2 cylinders down

[dedhead63]

I have a 1997 Merc 5.7 LX 4 bbl. The issue is that 2 starboard side cylinders seem to be dead! The plugs are new and are only wet with fuel. The engine will idle fine, but under load bogs down. The cap and rotor were replaced last season, however the wires are at least 8 years old! I know, its boat abuse. I did rotate and replace the plugs with no luck. New wires will go in tomorrow. Am I on the right track? Or do you think I have bigger issues. The engine only has 300 hours on it and it ran fine in the spring before being winterized.
Its the 1st two from the front if that helps.
PG

[Bootstrap1]

uh yea, replace those wires dude. Put a timing light on the wires and check to see if it flashes, thats a real easy way to check for spark.

[Don S]

The engine will idle fine,

An engine will not idle "FINE" with two dead cylinders. I have heard customers say that before, only to find no compression on 2 cylinders. It may sound fine to you, but it's not fine.
Have you checked to see if you have spark from the two dead cyliners plug wires? Have you done a compression check?

Its the 1st two from the front if that helps.

Does that mean one on each side? If so, check to see if the wires are in the correcto location on the distributor cap.

[Bootstrap1]

An engine will not idle "FINE" with two dead cylinders. I have heard customers say that before, only to find no compression on 2 cylinders. It may sound fine to you, but it's not fine.
Have you checked to see if you have spark from the two dead cyliners plug wires? Have you done a compression check?



Does that mean one on each side? If so, check to see if the wires are in the correcto location on the distributor cap.

This was going to be my next suggestion, but I didnt want to scare him yet...

yea, check compression....

[dedhead63]

I will do a comp test tomorrow. The two cylinders are on the same side.
Thanks for the quick reply.
PG

[dedhead63]

Ok pro's.. New wires, re-gap plugs and 150-180 on my compression test. Still poor power at all under load conditions. I did pull the wire off one of the suspect cylinders and the alarm sounded and the engine began to spudder.

[bomar76]

Swap those 2 spark plug wires to the other plug...
i.e. put the wire now located on spark plug 2 on 4, put spark plug wire that was on 4 on 2.

Report back with results.

[dedhead63]

All the wires are new. The motor runs fine at idle and when I remove a wire I get and alarm and the motor misses. The issue is under load! My mech said it might be a valve issue, I'm meeting him tomorrow to check it out. I hope its not a major issue I just sunk 4k into this engine and drive last year. It has low hours, but still I'm thinking maybe just replacing the engine. It has a Bravo 3 drive that just had the transom assem replaced last year.

[Don S]

The motor runs fine at idle and when I remove a wire I get and alarm and the motor misses.

I have no idea what your problem is, but the alarm when you pull a plug wire off is wrong.
The only alarms you have is Gear lube low, High coolant temp, and low oil pressure.

I'm betting on crossed plug wires and so far out of time it sounds ok at idle.