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Mercruiser 7.4L MPI slowing down

Old 08-05-2019, 09:29 AM
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Originally Posted by Scottd21


So your still working on that? I’m not sure exactly what a boat-in-a-box is but it would basically allow them to bypass pretty much all of the boats wiring to see if it’s an electrical issue.
https://m.autozone.com/greases-and-g...1-5oz/898352_0

is that the same type of spray?
Yes and was wondering about the boat in a box to rule out a harness issue. Moving on most recently to testing the pick up coil, and swapping over spark module as well as coil among other things prior to pulling it apart to check injectors.

CRC has 14086 Freeze Spray. It's not for break away but specifically for testing electrical components.
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Old 08-05-2019, 11:09 AM
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Originally Posted by Scottd21


So your still working on that? I’m not sure exactly what a boat-in-a-box is but it would basically allow them to bypass pretty much all of the boats wiring to see if it’s an electrical issue. I’m not sure exactly where it hooks in so I am using my engine and fuel but the actual boat is being run by the boat-in-a-box.

Who makes freeze-it? When I google it I get hair spray. Does it cool to -65 if so it’s probably the same as an autozone type of freeze spray. This is called freeze off:
https://m.autozone.com/greases-and-g...1-5oz/898352_0

is that the same type of spray?
Originally Posted by BillK
That looks like something different, not sure if it will work. I put a link in my original reply. If you want search use "Freeze It Electronic"
That is different. We use that ^^^ "Freeze Off" alot for what it is made for - removing heavily corroded bolts/nuts/etc. An application it works great for is frozen from corrosion steering ujoints on vehicles. Toyota, GM,and Polaris are the more common.
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Old 08-06-2019, 10:50 PM
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Originally Posted by BillK
That looks like something different, not sure if it will work. I put a link in my original reply. If you want search use "Freeze It Electronic"
okay thanks Bill. I was able to get it at a Grainger store locally I was confused because the same company makes one for bolts and they both cool to - 60
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Old 08-07-2019, 06:39 AM
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the electronic cool spray will leave no residues and would have nothing that would be corrosive/contaminate to electrical systems
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Old 08-09-2019, 01:23 AM
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My mechanic ran it on Wednesday for over an hour and it did not occur. It was pretty cool outside so that likely was the cause. They ran it a second time and when it occurred they tried spraying freeze it on ECM and did nothing.

today he ran it again today and it took a while but after over an hour it slowed down and he then opened hatch and it cleared it temporarily. So opening engine hatch cleared it in all but one time (the time it didn’t it was pretty warm outside). He tried replacing my ignition module because he said it’s located in distribution box but if issue persists he said I may need to add a vent for the engine. Couldn’t this possibly add a lot more noise as well? Maybe a 12v batt exhaust fan

Any ideas on what could be heating up and how I can cool it off?
Thanks

Scott

Last edited by Scottd21; 08-09-2019 at 01:34 AM.
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Old 08-09-2019, 12:34 PM
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No idea on this end, but you have a blower lready

I still don't see opening the hatch and its all good. Probably is heat related, but my guess is still a bad connection somewhere.
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Old 08-09-2019, 11:51 PM
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Originally Posted by AllDodge
No idea on this end, but you have a blower lready

I still don't see opening the hatch and its all good. Probably is heat related, but my guess is still a bad connection somewhere.
okay well he actually replaced the ignition control module today but couldn’t test it, I am hoping that it’s that. Will find out this weekend
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Old 08-10-2019, 08:33 AM
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Mefiburn's diagnostic service to rule out the ECU is only $80 plus shipping both ways. I'm going to do it for mine as well after reading information elsewhere regarding these years and engines ECU's causing the issues we're having. I figure that's the only way to truly rule it out. They can then repair your ecu for $500 or less per their website.

Good luck this weekend. I replaced and tested some ignition parts and PCV yesterday for 4 hrs. in the Fl heat and humidity and now to blown out to go on the water in 102* heat index. Going to pull the ECU and injectors instead, fun times!!
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Old 08-10-2019, 05:35 PM
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Originally Posted by Tractionless
Mefiburn's diagnostic service to rule out the ECU is only $80 plus shipping both ways. I'm going to do it for mine as well after reading information elsewhere regarding these years and engines ECU's causing the issues we're having. I figure that's the only way to truly rule it out. They can then repair your ecu for $500 or less per their website.

Good luck this weekend. I replaced and tested some ignition parts and PCV yesterday for 4 hrs. in the Fl heat and humidity and now to blown out to go on the water in 102* heat index. Going to pull the ECU and injectors instead, fun times!!
that might be something for offseason if it persists since I can still run my boat. Is it easy to get to and remove the ECM though?
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Old 08-11-2019, 11:20 AM
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Originally Posted by Scottd21


that might be something for offseason if it persists since I can still run my boat. Is it easy to get to and remove the ECM though?
Absolutely its toward the transom behind the electronics box on the port side of the engine. Four bolts and a clip in harness fore and aft.
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