I recently fixed an oil leak by replacing an o-ring on a plug on the HPO rail on the passenger side. Some of you may remember that thread. Anyway, while I was waiting on the o-rings, I got into some exhaust work, and now I'm running the stock downpipe only as my exhaust system. By that, I mean that everything downstream of the stock downpipe was deleted. I never started the truck between the o-ring work and the exhaust work.

When I fired up my truck after reinstalling the HPO rail plug, it started up, and the RPMs went down to about 500ish, which is normal, but then they dived just slightly lower, and all of a sudden, this strange high pitched exhaust note came out of the exhaust. It lasts about five seconds and then ends abruptly. The best way I can describe it is "Bzzshhhhhhhhhhhhhhhh-thp". If I rev it during that time, the RPMs will rise normally, but the exhaust note is a much higher pitch than after it quits. After the noise quits, it appears to run normally. No warning lights or anything.

It does this on every cold start. I can try to record it on my next day off if it'll help you guys to help me. This problem never happened before I replaced the o-ring and cut off the exhaust, and now it happens on every cold start. It happens immediately after the RPMs go down to 500 after startup and lasts about five seconds after that before ending abruptly, at which point the engine runs fine.

I'm wondering what's causing this issue and how I can fix it. Any help, questions, or comments are welcome and appreciated. Thanks in advance, guys.

 

The way the stock downpipe is I wouldn't be too suprised if somehow it is making the sound you are hearing. Have you run the truck for a while to get what air out of the system you got in changing the oring? Thinking out loud, maybe there is air in it causing the rpm drop, then the weird sound from the downpipe. Like I said, just a thought.

 

Sounds like the EBPV is cycling (self test) during a cold start up.
If so the sound is normal, especially with no exhaust.
You can unplug the EBPV to verify.

 

I'm with Jim on this, but it also sounds like the turbo could be scrapping till it gets enough lubrication.

Unfortunately the EBPV diverts oil to make it work, which i'm not 100% positive if its on the in or out side of it. Either way is not very good IMO.

I'd check my turbo at that point.

 

forgot about the ebpv. It gets mentioned so many times, and still I forgot...

 

It's like a slow eating cancer for our trucks if you ask me.

 

I was not aware of this. Any specifics on just what exactly takes place, how many times, duration, etc?

Thanks,

 

It will turn on about 3-5 seconds after startup and stay on for a few sec. if you have stock exhaust it is hard to hear, but if it is straight piped you can hear it clearly.

 

I have 4" exhaust and have heard it. Was thinking I should look into it.
Next time, I'll watch the actuator arm movement to see it taking place.
Thanks!

 

The way you describe the timing here sounds exactly like the way my noise is timed. So is the noise normal or is it a symptom of a problem?

 

The noise is normal. You can unplug the electrical sensor at the base of the turbo on the pedistal to verify that's what the noise is. I always just left mine unplugged. Its annoying and causes lower fuel mileage and power loss in the winter

 

We're having problems with flooding at the moment, but when I get a chance, which could be a week or more, I'll unplug that connection and verify the EBPV as the source of the noise. I'll update this thread at that time.