knock retard

[Craig 94 TA GT]

I just finished the rocker/spring/lifter/pushrod install, and used the engine running method to adjust the rockers. Now I'm seeing knock retard when I'm driving??? I already put the LT4 module in a while back. Could loose/tight valves make this problem?
BTW, here's what I did to adjust...tightened (barely snug) the nut on each rocker at TDC. Then, I started the engine, and went 1 by 1 tightening each rocker, using a stethescope, until the most obvious loud clanking was gone. Then I tightened it more - 1/2 turn for the preload on the lifters, and finally tightened the locks. I'm using the OEM Comp Cams lifter replacements - not the COMP Rs.

Oh yea, the BLMs are still high on the driver's side I'm completely out of ideas. Thanks for any input.

[94 formula]

To do mine I just tightened the rockers down until all the wiggle was taken out of the pushrod and then went another half turn. I'm not noticing any type of clacking. I haven't had the chance to hook it up to my computer yet I'll get that done this weekend.

[Craig 94 TA GT]

I guess I'll try to retighten, only using 1/4 turn on the preload now...
When it was cold, open loop, it pulled 4 degrees of timing at one point. Once it got into closed loop, it "settled" and I was seeing .1 retard at idle, and roughly .2 to 1.5 when driving.

[Kevin - Blown 95 TA]

The usual troubleshooting for KR is to put some good premium gas in there - 100 octane race gas if you can get it (unleaded, of course), otherwise 93 with octane booster, and see if it has any effect on the count and timing being pulled. This way you can see if it is real knock or false knock. If false knock, then look for a mechanical noise like header or exhaust hitting somewhere, or other banging which the PCM might sense.

You might just have bad gas, but it might be something else like rocker arms hitting retainers, too. Gotta look at all the little things. I use about 1/2 turn total on the rockers with both Crane and GM lifters. I've had seemingly unexplainable KR once in a while, but there's usually a reason, and a lot of the time it turnes out to be the exhaust; but, if not that, then look at the other stuff.

Oh Yeah, Almost forgot to add, if there's a misfire, that might also be a cause.

[Craig 94 TA GT]

Thanks for the info Kevin...

I believe it's false knock because I scanned it on the same tank of fuel before and after the valvetrain work. Before, it showed 0.0 knock retard. So it has to be something I did during the install.

But I thought the LT4 KM was supposed to eliminate the false knock, or does it not? I'll check the valve covers to see if the rockers are hitting them. I did simply bend the support brackets to fit the RRs, so I can see that it's a possible cause. I just hope the lifters didn't somehow turn sideways and bend the retainers...then again, I'd probably hear that when it's running.

[fastTa]

Craig I think Kevin meant that your rocker arm might be hitting your valve retainer. If you had a bent or distorted lifter retainer your motor wouldn't be very happy and would let you know it.

Did you use 7.200" length pushrods? Did you use the stock retainers and valve locks? Maybe just try the suggestion that Kevin said about trying some higher octane fuel. That is one of the best ways to help narrow the possibilities on KR down.

[Craig 94 TA GT]

Oops, thanks for the clarification Kevin. The rollers on the rockers look like they're making solid contact with the valve stem end rather than the retainer. However, I haven't visually seen the rockers it past 2k RPM. The pushrods are the stock length, CCA-7940-16...although they "seemed" like a thousandth or two longer than the stockers.

But again, I'll be happy to throw in higher octane fuel or octane booster, but I'm confused as to why the fuel problem would just show up. I must have scanned it 5+ times on that tank trying to read the BLMs, previous to the valvetrain work. But as soon as I scanned it after, the KR started showing up. In fact, after the initial scan, I took it to the gas station and put in $20 - 8.2 gallons of 91 octane, 76 fuel (same gas, same station I always go to) and am still seeing KR.

I did notice that when I finished adjusting the rockers, it seemed awfully quiet for my taste; especially RRs are supposed to be louder. If they were too tight, wouldn't it run quieter considering the valve never fully closes?

I just readjusted everything with the motor off and now it seems a lot louder. The only thing that gets me is...is this normal valvetrain noise or clacking from being too loose. It's getting late, so I guess I'll take it for a spin tomorrow and check the readings. Thanks for all your advice.

[Craig 94 TA GT]

I was just analyzing my data more closely and realized it was actually pulling over 9 degrees at a point. But at other times, knock retard is at 0.0. I cannot find a relation between acceleration, mph, RPM, and knock retard according to my charts

I readjusted the rockers and am gonna take it out for a spin. I hope the KR goes away...

EDIT:
I just came back from a drive and found this: the KR didn't exceed 0.6 this time. However, it only hit this high whenever I goosed the throttle. When I let off, or at idle, it will usually sit at 0.1 or 0.0. I did also notice that I have an exhaust leak on the passenger's side manifold to y-pipe. Could that trick the LT4 KM into thinking it's knock?

[94 formula]

I'm not sure about the exhaust leak causing the false knock but what about your air fuel ratio for the passenger side how does that look? Also do you think you have it adjusted right now?

[Craig 94 TA GT]

The BLMs show a perfect 128 for the passenger's side. The leak, of course, is after the O2 sensor so I don't think it would throw off the readings. The driver's side reading is a different story. And I believe I have the RRs adjusted correctly now...at least I think

[Joe 1320]

Oh Yeah, Almost forgot to add, if there's a misfire, that might also be a cause.

Might be worth paying a little more attention to that last line.

[fastTa]

I did also notice that I have an exhaust leak on the passenger's side manifold to y-pipe. Could that trick the LT4 KM into thinking it's knock?

It is definitely possible. Since the speed of sound through water is much greater than the speed of sound through atmosphere, a small exhaust leak can definitely be triggering the KM. Fix that leak and see if it helps. It sounds like the majority of your KR may still be orginating from your rockers though.

[Craig 94 TA GT]

Thanks for the replies guys.

Kevin (fastTA), I put a temporary stud to replace the broken bolt on the manifold to y-pipe. Hopefully this will hold up until I get some headers. I'll tighten it down tomorrow and check the readings. Hopefully, the KR will be completely gone. If not, I'll try adjusting the rockers again.

Joe and Kevin (Blown TA) I will look into a misfire - especially if the previous things don't help.

BTW, I've read on cz28.com that some have put the LT1 KM back in, rather than the LT4, and claim it's not reading any false knock the LT4 was picking up. Sounds fishy, but can it be true??

[Kevin - Blown 95 TA]

I would worry less about which knock module is in there than what's causing it in the first place. The LT4 module was for the LT4 Vette with it's roller rockers, but they also used the plastic valve covers to absorb the sound & give extra clearance for the rockers. There's all kinds of schemes to desensitize the knock circuit, but a healthy car doesn't get knock unless the fuel is causing it. By healthy, I mean no exhaust banging & rattling, rockers adjusted properly, not overheating, not lean, no vacuum or exhaust leaks, no rods a knockin, no misfires, etc... Now, if you feel that you have done everything right and can't get anywhere, you can redo the knock sensor with more pipe dope and see if it gets rid of it or do the resistor mod. Some guys have even figured that the little blue (I think) wire that comes from the sensor needs shielding, so they used a coax cable in it's place and grounded one end to get a clean signal. You shouldn't have to resort to that, but thought I'd mention it. You can also get LT1 edit and control all aspects of the knock retard and the timing it pulls.

[Craig 94 TA GT]

I thought that too...the composite covers damper the sound, so I'm sure the stock covers are no help. But this is my findings:

I did my best to temporarily fix my exhaust leak...I can still hear a tiny bit of ticking, but I am not 100% sure if that's still the leak. However, I took it out for a drive, and sure enough, as soon as I started it, the PCM pulled 5.4 degrees. By this, I mean as soon as the RPMs hit 900, it immediately registered knock. After a moment, there was no more retard. A bit later, when it was still cold, it hit 0.1 for a second, then went away. After it warmed up, no more KR whatsoever. So I'm thinking...I still have a slight exhaust leak that's registering as knock. When everything heats up, the pipes expand a bit, and seal off the tiny leak I have. So when it warms up, no more KR. Is this possible, or wishful thinking?

BTW, I have been have the split BLMs at idle problem...usually 142-150 on the driver's side, and 128 on the pass. I just changed the MAF ends back to the stock ones...and after I attempted to fix this leak (on the passenger's side) the BLMs changed to 128 on the driver's, 120 pass. I'm happy it's shifting correctly, but I'm just confused as to how this happened.

Thanks again so much for your guys' help.