Merc 260 Injectors & EGT

Randy - 

I have a 260 centerhorn (1997) which has been running great, until this winter.  I have an EGT temp sensor on both sides and as time goes on it seems to be running hotter with less and less RPM. (1200 to 1300 degrees) Could my injectors be clogged?  How do you check this and how can they be cleaned?  The water temp gauge rarely goes above 100 degrees.  Compression is 132 to 139 lbs. Premium gas and Mercury Synthetic Blend oil. 

 Kevin Taylor  1988 HST



From your description your motor sounds healthy. The compression is good and the temp is fine. Water temp I mean. Here's my opinion of EGT gauges. They vary. Unless you blow it up and don't go to that temp again you'll never know what the edge is. I've had EGT's read 1450 and the motor was totally happy. I've also seen them burn down at 1000 degrees so who knows. In the past we have seen the probes read higher as they get older. I guess what I'm saying is read the piston domes and compare to the EGT. Then use the EGT as a reference. Now where did your performance go? Here's my thinking. The 97 2.5's have titanium nitrated piston rings. They peak out at about 25 hours. That's not a typo. If you have , lets say 100 plus hours on, they're probably shot. They will still show good compression but the rings just don't perform. If you have a lot of hours, I'd look there. That motor came with a A49 ECU chip. Check or better yet replace the Kinser fuel filter every year. Take it off and blow through it. If you can't feel your breath on the other end easily chuck it. I've seen this at least 5 times a year cause a 2.5 to lose power. This would be my first bet. The EGT's don't show an increase in temp because the motor is making marginal power. I'm curious so let me know what you find. Hopefully it's that simple and it works. Back to the chip. The 49 chip is actually pretty rich. If your rings are healthy and fuel flow is ok you might want to try the A48 chip. It's the 97 drag curve. I've run it for 5 years and all my boating buddies run it. Most of the time it's an instant 200 rpm. Much crisper acceleration. Just make sure the motor's healthy and you've got good fuel delivery. If you can't find a chip and want one let me know as I keep at least 10 at all times. 

Hope this answers some things and helps find the lost rpm.



Please submit whatever questions you have to  All questions and answers selected will be displayed on this page as they come in.  Note: though all boaters are welcome, priority may be given to I.H.R. members.  Randy can not be held responsible for any advice given.  Though his information and expertise is second to none, he has no control over what you do with your boat.  It is up to you to boat safely and act responsibly, and his advice is only to be used as a guidance for your high performance boat/motor of which you are the one responsible for the risks involved.

Mark C.


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