I've got a very unique chirping noise coming from the rear of my engine bay -- I'm looking to get some insight on what you might think it is.

A little history:
Two nights ago I met up with a friend (I'm back home for break from College) and we went out just to cruise around town. We got on an open stretch of highway and he wanted to see how the car felt on the bottle. So I opened the bottle and sprayed it at about 3600rpms from a 60 roll. The car backfired and sputtered pretty hard so I let off pretty quickly. I purged and tried one more time and the same result. It was behaving similarly to when I was getting some spark blowout, so yesterday I decided to pull the plugs and see how they looked. This is basically what I found.




There was a little green on the top, which I know is from the nitrous. The white is what really concerned me. I haven't had the car dynoed on the spray , but I've always run the kit a little on the low side of nitrous pressure (~980ish) just to be safe with the wet kit, I know that NX jets their kits a little rich anyways. I did seafoam my car (all three steps) about two weeks ago, so that would probably explain the white on the plugs.

So I replace all the plugs and gap then at .033 and start the car back up. Pretty much right after it starts back up, I'm hearing a chirping. I popped the hood and looked and it sounded like it was coming from the rear of the engine bay. I know the acoustics inside a garage with the engine bay can trick you, but it definately seems to be coming from the back. I was hoping it'd be a quick easy fix and I sprayed a some silicone lubricant on the tensioner pulley, but to no avail its still making the noise. It seems to speed up with the rpms, but it isn't constant when the engine slows back down.

Here is a quick vid (apologies for low quality) of the chirping and a slight rev. Any one who has had this happen, or can explain it. I'd really appreciate it.



Some background info so you don't have to ask:
Its a '94 Z28 Automatic. I've got the LT4 Hot Cam kit with the basic supporting bolt-ons. The plugs are NGK TR6s gapped at .033. The serpentine belt has less than 5,000 miles on it. The car still drives, but with it sounding like its kind of coming from the passenger valve cover, I'm parking it until I can get it figured out.

 

i would pull the valve cover and check your rockers. could even be a bent pushrod

 

I cant play your video right now, but a bent or out of place pushrod can make a very strange squeak or chirp sound. Would also run like ***.

** Also, how much are you spraying? With the recommended 150 NX jets I went up to 14:1 on my AF up top. We backed down to a smaller nitrous jet and the AF was fine. Once its running right get to a dyno and get that thing checked out.

 

I'm going to pull the valve cover now and take a look. Does the sound seem similar to that of a valvetrain issue?

Its not running like complete crap, it stumbles a little bit at idle, and sometimes doesn't stay smooth at a specific rpm when cruising, but it has never been perfect. At WOT it didn't skip a beat all the way to 6000.

I'm spraying a 100 wet right now (which is what I had in there a couple nights ago). I plan on getting it dyno tuned for the spray once I can get this figured out. As soon as you see/hear the video, let me know what you think.

Thanks again for the help.

 

yea it sounds like valvetrain to me, but thats my $.02

 

Sounds like valvetrain. Pull the cover and see what you can see.

 

I just pulled off the valve covers.

All of the pushrods and rockers look good. Anything you'd suggest I'd do before I put it back together?

I'm going to adjust the valvecovers per Shoe Box's writeup (http://shbox.com/1/4th_gen_tech2.html#adjust_valves). Anything else?

Thanks again for the help guys

 

lifter?

 

see if setting all the rockers to zero lash helps, from your video it sounds to me like a rocker is out of lash. i had a lot of problems with mine, bought hardened pushrods and triple checked each rocker after doing them all like a third time and it all cleared up

-Chris

 

did you physically roll all the pushrods on a known flat surface, or did you just look at them?

 

to me it sounds more like an accessory squeak than valvetrain... perhaps the idler pully, A/C, w/p... etc...
take the belt off and start it back up to see if it's still there. if it is then i'd venture into the valvetrain or look at the w/p more closely. buy an automotive stethascope.

 

I'm back home for the holidays so I'm in the process of tracking down the tools so I can get the rockers back to zero lash. They are the originals (I was told the stockers are hardened, so I didn't need to do them with the cam install).

I looked at them and rotated them. If any of them are bent, it is so minimal I didn't notice. I didn't think to roll it on a flat surface. I might just go snag a new set of hardened pushrods while I'm putting it back together.

That's what I originally thought it was, but the sound kept seeming like it was coming from the valve covers/backside of the motor when I put my ear down towards the motor. When I'm turning the motor over to readjust the valve lash I'll see if I can hear it. I'm going to have a gander at all of the accessories to see if they're making any noise too.

 

not sure if you've tried it yet but have the car running so you can hear the squeak and kick on the A/C, my A/C clutch started going out and was a constant little squeak until i would turn on the a/c then it got a lot louder. also, by just looking at/rotating the pushrods won't help unless they're out. you can only see about an inch of each, the other 6" is inside the head. good luck on finding the problem!

-Chris

 

It is definately valvetrain related.

I pulled all of the pushrods and went ahead and bought a new set of OE Replacements. I just finished preloading all of the rockers and I'm trying to button things back up before I start it up.

Thanks for all of the help guys. I'll keep you posted.

 

if you have a manual tranny... just for giggles... check to make sure the dust cover is still in tact, not bent and possibly hitting up against the flywheel.