We got quite a gremlin going on and am hoping someone has heard of or experience the following. Newly rebuilt 5.3 single turbo with a BTR turbo cam. CSU blowthru, dominator ecu with a new Holley ls1 harness. When we first fired it up, idled great and wicked well. We checked the exhaust temps and we noticed that #1,#2 and #7 were 100 degrees colder than the rest. Pulled plugs, timing mark on the plugs, but slightly darker than the rest. You can unplug the coils and it still idles and not much change noticed. The temps come up on the cylinders but steadily stays 100 degrees cooler than the rest. Plugs pulled one at a time and all have spark. So far this is what we done to try to find the problem.
- switched plugs from cool the warm clyds and then put in new plugs
​​​​​​-switched and changed plug wires
-switched coils around, then pulled coil packs and harness off a known good engine
- ensure both heads are grounded individually to battery ground, block to chassis ground.
-inspect valvetrain, manually rotate engine to ensure all valves were lifting in correct order
- hooked up another dominator ecu and tried a different tune. All parameters checked for proper setup.
- battery stayed charged or was charged to maintain max voltage
- intake pulled to check for vacuum leaks or obstruction
​​​​​​- banged our frigging heads against the wall.

plan for tomorrow is new crank and cam sensors, try a different carb and check lifters to see if they are collapsing (no clatter heard, but running out of ideas). Any help or ideas would be appreciated.

 

What intake are you using with the carb setup?

 

Super victor jr with a CSU blowthru

 

We did pull carb to check jets and a general look over. Kevin builds a great carb. This fired up and idled on 1st try with out a single adjustment

 

I would suggest running a compression test. Low compression can also cause low exhaust temps in a cylinder(s) at idle and will pick up with RPM.

 

Did compression test. All cylinders good and pretty even

 

Plan leak down tomorrow if other tricks don’t work

 

Sitting here thinking about it. Compression was a cold engine. Wii maybe retry with it hot

 

Cold or hot doesn�t matter really. All Your trying to do is get a comparison. I do mine cold. Will usually read a little higher when warm, but your good if you�ve done it cold and they are all close.

 

What other issues are you having besides the colder corners? Any power or drivability concerns?

Manifold distribution and header design will cause this. Most likely manifold distribution. It�s not necessarily an issue.

Since you�re using the dominator, it may be beneficial to switch to efi so that you can individual cylinder tune it

 

Had similar problem with my lq4 swap into a v6 car my companion cylinders weren't firing 1368 were cold check tour coil wiring I swapped my coils from bank 1 to bank 2 and it went away the pin out is differnt were the colors land.

 

1. Don’t want to get into the efi vs carb issue
2. We did switch coils paying attention to pin out. We even put 2 new banks of coils from a good car.

as for issues, the car idles good and even wicks strong. It doesn’t sound at all likes it’s missing. Hell, one person came in while we were messing with it and said, damn that sounds strong. You can pull the 3 coil wires from those cylinders while running and you can’t tell a difference. Clearly hitting on 5 cylinders. Getting ready to recheck the compression and possibly do a leak down. Going to change the cam and crank sensors just to take them out of the equation.

 

Do you have the correct firing order in the ecu?

 

Yes. One of the 1st things we checked. We even tried another ecu and put a ls1 base calibration in it. I almost think it’s mechanical. Heading for shop now. Will keep all those interested updated. Thanks for all the inputs.

 

Found it, sticking valves on those cylinders. Don’t if guides, grime or bent valves. Off comes heads, oh boy. Thanks again to everyone

 

Well, at least now you know. Half the battle fought and won.

 

Valves aren’t bent or compression check would have showed this. A sticking valve is generally caused from too little guide to stem clearance or an engine running really hot. Either way, keep us posted please.