and I want to know what. I was thinking if the timing was even more retarded like 10* ATDC that the explosion might still be going when the exhaust valve opens and cause it to pop. But the truck I messed with when he revved it up ran perfect. It just popped that one time.

[rancherman]

where is it popping at? exaust?ok, I re read you last post, and I got my answer. I think you nailed it with the late timing... possible bad joint on the head pipe drawing in more O2 to flash the remaining charge?also, a crack in the exaust manifold will do it too! (draw in O2)

[Mopar1973Man]

Well between way late valve timing (loose valve lash), late ignition timing (mis-adjusted), and air in the fuel (longer to pop pressure) you could have some seriously wacky things go on.

[ISX]

This is a bigger mystery than I thought. I think everyone knows what things will make things run weird.. But what makes them pop?

[ISX]

This problem is running rampid on CF so I asked ykdave over there about it personally and he gave some insight that will provide some help. I had a hunch it was from fuel still burning after the exhaust opened but I thought it was a little far fetched, but he seemed to back it up.

Like you know, it could be many things! Low timing - results in late combustion and a buildup of fuel in the cylinder as it cannot burn completely when the flame from is chasing the piston down. if the flame is still burning (smoldering LOL) when the piston is coming up on the exhaust stroke you get a pop! Low fuel pressure or air in fuel - same end result bad injector - again, same end results. Poor atomization resulting in poor combustion and fuel buildup, as well as pop pressure effecting the injection event timing valve lash- too tight of valve lash can lead to valves not sealing 100% at higher rpm, as well as lash being too lose/tight effects valve timing to a small degree. and probably 6 billion other thinkgs that dont come to mind right away LOL

[rancherman]

when were they usually popping? ie: idle, cold engine, no load... fast idle, hot engine, under load...I can see if there was a bad injector, it's puking 'heavy' partially unburned exhaust into the manifold, where the heat from the healthy cylinders will go ahead and lite it. But I sure would think it'd have to be 'up to temp'.My 903 had a slight miss... and it actually had raw liquid fuel running past the v-bands..(on cold start) The V-8 uses quite the jungle jym to plumb the turbo... made it easy to figure out which cylinder flamed out. turned out to be a galled injector/bent pushrod. Thinking back, it was kinda popping too...a intermittant soft 'huff, puff, pop'.... But it had to be hot first... it's a little harder to pick up on a slight miss with a v8.. opposed to a 6!I assumed in my first reply to your op, 'backfire' was what you were trying to explain! I assumed wrong... again.

[ISX]

when were they usually popping? ie: idle, cold engine, no load... fast idle, hot engine, under load... I can see if there was a bad injector, it's puking 'heavy' partially unburned exhaust into the manifold, where the heat from the healthy cylinders will go ahead and lite it. But I sure would think it'd have to be 'up to temp'. My 903 had a slight miss... and it actually had raw liquid fuel running past the v-bands..(on cold start) The V-8 uses quite the jungle jym to plumb the turbo... made it easy to figure out which cylinder flamed out. turned out to be a galled injector/bent pushrod. Thinking back, it was kinda popping too...a intermittant soft 'huff, puff, pop'.... But it had to be hot first... it's a little harder to pick up on a slight miss with a v8.. opposed to a 6! I assumed in my first reply to your op, 'backfire' was what you were trying to explain! I assumed wrong... again.

Well these are CF guys so.....they pop when they are at WOT lol. Seems there is one over there every other post. I just started gawking back there over the last few days. Just can't believe they have such a problem with timing. Does make sense that if it were hotter then it would have enough heat to keep the combustion going into the exhaust phase.

[rancherman]

you ain't wrong on the continuing of 'burn' way after the ex valve opens!I worked on a a v8 perkins in a tractor... no muffler, just a straight pipe up out the hood. (no turbo either)under heavy load, at night, I had a orange/red plume extremely visible 4 foot above the stack..... and the stack itself was RED!!! turns out it was way late (1 tooth) on it's timing... a simple r and r had it running right. Joys of buying others hack jobs??Pop @ wot?? I give up. Sure would like a sound byte to hear just what they are describing...

[rancherman]

to me, this popping occurs about 1/2 of the way 'back into it'... right after a high speed spin down.

[Mopar1973Man]

Here is a run away Cummins...

My thoughts are excessive fuel that is unburnt in the exhaust stream that is being ignited by another exhaust port creating the pop. Other than that the exhaust stream should be technically exhaust gases (spent fuel) so if there popping in the exhaust stream then I would say excessive fuel or incomplete burning of fuel.

[rancherman]

I wonder if they checked for a pulse?

[ISX]

No that one sounded more like it had some other issue that was hindering fuel, clogged fuel filter, who knows. What I am talking about is actual popping like backfiring caused by the combustion still taking place when the exhaust valve opens, which means very retarded timing is a key culprit.

[AH64ID]

I am not 100% convinced it's only retarded timing, but that could be the disconnect between the CR and 12V world. But, on a CR the timing is retarded from the factory, to a low of -9.5° ATDC (not looking at less than 1000 rpms) and a high of 9.2°. This thread appears to be talking WOT and rpms, so 3,000 rpms and WOT on a CR is 8.0° of timing on the main event. The main event is 2005us long, or at 3,000 rpms, 35.8° of injection. That means the injector is open until 27.8° ATDC and then 14.4° later a post injection event starts, which is 4.5° long, so now at the end of fuel injection we are at 46.7° ATDC. That's at 3000 rpms. At 2000 rpms the injection stops at 29.5° ATDC, there is no post. The 5.9 CR's also have cam timing that opens the exhaust valve earlier than previous models. But all that OEM stuff is assuming a good complete combustion, and maybe that's the difference on the 12V's with pop is that it's not complete combustion?I know that some of the 03's get popping from too much timing, more of a stutter/pop than a pop out the tailpipe. Pop is also possible on the CR's from too low of a rail pressure, and that may lead back to what you are talking about. Generally too low of a rail pressure just exhibits HOT EGT's, but rarely a pop. Consider that same scenario above at 3,000 rpms. If the pressure is 1/2 of what it should be, 11.6K psi, then the end of all injection is at 64.2° ATDC, that's a LONG ways down the powerstroke. Also consider the 6.7, in factory form it has 2 late injection events designed to put raw fuel out the exhaust port and they don't pop. Is that because they are injected on the exhaust stroke?ISX, I know you have plaid with cam timing at what crank position does the exhaust valve crack?

[ISX]

Ok it was my theoretical explanation to why they popped based on nothing I can prove (CF people). In my video at 0* you sure didn't hear mine pop, it just petered out. I don't know if going to -10 or further would make it pop though and I didn't floor it so maybe if I did it would pop. I think it's evident all the guys who talk about them popping just hold it to the floor to see if the symptoms magically go away. My truck has never popped so I have no idea about the issue other than when I helped the one guy and while his truck was still purging a few air bubbles and he held it to the floor, it revved way up as it finally got the air out and popped a few times. I'll have to dig up the valve things you want. I know the exhaust valve opened way before BDC, like 20* or something.

[AH64ID]

It's defiantly interesting. I would think that if the timing were retarded enough to cause that late of a flame you couldn't rev that high on a single injection event motor. The only reason a CR can run such retarded timing is because of the pilot injection. At 2,000 rpms the WOT timing is -5.8°, and it's making at least 210/555 at the crank.

[ISX]

http://forum.mopar1973man.com/threads/3718-Actual-Degrees-of-Valve-Actuation 60* BBDC it opens... Why is it called BDC/TDC, Center of WHAT!

[AH64ID]

Why not call it TDC? The crank is at the center of the top semicircle for TDC, and BTC is the center of the bottom semicircle.

[Wild and Free]

You guys make these simple little B series way to complicated. Throw in timing for the old 855 cummins where you mechanicaly set injector timing and depending what series 855 it was and what it had for a cam ect you get into inner base circle and outer base circle timing settings. Then you have to shim the cam follower housings on the side of the block to get the base timing and get the cam followers shimmed correctly or the injector timing is not going to come in anywhere close.