Engines are 2003 5.7 Captains choice(MPI), 835 hours. I have been chasing this power loss for manymonths without success. Both engines seem to run the same up to 2500rpm or so, and even run the same at higher rpms until they have beenrunning for 20 minutes or so. At that point the port engine makesless power than the starboard and needs much more throttle tomaintain equal rpm. At speed it acts exactly like the engine didseveral years ago when it had a burned valve and no compression onone cylinder. Back then the miss was not noticeable to the ear athigh rpm but the same throttle advance was needed. Only now I havegood compression on all cylinders (180 plus/minus 10). Also when atidle it does not “rattle” like it did when a cylinder had nocompression and also the plugs all appear dry and a good consistenttan. So I think it is firing on all eight at lower rpm (trolling andreturning to the marina) but not at high rpm. And on rare occasionswe can go to high rpm for some time and not have the issue, althoughit usually shows up before the day is done. Both engines have newraw water pumps and no overheat issues are detectable.
So far I have checked fuel railpressure when the problem occurs and found it the same in bothengines all the way to WOT. Rails hold pressure after shutdown whichmeans an injector is not stuck open. All injectors are correctlyplugged in. I have put in a new rotor and distributor cap and haveswapped coils with the other engine. I also have swapped MAPsensors. The throttle controls/cables have been inspected and aresound. The rpms shown on the tachs agree those on the scanner. Arecent scan showed no significant differences between the engines atidle. At 4000 rpm (throttles set to achieve this on both engines)the scanner showed the port engine (weak one) at 51% throttle, 15.2GPH fuel flow and 25.9 HG manifold pressure. The starboard engineshowed 38% throttle, 13.2 GPH fuel flow and 22.5 HG manifoldpressure. Advance (29/28 degrees) was essentially the same on bothengines. If you presume one dead cylinder on the port side engine,resulting in only 7/8 of the fuel being burned, you can thencalculate that both engines at 4000 rpm are actually burning the sameamount of fuel (13.2 GPH) to generate the same power (4000 rpm),which supports the dead cylinder theory.
I have put the boat (now in Mexico) onthe hard until next fall and returned to Florida. What I am tryingto do now is come up with a plan to find the problem next season butI am about out of ideas. It sounds electrical to me because of theintermittent (possibly heat related) nature. When I return I intendto swap computers (longshot but easy to do) and then swap plug wires,although they are fairly new and genuine Crusader so unlikely to bethe issue. Then, other than the wiring harness plugs between thecomputer and coil (hard to check but I will inspect), abouteverything electrical (except injectors) has been replaced orswapped. I suppose I can also swap all the injectors (bigger job)and at that point I think have exhausted the electrical and fuel sidepossible issues.
So I am down to a few unlikelycandidates which could reveal the problem. If that does not work Iam looking for ideas on where to go next. Maybe some of the pros onthe forum have solved a similar problem that had an uncommon cause.Thanks for any suggestions or theories.
So far I have checked fuel railpressure when the problem occurs and found it the same in bothengines all the way to WOT. Rails hold pressure after shutdown whichmeans an injector is not stuck open. All injectors are correctlyplugged in. I have put in a new rotor and distributor cap and haveswapped coils with the other engine. I also have swapped MAPsensors. The throttle controls/cables have been inspected and aresound. The rpms shown on the tachs agree those on the scanner. Arecent scan showed no significant differences between the engines atidle. At 4000 rpm (throttles set to achieve this on both engines)the scanner showed the port engine (weak one) at 51% throttle, 15.2GPH fuel flow and 25.9 HG manifold pressure. The starboard engineshowed 38% throttle, 13.2 GPH fuel flow and 22.5 HG manifoldpressure. Advance (29/28 degrees) was essentially the same on bothengines. If you presume one dead cylinder on the port side engine,resulting in only 7/8 of the fuel being burned, you can thencalculate that both engines at 4000 rpm are actually burning the sameamount of fuel (13.2 GPH) to generate the same power (4000 rpm),which supports the dead cylinder theory.
I have put the boat (now in Mexico) onthe hard until next fall and returned to Florida. What I am tryingto do now is come up with a plan to find the problem next season butI am about out of ideas. It sounds electrical to me because of theintermittent (possibly heat related) nature. When I return I intendto swap computers (longshot but easy to do) and then swap plug wires,although they are fairly new and genuine Crusader so unlikely to bethe issue. Then, other than the wiring harness plugs between thecomputer and coil (hard to check but I will inspect), abouteverything electrical (except injectors) has been replaced orswapped. I suppose I can also swap all the injectors (bigger job)and at that point I think have exhausted the electrical and fuel sidepossible issues.
So I am down to a few unlikelycandidates which could reveal the problem. If that does not work Iam looking for ideas on where to go next. Maybe some of the pros onthe forum have solved a similar problem that had an uncommon cause.Thanks for any suggestions or theories.
