deuce exhaust sound...HELP!

[usmarines72]

Hey guys I need help troubleshooting my deuce. Here's the scenario. At idle (700-800 RPM) the exhaust has a very noticeable duh,duh,duh,duh sound. When I get up on the passenger side fender, the vibration of the truck is incredible. So much so, it's hard to see clearly b/c it is vibrating your entire body. Upon pulling the throttle out to have the truck idle at 900-1000 RPM, the once very noticeable duh,duh,duh,duh exhaust sound is not as noticeable and the vibration goes away.
Now when looking at the exhaust it is white and does smell of diesel (not antifreeze) more so at the low idle of 700-800. However, when you increase the idle to the 900-1000 the smoke is not as noticeable. In other words the smoking goes down.
I have new fuel in the truck, new filters all around including the air filter.
Thinking IP? Injectors?
About the truck. It has the original LDT-465-1C Hercules with 7k miles on her (not a rebuild). Oil pressure at 60 PSI. It is an '86 USAF contract truck

Here's a clip of the kind of sound the truck makes at the low idle. The sound is at the 18 second mark.

[media]http://www.youtube.com/watch?v=pxnHxikcwAk[/media]

 

[wsucougarx]

Hmm, not sure what would make that sound. Could it be a plugged injector? Referring to the video, what would make the truck have that sound at the 18 second mark? Lugging?

 

[Goose2448]

Sounds Like a Desiel too me.

 

[usmarines72]

Well it does sound like a diesel however what is the cause for the sound? My other 4 deuces do not sound like that. Rather they have a nice exhaust purr without the punctuated duh duh duh duh duh duh etc sound. No one has any ideas?

 

[Divemaster920]

Sounds like Lugging to me.

 

[G-Force]

Sounds like you have a dead cylinder. When the truck is idling, loosen the fittings for the injector line at each injector one at a time. If that cylinder is firing the idle speed will change and the engine will run rough. Tighten the line back up and go to the next cylinder until you find the cylinder that is not firing.

 

[GoHot229]

I'm leaning twards G-Force Wonder if a rocker lost adj. or a bent pushrod? At idle, you pull out the dash cable to hit the sweet spot and set it there for idle, "vibration bad" and will destroy things, the TM actually addresses this very thing.

 

[rlwm211]

I also agree with G-FORCE.

I listened to the video a couple of times and the poppling would be indicative a valve leak. I think the advice to check for which cylinder is the offending one would be wise and also would help in the diagnostic process. A compression test would be most informative if you find a problem cylinder.

Sometimes a valve problem will be most obvious with heavy engine loads and would appear to disappear on cruise at speed.

It is possible it is something else.

Hope this helps


RL

 

[Billy Bobbed]

Id have to agree with G-Force.

 

[rlwm211]

I am thinking it may be a burnt valve.

RL

 

[73m819]

id say a BURNT valve rather then a stuck valve, at low rpm you will get the dead cylinder hence the sound and the vibration, as the rpm picks up there is enough rpm to give some compression and a hot cylinder

211 you beat me to it

 

[eddiec]

Low IP pressure can also cause this problem. An easy way to check pressure is to just turn up pressure while at idle and see if miss goes away. Low pressure will cause fuel to glob in instead of mist.

 

[badgmc56]

If it's shaking that bad at an idle, then I would say you definately have a cylinder that is not efficient. When you load the engine the weak cylinder is more likely to effect the exaust sound. Sounds to me like a possible fuel delivery problem or a weak valve spring or leaking exaust valve. I would take a compression test first, then pull the valve covers and inspect the valve train for obvious failers. If there is a broken valve spring you will be able to see it. Rotate the engine till both valves are closed on the cylinder you are checking. Shake the spring to see if there is considerable looseness. Make sure you look very close at each spring. Hope this helps ya. Bob C.

 

[tm america]

i would think you have weak valve spring or a burnt exhaust valve .since the duh duh sounds louder than the rest of the exhaust noise which would happen if the exhuast valve is open on ignition.it would also give you a loose of power and smoke since it would not be burning all the fuel.if an injection pump was messing up it would not be firing on that cylinder and there would be a lack of sound when it is suppose to fire and there wouldnt be smoke cuz it wouldnt be getting fuel

 

[usmarines72]

Thanks for all your input guys. You guys gave me a great starting point to go from.

 

[73m819]

a weak exhaust spring or burnt exhaust valve, a broke spring will give ypu a click, almost has to be exhaust because of the sound , dont beleive you would here the sound if its intake, just get the vibration

 

[stumps]

i would think you have weak valve spring or a burnt exhaust valve .since the duh duh sounds louder than the rest of the exhaust noise which would happen if the exhuast valve is open on ignition.it would also give you a loose of power and smoke since it would not be burning all the fuel.if an injection pump was messing up it would not be firing on that cylinder and there would be a lack of sound when it is suppose to fire and there wouldnt be smoke cuz it wouldnt be getting fuel

Uhmmm? If the exhaust valve is open on ignition, you won't be getting any ignition. This is a compression ignition engine.

-Chuck

 

[wsucougarx]

speaking of clicking sounds. What is up with the clicking in this engine. USMARINES72 does your engine sound like this one?
[media]http://www.youtube.com/watch?v=KHW1_q9naYM[/media]

 

[usmarines72]

No Mike, luckily it doesn't sound that back. My truck doesnt have any clicking sounds. Just the exhaust sound like it's missing or something. Wow, that vid truck has been abused to say the least:-0

 

[stumps]

speaking of clicking sounds. What is up with the clicking in this engine. USMARINES72 does your engine sound like this one?

Judging by the number of times that truck has been dunked hot into cold water, I would bet on an exhaust manifold with a big crack in it next to one cylinder's exhaust port.

-Chuck