Converting from 502efi to 525EFI
 

Converting a Black Thunder from 502/540efi engines to Merc Racing 525 efi. Does anyone know of common issues that may arise in this swap. I m worried about electrical connections and sending units to the new livorsi guages. Everything worked for the 502/540s.

Any help would be great!!!!!!!!!!!


Thanks in advance, JCB

Fixx
 

theirs a adaptor harness needed, also i think you may have to change your gauges because of the newer style ecm..

Carl c at donzi.net went from a 8.1 ho to a 525 efi and still his guages dont work and that was over a year ago..dont know what the hold is, i think it has something to do with the smart craft stuff that merc is using nowadays....old stuff is analog and the newer stuff is digital..

here's the trend but theirs alot of reading..

http://www.donzi.net/forums/showthre...hlight=525+efi

I've done a few of those conversions. You'll need an adapter harness, analog conversion box and some good electrical knowledge. My shop is in Spicewood, not too far away. Give me a call if you need some help or parts
830 6935591.

Bob Lloyd
Full Throttle Marine

Thanks guys for the responses. All is helpful.

FYI, this is going in a 97 43 BT that a close freind and i did a rerig on over the winter. Original engines were 502 efi mags that Ateco rebuilt to 540/550hp. THis is the 2nd time that the #7 cylinder has gone on the port motor within 8 hrs due to a lean condition. Both times the engines were dynoed and the 2nd time, they had 02 sensors in them to check air/fuel ratios {which were ok 8 hrs ago} now we are switching to carbs and making these back ups for the new 525s.

It may not be a lean condition. I bought a used boat and would burn down #6 from time to time. I had water pressure gauges on boat engines and both showed good pressure. I rerouted the intercooler lines overboad and to my surprise when I did this I noticed one had a steady stream of water and one was intermitent. I had pickups on the bottom of the boat. Well I lowered that pickup about 1/4 inch and the problem was solved. Never burnt a piston again. It looked like a lean condtion everytime the engine was tore down. Well it was the water pickup not being down far enough and was getting air in it. Just something to keep in the back of your mind.