pipe popping

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Ironmike

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I've had this issue since the end of summer and it's iritating the crap outta me.

When COLD, i have a popping from my left tailpipe. From around 2500 RPM up. I mostly goes away when the thing warms up. Mostly. It's annoying and embarassing when leaving cruises and such.

I've been thru everything and all I know is what is ISN'T. It isn't plugs, wires, valve adjustment...........I can't see , feel or hear an exhaust leak.
I need to get this resolved before moving on to other projects.

It's an IMM built 410 around 520 HP with a solid Comp cam, MSD ignition and Dougs headers. Holley 950.

The thing still runs....should I say HARD....so I'm stumped. I'm kinda thinking I got a sticking exhaust valve, but don't know.

Any thoughts from you guys really helps. Brian if your there please chime in!

Thanks guys!
 
Maybe just a lifter or valve sticking. They pop when the valve is burned but that doesn't normally go away when warmed up. How many miles on engine.
 
3900 miles and a few passes. I do run it a bit hard on the street sometimes. It's fun humiliating Mustangs.
 
well, yeah. Definitely 1 cylinder, and like I said, it pretty much goes away after she's warmed up. I can still hear it once in awhile, though. I'm thinking I might have to pull the head if I can't figure sumpin' else out.

It doesn't pop at idle(1250). And, I can't say for sure I hear it with open headers. Maybe just too loud to hear anything else.
 
I would check compression on that side cold ...I have seen a bad/burnt valve warm up and expand just enough to stop popping
 
Popping in the exhaust is the introduction of oxygen in the pipe where the exhaust is still hot enough to cause a secondary combustion. If it is a stuck valve and it calms down when heated up (this is not how sticking usually works) and doesn't get any worse when you adjust it you should send that valve to a metallurgist, because it's got something special goin' on in there.

So, headers or manifolds?

Left side is the side that hangs low on cheap headers, and provides a safe "dry docking" action against large bumps. Left side is also the hardest side to tighten the rear bolts. If you have power brakes, the whole area is hard to even look at. If you have power steering, that's the side where the steering box smacks the headers around (or where somebody had to smack em' with a hammer to make them fit). It is literally the perfect place to get an exhaust leak. If it's small enough that it doesn't happen at idle and it goes away after heating up, it's probably not big enough to actually feel or hear a puff out of, but as soon as you get some gas velocity over the crack, it does a little venturi effect and sucks in some air. Once the engine is up to temp, the gasket is heated up and the crack shuts.

I bet it's the exhaust gasket, because it's always the exhaust gasket. And it's always the exhaust gasket between 5/7 right where there's no good way to get in there.
 
IF you pulled a plug wire one by one would it rule out a burned exhaust valve? Sure you would get unburned gas into the exhaust but if the tone differed, you may find it a good diagnostic.
 
No cheap headers here. Dougs. No steering hitting either. And, no choke on a Holley 950HP.
I've been thinking burnt/cracked valve, too.............along with maybe some weird header gasket leak I can't find.
Also, I've never put a torque wrench on a sparkplug in my life and I ain't gonna start now.
I'm gonna have to figure it out soon cause I have other things that need attention. Moser axles, new driveshaft, etc.

Think I'll do a cold and hot compression check, then move on to pulling the header if need be. Can't think of anywhere else to look.
 
Do you have brakebooster?
Is the vacuumhose connected to the intake near an intake port, or just the carb/base?
Could be a possible leak there.
 
mis adjusted valvetrain allowing one valve to be held open when warmed up or a burnt valve. DO compression test hot and cold on that side...
 
Just happened to think. If you are having a hard time locating this noise try a stethoscope.I use mine all the time to listen to pulleys, bearings, intakes, whatever. Put the sensor on each exhaust runner and listen for the sound.
 
no brake booster. Definitely not mis adjusted valves. I think a comp. test is coming........
 
You can always do the process of elimination thing, remove #1 spark plug wire and test drive. No change, hook #1 back up and pull #3 etc... until something changes. A compression and/or leakdown test may help, if only to confirm the engine is healthy.

Sticking valves and leaky valves generally get worse as the engine heats up, and broken valve springs are more RPM related. However exhaust leaks may seal up as things heat. I think that's your problem. Replacing header gaskets is fun, so start there. Also look for tiny soot trails at the collectors, and any other exhaust connections.
 
Ironmike, one more thing to consider...

When it starts popping is it erratic or does it sound more like a constant miss? If it's erratic it could be excess fuel getting into the header pipe. The heat of the pipe with the raw fuel gives a loud pop sound. Looking at your old posts, you mentioned an Edelbrock mechanical pump, are you running the model rated for 6 PSI? If the problem is excess fuel it could be dirt in the needle seat, to high of fuel pump pressure, floats sinking or mis-adjusted. If you have clear sight plugs in your float bowl you can usually see the bowl overfill when it's popping (when the problem is occurring).
 
Mine did a similar thing. Random popping from the passenger side, mostly while idling or cruising at a steady RPM.

Engine had approx 2k miles since rebuild and when I swapped the heads, I had a burnt valve on that side. I was a little surprised but the shop said the valves had seen quite a bit of use/rebuilds and ended up replacing two others as well that were iffy.
 
My first guess would be and exhaust leak.
Buy a cheap thermo pointer and see if any of the headers show a different temp.
If that all checks out, do a hot / cold compression and leak down check.
 
Did a compression test and a leak down. Here's what I got.

Started her up and got it to 155 degrees. A little warm, but not warm enough that the popping from exhaust stops. Do a compression test and the results were astounding.(in my book).
Low of 174psi and a high of 178. Cranked each cylinder 5 times. I was pretty impressed. I've been doing these tests since 1976 and never had one that consistant. Maybe a testament to Brian's engine builing skill?

Time for the leakdown. Had to buy one since I never had the need, so I bought an OTC Dual gauge from Summit. Read all the instructions, blah, blah, blah, and Holy Crap!

According to the gauge, I have roughly 33 percent leakdown each, in all 8 cylinders. It's so far off, their chart don't even go that low. I cannot for the life of me believe those numbers. I could hear a very, very faint leak through the breather every cylinder. I had to turn of my stereo and heater and put my ear to the damn thing to hear it.
Never did hear a leak through the left tailpipe. Which is good.

This thing burns no oil, doesn' smoke, hardly any blow by(Total Seal rings), and hasn't lost any power from day one. Still brutally fast for a street car.

I'm thinking either: A. did the leakdown right after the compression test. Maybe the raw fuel washed the cylinders of oil.

or B. engine was pretty cold by the time I did it.

or C. my new OTC leakdown tester is a piece of crap

and finally D. Somehow I really do have a lot of leakdown and the car shows no symptoms.

Give me your thoughts. It might help me sleep tonite.
 
I would borrow a known good tester and try again since all of them are showing about the same thing. Sounds like you may have gotten a bad one.
 
I'm probably gonna buy a Moroso. On the other hand, maybe the thing is leaking that much. Hard to believe but it's my luck.....
 
I know it's a new engine, but I know for sure a loose guide can cause a pop cold,, till everything expands, and the valve centres out.. Ferds were bad for it.. my .02

More likely an exhaust leak though...
 
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