7.4 MPI - bad sound

K

Kimpa

Member
Jan 9, 2017
31
Boat Info
270 Sundancer 1998
Engines
7.4 Mpi
Hello!

Im got a new problem with one of my engines, when it's warm this sound accours. (Se the video)
The sound is sometimes louder and sometimes almost gone.



Last year i changed the belt, belt roller, waterpump, manifolds and risers om both of my engines so i dont think it's belt related.

My boat is a 340DA with ZF IV63 v-drives.

Any ideas?

Thanks / Kim
 
that knock sounds very similar to the knock my starboard engine was making when I had a dead fuel injector.....will that engine reach WOT rpm range?.....mine would not, so that is why I had a mechanic use an analyzer to locate the problem....as soon as the injector was replaced the knock went away....

good luck....

cliff
 
Thanks for all advices, next week in going to troubleshoot the engine.

Ill return with results.

/ Kim
 
CliffA said:
that knock sounds very similar to the knock my starboard engine was making when I had a dead fuel injector.....will that engine reach WOT rpm range?.....mine would not, so that is why I had a mechanic use an analyzer to locate the problem....as soon as the injector was replaced the knock went away....

good luck....

cliff
Click to expand...

Hello, i have 5 blades props wich gives better fuel economy at lower speed but the downside is lower topspeed and max rpm's

So i can't tell about the WOT rpm's, the engine goes even and smooth so i dont think i miss a cylinder.

I had 7,4 MPI's before and also friends and i have heard a little knocking in every engine i think.

But i can get hold of a analyzer and i think i will make a test.

Thanks / Kim
 
Kimpa said:
Hello, i have 5 blades props wich gives better fuel economy at lower speed but the downside is lower topspeed and max rpm's

So i can't tell about the WOT rpm's, the engine goes even and smooth so i dont think i miss a cylinder.

I had 7,4 MPI's before and also friends and i have heard a little knocking in every engine i think.

But i can get hold of a analyzer and i think i will make a test.

Thanks / Kim
Click to expand...


does the engine at least match the WOT rpm's of the other engine?....my engine started fine and idled fine also even with a dead injector.....

cliff
 
CliffA said:
does the engine at least match the WOT rpm's of the other engine?....my engine started fine and idled fine also even with a dead injector.....

cliff
Click to expand...
Ah.. okey.
Well i don't really know.. it was a while since i made a real WOT test.. In my country (Sweden) we have so much Islands around and i dont open the trottle that often, but did your mecanic se the bad injector straight away with the instrument?

/ Kim
 
Kimpa said:
Ah.. okey.
Well i don't really know.. it was a while since i made a real WOT test.. In my country (Sweden) we have so much Islands around and i dont open the trottle that often, but did your mecanic se the bad injector straight away with the instrument?

/ Kim
Click to expand...

it took him a few mins while watching the analyzer as the engine was running.....but not too long....

cliff
 
CliffA said:
it took him a few mins while watching the analyzer as the engine was running.....but not too long....
cliff
Click to expand...

Sounds good, im going to rent the instrument over the weekend and also trubbelshoot the thread's main issue, ill come back with the results.

/ Kim
 
Kimpa said:
Sounds good, im going to rent the instrument over the weekend and also trubbelshoot the thread's main issue, ill come back with the results.

/ Kim
Click to expand...

unless you know how to interpret the data from the analyzer you may not be successful doing this yourself....

good luck...
cliff
 
Well i found the problem, it was a lifter and rod with to little oil, i opend the other refil oilcap and squirted some oil and the sound dissaperd.

Why this started is still in the to do list, that lifter is the highest point of the engine because it's leaning a little, i have good oilpressure and it might be a clogged oil chanel perhaps

/ Kim
 
also be sure you are running the correct weight of oil...too thick oil might not get pumped around the engine properly....

cliff
 
I have seen the roller lifters make noise like that on a SBC in a GMC Yukon
 
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