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I don't know if you are taking your car to a dealership but they are supposed to have a Picoscope which is a laptop based labscope and they really only use it for NVH (Noise, Vibration, Harshness) but they should be able to find it...and I stress SHOULD !!
I don't know if you are taking your car to a dealership but they are supposed to have a Picoscope which is a laptop based labscope and they really only use it for NVH (Noise, Vibration, Harshness) but they should be able to find it...and I stress SHOULD !!
I think having a tool like this would be the end of my sanity! There would be no end to finding problems I never knew I had LOL! But it would be great if a friend owned one if I really "needed" it.
I think having a tool like this would be the end of my sanity! There would be no end to finding problems I never knew I had LOL! But it would be great if a friend owned one if I really "needed" it.
You are lucky if you can find one in a hundred repair shops that use ANY type of scope…that’s why they guess when diagnosing cars !!!
they mentioned it could be the fuel pump or injector noise. I reminded them it's not tied to RPM, and the HPFP is cam driven. I also reminded them that the other C7s I've driven did _not_ make this noise.
Sweet. Not only did they not find anything abnormal, they also have decided to send me a bill for $227.
OPERATED VEHICLE TO BRING TO TEMPERATURE, PERFORMED INSPECTION AND WAS UNABLE TO DUPLICATE CUSTOMERS CONCERN AT THIS TIME. TEST DROVE VEHICLE TO BRING TO OPERATING TEMPERATURE AND WAS UNABLE TO DUPLICATE CUSTOMERS CONCERN MULTIPLE TIMES. Correction: NO FURTHER REPAIRS PERFORMED AT THIS TIME.
Sweet. Not only did they not find anything abnormal, they also have decided to send me a bill for $227.
Next time you have an issue I can save you some money. I'll only charge $100 to take your C7 for a joy ride and tell you I can't find anything wrong with it.
First warranty I've had where preemptive concerns aren't covered, only explicitly broken things.
I'm still pretty pissed that they performed paid work without authorization, though. As far as I'm aware that's super illegal here, and was specifically why I scheduled this particular appointment. The sketchy dealer close to me would only schedule an appointment after I approved a charge, with the caveat of "it'll be waived if we find an issue covered under warranty." This dealership had no such communication, just "looks like it's covered under warranty, let's go"
Well after almost two hours of arguing with the service writer, some manager came on the line and said basically "you're right, we don't have any legal document from you authorizing the charge. we don't feel that it is necessary, since we work on the pretense that a verbal agreement with our customers is good enough. nothing in this world is free."
he went on to say that I can pick up free of charge but with a reminder that further service will have a diag charge.
pretty sure there won't be further service unless the engine physically fails from this sound. otherwise, I guess it's "normal operation" according to chevy.
In their defense, the rattling was absent for the entire drive -- which is markedly longer than it has ever been absent before. Perhaps it never showed up for them? Just checked the odometer and they drove it, as requested, for 10-12 miles. It ought to have happened at least once in that amount of time.
Maybe I don't close the hood correctly or something completely asinine like that. I'll see if it does it over the weekend with me just opening and closing the driver door. If by some miracle it doesn't happen, I'll open and close the hood, see if that starts it again.
... except that can't be it, because I've heard it with the hood open numerous times. Back to the drawing board.
I have had several where the check valve in the fuel feed line where it dives under the intake rattles at about 17 Hz. It never times up with engine or drivetrain because it is coming off the fuel feed pump in the tank.
The line going up to that is BARELY clearanced off the firewall behind the engine and, as we all know, there ain't much sound deadening material in Corvettes.
In my experience, it seems to be louder / more noticeable on cars that sit a lot and drive little.
Replacing the short section of line does quiet it down but the noise never goes away.
All DI GM V8 engines make noise on this valve, you just can't hear it on trucks or Tahoes due to greater clearance around the fuel supply line, heavier sound deadening material, and fuel tank not attached to the vehicle body.
My $0.02, YMMV, HTHY
Aha, the first person to acknowledge such a noise! Congrats @abflyboy you get the grand prize, which is more questions.
What you're describing could easily be something the tech fondled checking for failed parts while diagnosing. Wonder if there's enough slack or play in it to have been pushed away from the firewall? Or clipped back in somewhere?
I'll have to poke around. Any chance you have a part number or something I can reference to know which line I'm looking for?
I have had several where the check valve in the fuel feed line where it dives under the intake rattles at about 17 Hz. It never times up with engine or drivetrain because it is coming off the fuel feed pump in the tank.
The line going up to that is BARELY clearanced off the firewall behind the engine and, as we all know, there ain't much sound deadening material in Corvettes.
In my experience, it seems to be louder / more noticeable on cars that sit a lot and drive little.
Replacing the short section of line does quiet it down but the noise never goes away.
All DI GM V8 engines make noise on this valve, you just can't hear it on trucks or Tahoes due to greater clearance around the fuel supply line, heavier sound deadening material, and fuel tank not attached to the vehicle body.
My $0.02, YMMV, HTHY
Originally Posted by squirrelchew
Aha, the first person to acknowledge such a noise! Congrats @abflyboy you get the grand prize, which is more questions.
What you're describing could easily be something the tech fondled checking for failed parts while diagnosing. Wonder if there's enough slack or play in it to have been pushed away from the firewall? Or clipped back in somewhere?
I'll have to poke around. Any chance you have a part number or something I can reference to know which line I'm looking for?
Having just gone through this myself, it sounds like the check valve in the low pressure feed line to the HPFP has failed. That's the noise it makes and it can be intermittent. It's usually more pronounced after driving the car hard.
C7's and Gen 6 Camaro's have tuned parameters to mitigate the hpfp noise. But don't get the two confused. That noise is a bad check valve. That fuel line connects directly to the HPFP and is what causes the reverberation sound since its being driven by the camshafts fuel lobe.
So the check valve looks to be in the pipe labeled #26 in this diagram, part number 12703596
From what I can see that's normally running up between the intake runners for cylinders 5 and 7 (or 6 and 8? can never remember). From there it connects to... a fuel line that runs down the back of the engine, presumably?
Are you saying the fuel line is against the firewall, more or less, and the failed check valve sound allows that to travel through the fuel line into the firewall, making a hell of a noise in the cabin?
The fuel line has a disconnect on the drivers side and then you have to get under the intake manifold to get to the HPFP side of that line. You won't have to do anything on the back of the engine. It's on the drivers side of the car. It's not that difficult to replace. Just be glad you have an LT1 and not an LT4 so you don't have to R&R the blower.
The routing of the fuel line to the fuel tank has nothing to do with that noise other than where you hear the failed check valve from the drivers seat. It makes it sound like it's in the dash somewhere.
So whatever they did to perform the inspection seems to have resolved the issue, at least so far. I've only opened the doors and hatch so far.
It's really feeling like they mucked around in there and moved whatever was making the sound away from the firewall. The fuel line theory is the most solid sounding one so far, and falls in line with the feeling I've had the whole time that something is bouncing against the firewall.
More to come. I'll be poking around the engine bay tomorrow evening. As soon as it starts happening again I'll order up one of those fuel lines and replace it -- It's only 40-some bucks, it looks like.
So the check valve looks to be in the pipe labeled #26 in this diagram, part number 12703596
From what I can see that's normally running up between the intake runners for cylinders 5 and 7 (or 6 and 8? can never remember). From there it connects to... a fuel line that runs down the back of the engine, presumably?
Are you saying the fuel line is against the firewall, more or less, and the failed check valve sound allows that to travel through the fuel line into the firewall, making a hell of a noise in the cabin?
YES
Hopefully the noise never comes back, but ...
You can fold up a shop towel and work it down between the firewall and supply line. It will 'change' the noise, for lack of a better word, and help you isolate.
I have one coming back in to me next week that I diagnosed but he declined the replacement.
He said it was MUCH quieter after I did the rag thing on the supply line. I did not leave the rag in there. He said that he would monitor it and would go ahead with the replacement if it got bad again, but once he knew what it was and that it was not detrimental to reliability or vehicle operation, he was no longer worried about it.
I am curious if his noise came back and will be sure to ask him about it.
