MerCruiser 7.4L 310HP Running Rough and throwing code 43 Continuous knock
 

Last year I feel the boat was running well, not bad, It was running rich and when I would rev the engine it would almost always die when it got back to idle unless I gave it a little gas. I never checked for any codes or anything like that. The engine coupler went out late last year and I got it fixed last week. The mechanic said the boat was running rough and throwing code 43 continuous knock detected. (This is after unwinterization). Do to the short time frame and the distance I had to drive to pick the boat up from the mechanic I figured I would try to resolve this issue myself. At idle when on the scanner it did not show up that it was knocking. When we took it out on the water and I started getting on it it started showing knock and retarding the timing. it did feel more rough then I remember, but it is hard to tell since it had been 5-6 months since driving the boat. When we got back to the dock the transom was covered in soot. I had a 9 hour drive ahead of me so we loaded it on the trailer and I brought it home. I have bought new plugs and wires since they needed replaced and plan on finishing this up tonight.

The Cap and Rotor were replaced by the mechanic, but only after he started it up with my cap and rotor on it so I dont believe it is timing related. The service manual says to check the Knock Sensors next. I dont know how often these go bad..



Has anyone had this issue before?

Any Ideas?



More info : The boat has 246 hours on it and the scanner showed that also. It is in a 2000 Baja 272 and last year on GPS it was able to run 59mph with a Mirage 23P.

Timing is the first place I would look, put it in service mode and see where it is, obviously its running fat..........there's a single wire going to the sensor from the mpi harness maybe it came off its a weird connector

I no longer have access to a scan tool.. Any idea what they cost?

Alot of these mechanics seem to have been fumbling firing orders lately . J.s..
And going outside of 18436572 the right wrong way can get full knock retard also

Is there a diagram on where the wires are suppose to be on the cap and on which plug?

Thunderbolt ignition?

I believe it is the Delco HEI.

You can make a code reader with a resistor type LED and a paper clip. Find the DLC connector and insert the LED (radio shack and the like) , then insert the paper clip. Turn ignition to ON (don't start) and count the flashes.

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Your running rough and have soot, Yes check timing

Would be best to have a serial number but being a 2000, it should be Delco EST. Timing should be 8 BTDC, plugs MR43LTS at 0.045 gap

Doesn't matter which wire is started where, only that the firing order is correct as airjunky posted. Distributor rotates clockwise when looking down from top

Also, the knock sensors do go bad, but not that often. Find the blue wire connected to the sensor below the exhaust on starboard side and make sure it is NOT tie wrapped to the plug wires. The plugs firing will set off the knock module

Im sure there are some good videos on youtube on adjusting timing... never done it before.. Looking at the service manual it looks pretty intimidating. Any tips?

I have two knock sensor's if you need one, Im by the KS speedway, I had a 272 also back in the day 502 mag mpi, great boat

Edit: make sure its on TDC and the #1 plug wire is where the rotor is pointed at.

Look at the harmonic balancer and find the degree markings. Take a white grease pencil and mark 8 BTDC.

Have the motor running until it's up to temp. Connect a timing light to plug wire number 1, which is front plug on port side. Connect positive and negative leads from timing light to battery post.

Insert the paper clip in pins A and B, then adjust rpms to 1800. Point timing light at balancer to see if 8 BTDC lines up with tab on timing chain cover. If it does your in time, if not, loosen distributor clamp slightly and rotate distributor until 8 lines up. Once lined up, tighten bolt on distributor clamp, and recheck timing.

Remove paper clip.

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A loose coupler ( not properly torqued , wrong bolts,ect) can trip knock sensor. Once it takes enough timing out , you will see a dirty transom. Probably something simple , but something to check if you exhaust other ideas...Good Luck!!!

I will keep this in mind if I find out that it is in fact a knock sensor. However I am in Dallas now so not sure what good that would do me..

Thanks!

Awesome.. Yeah a quick youtube video and im not so intimidated anymore. Ill check the order tonight when I replace the plugs and wires and then sunday ill purchase a timing light and check that out and hopefully get to take the boat on the water!

Why in the world would you move to that God forsaken place, I use to live in the Colony when it had 5k people, now it has 55k

BTW if you do need a knock sensor (doubtful but maybe) I've found the Rock Auto has the cheapest price on them

I work in IT Consulting and the market is great down here... better market = $$ gotta go where the money is!

If your single you moved to the right place..........if your married you moved to the wrong place...............LOL a buddy of mine is in Plano he has a 272 Boss, boats up on Texoma, he's a home grown boy so he talks funny

Just a thought, buy a cheap mechanics stethoscope at parts store, listen at the head bolts and free rev the engine. If the engine really has something stimulating the knock sensor you will hear it. If it's from the rear of the engine you may need to run the engine with the outdrive off the boat to rule out drive noise. A lot of parts are turning in the outdrive even when the drive is in neutral.

Swapped the plugs and wires tonight. The plug wires didnt look terrible, they just looked old. two of the spark plugs that came out were a little wet. nothing crazy, all the rest seems pretty fine. I am going to purchase a timing gun tomorrow and hopefully back the boat in the water and time it Thursday or Sunday.

All 55k of then are often sitting in the main st construction disaster at the same time now too..

And my folks are from Kansas, my money says he is going to enjoy Lewisville big time . At least Little Elm park is a good draw now

If need to be, I am in Arlington TX and have a lake very close by for testing boats. I mostly likely could fix this or least look into the problem(s) for a proper pinpoint of the cause. I have been known to fix a boat or 2. But I wont say how many. I do this for living, have all the tools and all the scan tools ever needed and of course have to charge you for the services. Just so we are on the same page.

One of these days ill get John to come out to lewy and play .
Maybe if i promise him some free wakesurf lessons . Behind a twin engine formula . With a blonde girl driving , while i drink beer .

James your funny. the only thing I could do for and on a wakeboard boat is make a good ballast system, 6: 3" 245 lbs. worth

Well guys/girls I got out on the lake today. Checked the timing it was set to 10° BTDC. But I think it was a mixture of the cap and rotor needing replaced that fouled 2 of my plugs and old gas. It seemed to run fantastic. Seemed really responsive even though I don't have a scan tool to tell if it's knocking, it was a night and day difference. I'll know more once I get out there for a longer day, but for the time being I am happy with how it ran. Thanks all for the input! If any of you get out to lewisville let me know!

Ill be out there next weekend. Wont be in the 272 , its down having rear engine cover redone. But ill be out there in something between a 36'silverton and a 22'wakesetter.

We have some friends coming to town this weekend so probably wont make it out to the lake.. We do need to get some people together in the OSO community to one of the local lakes for a meet up. Maybe a small poker run!