anyone know what causes misfires?

[c9legendzum]

i just bought a 1996 four winns 238 vista and test drove it once. the engine was misfiring so the owner paid to get it fixed. what he told me was that one of the injector wiring was not giving connection. so he got it taken care of. second test ride went good. i took the bought home, and my first ride out was also good. everything worked as it should. several times starting and stopping the engine with no problems. the next weekend i take it out and the same misfiring happens. been trying to determine the cause now. all fuel injectors run at the requirement, spark plugs might be old but each of them fire. fuel treatment added, fuel/water separator filter changed, fuel filter changed, and hoses checked and changed for any possible cracks. is there anything i missed? oh by the way. the engine also shakes slightly. i think the timing belt might be correct cause how can it run good one day, misfire the next day then run good again and misfire after that? if anybody could help me out please that wouldd be great. tomorrow i will remove the distributor cap and check the inside for corrosion. im thinking of changing the spark plug wires also for the heck of it and hope for the best.

 

[Chris]

Unfortunately, the cause could be from numerous things.

It can be igntion related, timing related, fuel related, or even computer related.

What I usually do first with that type of problem, is that I pull each of the spark plugs and see if what kind of shape they're in. I would specifically look to see if any specific ones are wet, or if they're burnt differently from the others. If you find one that seems like it looks different from the others, that could be a clue. It seemed like you mentioned that they're a bit old, so as a first step, I personally would replace them and at least you can eliminate one potential cause.

Let us know how you make out.

-Chris

 

[c9legendzum]

i changed 6 of the 8 that i could remove. one was wet, the other was a little bad. the rest looked semi good still. the engine still acts the same. one thing i noticed though is that when i had one plug off and turned the engine on, the engine did not shake. so i will go ahead and change spark plug wires. i dont think thats the problem either. any idea about how to check the fuel pressure?

 

[Chris]

The condition of the plugs will give you a hint as to whether all the cylinders are firing. If you've got wet ones, that could mean that those plugs aren't firing all the time, or at all.

I always look for differences between them.

Have you checked the compression?

The timing chain/belt I would imagine you can check by wrenching a bit on the fly wheel to see if there's excess play or not.

Keep us posted on how you make out.

-Chris

 

[c9legendzum]

ok i think i have narrowed it down to just that spark plug i found was wet. i dont think its water. but it doesnt smell like gas or look like oil. although i can be wrong on either of them. if its water, im sure the exhaust manifolds have to be checked and cleaned. what if its gas or oil? the old plug i removed was wet, the new one i replaced, just checked a week ago, is wet also. so what causes a spark plug to get wet and how can i fix that (being it not water)?