Temporary loss of power

[Tunabass]

5.7 EFI. Serial number OLO12923

i thought I posted earlier so apologies if this is a double post. Recently I posted about a lot of piping sounds and severe loss of power. Unable to get on plane. Replaced cap, rotor, plugs and wires and it ran great for the ne t day. Today after a few hours fishing and while. Ruining at 3200 I get a temporary (half a second) loss of power (drops about 400 rpms and then comes back on its own before I can even grab the throttle. The alarm also sounds for a second. Occasionally a cough or pop would accompany this but not always. It did it about 3 times this morning and about every 3 minutes for the last hour I was out. Only does it above 2500 or 3000.

baffling as before my recent fix it would make a similar pop sound when I couldn’t get on plane. Then the next day it was perfect. Today it was ok in the am but bad in the pm. Underway today for about 10 hours. Any ideas? Thank you.

 

[Rick Stephens]

I’d think about cleaning connections, especially grounds from battery to block and block to ECM.

 

[ryan04]

What are the odds your timing is off? When the distributor was put back on perhaps it was put on in it's "slipped" position? The bolts that hold the distributor in place could have loosened off enough for vibration to turn the distributor slightly. If your getting pinging sounds with hiccups and loss of power it's possible your timing is just off and your cylinder heads are complaining about it with some pre detonation occurring. At a quick glance with the available knowledge that's my shot in the dark haha.

 

[Tunabass]

I’ll check the grounds and distributor for tightness but I literally just did this three days ago. Also a guy I know with the same boat and engine said he use to carry a spare coil pack. He said they were like $350 bucks. A quick google search only brings up ignition coil but no where near $350. Is there something else or is he just calling it the wrong name. Thanks.

 

[Scott Danforth]

poping or pinging? not sure what piping is

if your poping, especially thru the intake your running lean most likely due to poor quality fuel and your timing is probably off

if your pinging, your running lean, have carbon or debris in your combustion chamber, have low octane fuel and/or your timing is probably off

check the contents of your fuel filter

check your timing

check your compression

check your fuel pressure

its not the coil, never is the coil. only 3 out of a million coils changed by back-yard mechanics are actually bad. anyone that would spend $350 on a $40 coil is an idiot and one that licks windows while carrying a juice box and wearing a helmet

even a batch of coils for an LS motor (8 of them) are no-where near that price.

 

[Tunabass]

similar symptoms and it looks like a coil replacement fixed it. Thoughts?


https://forums.iboats.com/forum/engine-repair-and-
maintenance/mercruiser-i-o-inboard-engines-outdrives/9993902-mercruiser-5-7-momentary-engine-cutout

 

[alldodge]

Maybe MPR (main power relay) and/or its connections. Swap FPR with MPR
Maybe kill switch
Maybe key switch and/or connections

Assuming Bravo drive

 

[Tunabass]

It is a bravo 3 drive. Not sure what FPR or MPR is. There is no kill switch but I’ll check wiring on the key. When it does it, it feels like the key gets turned off for a split second. All electronics stay on and I get the one or two second alarm sound.

 

[alldodge]

Main power relay
Fuel pump relay

They are both next to the ECM and are small square and probably black

 

[Tunabass]

I have a two battery switch as well. Wish I would have switched it while I was out to see if it kept doing it or not.

 

[Tunabass]

I checked a few things today and took it out. I want to check/replace only one or two things at a time so I can identify for sure the issue. Ignition wires are good on back of ignition. 20 amp fuse had a little corrosion behind dash so removed and cleaned. Underway it did the same thing. This time I switched batteries after an hour and it did the same thing. Voltage while cruising on one battery was anywhere between 13.4 and 14.6 while maintaining same speed. I though that was odd. I forgot to look at voltage for the first battery the first hour. Also cleaned and tightened a few grounds in the console.

 

[Tunabass]

Does no one think it could be the ignition coil? It literally feels and sounds like the ignition is turned off for a split second. Is my logic wrong?

 

[alldodge]

Does no one think it could be the ignition coil? It literally feels and sounds like the ignition is turned off for a split second. Is my logic wrong?

Its hardly never the coil. The thread in the link you posted was the coil but it was also a MSD coil. Many say MSD stands for Marine Stopped Dead, but if reading the thread he said it was leaking oil from it

I would think it could be inside the distributor, the module or the coil

https://www.mercruiserparts.com/bam/subassembly/31844/2704/70

Need to test

 

[Tunabass]

Alldodge, do I do this test with battery on or off? Thank you.

 

[dubs283]

I’d think about cleaning connections, especially grounds from battery to block and block to ECM.

this

also verify harness ground is on the same stud (preferably stacked next to) the main battery cable ground

 

[alldodge]

Test is done by measuring ohms (resistance) with no voltage key OFF, distributor wiring disconnected

 

[Tunabass]

I was able to do part of the test. The part I could complete was measuring resistance between the gree and white lead where I got a steady 834. I must not have the right settings on my voltmeter to do the two previous tests. My ohm setting options on the meter are 200, 2000, 20K, 200k and 2000k. Trying each of these settings I got 1 on the meter. Do I need a new meter?

 

[alldodge]

The Rx1 scale in your case would be 200 and it should read infinite, meaning greater then 200. So if you set it on 200 and probes are not connected to anything, this would also be the reading you want when its connected to white and distributor housing, and when connected to green and distributor housing.

Does sound like your distributor is ok and your back to a bad connection somewhere

 

[Tunabass]

This problem only happens above 3k rpms. If it was a bad connection wouldn’t it do it at any RPM? I’ve been out in flat calm and rough. Sometimes it does it a lot sometimes not for hours. Am I maybe going down the wrong rabbit hole? Should I look elsewhere?

 

[alldodge]

The thing that catches my attention is the alarm sounds for a second. The motor is reading a fault or its loosing power. If the motor is getting a knock reading there would be a code 43. With no codes I back to thinking power loss