wierd sound after running good for 2 weeks

[z9_87]

After having my heads resurfaced due to bracket bolts failure and the car overheating i got the thing running well about 2 weeks ago. It has ran great ever since. Even took it on a 3 hour road trip. Ran great and even got 26mpg!
Took it out for a cruise tonight and it made a weird sound. Can't pinpoint it, it just happens under light acceleration and then after about 1/2 hour it goes away. It doesnt happen in neutral or park so I can only listen while driving. It comes from the pass side and at first I thought it was a knock or detonation, but I want to rule that out cause i'm running 12* and 93oct. When it happens it feels like a missfire and it bucks a little. The sound is like when you push on aluminum and it finally gives. When it happens if I punch it, it goes away instantly.
No codes. Temp and oil press is good.

 

[Camman]

did you rule out an exhaust leak? I wouldnt think it would take 30 mins to seal, but who knows

 

[z9_87]

I kind of did because I've never heard of an exhasut leak causing nothing more than noise. Plus besides where the header bolts to the head and where the collector joins the exhaust, there are no other spots for leaks.

 

[Camman]

sorry, missed the part about it feeling like a miss

well, maybe your egr is slightly stuck open. Or you have a dead spot in your tps. I honestly cant think of anything else, although I think the egr would still cause you to miss a little at wot.

 

[nito88stang]

might be an exhaust leak at the header. If the leak is small enough it will seal once the header heats up and expands a bit.

 

[z9_87]

No egr, but I'll check the TPS voltage through it's range of motion even though i have no codes. And I'll check all the bolts and feel for exhaust at the head.

 

[z9_87]

Well everything checked out fine, TPS voltage is at .97 at wot. No exhaust leak. I was thinking something with the fuel. Cause it is an on again off again problem. So I put some seafoam in the tank and I'm going to run a little through the intake to see if it cleans the injectors, also put a new fuel filter in and so far i've had no problems since the fuel filter and seafoam.

 

[Daggar]

Thinking out loud here:

You may have a weak fuel injector. I can only imagine what a warm one might act like vs. a cold one, but I'll assume for a moment that when the injector is cold that it's not operating correctly. The reason I bring this up is that if you have one cylinder that is detonating due to a lean condition, it can sound much like an exhaust leak. You say you have a 30 minute window where you can trouble shoot. I would suggest a cylinder balance test and see if it reveals anything. It may also be worth your time to check around town for any shop that has an injector test/cleaning stand. Shouldn't cost you much more than a couple bucks per injector, a lower intake gasket, and your time. The reseal of the upper plenum might also do it some good if it ends up being the culprit. Good Luck.

 

[z9_87]

I don't know why I would need a new lower intake gasket but I might pull the injectors and have em tested. On my previous post, I spoke to soon, took it out for awhile today and it started off fine then after a while it was missing and then it was okay then missing.