LS1TECH - Camaro and Firebird Forum Discussion - Generation IV External Engine

6.0 LY6 single cyl misfire only when hot and at idle HELP!

MtnVan — Tue, 19 May 2026 14:37:43 GMT

I am out of ideas on this one and hoping someone has some guidance.

2008 LY6 6.0 NON-DOD 100k miles express van, zero mods.
Starts cold, smooth idle, zero ticking, no cel, no misfires on live data.

Drive it up to operating temp, drives smooth, runs great. Zero hesitation, no stumble anything above 700 rpm. No misfire on live data.

At op temp, at a stop, at idle it has a very slight stumble, idles at 500-600 rpm. Isn't as smooth as it used to be, so I checked for misfires and getting misfires on cyl 6 but no CEL. On a long road trip (1000+ mi) it did pop a p0306. So far no cel for round town driving. I live rural, my drive to town and home is typically 60+ miles.

Due to mileage I changed plugs, wires (AC Delco, stock spec). No change

I own a fuel injector cleaning machine, so cleaned all the injectors. None leaked down under testing, all spray patterns look the same and volume tests are all within parameters. No change

Swapped plugs, wires and coils between 8 and 6. No change

Swapped injectors between 8 and 6. No change

Replaced the valley pan and intake manifold gaskets. No change

Visually inspected wiring harness, can't see any breaks or rodent damage.

Since this is not the Displacement on demand it has the old style lifters.

My next step is to pull the head and inspect the lifters and cam. Seems very odd that it only happens at idle when at operating temp, no tick, smooth at 700 rpm+. The stumble at idle is hardly noticeable, but I know the vehicle.

Update--- today I pulled the valve cover, all rockers are moving as they should. Did a compression test and it is at 90 psi on cyl 6, 150 on cyl 8. Assuming a valve is not closing. Will do a leak down and see where it is leaking.

Hoping I am forgetting something before I pull the head.

Thanks for any help and insight!

Anyone ran DeWits Direct Fit HP radiator in a 4th Gen F-Body?

FCar2000TA — Thu, 14 May 2026 01:58:04 GMT

I am going to replace my 27 year old radiator because it has sat for two extended periods now. So, has anyone had any experience with the DeWitts HP Series radiators? They are still "direct fit" they just have 1.25" tubes.

DOD Valley Cover

vjjack04 — Tue, 05 May 2026 02:02:24 GMT

I see there are some different options for these DOD (delete) valley covers. Is there one that's more favored than the other?
Pretty simple part and question (I hope).

How about this one....

ICT BILLET |

#826551605

ICT Billet 551605 LS Gen 4 O-Ring Valley Pan Cover Plate

Large oil pan - bellhousing gap - should I ignore it, shim it, or delete bolts?

StorminMatt — Fri, 01 May 2026 00:21:54 GMT

I know that you are supposed to loosely bolt the oil pan to the bellhousing while tightening the oil pan bolts in order to ensure that the oil pan and bellhousing are properly aligned. But I am using an aftermarket swap pan (Sikky). And I just can�t close the gap between the oil pan and the bellhousing. It looks like I am left with a .031� gap.

Sikky seems to think this is no big deal, and that I should just install the bolts and be done with it. But GM says that anything over .006� is a problem. Also, you can literally SEE the bellhousing flex as you tighten the bolt to close the gap. This just seems like it would cause bellhousing alignment issues. But maybe I�m overthinking it?

Another option is to shim this gap. Interestingly, I can get a .8mm shim, which works out almost perfectlt to .031 inches, and the little bit of movement can take care of the rest. But Sikky thinks shimming the bellhousing is completely unnecessary and could cause problems. And finally, I can just leave the bolts out. Many aftermarket pans don�t even have provisions for those bottom two bolts (probably for the reasons I�m dealing with), and work fine. Sikky seems to think this would be OKAY, but less than ideal. So what would be the best option?

2008 L92 with Edelbrock Cross Ram Intake (Ozmo Contoller)

Shanems10 — Mon, 27 Apr 2026 23:40:55 GMT

I have searched the internet looking for answers, but have decided that I would post for some Help I have a 2008 L92 415ci twin turbo with a T56 trans in a 1967 mustang. The engine is new and just trying to break it in. I am having problems with the engine with a dead pedal. I have checked the throttle bodies and they are opening but the engine is not increasing in RPM. When I try the Ozmo controller in says that the unit is trying to load map from the Ecu. I also do not know if the software is any good. This just started before it was showing live data on the 2 throttle bodies. any help would be great,