installed the wrong plugs and everything has been downhill since.
While it shouldn't have had to much of an ill effect, things may have changed internally inside the engine being it had a loose spark plug and it compromising the spark plug end 'Plus running with to short of plugs may have helped carboned up the engine cylinders & heads giving the engine a rich running appearance.
You may eventually want to try performing a cylinder compression test and possibly a leak down test just to see the overall condition of the engine should nothing else become evident. If the plugs were fuel carboned black, there are some techniques mentioned both here at iboats and online about cleaning the cylinders by way of ever so carefully using water and running the engine.
Also, for what its worth while I was prepping for setting the timing, I couldn't even budge moving the distributor and it took a lot of effort to loosen the bolt holding it down. Keeping in mind that it ran fine prior to me changing the plugs, how likely is it to be out of proper timing al of a sudden?
The chances of a dramatic change of ignition timing are low if/had you know for sure the distributor has not been moved by you or anyone else specially in a time frame...None the less, checking base timing is always part of the diagnostics game which also includes checking to ensure the timing is still advancing and reaching the near max degrees at higher RPM. In your case you should be advancing up to right around 23 - 30 +/- a few degrees (< just depends on load) at around 3000 RPM.
Now that the bolt has been backed off, it could have changed the timing a bit plus the work of trying to move it may have possibly changed it too... Yes it's still worth checking timing but you shouldn't have to move or loosen it up first just to check if it's in range.
Move it if it's out of range.
It just dawned on me. While I was cranking the engine and it wouldn't start, I took it out of gear and goosed the throttle and I noticed that the injectors stopped squirting fuel down after getting more than 1/4 of the way up throttle, at the time it happened I figured it must be a computer controlled safety thing, but now I am wondering if I may have a fuel pressure issue.
This system has what is know as a clear flood mode which it will stop fuel flow out of the fuel injectors once the throttle is advanced to a programmed percentage setting within the ECM. Engine models very for what throttle percentages activates the clear flood mode. Some are at 50%, some are 75 and 100%. I don't recall what yours would be as there is no official written word for each engine model.
The important thing is that you see fuel coming out of the injectors while in neutral/idle position. In some cases to help with checking the IAC for non proper operation, it may be helpful to open the throttle plate about/almost 20% to see if giving the engine more air will help start the engine easier., < That mentioned, if you happen to go to far, you lose fuel injector pulses by entering clear flood mode...But once you find your % range, you can sometimes go past the range to get your fuel injector pulses back unless yours is set at 100%...Then back the "Throttle Only" down.
Yes checking fuel pressure is going to be part of the diagnostics too. You need a special fitting from Mercruiser to go inline of the inlet fuel hose right at the back of the throttle body.
