3 Dead Cylinders on Merc 233 Ford 351W

[75Cobalt]

I have a 1975 19ft Cobalt it has a 233 Merc.

The problem I have is that 3 Cylinders are dead. They have spark. But at idle when I disconnect each plug wire three cylinder have no effect at all on the performance. The dead cylinders are 2,3,4. Anyone have any ideas for me? All other cylinders greatly effect to performance of the engine when I disconnect the wires.

 

[mkast]

Re: 3 Dead Cylinders on Merc 233 Ford 351W

What's the compression in these cylinders?

 

[Bt Doctur]

Re: 3 Dead Cylinders on Merc 233 Ford 351W

Yep, compression test first (with all the plugs out and carb wide open)

 

[75Cobalt]

Re: 3 Dead Cylinders on Merc 233 Ford 351W

#1 150
#2 120
#3 120
#4 130

I have not tested the other side of the engine.

 

[75Cobalt]

Re: 3 Dead Cylinders on Merc 233 Ford 351W

i will double check. but i am almost positive that it is correct. just doesnt seam right for three to be dead on one bank.

 

[75Cobalt]

Re: 3 Dead Cylinders on Merc 233 Ford 351W

Yes, mine is a 351W

 

[searay3]

Re: 3 Dead Cylinders on Merc 233 Ford 351W

Check the plug wires and ends (connectors). Also inspect the cap and rotor, etc. You have compression. I have seen weak ignition systems that will spark out the coil tower and even at the block with a spark plug attached and not fire under compression. Age of the wires, they break down over time.

 

[75Cobalt]

Re: 3 Dead Cylinders on Merc 233 Ford 351W

Plugs, Wires, Cap, Rotor and points and condenser. all new

 

[Bt Doctur]

Re: 3 Dead Cylinders on Merc 233 Ford 351W

sounds like the firing order if off.
what order are they in now?

 

[KRH1326]

Re: 3 Dead Cylinders on Merc 233 Ford 351W

Make sure and double check: 1-3-7-2-6-5-4-8 it is way too easy to crosswire. also make sure not 1-5-4-2-6-3-7-8 (old 302).

PS If someone tells me how, I would post 3 large pdf files that I have:
OMC 64-86 Repair Manual
OMC 86-98 Repair Manual
OMC Wiring Diagrams ALL

 

[Bt Doctur]

Re: 3 Dead Cylinders on Merc 233 Ford 351W

The dist. rotation is CCW on the fords, check that first in case you got a reverse rotation motor.
351W,all351, and 351HO use 1,3,7,2,6,5,4,8

 

[75Cobalt]

Re: 3 Dead Cylinders on Merc 233 Ford 351W

Right now i am not near the boat to triple check the firing order. But if the wires were that crossed you would think that it woudl be back firing. Am i wrong?

 

[75Cobalt]

Re: 3 Dead Cylinders on Merc 233 Ford 351W

Well i check the wires per the firing order that you guys gave and i had a couple of wires crossed. Yes, it was the #2,3 and 4 cylinders. But of course teh battery is dead. but i think the problem has been corrected. Thank you so much for all of your help. Some times you just dont see to obvious fix.

 

[KRH1326]

Re: 3 Dead Cylinders on Merc 233 Ford 351W

I can't tell you how many times I crosswired boats and trucks and cars. The first second and third thing I look for. Or did the old 302 firing order instead of 351W. You get the idea.

 

[75Cobalt]

Re: 3 Dead Cylinders on Merc 233 Ford 351W

i will just leave out the part that i have been an aircraft mechanic for 13 years. But now the first time the easiest thing to fix is over looked

 

[Bt Doctur]

Re: 3 Dead Cylinders on Merc 233 Ford 351W

Join the club, the easiest thing to overlook is the obvious.

 

[paolinij]

Re: 3 Dead Cylinders on Merc 233 Ford 351W

The dist. rotation is CCW on the fords, check that first in case you got a reverse rotation motor.
351W,all351, and 351HO use 1,3,7,2,6,5,4,8

Can you tell me where the #1 wire attaches to the distributer cap? I can go from there. Thanks.

 

[Don S]

Re: 3 Dead Cylinders on Merc 233 Ford 351W

Start a new thread with your questions, don't just change the subject and hijack someone elses post.