dirtlawyer

Looking for some wisdom here...

We recently rebuilt my 1995 502 Mag EFI into a 509 EFI. We installed a roller cam/roller rockers, inconnel valves, high compression pistons (10:1), replaced the fuel injectors, added CMI headers, a Vortech flame arrestor and reprogrammed the ECU.

We dyno'ed the motor and found a slight dip in the fuel delivery in the 3500 to 4000 RPM range, but nothing that the dyno shop was really concerned about. This weekend was the second time I had the boat out and we detonated a piston (#7). this is the second time it has happened (we replaced the fuel injectors with larger ones after the first detonation) and I am concerned that there may be a problem with the EFI system on this motor. We are considering converting it to a carbed motor - will this help? Has anyone had a similar problem.

Dyno #'s - 529.1 HP at 5100 RPM.

Any input would be greatly appreciated.

IRONMAN

Did you increase the fuel pressure also?

John B

Dirt,

What octane fuel do you think you are using? How was your ECU programmed. Do you have a working detonation sensor in your system? Check your fuel pressure up to WOT (wide open throttle). Read the post PLEASE HELP BAD 502 on fuel problems.
Check your spark plug heat range, should be cold or colder than stock. Been there done that.

Good luck, JB

Turbojack

I wish I was not an expert on this but here goes. First question is what does piston look like? #7 is the one that I lost the most. #7 fires after #5 in the firing order. If the plug wires are too close you can detonate #7 by induction from the #5 plug wire causing the plug to fire before time. Other major problem with #7 is also heat. How hot are you running your engine? Since 7 fire right after 5 there is more heat in piston.

Major caused of detonation are:
Lean fuel
quality of fuel (octane)
timing (30-34 max)
Engine block temp (cooler the better)
Hot intake air temp

Programing may be the problem because it may not be set up for the high compression you are running.

You can detonate a motor at 3500-4000 just as easy as you can at 5000 if things are not right. I know, last year I lost 2 pistons & never pulled more that 4100 all weekend.

Vinny P

This is exactly what I am worried about. Last week I posted a topic on just this problem. Making power out of a 454 magnum or a 502 is not a problem. It is the E.C.M. re-mapping that worries me. How can you be sure that the guy re-mapping is doing it right? The answer---YOU CAN'T--- This is a problem that will be bothering me for a long time. In my old Drag Race (CAR) days, it was easy to make tons of power and jet a Holley Carb and not worry about burning holes in pistons. Now along comes E.F.I. while I think that it is a great system ( left stock ) modifications are not only expensive but very risky. You can spend good money on heads, cams, valves, etc. but what good is it if the E.C.M. isn't keeping the injectors open enough, along with all the other important engine functions that it controls, and we can not control. If the engine doesn't work together as a matched package, you may as well leave it stock. I don't see how companies can advertise re-mapping E.C.M.'s with just the little information that you give them over the phone. It seems to me that this job can only be done correctly if it is done on a dyno. Trying to make these E.F.I. motors something that they are not, just doesn't seem to be practical. I was thinking about doing motor work, but the more I think about it, the less inclinded I am to do it.

H2Xmark

well from what i know they{merc} have 3 style ecm's version 1
was 92? mapping software, easy to remap &program, them mercury had to change it with GM {delphi} so they came out with version two, which is coded, only GM, mercury and I hear two other companys have the correct codes to remap this ecm. version 3 started in 1999 and it is not coded, easy to remap, them they came out with the 555 system smartcraft? and that is anybodys guess, I would get with Dustin Whipple he would know what type ecm and who can program it for you, some of this might be a little off but it should be pretty close to the truth,

jdelo

I agree with Checkmate454MAG it is a pain in the A@$. Any modifications you make heads,cam etc the ECU has to be remapped. I understand that there is only 3 people who have the software and understand all the BIN files written in SAE code (Society of Automotive Engineers) Hey H2Xmark do you have the software for the MEFI 3 . I've searched high and low for it and even talked to Dustin Whipple. He told me in time it will be available. I'm at the point now were I am looking at aftermarket ECU's

JDELO

dirtlawyer

Thanks for all of the replies.

Unfortunately, it looks like what I feared is being confirmed - EFI's are not friendly towards hi-perf mods. At this point, I think I'll probably convert it to a carbed motor and run it a little rich to avoid future detonation problems.

Turbojack - thanks for the info - of your 5 criteria, I can safely say that 3 are not the problem:

Lean fuel - I think this is the problem

quality of fuel (octane) - was running 94 octane (filled up before I went to the water)

timing (30-34 max) - right on target

Engine block temp (cooler the better) - water temp running 165 consistently

Hot intake air temp - don't know about this one.....

I'll look into the plug wire issue; however, the rigging is pretty clean and I don't think that this is the problem.

Checkmate454mag - I agree. The worst part is that the people that re-map ECU's don't take any responsibility and/or liability for their errors.... it always amazes me that computer programmers, in my experience, are the only professionals that are hired to do a job, then they either screw it up or screw something else up. Nonetheless, the client pays them for their work, then calls them back to fix the problem that they created, which, the client pays for again.... This is one boat owner that is not going to be a guinea pig...... I'm getting rid of the EFI system.

Vinny P

The more I hear about this re-mapping bull, the less likely I will be to modify my stock motor. I feel it is better to leave the programing to the guys at Mercruiser. My next and only upgrade will be to an HP500EFI. Not a huge difference in power from what I have now, but good enough. If nothing else it will add to the resale value.

dirtlawyer

Saw the motor today in its torn down state - definitely not just one (1) piston detonated - looks like several (4 to be exact) were beginning to melt down.

Off comes the EFI, on goes the carb.