26sonic

i have a 1998 502 efi in a 26 ft boat . have added to the engine the following upgrades : rev. marine exhaust , adj. fuel reg( set @ 42psi), k+n flame arrestor, msd ignit., ecu reprog. (az speed +marine ) ngk plugs gapped @.40 and bumped timing from 8deg to 10 deg. . am using a 24p 4 blade bravo 1 prop spinning 4800-4900 wot @ 66mph . just labbed that prop and now run 68.5 mph 5100 rpm wot. question is after doing these upgrades my low end throttle response is'nt any better than stock , mid range is better , but from 3/4 throttle to full throttle the engine does'nt really pull any more ? it's like it has a flat spot on top? originally before all these changes on my stock engine with just k+n flame arrestor and 23p 3 blade labbed prop spinning 5000rpm wot was able to hit 69-70 mph gps ? i'm dissappointed thought i should have gotten better results !! could it be the ecu is prog. wrong ? fuel pressure wrong ? any ideas ?

Trippin

Last I knew one could not "re-program" an EFI ECM unit from Mercruiser. One could only confirm or dispell a problematic function within the EFI system, seek and destroy type diagnosis. A total system reset function would be about the most dramatic function you could expect from the EFI remote scan unit.

I could be wrong however I am not discounting the fact that there may be and probably is someone out there with a utility to "reprogram" an EFI ECM, if there is I want a copy of the software cause it'll be in the form of a laptop unit with EEPROM re-write capability. But certainly will not be factory authorized equipment and just the shear implication of it's use would not only void any warranties you may have from Mercury but could leave you civily liable if your power plant has a serious malfunction and subsequently injures someone on your vessel, blah blah blah... Anyway;

Your timing at idle from the factory is set @ 14deg BTDC, max advance @ WOT is 34deg BTDC. I would suggest: Re-installing your 3 blade, re-set your idle timing to factory spec, of course to do this you must put your engine in base timing mode first, install a fresh set of NGK-BR6FS plugs - gap to .035, and change your oil and filter while your at it, maybe go to a full synthetic. Then take her back out and see what happens, sometimes the simplest of adjustments make all the difference. As long as you have at least 3-7psi in the main fuel line that is sufficient volume for the high pressure pump to deliver it's fuel supply to the VST, rail, and back again.

Just my opinion.

26sonic

ttt

obnoxus

What does your transom look like after a day of hard running?

Raylar

26Sonic:
First you state you have changed your prop from a 23p to a labbed 24p, this could mean more than a 1" to 2" increase in pitch for your boat and this would need about 40 to 50hp increase in your motor to need this additional pitch. I doubt the changes you have made have given you even 20HP, hence you are probably overpitched. The running condtions you describe seem to point to this. I would put a 23p prop back on and see what happens. If this doe not help then consider the following: Your 502efi being a 98 model should have a MEFI3 type computer. There are many people in the industry who can reprogram these with software. Some of your mod's like the exhaust are fairly significant and I would guess the programing might still be a little off. You might want to run the boat at WOT under load and shut it off quickly after the run. Pull a couple of plugs and check them. If the pluggs are real black and soty then the computer could be giving you to much fuel at WOT. If they are light almost white or light grey the computer setting is probably to lean. This lean can damage your motors real fast so don't run a lot if this is the case. The plugs should be tan and clean if the fuel setting at WOT is right in the computer.

26sonic

raylar the 23p 3 blade merc prop was labbed to run 5000rpm wot(originally ran 4800rpm wot). after doing my upgrades I tried running a stock 24p 4 blade bravo 1 prop but could only turn it 4800-4850 rpm wot so that is why i had that 24p labbed to run 5000-5100rpm wot which increased my speed from 66mph gps to 68.5 mph gps. I really like the way the boat handles the rough water with the 24p 4 blade that is why I want to stay with it .I checked the spark plugs and they look tan to me but I still see some black soot on the transom ? could the programming I had done from az speed and marine be off ? this was done prior to my exhaust change , all other upgrades were done at the same time pre- exhaust.

amarket1

You can try calling Mark@Precision Marine Kenner,La he is an EFI wiz and can help you.His # is 504-469-7463

26sonic

amarkrt1 i did call mark and discussed my problem with him , very knowlegeable and am going to send my ecu to him , he also made some suggestions and hopefully will get me running at peak performance !!

tomcat

26Sonic:

Your drive height is probably on the deep side? This is good for the three blade, but adding a four blade to a deep drive always costs top end (~2-4 mph) because you actually have too much blade in the water. But then again that is why it is better in the rough. When they labbed the 24, they probably took some pitch out. If you can achieve 70 mph with the four blade after ECU tuning you will have the best of both worlds. I wouldn't expect anymore than this due to the HP gained from your changes.

26sonic

any other suggestions ? sening my ecu out to precision marine this week will keep everyone posted on results.