Hi All,
I'm trying to diagnose a situation that I can't wrap my head around. I've got a rough but stable idle that I can control with the IAC. Rev'ing the engine seems labored with slow throttle response.

I've pulled each of the spark plug wires and I get consistent sparks at the plug ends of the wires. I've circuit tested each of the wires to the Injectors and the circuits are good and blinking when the engine is on. The mystery surrounds the fact that if, while the engine is running, I pull the spark plug for cylinder 1 the engine doesn't seem to care, the rough idle stays the same. When I pull any of the other 3 wires (cyl 2-4) the engine will sputter out...

I know there is good spark on cylinder 1 and changing the plug out doesn't change the symptoms. I put a screw driver to the top of the injector and I hear a consistent clicking so i'm lead to believe there is fuel flowing. I started the engine with plug 1 out of the engine and it starts and I get random combustion out the top of the spark plug hole in the valve cover. No spark nearby but maybe igniting the fuel from the heat of the engine, not sure on that one....

Any other tests or ideas you guys may have on how I can continue to narrow this down?

My small brain thinks fuel + spark = bang but pulling the plug on cylinder 1 and nothing changing in the idle conflicts with that...

Many Thanks,
-Jeremy
2005 MSM

 

You should start by posting your tune so we can look at it.

 

please post your current tune.

 

Apologies, msq and data log attached.
Thanks for taking a peek!
-Jeremy

 

Mudflap, my setup is similar to yours and i recently converted to LS coils (D585) my thought is that the issue lies somewhere with them. I converted from batch fire fuel and spark to sequential on both and I have 1000 cc injectors. If possible can you post your MSQ or compare mine to yours to see if there may be a setting I'm missing? FWIW i'm running an MS3x and not the MSPNP.

Thanks much!
-J

 

2 second look: Your AFR is 18:1:? Your timing is 25deg (should be more like 10-15)? Your Accel Enrich is super aggressive. I'm surprised this runs at all.

 

Mudflap, if there is a misfire there will be excess oxygen in the exhaust stream giving an artificially lean result.

After you get that fixed you can do a compression test on all cyls to see if cyl 1 has a problem.