niqht

And I hope this is an ok place to post this.

Short story - I'm a tech at an independent Honda/Japanese specialist. We do work on domestic, but it is less advertised. I pretty much do all the diagnosing and this one has me atm.

Car was grabbed by a car lot, one that we trust and doesn't sell junk, and they said it has been to others that have done compression tests, etc.
It is absolutely not any specific dead cylinder(s). It only gives a random 300 code, idles like a cam, but gets no better when revved. It has 11-13" of vacuum that fluctuates back and forth quickly.
At idle, the front O2's stay pegged rich. Off idle, steady rpm, they stay pegged lean. O2's and harness is clean. Only other thing I've done is pull the rail and flipped it over to check injector spray.

The last detail... the car is a pristinely clean 2002, 29k miles, of the Firebird variety, with a slushbox. There is nothing to suggest any bad vibes about this car. Though, I am leaning to cam timing, it's just such a pain in the *** to check. Sorry guys, I am spoiled by the 4 cylinders.

Any ideas? thoughts? experience?

zacht

iTrader: (18)

does it actually run bad? some cams can cause a random misfire code. and some with cams burn lean (false lean due to overlap) at lower rpm's or idle.

JaYZeig

iTrader: (11)

do you have access to a scan tool that will allow you to view sensor outputs? id possibly start lookin at a maf sensor or map sensor first..try unpluggin the maf and see if it runs better/more responsivly.

ZeeOSix

Is that the vacuum level at idle? If so, that seems kind of low. Possible vacuum leak?

niqht

Given the rich at idle, it runs worse as it warms up. Gets to be a pain fighting the stalling. You can smell the cat.

MAF shows ~8grams at idle. up to 150 with a punch of the gas. I have used an air blower to get the MAF reading higher and I can watch the O2 voltage come up, but that was difficult to maintain and I didn't notice a difference in smoothness.
MAP agrees with vacuum gauge. There is practically no where on this motor to leak vacuum to. Even so, it should improve with higher rpm.

iraqi devil

coolant temp sensor?

niqht

ok, it has a broke valve spring. Something I've never seen before, but apparently it isn't stock. It does have titanium retainers and straight springs with green paint marks. Ordered an OEM dealer spring and it has the tapered top.

Do I have the wrong part from the dealer or is this an aftermarket spring kit?

87silverbullet

iTrader: (11)

Can you get us a pic?

usmcz28

iTrader: (3)

I'd say grab a borescope and check out the cylinder to make sure you dont have a damaged piston. If that spring broke i'd bet there's some more damage other than that spring.

niqht

I could maybe get a pic but there isn't much to it.

We used to have a bore scope but it vanished. I doubt I could get it in that plug hole anyway.
It didn't drop a valve, it just wasn't closing. I don't know what kinda clearances domestics run. In Honda land it would have hit the piston, but here I never heard any noise.

joecar

The non-tapered springs indicates a cam was installed and springs/retainers upgraded to support the cam.

If you post a pic of the broken spring, someone can identify it and you can get a like replacement.

The fluctuating vac gauge is a sign of a problem with a valve.

SOMbitch

iTrader: (8)

I agree with Joe and that means you are more than likely asking for trouble with stock spring(s)...

niqht

I'm with you, but it isn't my call. I may not know domestics, but I know performance. They got a square spring from a head shop we use, the ti retainer doesn't fit snug in the spring and the retainer is scored. Only a matter of time before it splits in half.

In other news, it is running much better with consistent 18" vacuum, but still dead on number 8. Valve has to have been tweaked...
Doing a leak down when it cools down again.

blk~2000~Z28

I had same exact problem and I did find my exhaust valve tweaked. I also had 3 broken inner springs, I would replace them all if you are diving into the motor to change the valve.

joecar

Bent valve...

If your shop doesn't do the job right, you will end up breaking the customer's engine, and he will hold your shop responsible for it... you would be better off to farm this out to an LS1 speed shop.

ls1 1990 VN

Best advice yet!

Had a workshop that was good on Gen 1 engines rebuild my LS1 & it ended up being a very bad mistake, still ended up costing me & them a lot of $$$$$ to get it rebuilt again 1800km later.