2003 Mercruiser 6.2 MPI -- Poor Performance after Winter

[jfried]

Hey Everyone,

I've got a 2003 Cobalt 226 with a Mercruiser 6.2.

When I got it out on the water for the first time this year, I noticed notably poorer performance than usual. Idle was a little rough, and even after a full warm up, and reasonably long ride, the boat seemed like it was "missing" something. Time to plane was noticeably longer, and I was only able to get 45-46mph at the top (~4500 rpm), where I'm usually able to get it up to the low 50s (GPS).

When the marina who summerized took a look, they said it was probably some bad gas (made the mistake of leaving it full over the winter), and that I was in need of a "tune up" this summer.

My question is, does this make sense? Is there anything I can put in the gas to help clean out whatever's inhibiting my performance, and what's actually involved in a tune up on these MPI engines, and how often should they be done?

 

[alldodge]

what's actually involved in a tune up on these MPI engines, and how often should they be done?

Opinion and others will differ, and will be along shortly

A motor taken care of will not need plugs, cap and rotor for many years, and even then may just replace for giggles. Replaced mine the first time at about 20 years and 600 hours, all looked good and made no difference afterwards. Plug wires after 15 to 20 years. Clean/check flame arrestor when doing yearly maintenance (lube, alignment, filters, etc as needed) before a winters nap.

So to tune up an MPI should not be needed very often unless you are experiencing something that needs to be looked into. So far as the performance, this can be old fuel, filters, dirty hull, other things. Since this is your first time out, burn though that gas and refill and see where your at

Edit: probably should add, I'm talking fresh water

 

[jfried]

Opinion and others will differ, and will be along shortly

A motor taken care of will not need plugs, cap and rotor for many years, and even then may just replace for giggles. Replaced mine the first time at about 20 years and 600 hours, all looked good and made no difference afterwards. Plug wires after 15 to 20 years. Clean/check flame arrestor when doing yearly maintenance (lube, alignment, filters, etc as needed) before a winters nap.

So to tune up an MPI should not be needed very often unless you are experiencing something that needs to be looked into. So far as the performance, this can be old fuel, filters, dirty hull, other things. Since this is your first time out, burn though that gas and refill and see where your at

Edit: probably should add, I'm talking fresh water

Thanks. Hopefully running through the old gas will solve most of the issues, as my fuel filter has been replaced, hull is clean, and yes, I'm in freshwater.

 

[Scott Danforth]

How old is the gas?

 

[jfried]

How old is the gas?

Would've put it in likely in late august.

 

[Scott Danforth]

So you have 9 month old gas. I would suspect the fuel

 

[williemon]

On my mpi indmar, i had a bit of a mis after winter. Turned out i had some. Logged injectors. I pulled and cleaned them all but to start with, i pulled the plugs and found two that were off color. One was dark and sooth. Its injector was leaking fuel due to particles in it. Another one was very white. It was running lean due to a clogged injector inlet.

 

[jfried]

So here's an update.

Tried to run the boat (WOT) to get rid of the bad gas.

As soon as I get above 4000 rpm, I get a "bang" from the engine bay, about once every 2-3 seconds. I've also got a little bit of a "hissing" sound at idle, if that makes sense.

Is this the boat misfiring because of the bad gas?

 

[alldodge]

Is your bang a backfire or knock or an actual bang?

 

[jfried]

It's an actual bang.

 

[alldodge]

Started off with only an issue of WOT rpm being a bit low, now you have a bang every 2 to 3 seconds. Don't see fuel causing a bang, need to look around real close as to what it might be. If unable to find the location, take someone with and be watching the motor.

 

[jfried]

The bang may have been there all the time. I initially thought it was a bottle of drive lube bouncing in the bilge area -- but it is not.

 

[thegoat86]

I am having the same issue AD, I don't have the fuel problem though. My fuel is less than one month old. I assume the cap/rotor/plugs were stock because they were in bad shape. Heavy carbon on three, and dark brown on one. Cap was far corroded. I replaced all because of the corrosion and wear plus the performance was bad. And motor was misfiring heavily. Boat has around 576hrs on motor. Initial running after those items changed yielded great results. No misfire and ran strong. Then I let it run on the muffs for about 30mins at idle and the performance issue came back. Def sounds like misfiring. I am going to change the water/fuel separator again today. But before I start throwing money at it, any suggestions?

Jfried, did you check the plug wire locations on your cap? I had all of them but two right and it made a bang as there was predetonation. idled ok but had quite a pop under load. Recheck that. Put the motor to TDC then check if rotor is pointing at #1. Don't go by the marking on the cap as some tend to do.

 

[alldodge]

The bang may have been there all the time. I initially thought it was a bottle of drive lube bouncing in the bilge area -- but it is not.

Really with a bang I might have to pull the drive to see if there is a u-joint coming apart. U-joints normally cause some vibration

Goat I would lean toward the carb rebuild, but lets not hijack jfried. Start another thread and I'll go look for it, others should be around also

 

[HT32BSX115]

So here's an update.

Tried to run the boat (WOT) to get rid of the bad gas.

As soon as I get above 4000 rpm, I get a "bang" from the engine bay, about once every 2-3 seconds. I've also got a little bit of a "hissing" sound at idle, if that makes sense.

Is this the boat misfiring because of the bad gas?

Probably not with only 9 month old gasoline.

However, It's not really safe to run at WOT to "get rid of 'BAD' gas" (If it's REALLY bad)

You run the risk of detonation. It's really much better to drain some out, maybe to half , to 1/4 tank...... and refill with fresh gasoline

Also, if something is "banging", you need to find the problem before running at high speed or something may break. ($$$)

 

[jfried]

Thanks for the advice guys. I'm obviously done with the WOT until I can get the tank drained. Hopefully next weekend.

What's interesting though, is that even when I had the "bang", it didn't seem to affect performance at all.