Slant Six Forum :: Fluttering (?) exhaust sound

At idle but upon acceleration I am getting a bad fluttering response from the engine. It's as ifthe air/fuel mixture is not coming in steady but in a consistant, on/off pattern. I don't think it's timing because it will level out periodically.

Is it possibly the accelerator pump?

Quote:

Cut back on the baked beans and dairy products.

D/W

I stink at describing things I guess.

Quote:

I stink at describing things I guess.

...cutting out the beans will reduce the stink you describe.

D/W

Sorry, should have reread it before I posted. It happens at idle, but is pronounced upon acceleration. It almost sounds like an outboard motor at idle. Acceleration response is slow and has a very rhythmic fluttering sound.

Dan, Just out of curiousity, what does the 3/8" gap do, in terms of diagnosing a plug problem?

Motor starts and idles O.K., but a detectable miss can not be isolated to any one plug wire.(when motor is cold) It almost seems to be a different one missing each cycle.

Condition is extremely pronounced when motor is cold and only under a load, it will not pull it is missing so badly, but miss goes away when I let off the throttle. Once it's warmed up about 10 minutes, the motor runs pretty darn good and strong.

Recently upgraded to super six and fresh 2280 holley

Before I do anything, the exhaust is cracked in half and needs replaced before I catch a ticket for noise pollution.

OK, so you did an intake and carb swap and the symptoms were the same both before and after?

it's possible you could've replaced a floor-cracked 1bbl intake with a floor-cracked 2bbl intake

EGR system is disabled. I flipped the EGR and I believe this seales it shut this way.

Has anyone ever had valve train problems that created this type of condition?

Author:	bbbbbb9 [ Thu Aug 18, 2005 6:57 am ]
Post subject:	Fluttering (?) exhaust sound
At idle but upon acceleration I am getting a bad fluttering response from the engine. It's as ifthe air/fuel mixture is not coming in steady but in a consistant, on/off pattern. I don't think it's timing because it will level out periodically. Is it possibly the accelerator pump?

Author:	SlantSixDan [ Thu Aug 18, 2005 8:25 am ]
Post subject:
I'm not sure how to parse "at idle but acceleration". Is this fluttering sound at idle, on acceleration, or both? What do you mean by "a fluttering response"? What exactly happens in terms of sound, motion, etc?

Author:	Dennis Weaver [ Thu Aug 18, 2005 8:29 am ]
Post subject:	Re: Fluttering (?) exhaust sound
Quote: At idle but upon acceleration I am getting a bad fluttering response from the engine. It's as ifthe air/fuel mixture is not coming in steady but in a consistant, on/off pattern. I don't think it's timing because it will level out periodically. Is it possibly the accelerator pump? Cut back on the baked beans and dairy products. D/W

Author:	bbbbbb9 [ Thu Aug 18, 2005 8:31 am ]
Post subject:
Sorry, should have reread it before I posted. It happens at idle, but is pronounced upon acceleration. It almost sounds like an outboard motor at idle. Acceleration response is slow and has a very rhythmic fluttering sound. I stink at describing things I guess.

Author:	bbbbbb9 [ Thu Aug 18, 2005 8:32 am ]
Post subject:	Re: Fluttering (?) exhaust sound
Quote: Quote: At idle but upon acceleration I am getting a bad fluttering response from the engine. It's as ifthe air/fuel mixture is not coming in steady but in a consistant, on/off pattern. I don't think it's timing because it will level out periodically. Is it possibly the accelerator pump? Cut back on the baked beans and dairy products. D/W lol It happened suddenly too. I'm going to check the timing and then if that doesn't help, rebuild the carb!

Slant Six Forum https://www.slantsix.org/forum/

Fluttering (?) exhaust sound https://www.slantsix.org/forum/viewtopic.php?t=14075	Page 1 of 2

Author:	Dennis Weaver [ Thu Aug 18, 2005 8:38 am ]
Post subject:
Quote: I stink at describing things I guess. ...cutting out the beans will reduce the stink you describe. D/W

Author:	Dennis Weaver [ Thu Aug 18, 2005 8:40 am ]
Post subject:
You're not describing a miss by any chance, are you? D/W

Author:	bbbbbb9 [ Thu Aug 18, 2005 8:41 am ]
Post subject:
Quote: Quote: I stink at describing things I guess. ...cutting out the beans will reduce the stink you describe. D/W YOUUUUUUUUUU one Funny Ferra

Author:	SlantSixDan [ Thu Aug 18, 2005 8:52 am ]
Post subject:
Quote: Sorry, should have reread it before I posted. It happens at idle, but is pronounced upon acceleration. It almost sounds like an outboard motor at idle. Acceleration response is slow and has a very rhythmic fluttering sound. You've got at least one dead cylinder. Could be due to anything from bad spark plugs or plug wires to burnt or too-tight valves to vacuum leaks at the intake manifold gasket. To figure out which cylinders aren't firing, disconnect spark plug wires one at a time with the engine idling. You will find one or more plug wires that do not change the engine idle quality/exhaust sound when disconnected. Those cylinders aren't firing. Next test: loosen the dead cylinders' spark plug wires so that there's a gap (inside the boot) of about 3/8" between the plug wire terminal and the spark plug terminal. Go listen to the exhaust and see if it's smoother. If it is, you've got some failed or very dirty spark plugs; pull them and inspect, correct whatever problem caused them to fail or foul, and replace the plugs. Post some results and we'll move on from there.

Author:	'74 Sport [ Thu Aug 18, 2005 9:33 am ]
Post subject:
Dan, Just out of curiousity, what does the 3/8" gap do, in terms of diagnosing a plug problem? Jerry

Author:	SlantSixDan [ Thu Aug 18, 2005 10:07 am ]
Post subject:
Quote: Dan, Just out of curiousity, what does the 3/8" gap do, in terms of diagnosing a plug problem? It raises the secondary voltage so that the spark can jump a dirty gap in the combustion chamber -- this is what the old "series gap" spark plugs used to do (it's also what those JC Whitney "ignition intensifiers" used to do).

Author:	Slant6Ram [ Thu Aug 18, 2005 10:49 am ]
Post subject:	Me too
I've got a similiar condition that I have been meaning to post about. I've been doing all the normal stuff hoping that I'd find the problem, but have had mixed results. Here is my description: Motor starts and idles O.K., but a detectable miss can not be isolated to any one plug wire.(when motor is cold) It almost seems to be a different one missing each cycle. Condition is extremely pronounced when motor is cold and only under a load, it will not pull it is missing so badly, but miss goes away when I let off the throttle. Pumping the gas to try and force it to go, floods it, and it will eventually stall if forced. I can't duplicate the condition in park, only under a load. Once it's warmed up about 10 minutes, the motor runs pretty darn good and strong. It take a very long time to warm up in the driveway, so I drive till I hit a hill, and then pull over as it lugs and misses.(but doesn't stall) As soon as I pull off and park a moment, it's warm enough that I can pull out and drive normally again. Then it's good until I shut it down and let it cool for more than a few hours. I've recently replaced all of the following parts: Spark plugs (helped cold starting, but didn't help with miss) Coil, Wires, Cap, Rotor, ECU, Balast Recently upgraded to super six and fresh 2280 holley Rebuilt distributor, didn't change condition, but helped ping Replaced radiator, so no coolant leaks any more at all. Truck has been running this way a long time and the new parts help it cold start and run better when warm, but it always runs bad cold. I was having a lot of cold starting problems, but plugs and choke adjustment seem to have finally resolved that. Next, I'm looking for a sticking valve or lifter, and I know that this motor is pre-hardened valve seats (1972 motor), but valves where adjusted 3k ago. Before I do anything, the exhaust is cracked in half and needs replaced before I catch a ticket for noise pollution. So many projects, so little time. Sorry for jumping your topic, hopefully we can compare notes rather than confuse the issues.

Author:	SlantSixDan [ Thu Aug 18, 2005 11:53 am ]
Post subject:	Re: Me too
Quote: Motor starts and idles O.K., but a detectable miss can not be isolated to any one plug wire.(when motor is cold) It almost seems to be a different one missing each cycle. It very likely is. Quote: Condition is extremely pronounced when motor is cold and only under a load, it will not pull it is missing so badly, but miss goes away when I let off the throttle. Once it's warmed up about 10 minutes, the motor runs pretty darn good and strong. I've seen this symptomology due to unintended EGR (that's exhaust getting into the intake tract via some path that's not supposed to be there. Cracked intake manifold floor, cracked EGR passage, faulty EGR valve.) Once the manifolds heat up, the crack self seals, just like external exhaust leaks via manifold cracks that stop going "Tff! Tff! Tff!" once the engine warms up. But, I've also seen it due to plain ol' vacuum leaks, in the intake manifold casting itself or at the manifold-to-head junction, that likewise self-seal when they warm up. Aluminum intake manifold, or iron? Quote: Recently upgraded to super six and fresh 2280 holley OK, so you did an intake and carb swap and the symptoms were the same both before and after? That suggests the problem is NOT manifold related, though it's possible you could've replaced a floor-cracked 1bbl intake with a floor-cracked 2bbl intake (or swapped a faulty EGR valve from one manifold to the other). Quote: Before I do anything, the exhaust is cracked in half and needs replaced before I catch a ticket for noise pollution. Well, shee-yoot, that could be a big part of your problem, right there! Cracked-in-half exhaust manifold means exhaust is getting to the outside. Until the engine is warmed up, the thermostatic air cleaner sucks intake air from right off the middle of the exhaust manifold. Could be that you're sucking exhaust into the intake tract, causing the engine to run poorly and miss. Disconnect your air cleaner's vacuum damper door actuator (the round pod atop the snorkel) and see if the symptoms change.

Author:	Slant6Ram [ Thu Aug 18, 2005 1:57 pm ]
Post subject:	More
Thanks for the input Dan. Several of your suggestions do not apply, so I will clearify, maybe you'll get a better idea of what I should do next. Iron intake manifold, yes, recent install. Visual inspection found no cracks, but I'll pull the carb off and look again. EGR system is disabled. I flipped the EGR and I believe this seales it shut this way. I will go back and double check for leaks. Minimal Vacuum system has only brake boster, pcv , dist, and choke pull off. I need to check the whole thing for vacuum leaks again, but I just installed the manifolds, stupid cheap gaskets, but I used high temp sealant as well. Non of the plugs looks particularly lean upon inspection, but If the leak is sealing as it warms up, I guess it wouldn't show on the plugs. Quote: OK, so you did an intake and carb swap and the symptoms were the same both before and after? Yep, pretty much. I thought the old 1bbl carb was worn out and causing the cold running problem, so I swapped to the 2bbl hoping to seal up any intake leaks in the process. Now I've changed from the BBD to a 2280 because the BBD had worn throttle shaft and I thought it might also be the cause. Each carb has run different and required tuning, so it is hard to make direct comparision, but the poor running when cold has become a very specific condition since I've got the cold starting problems fixed. Guess it could still be a choke problem, but it seems worse and I'd expect pumping the pedal could work though that kind of problem. On that topic, I want to rule out fuel problems, It runs great once it's warmed up and the clear fuel filter is full while running. Even when it's sputtering, stepping on the pedal seems to work the accelerator pump considering the cloud of black smoke it produces in my rear view mirror. By cracked exhaust, I mean the exhaust pipe down under the truck. The exhaust manifold is crack free and I inspected it pretty well before installing. Quote: it's possible you could've replaced a floor-cracked 1bbl intake with a floor-cracked 2bbl intake I hope not, but it's easy enough to check. Has anyone ever had valve train problems that created this type of condition? If I wasn't so wrapped up in other projects, I'd be pulling the head off and replacing it with one of the newer hardend seated versions I have in my stockpile. I just don't want to do it until I'm pretty sure it's necessary. I've been avoiding taking the truck far from home in case something is in danger of failing, but I can't figure out what. Now the only time I'm driving the truck is short trips, which makes the problem all that much more annoying.

Page 1 of 2	All times are UTC-08:00
Powered by phpBB® Forum Software © phpBB Limited https://www.phpbb.com/

Author:	SlantSixDan [ Thu Aug 18, 2005 2:23 pm ]
Post subject:	Re: More
Quote: EGR system is disabled. I flipped the EGR and I believe this seales it shut this way. I've never tried doing it this way -- I like to use a blockoff plate, myself. Quote: Has anyone ever had valve train problems that created this type of condition? Is this a solid-lifter or a hydraulic-lifter engine? The thing that bugs me about the idea of a valve problem is that valve-related causes of this kind of poor running tend to be the opposite of what you're experiencing (that is, engine runs fine cold but worsens as it warms up).