RPP conundrum

The General · 28-03-2011, 09:05 AM

Hi, my p20 is running a 225 promax and is currently down on revs. It will only do about 5k rpm. We've tested the sparks and fuel and all appear to be right, compression is fine, it has just lost it's top-end grunt. Could it be the oil we are now using (quicksilver with the orange label)? We have a 27" prop and it has previously run fine with it so i don't think it's the prop. The change happened when we were in the Exmouth boxing day fun run, suddenly for no apparent reason it just wouldn't rev to it's normal scream.

Any thoughts, ideas would be greatly appreciated.

Renegade · 28-03-2011, 09:24 AM

Quote:

Originally Posted by The General

Hi, my p20 is running a 225 promax and is currently down on revs. It will only do about 5k rpm. We've tested the sparks and fuel and all appear to be right, compression is fine, it has just lost it's top-end grunt. Could it be the oil we are now using (quicksilver with the orange label)? We have a 27" prop and it has previously run fine with it so i don't think it's the prop. The change happened when we were in the Exmouth boxing day fun run, suddenly for no apparent reason it just wouldn't rev to it's normal scream.

Any thoughts, ideas would be greatly appreciated.

Not had much experience with mercs, does it sound like its down on a cylinder? possible injector problem? coils?

The General · 28-03-2011, 10:23 AM

All the cylinders are fine and we had the coils tested and they are ok. Perhaps injectors, I'll take a look at those.

still no worries · 28-03-2011, 10:24 AM

it could be the stater

Hydrostream · 28-03-2011, 12:36 PM

Get the injectors serviced. Could try blowing back through the injectors with compressed air, do this over a clean sheet of paper to see does any crap come out.

I use a 1" piece of 3/8 fuel hose that fits on the end of an air blower, fits snug over the end of the injector. Hold it on tight and blow.

Spray some carb cleaner into the injectors first and let them sit for a bit before.

Renegade · 28-03-2011, 03:21 PM

Some of the probs i have had with injectors is the slightest bit of muck clogging them up will upset the spray pattern and it definately does affect the running, again i have never dealt with your engines but possibly a starting point.
I have had rust get into injectors where water has got into the fuel.
Paul

The General · 28-03-2011, 03:48 PM

We'll try with the injectors. When we took the fuel filter and water separator off, they were clogged up with bits of rust and gunk so maybe some's gone through. Thanks for the tips Gents. I'll report back once injectors are cleaned.

larby · 28-03-2011, 04:48 PM

In that case have you checked everything else in the fuel system properly? Things may seem to be fine but still may not be able to cope with the requirements at full RPM?

James

Renegade · 28-03-2011, 06:23 PM

Quote:

Originally Posted by The General

We'll try with the injectors. When we took the fuel filter and water separator off, they were clogged up with bits of rust and gunk so maybe some's gone through. Thanks for the tips Gents. I'll report back once injectors are cleaned.

If that is the case, i would consider changing any fittings you have that could be causing the rust, i pressume you dont have a steel tank? and while your at it if fuel lines have not been changed for a while do them, fuel injected motors don't like tthese sorts of little problems lol.
All fuel flow must be spot on.
Good luck mate

freedom · 29-03-2011, 02:35 PM

Quote:

Originally Posted by The General

Hi, my p20 is running a 225 promax and is currently down on revs. It will only do about 5k rpm. We've tested the sparks and fuel and all appear to be right, compression is fine, it has just lost it's top-end grunt. Could it be the oil we are now using (quicksilver with the orange label)? We have a 27" prop and it has previously run fine with it so i don't think it's the prop. The change happened when we were in the Exmouth boxing day fun run, suddenly for no apparent reason it just wouldn't rev to it's normal scream.

Any thoughts, ideas would be greatly appreciated.

The injectors were done a few years ago, but, if theres rust in the system,

i rekon it sounds like they could be done again. was that in the seperator in the boat, or the one on the motor? Had a problem with it a year before i sold it to you, fuel didnt seem like it was getting through,would start up and then immidetly cut. did a comp test etc and was all good, but myself and burty were stumped. sent it to burt,down at mobile marine at the time, and it came back absolutely fine, never had another problem with it. Don't know if that helps in the slightest but just thought id give you a bit more history

The General · 07-04-2011, 01:58 PM

Thanks all for the posts. Problem is now fixed. After checking compression, injectors, stators etc, fule lines and separators, it turned out to be the spark plugs. They had degraded such that when put under pressure at high rpm they couldn't take the strain. Some new high performance plugs in and all is good. Fingers crossed it stays that way...

It looks like we will be in the fun run on 23rd April at Exmouth after-all.

Thanks again all for the help.