tpenfield

A few years back when I got my Formula 330SS (1996 model year), I added the SJE Full closed cooling systems to the engines. Twin Mercruiser 7.4 LX MPI (gen 6).

Fast forward to this year, I have noticed that the engines are getting a bit of carbon build-up and I did a decarb process to provide some relief. However, I am interested in addressing the carbon issue and figured that the engines may be running a bit on the rich side. The plugs on the starboard engine are black, but not fouled. The plugs on the port engine are more brown and look OK.

I have come across some info regarding the ECM units and the fact that they need to be changed ( i. e. Different) when closed cooling is added to an engine. The ECM units on my engines are the MEFI-1 variety. When the surveyor did the engine checks during pre-purchase it was noted that both controllers showed considerably less engine hours that the overall hours on the boat. One was 189 hours and the other was 449 hours, with 740 (ish) hours showing on the hour meters at the helm.

So, I am assuming the ECM units were replaced at some point and I will be checking the part numbers accordingly. The ECM units are supposed to be mercruiser pn 807268T3 for my engines, based on serial number, etc. (0F802036 and 039 are the serial numbers of the engines)

I have not been able to find any different ECM for a closed cooling option for these engines, only found the ECM for the newer versions that had the fuel cooling system ( mine have the VST fuel system)

So, my big question is what sort of tweaks would there be to the ECM program for a closed cooling version of an engine? I would think that they would be pretty similar , but may account for a higher running temperature, even though the t-stats are the same. . . And the temp gauge readings are consistent with the t-stat ratings (160)

Overall the engines run fine. The only things that I have noticed is that they seem to be running slightly rich and the WOT RPM is a few hundred lower since I added the closed cooling kits. 4100 vs 4300 before the closed cooling.

Any info, insight would be helpful. I have checked out some info on the web, but nothing seems to spell out the differences/impacts when adding closed cooling in an aftermarket mode. . . Other than folks talking about having to get a different ECM.

I am thinking about getting the MEFIBurn software for my laptop to see what each engine is doing at a detailed level And if there are any codes, etc. Still wondering about the basic differences that closed cooling would bring into the picture and it impact on the ECM and the engine performance.

ezstriper

In most cases when running closed cooling the thermostat is changed to a higher temp, or at least engines with factory closed cooling run that way, if you did not change yours I don't see where the ECM would know or care anything but coolant temp, if you are running the same temps I would think the carbon issue is from the overly rich factory ECM seems very normal the way Merc set them up as most soot the transom up with thru hull exhaust...if you can fine tune your A/F ratio that should take care of the issue as long as there is not a lot of oil being sucking into the intake due to blowby...

airjunky

iTrader: (2)

160 is the reading from the scan tool not the gauge yes ? Just a bit of resistance in the ect circuit will cause the ecm 's observed ect to be lower than it actually is .

tpenfield

No scan tool as yet, just what the gauges say. FWIW - the thermostats that came with the SJE kits seemed a bit flaky and would let the temp oscillate between 160 and 180 at idle. So, I used the thermostats that were in the engine originally before the closed cooling. They seem to work fine and hold the temp more consistently around 160-165 F

I am just wondering about the 'folklore' that I am reading about ECM's needing to be changed once closed cooling is added . . . as to what they are changed to seems to be a dark secret from what I can tell.

ezstriper

ECM does not know how the engine gets it's temp...just works off the reading..now running it warmer should lean it down, but if it were me I would see if you could retune and run cooler...

sutphen 30

temperature compensation table needs agjusting.
but the injectors that are blackening the plugs really need to be checked.or more so,all of the,might be leaking all the time.

sutphen 30

temp sensor is in the thermo housing,connector w/ the yellow/black wires.

tpenfield

Well, doing a little more research, I found that Mercruiser specifies a different ECM / PCM for their newer SBC engines with closed cooling and also specifies a hotter t-stat for those engines. So, it would make sense that the engine running a bit hotter would need a different mapping within the PCM, versus the standard cooled engines.

I have not found any different call outs for the big block engines, so maybe it is just a small block thing.

There are probably some tweaks that could be done, but for now, I will look to other factors that would contribute to a slightly rich condition.

MDGperformance

When i installed fwc on a pair of merc 6.2 engines i had my merc rep come down and reflash my ecm for the fwc,not really sure what it changed but merc has a different tune although it still runs the same temp 160,if you have a local merc dealer he could call his service rep and find out if they have a different tune for your application,on the 6.2 they picked up about 10hp on the dyno

Trash

Before you do anything make sure the gasket in the thermostat housing has a little stainless rivet. This is necessary to conduct the current for proper ECT readings by the ECM. The wrong ECT reading (which has nothing to do with the temp gauge on the dash) might be in error causing the MEFI 1 to 'think' the engine is cooler than it actually is and thus make it run slightly rich.

DO NOT change ECMs.

If the gasket is correct AT MOST you would perhaps need to tweak the ECT vs Coolant Temp table.