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2000 M/C 5.0 0m012817. Two cylinders not firing

R

rick3452

Regular Contributor
Hi guys! 2450 hrs on boat all intercostal easy use. Recently started running rough above idle. I changed plugs, cap and rotor also had carb rebuilt. Still rough, At idle I started pulling one wire at a time off distributer cap. Two wires on the starboard side of the motor made no difference in the running at all. The others were noticeable. I pulled the wire off the plug that wasn't firing and tested it with a screwdriver and grounded it and the spark was good. Any thoughts?
thanks!
Rick
 
When were the plug wires last replaced? Use a multimeter and measure resistance in the wires and see if the two 'dead' cylinders ohm out the same as the others that are firing.

Also, if you're looking to measure spark, I would suggest an inline spark tester rather than grounding out a screw driver.
 
Worst case is a new short block. These run about 1500. However, you might as well bite the bullet at that point and get the long block. Rebuild cost is roughly another 50 percent more than buying another engine.
 
rick3452 said:
Thanks Chris, So if the compression is low, its pull the motor time? Ballpark cost of rebuild?
Click to expand...

Depends on what shape the rest of the parts are in. You can start to approach the cost of a complete drop in engine when doing a long block if the rest of the parts are in poor shape.

I would do the repower with a 5.7... I am not a fan of the 5.0Ltr engine.


What type of boat is it? Single or twin?
 
..."I would do the repower with a 5.7... I am not a fan of the 5.0Ltr engine. "

Me too! Both motors weigh the same yet one has a lot less power.

I'm thinking blown head gasket IF those two cylinders are side-by-side. Are they?

Jeff
 
Confusing thing to me is that it actually runs strong gets up on plane quickly 4400 rpm's no problem at all and only on six cylinders to be honest it's probably been like this for quite a while without me knowing because of the intercoastal cruising that I typically do at 1200 rpm's
 
DON'T Keep running it, and here's why. Had the same issue with one of my Chrysler 360s and the block was ruined. The exhaust gas blasting back and forth between the cylinders 'fire slotted' the block which had to be scraped.

Jeff
 
****** UPDATE***** Hi guys, did a compression test today #1=180 #3 =160 #5 =160 # 7 =160
# 2=180 #4= 20 # 6= 30 # 8= 180

On the two low cylinders I squirted oil in the cylinder and re-tested no change at all
Appreciate your thoughts and direction.... with almost 2500 hours on this 5.0 carb, motor, should I fix it, or put in a 5.7 reman or new?
thanks! Rick
 
put in a 5.7 reman or new

Dont waist time rebuilding a 2500 hr engine...........

A fresh 350/5.7L REMANUFACTURED long block.................~$2500-$3500 depending (confirm oil pan and oil pump, not all come with, if not order it with it already installed). All external accessories will bolt right up!

only issue is intake and carb if its a carb.

If your current is a 2bbl carb then a new/used manifold and new/re-manufactured carb will also be needed.

If it is a four bbl carb then the manifold should be good and a re manufactured 4 bbl for 5.7 will do the trick ~ $ 300
 
$4500 plus shipping, right? Gonna need that carb. They come with the cast iron intake, no need to go the aluminum. I have heard they are very good. You should be able to get a few hundred for your 5 litre core. Some classes in dirt track racing use the 5 litre. Marine blocks are normally cherry picked for minimal core shift and make excellent race engines. Commonly we found a higher nickel content in the cast iron as well. Why? It makes a longer life motor, by providing a higher quality cast and minimizing cylinder wear. My guess your problem will be that head gasket as mentioned early on by another fine tech. Expect to change your prop too, your old one will allow excessively higher rpm.
 
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I did a quick look.

I found this, It is complete long block minus intake and carb.

Brand new! Cant beat that price for new!

The three links are just suggestions. In the end it's your choice.

The three items would give you ~ 270+ hp

So you are looking at based on my quick look, ~$4000.000 for a nice replacement set up with a NEW engine!




Engine

http://www.atlanticmarinestore.com/mercruiser-5.7/

Manifold

https://bpi.ebasicpower.com/shop/al...3_1130&zenid=21b86403d75dea658cea8873f1b7b75c

Carb

https://www.carbcareusa.com/collect...marine-electric-choke-350-5-7-merc-crusader-1
 
Rick 3542- I bought a Michigan Motorz Silver pacakage three years ago, worked out very well. They tweaked the pacakage to not include things I didn't need (fuel pump), and include things I did want (TBV ignition vs Delco), and would honor the warranty (didn't need it) for a home installer vs requiring professional installation. In the end saved me a bunch vs getting a complete bobtail as I could reuse my original accessories

i would definitely take the advice and upgrade to the 5.7, just may need to step up one pitch on the prop. I went from a 4.3 to 5.0 and kept the same drive ration ended up going from 19" to a 21" prop but works just fine.
 
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rick3452 said:
****** UPDATE***** Hi guys, did a compression test today #1=180 #3 =160 #5 =160 # 7 =160
# 2=180 #4= 20 # 6= 30 # 8= 180

On the two low cylinders I squirted oil in the cylinder and re-tested no change at all
Appreciate your thoughts and direction.... with almost 2500 hours on this 5.0 carb, motor, should I fix it, or put in a 5.7 reman or new?
thanks! Rick
Click to expand...

Just curious, my guess is you tuliped a couple of intake valves, Pull the valve cover on the weak side, remove all rockers and put a straight edge across the valve tips. Are the intake valves sticking up higher on the cylinders in question?
 
Thanks guys for all the help! I found a guy here in Fort Lauderdale that replaces motors all the time. I'm putting in a NEW GM 5.7 Long Block,($3300 ) Also having him put a Johnson Crank mounted Sea Water pick up, and yes I have just enough room. A couple of years ago I installed a through hull sea water pick because of the issue with "Bravo-itis" Plenty of water now....
Really appreciate all you guys very much.
Rick
 
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