Decarb a Mercruiser 7.4 LX MPI

[bruceb58]

I f you really believe that each ECU has a different flash then it may be necessary to have them verified by someone.

 

[tpenfield]

Only traveled to the Delco Kokomo Plant once . . . I was working for an electronics manufacturer in Pasadena, CA and they got word that GM/Delco wanted us to start applying conformal coating to some of the parts that we supplied. The Marketing Dept decided that "I" should go out there to take a look at what they were doing. I don't remember much becoming of it . . . I think they eventually dropped the idea.

My next steps with the engines/ECM's would be to talk with the folks at MEFIBurn to see which version (Scan or Scan/Tune) I should get to be able to verify the contents of the MEFI's. I am thinking that the units are probably the same given that the checksum labels are the same, and hopefully the scan software will be able to see/read the checksum on the actual file on the EPROM to confirm.

If all checks out, then it may be something as simple as the IAC on the Starboard engine that is causing the rich mixture, but I will let the MEFIBurn software guide the way. Also, I'll see if there are any codes present on either MEFI unit.

 

[bruceb58]

You have a picture of these "checksum" labels?

 

[alldodge]

Have never seen or heard of Merc getting complicated with the ECM programing. Then and now, if you order an engine you get it ready to drop in and go. They don't have one for single install and one for twins. Be willing to bet a case of beer there all wrong the same.

 

[tpenfield]

The only thing that I have been able to decipher from the MEFI part ID numbering is that the last 4 digits of the MEFI 'product number' (i.e. 16220371 in this case) makes its way onto the second number on the label. So, the '0371' becomes part of the 860371KA prefix of the number that seems to be serialize, as you indicated.

I also noticed that on the other MEFI-1 part (16234539), which is Mercruiser exclusive, the second number on those units seems to start off with 864539KA . . .

Not sure about the significance (if any) of the '86' or the 'KA' in the numbering scheme.

 

[Tail_Gunner]

http://www.mercruiserparts.com/mercruiser_parts.asp

You need to find out which heads these 454's have...peanut heads....oval heads....square heads..they all flow much different along with the cam profile and give obd a call. Every time a head desgn..cam profile or injector change there would be a new tune calibrated to the engine and it sound's like you you have a heinz 57 going on there. Yes the bar codes are the tune in the ecu....Its quite possible you have a mefi 2 calibration in that module both 1 and 2 were loaded in the same module.....There eprom's and can be very easly programmed its just the pinouts that change.

https://drive.google.com/file/d/0B3waQufF7aAAQnVaNmlWQUI0Z2s/edit?pli=1

Page 11

 

[tpenfield]

Cylinder heads are the 10114156 casting, which would equate to oval ports. The thing about the number/barcode on the MEFI Units is that I have yet to find 2 of the same number . . . mostly by looking on the web . . . but it does make me wonder if the number is in fact a serialized number as Bruce had suggested.

Based on the model number 16220371, they are both MEFI-1 units . . . only the model # 16210729 are MEFI-2 units, as per the document in the link you provided.

So, does not sound like a bottle of Heinz 57 at this point, just not a lot of documentation on the MEFI markings, etc.

Any comments about the checksum labels? I have yet to find anything relating to that (yet both units have the same # on the label) The only other MEFI unit I found for a 7.4 had "FE28" as the checksum.

 

[alldodge]

Not discussing Merc's process of using check sum, but all other places including military using check sum, use it to check that the software loaded correctly. As revisions to software take place due to internal part changes, and response curves the check sum will change. My assumption would be that every so often there is a new parts in the units received from Delphi, can also include software mod's by Merc which change the check sum.

 

[tpenfield]

Yes, back in the old days of computers, checksum was often used to verify that a file actually got transferred from another media correctly and that none of the "1" 's or "0" 's were out of place. Of course this is back in the days when we had to toggle in the bootstrap programs using the bit switches on the front panel and load things from punch tape

So, if I take 2 MEFI units that have the same checksum, it is a pretty sure bet that the programs are the same. The MEFIBurn & TurnerPro software should actually let me re-calculate the checksum of the content file (i.e. program) to see if it matches the labeling on the cases of the MEFI units. However, I have no absolute way of knowing if that is the correct program file for my engines. I can only assume that it is, based on the fact that the engines run OK.

It seems that the Volvo Penta MEFI units that I have come across are more explicitly labeled than the Mercruiser parts.

 

[tpenfield]

You have a picture of these "checksum" labels?

Just catching up with this thread from a couple of months ago . . .



Here is the check sum label . . . both units had the same number, so to me that would mean the same program. The only weird thing is that the number is a hexidecimal number (0-F) and it is unusual not to see a letter in the number. Possible, but rare, I think.

 

[bruceb58]

Possible, but rare, I think.

Around a 15% chance!

 

[Tail_Gunner]

I cant speak to merc but have some experience with Volvo and mefi That check sum allow's merc to verify that the code on the label is the same as the software in the ecm. Just for giggle's can you scan that bar code with your smart phone ????? I assume there is some kind of common format for bar code's.

 

[tpenfield]

UPDATE:

I have not done anything with the MEFI units . . . they are probably fine. However, I did get the chance to test the engines out on a WOT run today.

Last year, before the decarb, I was getting 4000 RPM and 47 mph at WOT . . . today I got 4400 RPM and 52 mph . . .

So, it looks like the decarb did its thing as far as bringing the performance of the engines back to where they should be. :thumb:

 

[Tail_Gunner]

Good report they the engine's must be running quite rich to get that much carbon build up perhaps this is the first time they have ever been looked at. That almost looks a 70 hp upgrade.Before i tinkered with my engine carmel to black plug's were the norm every two years it was running extremely rich.

 

[tpenfield]

Good report they the engine's must be running quite rich to get that much carbon build up perhaps this is the first time they have ever been looked at. That almost looks [like] a 70 hp upgrade. Before i tinkered with my engine carmel to black plug's were the norm every two years it was running extremely rich.

Yea, based on the 10% RPM & speed increase, I had figured it was down about 25% of its spec'd horsepower. So, 77 of the 310 HP

 

[alldodge]

Nice response with the decarb. Mine was running rich also and during the rebuild they found my MAP sensor was bad. Its a 1bar standard sensor for GM

 

[tpenfield]

Nice response with the decarb. Mine was running rich also and during the rebuild they found my MAP sensor was bad. Its a 1bar standard sensor for GM

I might have the same sort of issue, as I think my engines are running a bit rich as well.

 

[Fishermark]

From your other post regarding water in your oil, it might be a good idea to let the readers know that a good practice would be to change the oil - or at least run it hard after using water to decarb an engine. Just a note for the future archive.

 

[tpenfield]

From your other post regarding water in your oil, it might be a good idea to let the readers know that a good practice would be to change the oil - or at least run it hard after using water to decarb an engine. Just a note for the future archive.

Yes, . . . note to self: change the oil immediately after a decarb :thumb: