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Jay Todd "Bullet"
05-17-2001, 12:54 PM
I have a 1997 Pro-Max 225 and I have made a few modifications. Alum. Flywheel, Exhaust Tuner, Removes the can, Drilled 10 holes in the mid section, changed heads to 35 cc, removed oil injection pump. THE PROBLEM: When I take the 31" Spinelli 4 blade off and install a 24" chopper the engines runs up to the "REV LIMITER" which in turn richens the fuel mixture 30-40% then the motor acts like it got a kick in the but and turns up to 7400 RPM. Mr. Hill at CDI said that does'nt happen. The local Mercury dealership has water tested for themselves and said don't worry, it's ok! The boat runs 93 mph@7400 with the 24 chopper and only 95@6400 with the Spinelli. But the chopper is easier to drive.

[Edited by Jay Todd "Bullet" on 05-17-2001 at 12:57 PM]

sosmerc
05-17-2001, 02:27 PM
Interesting problem....I would like to see what the motor would do if you ran it on a dyno and brought the rpm's up slowly until bumping the limiter. I would expect power and rpm's to fall off suddenly just as you hit the limiter. So has anyone been "fiddling" with your ECU?

Jay Todd "Bullet"
05-18-2001, 06:45 AM
My ECM is the original one from the factory in 1997. I got the letter from Mercury to change ECM and plugs..I did not because it runs to good. If you ease up to the limiter, it is difficult to get it over. But if you jump in the throttle, when it gets to 6700 rpm range it stays there for just a second or two and then it feels like you hit the nitrous button....weird but fun..Jay

WillyT
05-18-2001, 08:38 AM
Since no one is sure what is going on here, might as well try something simple. I recommend that you borrow another prop that will ALSO let you hit/exceed the rev limiter (a low pitch 4 blade or different style/brand 3 blade) to rule out that your 24" Chopper is not the "culprit". Maybe that Chopper starts to ventilate/break free right at the speed you hit at the rev limit. This could make the rpm go up. If the ventilation is not too bad, your speeds would still be good. If you hit the rev limiter with another prop, but don't get the sudden rpm jump, you may have narrowed it down. Wild idea, but better than doing nothing, I guess. On a side note, per my calculations, if you have the standard 1.87 gears, your slip with the 24" Chopper (at 93 mph) is almost zero (!), even if I add an inch for cupping. Something seems wrong here:

(25" X 7400) / (1.87 X 1056) = 93.68 mph

If you have the 1.75 gears, then the slip is about 7% (which makes more sense, but still sounds rather low). With the Spinelli, I get slips of around 8% and 14%, depending on 1.87 or 1.75 gears (again, adding 1" to the pitch for cupping). Whatever the slip is with the Chopper, if it is more efficient than the Spinelli, then the ventilation idea is probably dead wrong. Oh well; I'd still try it. By the way, I understand a lot of ProMaxes have self destructed without that recall modification. I hope you beat the odds. Mine ran great before and after the recall changes. Good luck, and please let us know if you figure out what is really going on.

Jay Todd "Bullet"
05-18-2001, 10:12 AM
I have tried 3 different choppers in the 24 to 28" with various modifications from DAH. The 24 that I am running belongs to a friend and he want sell. It has been thinned,balanced and blueprinted, sharpened and really hooks up well. It has had extra cup to equivalent 25"..so they say. Probably the true MPH is 90 to 92 which is still in the low slip range. This is with the boat empty...no gear. Bullet Bass Boat 20'with 15" of set back for good clean water. Other props don't give me the speed but they have similar effect on the ECM rev. limiter.

[Edited by Jay Todd "Bullet" on 05-18-2001 at 10:48 AM]

sosmerc
05-18-2001, 11:15 AM
I am assuming that your ECM has never been modified and that it is a "digital" model. If you do not have access to a dyno then how about taking along a mechanic with the DDT diagnostic tool for a ride. The tool can "Capture" data before and after you hit the limiter....it might be interesting to see what the various sensors are reading when the engine suddenly "comes alive" ! Are you running EGT guage by any chance? If so, what are your temps? Would also be interesting to know what your fuel psi is. My guess is that you are running extremely lean below the 6700...your fuel psi may be way too low for some reason. Better get this resolved because I think she is going to fry.

Jay Todd "Bullet"
05-18-2001, 12:48 PM
1) My ECM has never been off or modified
2) I don't know if I am digital or analog
3) I have had the DDT meter connected
4) I do not have the EGT gauge
5) I believe like you do that the engine is running lean
6) I have not ran a fuel pressure test
7) I have learned alot regarding 2 strokes over the past 10 years, but I am no expert. I do have a 6 year degree in the Automotive field and put 5 years in the automotive machine shop and 7 years in my own garage and taught in both secondary and post secondary schools. But 2 strokes are a different breed. However, one of my best friends is a Mercury Performance freek. He has been very instrumental in my boats set-up and modifications. ***** I do use a product called Petron. I don't know if you have heard of or use, but it works fighting friction. Similar products are Duralube and Prolong. However this product does not hurt seals and gaskets like its competitors. My engine runs 20 degrees cooler since I use their 2 cycle oil that exceeds TCW3. Also I used the product in my gear case and that tempt dropped approx. 20 degrees. It really works because it impregnates itself in the metal and I am a witness for its results.

sosmerc
05-18-2001, 02:33 PM
You have a digital ECU if you were able to plug in the DDT.
But first and foremost you should check fuel pressure. Also you can use the DDT and a fuel pressure guage to do a "pressure drop test". You pressurize the system, then fire each par of injectors for a preset period of time and note the pressure drop. Each pair of injectors should show the same drop. This test is done without the motor running. For example you might see readings like: 34PSI drop to 24PSI with injectors set to fire 50 cycles at 300 milliseconds. You can use the DDT to set for multipulse or single pulse. Whatever settings you use, the pressure drop should be the same for all pairs. If one pair is way different, then this would indicate possibly one of the pair is partially blocked. You would have to remove the intake to then disconnect each of the injectors one at a time and re-test to zero in on the suspect injector.
You never really said how the engine runs at idle or mid-range. Just curious.

Techno
05-19-2001, 08:30 PM
I'm confused on something here. You said you exceeded the rev limiter? How? I thought that's what a rev limiter did, limited revs.

Jay Todd "Bullet"
05-21-2001, 06:53 AM
sosmerc, My friends at the Merc dealership said I have the digital system. 4/97 Pro-Max 225.

The idle is great. The timing has been set up a few degrees. I think it is 3 to 4 degrees idle timing???

But the Engine runs great at all speeds. BUT like everyone else...I would like more!!!!

I tried a small ear 24 chopper this weekend and the motor would hit the 7000 RPM range any time you wanted it to. I eased the throttle up to 6700 and I pushed the choke button and it felt like it helped, instead of hurt or fall it acted like it picked up briefly. Maybe you are right. I may be running lean at the 6750 limiters.

[Edited by Jay Todd "Bullet" on 05-21-2001 at 06:56 AM]

WillyT
05-21-2001, 11:16 AM
I guess you should/could do the classic "full speed run and then shut down cold and read plug color" test. Might confirm the lean condition. Will need to use your Spenilli since that keeps you below the rpm at which this "enrichment phenomenon" occurs (if that is what it is). Good luck!