2001 5.0 mercruiser with carb.

[Dave 200 SSE]

I bought a 2001 Chaparral with 5.0 carb. The first thing I did is a complete tune up, plugs ,wires , cap & rotor, ignition mod in distributor , rebuilt the carb and checked the timing on it. I have had it running this summer but the problem I'm having with it is, # 3 cylinder spark plug fouls out with dry black soot. I have checked for spark on the cylinder and have it. My question to that is, would I have a bad set of lifters and cam shaft or something going wrong with the coil, or bad valve guides? I have readjusted the rocker arms to make sure they are properly set. Kind of lost to what could be the problem. Also did a leak down test on all cylinder, they all are good! Any suggestion would be Greatly appreciated ! Thank you for your time! Dave

 

[achris]

Check the lift on the valves of that cylinder and see if the cam lobes have a problem. If it was a coil problem (and I have yet to understand why people head straight for the coil when the number of genuinely failed coils is so small) it would show on all cylinders, not just one. Check the cap, the rotor, the lead, even the spark plug itself. But your problem is not the coil. If you have bad guides, the soot would be oily, not dry. I'd replace the spark plug first...

Chris......

 

[Scott Danforth]

first thought - bad plug
second thought - bad wire
third thought - wires crossed
fourth throught - bad cap

rotor and coil fire every cylinder so that cant be it

 

[DaveG55]

Quick check of plug is to just swap it with a different cylinder. Free too. Works for wires to if you have the old ones or enough length.

 

[Dave 200 SSE]

" Thank You for your suggestions"! I have tried changing the plugs around and have had the same results. I think I will try putting a new cap and rotor on and I do have the old spark plug wires, I'll try changing that one out as well. I have a hard time thinking that the motor is hurt at all with only 210 hrs on it.It definitely makes sense about the coil! There is one thing I did notice when checking the spark on the spark plug wire from the cap to the wire, when I removed it, there would be a spark that went from the center of the coil to the positive side terminal on the coil. Is that normal for that to do that? I'm not and expert when it come to electric! Thank You again! This is the first site that I have talked to other people that have experience in Boating. Very Helpful ! :happy:

 

[NHGuy]

The reason the spark jumps is that's the closest ground. If you want to check for spark put a plug in the wire and ground it.
Same as cars, EXCEPT, only do this if the bilge is absolutely clear of any possibility of fuel vapors.
Any fuel vapor and you could become a statistic.

 

[Dave 200 SSE]

Hello! Okay, now I have and electrical Question! Has anyone Ohm a sparkplug wire on a thunderbolt lv system? I'm getting 15.32 ohm on most of my wire's, is that to high of ohms for stock wires? Thank You for your response's!

 

[NHGuy]

The manual for my 89 TB IV engine does not give an ohm value. It only says there must be continuity.
Sounds like you already understand things, but here are some slim possibilities:
You can test the wires by running the motor in a dark space and spraying a water mist on them. Fails will arc to ground.
One post last year had the wires on backwards. Make sure you have the correct ends on the cap and the plugs. The plug ends have a catch inside them that fits over the tops of the plugs. They hold the top."nubs" on the spark plugs. The cap ends have a springy metal piece inside that holds against insides of the cylindrical towers on your distributor cap.
Also watch out that you haven't broken the insulator on that spark plug. I have broken the porcelain on a new spark plug before due to the shape of the water jacket marine exhaust manifolds. When torquing the plug, it snapped. Once I ground down a plug socket to reach past my exhaust manifolds, not so much of an issue.

 

[Dave 200 SSE]

Hello! Its been awhile ! I have a question for anyone that might have a Great answer! I took my boat out after having the motor totally gone threw and I have the same problem before, Running to rich! Checked the fuel pressure and it was at 9-10 lbs. Have rebuilt the carb twice, I checked the timing on it and I saw that the timing really doesn't advance the way I think it should. I have a thunderbolt V system. Has any experienced a bad ecm? Could a bad one create the problem I'm having? Thank You for your time!

 

[Dave 200 SSE]

For everyone out there and that gave me Great advise, Thank You ! I have learned a lot in this experience with this Boat! The one advise that I can give anyone who is trying to find out what problem you have with a motor is, Lean how to read a Vacuum gauge ! I found out that I have a bad came shaft! Thank You again!

 

[NHGuy]

Cool, cam changes are kinda fun. do it yourself!
But, you need to get the motor out because the front cover, where the cam lives, can't come off til the oil pan is off.
OTOH if you want it back quick, pay the man.