87 350 tbi exhaust chirp

[Sam71395]

Hello all, I have an 87 Silverado with a tbi 350 (15,000 miles on replacement) that is making a weird chirping sound that's coming out the tailpipe, it happens while accelerating and going up hills, at idle it's quiet. I checked compression and I double checked there are no exhaust leaks. Any ideas?

 

[scrap--metal]

I've never heard an exhaust chirp that I recall. Could it be a rubber mount on an exhaust hanger chirping as the exhaust vibrates or bounces around?

Also, how are you sure it's coming from the tailpipe under acceleration? Aren't you driving up in the cab? Acoustics can play tricks on a guy.

 

[Sam71395]

the exhaust is new duals and I shook the exhaust around pretty good afterwards to check for that. the sound definitely comes from the rear. the only time it completely went away now that i think of it is when the transmission was going out on it a few months ago. Could a flex plate be to blame?

 

[rusted nuts]

Could be a valve too tight or leaking Or bad plug, or wires

 

[Sam71395]

A valve might be a possibility, I will check that tomorrow

 

[Rusty Nail]

Didja check the earl?

 

[Sam71395]

UPDATE: Just discovered that i can get the chirp sitting still if i switch to the other fuel tank, the fuel pump in that tank is just about shot so it makes it run bad, but anyways, with it sitting still i can walk to the back and the chirp is clearly coming out of the tailpipes and it's the same sound coming out of each side, this is making me think that it is one problem affecting both banks, maybe/hopefully just a vacuum leak?

 

[rusted nuts]

UPDATE: Just discovered that i can get the chirp sitting still if i switch to the other fuel tank, the fuel pump in that tank is just about shot so it makes it run bad, but anyways, with it sitting still i can walk to the back and the chirp is clearly coming out of the tailpipes and it's the same sound coming out of each side, this is making me think that it is one problem affecting both banks, maybe/hopefully just a vacuum leak?

Is this TRUE Duals or do You have a cross over pipe?? Also How good is that fuel in the other tank??? Any water in that fuel causing a missfire?

 

[Sam71395]

yes it is true duals with no crossover, the fuel is good. one other thing I was thinking is that maybe a gasket dried out because prior to me purchasing it the truck sat for about 8-9 years

 

[Sam71395]

also I am guessing that head gaskets are fine with 15k on the motor, i think it would be unlikely that they both are bad at the same time unless I'm mistaken

 

[Sam71395]

Well, I am STUMPED, I checked valves, checked egr valve, complete tune up, good fuel, confirmed no vacuum leaks, there are other things i did that i am probably forgetting, I truly do not know what it is, the only thing i maybe can think of is that the mufflers are to blame, they are no name turbo mufflers from lmc truck, does anybody know if these are reversible or not? there are no markings on them indicating a flow direction.

 

[BadBowtie]

Factory spare tucked under the back??

 

[scrap--metal]

it is true duals with no crossover

If the pipes are separate without a crossover, the noise you're hearing probably isn't coming from inside either pipe. Nothing engine related should be chirping through both heads and exhaust pipes.

You're probably hearing a rub or vibration from somewhere else. Maybe both of your mufflers could be fubar, but that'd be odd since they're new and all.

 

[Redfish]

Do you still have the factory manifolds? Is the air injection system still intact? Could it be related to that somehow?

Sometimes the internal baffles in a muffler will break the tack welds and move around. Could your noise be a metal to metal rubbing inside the muffler(s)?

 

[Sam71395]

mentioning that it may be somthing else reminds me of something, now that i think of it. The transmission went out on it in march, and the day before when i was driving it, the transmission started acting up and the sound completely went away. Maybe related?

If the pipes are separate without a crossover, the noise you're hearing probably isn't coming from inside either pipe. Nothing engine related should be chirping through both heads and exhaust pipes.

You're probably hearing a rub or vibration from somewhere else. Maybe both of your mufflers could be fubar, but that'd be odd since they're new and all.