8.1 Loud Rattle Under Wot

[MEGA14]

Posted this in Ask The Tech but got nothing so I'll try here :

 

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I have a 2002 Silverado CC with about 140k miles and the 8.1/Allison 1000 .

 

This year , the truck started making a rattling sound under hard acceleration . It will also hesitate to shift from 4th to 5th unless I let off the accelerator , leading me to believe it's all about the Allison .

 

Problem is , I sent an email to Sun Coast Transmissions and Ron replied that he could not think of what would rattle in the trans and suggested it might be an engine/timing noise .

 

If that's the case , why the hesitation shifting from 4th to 5th ?

 

The only thing that's changed this year is a switch to Amsoil from Royal Purple . The truck pulls as strong as ever if not stronger . The truck weighs about 9400 lbs. as it is a commercial vehicle . Only mods done are a CAI and the syn fluids everywhere .

 

One last thing : The engine light never comes on when this happens .

 

Any help would be greatly appreciated .

[slomo007]

Is it a pinging sound? You could try out a tank of 93 or 91 octane to see if that would fix it, if it is a pinging issue.

 

Sounds like the shifting issue is different from the rattle issue to me also, I've never heard of a transmission rattling before.

[MEGA14]

Is it a pinging sound? You could try out a tank of 93 or 91 octane to see if that would fix it, if it is a pinging issue.

 

Sounds like the shifting issue is different from the rattle issue to me also, I've never heard of a transmission rattling before.

 

It's alot more pronounced than any pinging sound I've ever heard .

 

It sounds more like a hockey card clothes-pinned to a bicycle wheel in motion .

 

Don't know how old you are and if you know what I mean .

 

Besides , would an octane issue delay a shift from 4th to 5th ?

 

I will try it now that gas is cheap again though .

[slomo007]

Is it a pinging sound? You could try out a tank of 93 or 91 octane to see if that would fix it, if it is a pinging issue.

 

Sounds like the shifting issue is different from the rattle issue to me also, I've never heard of a transmission rattling before.

 

It's alot more pronounced than any pinging sound I've ever heard .

 

It sounds more like a hockey card clothes-pinned to a bicycle wheel in motion .

 

Don't know how old you are and if you know what I mean .

 

Besides , would an octane issue delay a shift from 4th to 5th ?

 

I will try it now that gas is cheap again though .

 

 

Wow, must be a pretty loud rattle. I'm afraid I can't help you much, like you said though with the price of gas go ahead and give it a shot but I doubt that's the problem with the latest info you gave.

 

Good luck finding a fix....free bump!

[dewfpo]

I too would give a tank of premium and shot and see what happens. If the engine is not performing properly (according to the ECM), it can affect shift points.

 

DEWFPO

[MEGA14]

Looks like you Guys were right .

 

I burned off the remaining 87 octane fuel and filled up with Sunoco 94 octane , drove for a bit then hammer down . No noise .

 

I just wonder if the Dealer can adjust the timing ( been told the 8.1's timing is controlled by the comp ) instead of my having to fill up on Premium Unleaded from now on .

 

A tune would probably take care of it but I don't see why I would need to do it .

 

Anyways , Thanks Guys .

 

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Unrelated : Parked the truck , came back and wouldn't start . Just that loud clack when you turn the key so it looks like I'll be changing my 3rd solenoid in 12 months .

 

Something's wrong there .

[dewfpo]

Looks like you Guys were right .

 

I burned off the remaining 87 octane fuel and filled up with Sunoco 94 octane , drove for a bit then hammer down . No noise .

 

I just wonder if the Dealer can adjust the timing ( been told the 8.1's timing is controlled by the comp ) instead of my having to fill up on Premium Unleaded from now on .

 

A tune would probably take care of it but I don't see why I would need to do it .

 

Anyways , Thanks Guys .

 

______________________________________

 

Unrelated : Parked the truck , came back and wouldn't start . Just that loud clack when you turn the key so it looks like I'll be changing my 3rd solenoid in 12 months .

 

Something's wrong there .

 

Sounds like you knock sensor is bad.

 

DEWFPO

[MEGA14]

Thanks DEWFPO , I will check that out .

 

Does this truck have enough sensors , lolz ?

 

My engine light is on because 1 of the 4 O2 sensors is gone , too .

 

They help figure-out what's wrong but they should come cheaper I think .

 

$250 every time just 1 goes , for parts and labor .

[dewfpo]

Thanks DEWFPO , I will check that out .

 

Does this truck have enough sensors , lolz ?

 

My engine light is on because 1 of the 4 O2 sensors is gone , too .

 

They help figure-out what's wrong but they should come cheaper I think .

 

$250 every time just 1 goes , for parts and labor .

 

I'd bet fixing that O2 sensor will stop your knock. Probably not the knock sensor then.

 

The bad 02 is probably making one bank run very lean causing the ping/knock.

 

DEWFPO

[jlcmotorsports]

I had a similar problem and sure enough, it was a batch of bad gas.