Juicedh22

iTrader: (6)

So I JUST got my 416 ls3 build finished, and I am running into an issue, i cannot seem to resolve... I have a misfire that I notice at low engine speed/higher gear and HIGH load (going WOT at really low engine speed) (between like 1500/2500 rpm is where i feel/hear it). Its always cylinders 2 and 6 according to the plugs... nothing shows up on the ecu, no codes, and the Tech2 doesnt detect any misfires...



Here are the things i have done to diagnose:
new spark plugs, didnt follow
swapped coil packs from side to side, it didnt follow
swapped plug wires from side to side, it didnt follow
swapped injectors from side to side, it didnt follow

compression test: all cylinders 90psi first stroke, and 190psi on the 5th stroke

leak down, only did it quickly on those two cylinders, but leakdown numbers were 7/10% respectively...

We hooked up a timing gun with inductive pickup to the cylinders one at time and drove around, and did not notice any hiccups or loss of reading (timing gun had a digital rpm display) on either of those cylinders...

Here is what all the driver's side and #4 and #8 look like:


And here is #2 after 30 minutes of drive time on new plug:


And here is #6 after that same 30 minutes...



At this point, I am clueless...

Realcanuk

I have a similar issue although not nearly as bad as yours. I have 2 cylinders that run a bit rich at idle. After having checked and rechecked many times I am starting to think it is something in the build. Ports, cam lobes, ??? I really dont know but I have it running well now, although that issue is still there. There is a table in HPtuners (gain vs cylinder) with which I suppose you could try and adjust fueling in those cylinders. This is not really the answer though. I am interested to know if you every find out whats going on. Good luck with it.

ana LoooL

Hello ...

this is a strange problem

I had a similar problem shortly before .... And It was broken the spark plugs after a few hours.... from normal driving


Later......

I found the the problem ..... It was the in coil packs......it"s sometimes had an electric retention




Good luck

Realcanuk

I remember having a strange missing problem which was very hard to diagnose. It turned out the harness under the coil pack was crushed during install. Took many hours to find the issue. Could be worth checking.