leatherbee408

Always had a occassional misfire mostly at idle on the Tech2 since the Turbo install. Does not set any misfire codes. Stock motor/Was running NGK TR6s with a .025 gap. I recently fouled them because of a dead O2 sensor so I tried the stock heat range with .040 gap plugs and the occasional mis-fire is still there. I thought I read somewhere that the computer did not like a tighter than the stock .060 gap. Could this be causing my scanner misfire?

The car runs very smooth fully in closed loop perfect O2/voltages and LTs are -7% with WOT @ 11.8AFR...Engine does not run at all rough and like I said it is only a occasional mis-fire on the Tech2 all thru out but mostly in the higher cylinders. When I fouled the plugs I took some compression readings and they were dead perfect.

The only other thing I could think of is I am still running the stock valve springs which I know is a no-no with FI, however I have not heard of this setting any mis-fire signals especially at idle. What are you turbo guys running for gaps....

Separate question is what are you turbo guys running for total timing and wideband AFRs in the 8-15 boost range on the street (not dyno) with stock motor....I have my timing set at 13 with full boost and once again my AFR is 11.8 on the street and close to 11 on the dyno-jet. Also I would love to see anybody latest PE/RPM and/or high octane timing tables with LS1edit if anybody cares to share.

Any info/help would be greatly appreciated...

IM QUIKR

What TT setup are you running? You are probably right that the springs need to be changed. The stockers are truely too weak to hold the valves closed and the LS6 springs are only marginally better. Step up to the comp cams 918 and you may see the misfire diappear. The spark is probably getting blown out and the gap most are running on the TR6 is .035

0Jeff @ TPE

I was running .035 on TR6's

leatherbee408

Running a HP kit 67MM turbos with custom air charge pipes. Their pipes always seem to hit the tires on hard turns (autocrossing) so I made my own with lots of clearance. I can't really find a happy medium with the exhaust, either too loud or not free-flowing enough. Right now I am running custom 3in. I made with Borla mufflers. Other than that the kit is awesome and my own opinion the best design out there. Obviously they have their other "issues", however I think there are plenty of other threads on that subject so I wont go there...LOL

You think even at an idle those weak stocks springs would give those misfires. The other thing is why would that not show up in a compression test as slightly less running compression. The engine has only 44K on it, however I do give it a good meal of boost every day.

When I change those valve springs I was thinking of swapping to ARP studs at the same time. Is it ok if I do one bolt at a time, or will this still disrupt the head gasket? I have done it on a regular 350 with no problems, dont know if the LS1 makes a difference being aluminum block?

Thanks a million

IM QUIKR

From what I remember the stock springs on an LS1 are 75#s and the LS6 are 90#s and the 918s are 130#s . The compression test should be normal because the test does not have the turbos blowing air under boost. With a compression test, you are just checking the integrity of the internals like the rings, seats, etc. I can't answer why it happens at idle , possibly a bad plug, wire, coil. Is it always the same cylinder? Have you looked at the valve springs, one may be broken already. I'm sure somebody else can chime in with more specifics.

Shinobi'sZ

If you have a Tech II or know somebody that does, don't scan while just idling. What I have done is went out and driven with the Tech II hooked up RTD (Real Time Data) Scan and looked for which bank was misfiring. It could be a spark plug wire, cracked plug, or coil.

A broken valve spring will cause the car not to idle good...normally.

xtream1

On a side note, I am and have been successfully running the stock '02 Z springs for about 20K miles so far regularly pushing 12 #'s without any issues. I did however recently break a stock used rocker arm trunion bearing retainer clip. I think using the stock valve springs is more of a cam lift/ramp issue than a boost issue.

Gatzer

An aftermarket cam will also show misfires on all cylinders without triggering a P0300 code. You can desensitize the misfire detection in the low RPM range, at idle, if you have a cam so it won't pick up false misfires.

For every 100hp over your cars stock hp, you should run 1 step colder for plugs and the gap should be reduced by .050 also.