Decarb a Mercruiser 7.4 LX MPI

[tpenfield]

Ok, I give up for now . . . I have searched various Mercruiser part sites, the engine manual, etc, . . . compared engines offered with closed cooling and those without. It looks like there is nothing that references the ECM part numbers for closed cooling versus raw water cooling. I only see some postings to threads (here and elsewhere) where the dealer replaced the ECM (or returned it to the factory for 're-flash) when a closed cooling system was added to the engine. The details of such remain a mystery and seems to be undocumented.

If anyone has some additional information, that would be great.

For now, I am going to verify the part numbers on the ECM's in my boat and see if that all check out. Then maybe get the MEFIBurn software to run diagnostics on the engines come Spring time.

 

[alldodge]

Just a note about the software (provided by Tail Gunner), the MEFI-1 has only 7 codes which can be seen, MEFI-2 has 15. The codes don't give you much info and only show up if there is a fault. So yours like mine can be causing a rich running engine but everything you see will say all within normal parameters. Hope the software will show more then my scanner

 

[Tail_Gunner]

http://www.obd2allinone.com/mefitune.asp

http://www.obd2allinone.com/mefituning.asp

[h=2][FONT=verdana,helvetica,sans-serif]Remote tuning[/FONT][/h] [FONT=verdana,helvetica,sans-serif]We can tune your controller remotely, anywhere in the world, if you have purchased our MEFIburn[SUP]TM[/SUP] software and you have a high speed internet connection while connected to the vehicle you want tuned. You will be able to watch your laptop's screen as the MEFI calibration parameters are changed and saved. Clear descriptions of what is being done will be explained as it is happening. Our price for remote tuning is $250. Call oremail us for details.

When you know exactly what you have give them a call...if you can get Bob...it's been so long i think that's his name, he is probably the best around with mefi tell him whats going on and he will give you clear direction and will know the protocols for merc and its closed cooling..Yes you will have to buy burn but its one hell of a tool.[/FONT]

 

[tpenfield]

Yes, I was thinking the MEFIBurn was the way to go. Thanks for all the document links, etc T_G :thumb: Hopefully, the folks at MEFIBurn can shed some light on the mystery of closed cooling versus the MEFI.

 

[tpenfield]

A new day and another thought. . .

Although I have not found any part number references for ECM's for closed cooling versus raw water cooling applications, I have a hunch why it has been bantered about in various Internet forums.

I thought that I would contact San Juan Engineering (SJE) technical folks to get their input and knowledge of the need (or not) for ECM changes when closed cooling is added to an EFI engine. They would likely be the ones to hear about it the most, if at all.

Will post back if I hear anything.

 

[Scott Danforth]

from memory from my life supplying heat exchangers to mercruiser

with closed vs raw water cooling, it is the same ECM, T-stat is different, software changes are coolant temperature raised, fuel and spark tables are different, knock sensor table is different

 

[alldodge]

Looking at Mercruiser parts site and going through every inboard closed cooling 7.4, the thermostat went to 160 around 1992. They were still carb engines at the time, and going to EFI through later years kept the same thermostat temp. The same thing happened with open cooling starting at S/N 0F305000 and higher or around 1996. Use 1996 Rinker because my 95 has a 140 degree

 

[tpenfield]

from memory from my life supplying heat exchangers to mercruiser

with closed vs raw water cooling, it is the same ECM, T-stat is different, software changes are coolant temperature raised, fuel and spark tables are different, knock sensor table is different

Hey Scott;

I am interested to learn more about your experience in this area. Yes, ECM would be the same type, but I would think the software changes within would make them a different Mercruiser part numbers (so it seems). Yet I don't see Mercruiser listing "Part # X" for raw cooling . . . "Part # Y" for closed cooling.

My hunch is that only when the closed cooling system requires/results in a different t-stat temperature, would the ECM (i.e. software within) need to be changed, as that would make sense.

I did send an email off to SJE, so I'll see what they have to say.

to AD's point, the Mark IV 454/7.4 engines ran the 143 t-stat, and then the Gen 5 and beyond versions of the BBC's have run the 160 t-stats. My closed cooling kit is a 160 and specifically meant for my engines (SJE MC-324 kit)

 

[alldodge]

I'll let it go but your serial number at both Mercruiserparts and Mercruiser shows a 160 thermostat for the engine in both VST and cool fuel. Gen IV blocks stopped in 91 and Gen V started

 

[Scott Danforth]

yes, loaded ECM's had different part number, ECM + software. ECM harware was same. I thought the temp was bumped to 160 from 140

 

[tpenfield]

FWIW - thermostat temp never was changed with my engines . . . was 160 before the closed cooling and is 160 now. Spec's are for a 160.

So, that is why I was thinking that the ECM should not have to be touched. Yet, I have encountered several threads throughout the Internet (one from our own Don S.) that stated the ECM needed to be changed (i.e. a different software map) when closed cooling was added to an engine that was initially raw water cooled.

but the story ends there . . . no information available from what I can tell as to the why and the 'from' and 'to' part numbers on any of the published Mercruiser information that I can find. Which leads me to believe that it may not actually be true in all cases . . . that you would have to do something about the ECM when you add closed cooling to an engine.

 

[Scott Danforth]

I know for sure the SBC's change thermostat temp, and even a bunch of the plumbing let me reach out to a few people and see what I can find.

 

[tpenfield]

I know for sure the SBC's change thermostat temp, and even a bunch of the plumbing let me reach out to a few people and see what I can find.

That would be awesome, thank you for doing that. . . :thumb:

I can definitely see where the ECM program would need to be changed if the thermostat changed as a result of a closed cooling system, but if the t-stat stayed the same (as was the case with my BBC engines) :noidea:

It might just be a SBC thing . . .

 

[tpenfield]

Just came across something as I looked at a few more engine model series on mercruiser parts web site. It looks like the newer SBC (5.0, 350/5.7 and 377) engines called out for a different "PCM" (ECM) based on cooling.

I have not found any call-outs for the big block engines (7.4, 496, 502, 8.2) . . . .

Nor did I see anything for the older SBC's (using ECM's). . . . So, it may be a SBC thing with the newer PCM units, and not an across the board sort of thing. :noidea:

EDIT: and it looks like there is a 170 t-stat called out for the closed cooling version of those SBC's and a 160 t-stat for the standard cooling version.

 

[Tail_Gunner]

yes, loaded ECM's had different part number, ECM + software. ECM harware was same. I thought the temp was bumped to 160 from 140

You are correct in the fact the fuel enrichment is (cold start) is extended. OBD will have the factory table's... there fortay is with large go really fast boat's and cars... our little runabouts it's the easy sqeezy for them. All that is need to know is what type of ecm and the burn calibration that's on the module..From there one copy of mefi burn..laptop with a wireless and a new fresh burn can be executed from cali to almost any location on earth in the boat and on the water...My has tech has come a along way..

Finally at home and can access some old pic's. Below is a example of the spefic burn code

 

[tpenfield]

Yea, I hope to grab some numbers off of the MEFI's in a few weeks. Just to see if the units are what they are supposed to be, given their apparent history as evidenced by the hour readings.

Someone on OSO brought up a good point that I had not considered . . . the conductive rivets in the thermostat housing gasket. If those are not providing a good connection to ground, then the engine controller may be getting a false reading of Engine Coolant Temperature . . . if it thinks it is cold, then it will want to make the fuel mixture rich. So, that is something I can check out.

As far as swapping out or re-flashing the MEFI/ECM, that seems to be a newer engine thing (like 2005 models and up) and pretty much a small block thing (5.0, 5.7, 6.2), based on the Mercruiser ECM part listings for the various engines. My MEFI-1 is probably too Neanderthal for that sort of sophistication . . .

 

[alldodge]

Thermostat for yours and mine is part number 807252 2 which does not have rivets. As a non-expert I don't see how the ECM knows the engine has or has not reached temperature via the ECT switch. MEFI-1 has one code (14) which is sent either open circuit (low not hot) and closed (shorted over heated). The MAP would have more effect on enrichment IMO other then injectors and pules width.

 

[Tail_Gunner]

Yea, I hope to grab some numbers off of the MEFI's in a few weeks. Just to see if the units are what they are supposed to be, given their apparent history as evidenced by the hour readings.

Someone on OSO brought up a good point that I had not considered . . . the conductive rivets in the thermostat housing gasket. If those are not providing a good connection to ground, then the engine controller may be getting a false reading of Engine Coolant Temperature . . . if it thinks it is cold, then it will want to make the fuel mixture rich. So, that is something I can check out.

As far as swapping out or re-flashing the MEFI/ECM, that seems to be a newer engine thing (like 2005 models and up) and pretty much a small block thing (5.0, 5.7, 6.2), based on the Mercruiser ECM part listings for the various engines. My MEFI-1 is probably too Neanderthal for that sort of sophistication . . .

Read page 11 on the pdf I sent you you may have a mefi 2 module with mefi 1 programing. In that scenario you should be able to flash the eprom to mefi 2 programming....it would be fun to tinker with...Either way 1/2/3 for a bone stock engine and bare marine system there all good enough to manage the engine. I can tell factory tune's are pretty mundane if that's the word..maybe weird and a new tune will pick up power and maybe econ.

LOL see what a little decarb can lead you...but as AllDodge has said a injector cleaning is a pretty big thing and could be root cause. My 2000 model tbi injector's were at 80% and only a few hundred hour's...dripping pretty badly one of the nice part's of tbi and after reading the carb cooling stuff the pretty black epoxy finish on the TB is now in serious jeporday im sure that paint insulates it from the cooling effect.

 

[Tail_Gunner]

Thermostat for yours and mine is part number 807252 2 which does not have rivets. As a non-expert I don't see how the ECM knows the engine has or has not reached temperature via the ECT switch. MEFI-1 has one code (14) which is sent either open circuit (low not hot) and closed (shorted over heated). The MAP would have more effect on enrichment IMO other then injectors and pules width.

Maybe I need to go back to school here but a ect is merely a resistor that is heat senstive in this case it resist's based off temp a 5 volt signal is sent in and 3 goes out hence your temp....I cannot see how grounding the housing would be any part of the circuit.

Nice schematic by tpenfield

 

[tpenfield]

I get 27-530451 as the gasket P/N for my engine and it has the rivets. No rivets for a thermostat . . .

Wiring diagram does show 2 wires to the ECT sensor . . . so maybe rivets are a non-issue . . . only for the gauge at the helm.