Decarb a Mercruiser 7.4 LX MPI

[alldodge]

Here is another plus for carbs. My Rinker has around 650 hours and I only replaced the plugs, cap and rotor near the end of last season. The plugs looked great (Original champion) and the reason behind it was the carb is working correctly. Only issue I have with it now is caused by not using it, only about 10 hours a year over last 7 or 8 years.

Yours just like mine can run rich and show no signs of codes. Steam cleaning the engine is bringing back the numbers, but I still see it as an old engine and it won't be long before it is back where it was. New or old the MEFI-1 is a bare basic EFI system, while it does work, if symptoms start to show, you can do little to determine what is causing the issue(s). It's either replacing parts, pulling injectors and have them professionally cleaned or swapping components if you have twins.

 

[alldodge]

Mefi 1 mefi 3 same same to me.....Ive been playing with a mefi 3 now for yrs on a 4.3... same tables yes more flexibility I have my time up 3..4 degree's to 1200 rpm for cam timing but other than that as soon as the fuel cell fails Pow off it come's.:flame:Ive tried tuning the mid band and as soon as I get it up to 13/1 there's this little thing called knock count's that creep up on ya.

Same tables more flex, I could use Eddie Young to clear things up , but from what he tells me.

Table length is the same but divisions are different.
MEFI-1 20, 40, 60 .....
MEFI-3 10, 20, 30 ......

So for a given room the ECM is programmed to a given point, as rpm increases do you use the next spot on the table. Without a dyno and oxygen sensor were stabbing in the dark/ Having the ECM tuned is best while running and collecting engine variables, other wise the temp sensors, MAP, throttle position or fuel pressure

 

[tpenfield]

Given the discussion about 'burning rich' and MEFI-1 tuning, etc. I am wondering if I should see about fixing the fuel mixture problem on the Starboard engine. To Rick's point, the problem of carbon build-up will probably be re-curring if the engine keeps running rich.

I have read in a few threads that a rich fuel mixture is often related to fuel system pressure & flow. I think my version of the Mercruiser MPI is before they put the fuel cooling module in (at least according to the parts diagrams).

Also wondering if I should add the MEFI computer software to my Christmas wish list (either MEFIBurn or Rinda) I think the MEFIBurn might be better, but I declare 'novice status' on MEFI units.

Additionally, my recollection during the pre-purchase survey is that the engine hours logged in the MEFI on the starboard engine (IIRC) was way low and not consistent with the the Port engine/nor the hour meters. So, I am thinking that maybe there was a new module installed along the way and it is not the correct program, etc. :noidea:

Thoughts?

EDIT: I found the engine hours on the ECM's from the survey - they are both different and inconsistent with the hours on the boat.

Engine Hours: Port: 736 (189.2 on ECM) Starboard: 747 (443.18 on ECM)

So, I could assume that they both were changed (or reset somehow?) during the life of the boat . . . port ECM is much newer than the starboard ECM

 

[alldodge]

You have the same setup as mine, it has a VST on top of the intake. The MEFI software could help but could also hurt if not done correctly. Mt point is, in order to correctly setup the ECM you need to know what the engine is doing. In order to correctly do this oxygen sensors need to be used. Changing the fuel curve without knowing the overall impact of the change can cause a rich or lean condition.

Prior to my repower and after listening and reviewing many sources, my plan was to remove injectors and have them professionally cleaned. The report received on the cleaning would push me to look further into other areas. If injectors came back with no problems, would look closer into MAP, temp, other sensors and retuning of the ECM. I have an unknown tuning of my ECM because it came from a twin engine Scarab from NY and the guy was going to put blowers on. This could mean that he messed with the tuning, just don't know.

If you get the software and retune to factory settings is one thing, but I would tread easy tuning to something else without full understanding of what is going on.

My opinion only

 

[tpenfield]

Thanks AD.

I know how to spell VST, but not sure what it is . . . prolly a pressure regulator for the fuel rail thing ? :noidea: I guess I should Google it a bit.

I plan to thread lightly on the MEFI/ECM program. I would be curious if for some reason the programs were different, given that the ECM's apparently have been replaced along the way. If they were different, my thinking would be to make them the same, but I would need to figure out which is right.. As far as custom tuning or tweaking, I don't plan on going there. Not really needed - factory spec is fine for me.

So, maybe I should check all the other stuff that can effect fuel mixture and then if all else fails take a look via the MEFI software.

 

[Tail_Gunner]

EDIT: I found the engine hours on the ECM's from the survey - they are both different and inconsistent with the hours on the boat.

Engine Hours: Port: 736 (189.2 on ECM) Starboard: 747 (443.18 on ECM)

So, I could assume that they both were changed (or reset somehow?) during the life of the boat . . . port ECM is much newer than the starboard ECM

[/QUOTE]


Yes your ecm was replaced.....I think.... Post your numbers off both ecm's you more than probably have one that was slapped in there as a quick fix and not tuned to your spefic 7.4 model yr and there are a lot of different 7.4/454 combo's out there....Hell you might have a mefi 2 on one engine and a 3 on the other. Ive seen crazier things. Below are the product ID's and on you ecm there should be a tune ID spefic to your engine.

Ahhh as for a stocking stuffer here's a thought.....Id be there already just to many project's going on already


http://www.dynojetcmd.com/cmd_marine.aspx

 

[alldodge]

The Vapor Separation Tank (VST) has 2 parts, a fuel bowl tank which has a float like a carb, and the other side is the high pressure pump. Your mechanical fuel pump keeps the tank side full. The high pressure pump in the VST supplies fuel to the rail. The regulator at the end of the rail regulates the pressure. If less pressure is needed the regulator sends the fuel back to the VST tank. The VST sitting on top the engine, ethanol and no return is what causes these engines to vapor lock so easy. Vapor locking can be fixed by plugging the tank return fitting and running the return line back to the tank

I would suggest first checking fuel pressure, and if that checks out pull injectors and have them cleaned. Injector cleaning is about 20 each

 

[tpenfield]

Yes your ecm was replaced.....I think.... Post your numbers off both ecm's you more than probably have one that was slapped in there as a quick fix and not tuned to your spefic 7.4 model yr and there are a lot of different 7.4/454 combo's out there....Hell you might have a mefi 2 on one engine and a 3 on the other. Ive seen crazier things. Below are the product ID's and on you ecm there should be a tune ID spefic to your engine.

Ahhh as for a stocking stuffer here's a thought.....Id be there already just to many project's going on already


http://www.dynojetcmd.com/cmd_marine.aspx

Thanks, AllDodge and Tail_Gunner for your insight and advice on the EFI system . . .

The body style of the ECM's is that of the MEFI 1 & 2 . . . so I'll check the numbers to see if they are consistent (I should be able to find the GM/Delphi numbers on the back side of the units, but I am not sure if I will find the Mercruiser number. According to the parts diagram for my specific engines it is supposed to be a Mercruiser 807268T3 ECM module . . . GM numbers would be 16234539 for the MEFI-1 and 16210729 for the MEFI-2 version.

The Mercruiser number would be specific to the engine type (right ???), yet the Delphi part number would be the same across all MEFI-1's (or -2's) (am I right in assuming that?)

If I find 2 different GM/Delphi numbers, then I would know that I have different versions.

The engines are all winterized, so, I would probably not want to do the fuel rail pressure testing until Spring time. I can check the MEFI part numbers before then.

 

[alldodge]

Thanks, AllDodge and Tail_Gunner for your insight and advice on the EFI system . . .

The body style of the ECM's is that of the MEFI 1 & 2 . . . so I'll check the numbers to see if they are consistent (I should be able to find the GM/Delphi numbers on the back side of the units, but I am not sure if I will find the Mercruiser number. According to the parts diagram for my specific engines it is supposed to be a Mercruiser 807268T3 ECM module . . . GM numbers would be 16234539 for the MEFI-1 and 16210729 for the MEFI-2 version.

The Mercruiser number would be specific to the engine type (right ???), yet the Delphi part number would be the same across all MEFI-1's (or -2's) (am I right in assuming that?)

If I find 2 different GM/Delphi numbers, then I would know that I have different versions.

The engines are all winterized, so, I would probably not want to do the fuel rail pressure testing until Spring time. I can check the MEFI part numbers before then.

Yes, The Delphi numbers should be the same on a given MEFI. Only the Merc number changes due to being tuned differently for the given engine. You should have the same Merc number on both engines

Here is a good link http://www.obd2allinone.com/mefitune.asp

 

[tpenfield]

Yes, The Delphi numbers should be the same on a given MEFI. Only the Merc number changes due to being tuned differently for the given engine. You should have the same Merc number on both engines

Here is a good link http://www.obd2allinone.com/mefitune.asp

Yea, I was thinking of getting the 'Standard Edition' of the MEFIBurn software that is shown on that website. Looks like it would have good viewing of the various input parameters plus basic programming features, if ever needed. I know that there is software from Rinda, but it seems like the MEFIBurn is better for the price.

 

[Tail_Gunner]

https://drive.google.com/file/d/0B3w...Z2s/edit?pli=1

That file should give you a fairly decent overview.

 

[alldodge]

https://drive.google.com/file/d/0B3w...Z2s/edit?pli=1

That file should give you a fairly decent overview.

Good doc thanks

 

[tpenfield]

It might be a month or so until I go to 'visit' the boat again. So, when I do, I'll post the information from checking the numbers on the MEFI units. Kind of a PITA, since I beleve they are labeled on the back side and I will have to take them off to get a look.

 

[JustJason]

I really don't understand the need for a decarb. I guess maybe if you are getting some detonation because of hot spots on a piston but not likely in a marine engine.

All marine engines run rich especially when compared to something automotive.

Boats that troll a lot build up a lot of carbon. But.....

I was just wondering out loud if you might get the same results after a 30 min WOT run around the bay

As Rick says.... It is typically nothing that can not be cleared up by running the snot out of it for 1/2 hour. Most marine engines need a good Italian tune up a couple of times a year.

The starboard engine on my boat does run rich, based on how the plugs look (black, but not fouled) Port engine plugs look normal. Both engines seemed to run OK. I was figuring maybe the carbon was building up on the valve seats and causing the lower compression and the high leak readings.

If you feel it is "running rich" the standard checklist of items would be to check fuel pressure, make sure the engine is heating up, check the ECT values via the scan tool so that the ECM knows the engine is heating up, check for injector leakdown and in most cases, pull them and send them out to be cleaned.

Yea, all I know is that I got really crappy leak test results at the end of the season this year and was considering a valve job. I did a bunch of 'decarb' with seafoam and water . . . then I ran another set of leak tests and got much better results. So, the valve job is back on the shelf for the time being.

I looked at your chart thingie and saw 1 cylinder come up. If your having a valve issue you more than likely have failing valve seals on that cylinder, and oil is getting down in there and coking up on the valve and seat. A good decarb with water will fix this, where a hard run around the bay will not. So you might want to keep an eye on it.

Other than that I have never seen somebody so obsessed with compression numbers enough to make charts of it all

 

[Tail_Gunner]

It might be a month or so until I go to 'visit' the boat again. So, when I do, I'll post the information from checking the numbers on the MEFI units. Kind of a PITA, since I beleve they are labeled on the back side and I will have to take them off to get a look.

While your at it you have one more little speed bump to add to the equation. Since you don't have or at least I assume you don't have the original ecm and tune....be aware the replacement ecu ..may be the "right" tune for that engine....it may not be flashed tor Tuned for a closed cooling system. Yes merc does have a different protocol or tune for closed cooling..what that is I do not know I assume it involves the start up enrichment time (choke)....Carry on very good thread something so simple can go quite deep...

 

[tpenfield]

While your at it you have one more little speed bump to add to the equation. Since you don't have or at least I assume you don't have the original ecm and tune....be aware the replacement ecu ..may be the "right" tune for that engine....it may not be flashed tor Tuned for a closed cooling system. Yes merc does have a different protocol or tune for closed cooling..what that is I do not know I assume it involves the start up enrichment time (choke)....Carry on very good thread something so simple can go quite deep...

That is a very interesting point and something that I had not considered . . . I am wondering if closed cooling would have an overall impact on the tuning, not just at startup. :noidea:

I will have to do some investigation, as closed cooling was not a popular 18 years ago as it is today. These engines have the full closed system block and manifolds.

 

[tpenfield]

Well, it did not take long and I found a few threads where it is mentioned that a closed cooling engine needs a different ECM/MEFI than an open cooled engine

Here is one with a response from our own Moderator Emeritus (Don S.) http://forums.iboats.com/forum/engin...closed-cooling

So, I will see if i can wrap some more substance around this issue, as I have not see any notes about different ECM's in the parts listings, but maybe . . .

I did notice some difference when I added the closed cooling, but did not think too much about it . . . could be causing the engines to run rich . . .

 

[tpenfield]

So, putting the 'puzzle pieces' together so far it looks like . . .

1. Engine is losing out on compression and leak test for the past couple of years since the pre-purchase survey, each year getting worse.
2. Looks like carbon build-up may be the culprit.
3. De-carb process showed some nice improvement.
4. Question remains as to why is it getting carbon'ed up.
5. Most significant change to the engines was full closed cooling systems added right after the purchase (I used same exact thermostats that were in the engine beforehand)
6. By looking at the spark plugs, it looks like the starboard engine is running on the rich side, the port engine looks better.
7. ECM's have been changed during the boat's life, but not both at the same time. Need to check the P/N's on the ECM's
8. Some information via thread postings is that closed cooling versions of an MPI/EFI engine have a different ECM (MEFI) than their open cooling versions.

Looks like closed cooling was not a factory option in 1996 when my boat/engines were made. It appears that closed cooling showed up in the 1998+ versions of this engine.

I have not found anything explicit about ECM part numbers (or differences) for closed cooling versions of the engines . . . it might be buried with a different serial number range for CC engines.

Anyway, my assumption is that the engines with full CC would be running slightly hotter than they were as OC engines. My engines run 160-165 per the gauges.

Anyone got more detailed information on ECM differences for closed cooling versions of an engine?

 

[alldodge]

Appears through those years the ECM stayed the same (MEFI-1) only the part number changed with a different tune.

!996 -1997 for CC inboard were 807268T3 for s/n 0K146524 and below, and 860251T1 for s/n 0K1465425 and up

Also found the 160 thermostat in both open and closed cooling engines clear up to 2000, also same for 454 mag MPI Horizon (502 heads)

 

[tpenfield]

Appears through those years the ECM stayed the same (MEFI-1) only the part number changed with a different tune.

!996 -1997 for CC inboard were 807268T3 for s/n 0K146524 and below, and 860251T1 for s/n 0K1465425 and up

Also found the 160 thermostat in both open and closed cooling engines clear up to 2000, also same for 454 mag MPI Horizon (502 heads)

Yea, MEFI-1 regardless of program... just looking at the specs of both the sterndrive and the CC inboard, it calls for the same # (807268T3) for both. My serial numbers are really low in the range ( # 36 and #39 beyond the start of the range for this series of engines)

So, I still do not see anything that spells out different part numbers for the ECM's for a CC and an open system. Maybe the tuning was not as precise in the MEFI-1 days :noidea: