Merc 350 mpi not producing full power

[Fun Times]

Re: Merc 350 mpi not producing full power

Is this a TBI motor...i think its mpi and a merc 555 40psi should be right. You can refereice the link i posted it cover's it all.

No, S.N. 0M011557 is an MERCRUISER 350 BRAVO HORIZON 350 MAG BRAVO MPI with an Manufacture Date of 06/29/2000 that uses an MEFI 3 ecm. So 30 psi is what he should be at.

His parts catalog,
http://www.mercruiserparts.com/selectDocs.asp?doc_nbr=809488+99

 

[Tail_Gunner]

Re: Merc 350 mpi not producing full power

No, S.N. 0M011557 is an MERCRUISER 350 BRAVO HORIZON 350 MAG BRAVO MPI with an Manufacture Date of 06/29/2000 that uses an MEFI 3 ecm. So 30 psi is what he should be at.

His parts catalog,
http://www.mercruiserparts.com/selectDocs.asp?doc_nbr=809488+99

V8 5.7L, 6.2L, MEFI-1, -3, (MPI, Cool Fuel on Port side, Gen+).
350 Mag MPI.......White Tip...... 30.....lbs...... (207) 805225A 1 [Keihin].
Bravo, Inbrd, Ski,
Black Scorpion
Ski (5.7L & 6.2L),
377 Scorpion
Bravo & Ski

It appears you are right i would post the ecm part number's on the ecu..40lbs vs 30 is very rich on mpi marine motor there rich out of the shoot,.

And some more: http://forums.iboats.com/mercruiser-i-o-inboard-engines-outdrives/350-mpi-swap-v6-carb-580037.html

 

[jdubslopro]

Re: Merc 350 mpi not producing full power

Plugs are new and indicate ideal burning. I would rather upgrade to a bravo than pay for a 1.5 alpha lower but I don't have any money left to throw that way. The engine cover indicates 5000 rpm max WOT. I had some difficulty getting past 4700 rpm over the weekend but I noticed a ding on the 19p that could've been a contributing factor to that. As soon as I squeeze the most speed out of it I'm selling the boat, I have some interested parties already I just want to make sure it's 100% before sale. My buddy's got a baja 232 for a great price I'm looking at...

 

[jdubslopro]

Re: Merc 350 mpi not producing full power

I just read through all the additional posts, thank you for your input. I'm going off what the mechanic said as far as fuel pressure, I have not yet put a gauge on it to verify myself. I still feel strongly that there's something not up to snuff as far as making the power, not in the propulsion the boat. It hasn't touched the rev limiter while in forward motion, I only reved it high enough in neutral one time to verify that there was a rev limiter, and it bounced off around 5000 or 5200.
I'm unfamiliar with a timing tape...I have a timing light with adjustable advance correction, and I painted the TDC and the 8? btdc timing marks on the crank pulley. When I timed it with the light set on 0? the 8? mark came up perfectly in the timing indicator tab. When I advanced the light to 8? btdc the 0? timing mark came up right in the timing tab.

 

[frantically relaxing]

Re: Merc 350 mpi not producing full power

IF the timing is advancing correctly AND the WOT fuel delivery isn't too rich or too lean, THEN your upper limit issue may be friction related rather than fuel or ignition related...

How's the drive alignment? The gimbal bearing? Torque and centrifugal forces working against a slightly mis-aligned input shaft may cause enough drag to slow your top-end ascent.

 

[Tail_Gunner]

Re: Merc 350 mpi not producing full power

Assuming est timing or it could be a t-bolt V...Go to page 4B-13 for the actual curves

 

[QC]

Re: Merc 350 mpi not producing full power

Pretty nice video. I wish he had said "burn" instead of "explosion", and he goofed a little on using degrees and piston in the same sentence. They need to remember some people might get confused about degrees being applied to something going up and down. Should have been Crankshaft degrees and piston travel. I know it is nitpicking, but words matter. Easy to be a critic, but I really like the flavor of the whole thing

 

[Fun Times]

Re: Merc 350 mpi not producing full power

[http://www.boatfix.com/merc/Techbk/95/95HGB4.PDF

Electronic Spark Timing (EST)
IMPORTANT: Failure to follow the timing procedure will result in improper timing causing performance problems and possible severe engine damage.

Hey Tail_Gunner, Just to be safe, I thought I better let everybody know that the timing instructions givin are for a 3.0l 4 cylinder carburetor engine, not the MEFI 3 MPI V8 engine the O.P has. Timing set up is done a little differently between the two.

Using "EFI Ignition" on page 4B-8 would be a better suit for this engine except for step #2. Manually adjust the engine throttle to 1800 RPM. Most MEFI 3's raise the RPM up automatically.

Based on his earlier description of setting timing, I would say he should be good to go timing wise.

 

[Tail_Gunner]

Re: Merc 350 mpi not producing full power

Hey Tail_Gunner, Just to be safe, I thought I better let everybody know that the timing instructions givin are for a 3.0l 4 cylinder carburetor engine, not the MEFI 3 MPI V8 engine the O.P has. Timing set up is done a little differently between the two.

Using "EFI Ignition" on page 4B-8 would be a better suit for this engine except for step #2. Manually adjust the engine throttle to 1800 RPM. Most MEFI 3's raise the RPM up automatically.

Based on his earlier description of setting timing, I would say he should be good to go timing wise.

Yes your are right but look deeper the pdf includes 3.0 to 8.1.... I did not take enough time to point out my intent. I am assuming he has correctly set the initial timing correctly..... the point of the timing tape and the vid was to show him how to determine if his timing is... actually advancing.... in the upper rpm ranges and correctly. Page 4 b13 show's the actual curves they may vary slightly from his mefi tune but very little and if it is not advancing which is the whole point... then his power issue should be resolved. If you read thourgh all of his post you will see he has advanced his timing manually and picked up some power which is why this whole tape deal is being posted.

Your point is well taken the mefi use's a timing tool rather than a shunt..

 

[jdubslopro]

Re: Merc 350 mpi not producing full power

Brand new gimble bearing, alignment is perfect. From the way the plugs look it looks to be ideal burn condition. Motor starts with ease within 1-2 seconds of cranking. Drive lube and impeller are new.

 

[QC]

Re: Merc 350 mpi not producing full power

If everything you post is accurate then this is hull and setup issues. My .02

 

[jdubslopro]

Re: Merc 350 mpi not producing full power

Why do you say hull issues? This is the same hull that performed the same last year. it is clean, this is a freshwater boat that is trailered not sitting in water. Setup? Assume you might be referring to trim? Trim is just below the point of cavitation...the point where it reaches max speed before losing speed and raising rpm.
Is anyone local?

 

[QC]

Re: Merc 350 mpi not producing full power

Well, it has to be something. More horsepower equals more speed if all else is equal. So something isn't equal, or something is wrong. If the drive is right, the engine is right, then it has to be trim or prop or hull. I don't know any other things to consider. Not trying to be a jerk here, but we have to eliminate something. If I was local, I'd volunteer to be out with you this weekend. BTW, where is local?

Go back to my first posts. Where did you get the "260" info?

 

[jdubslopro]

Re: Merc 350 mpi not producing full power

Local is western MA. The 260 might be off by 10 hp I thought the 97 4bbl 350 was 260 maybe 270 hp.

 

[QC]

Re: Merc 350 mpi not producing full power

But where'd the speed numbers come from on the 260? I understand your 4.3 did well, but just trying to find something with a clue. I haven't read the whole thing through recently. What prop now, what exact RPM and what speed GPS? Have you ever propped down to 4800ish at WOT?

 

[jdubslopro]

Re: Merc 350 mpi not producing full power

I had the boat out yesterday. Still 19p 4 blade aluminum. I trimmed up a bit too high lost speed and rpms went up to 5400 for a second, so I know it's not overpropped and its not hitting the rev limiter.

 

[frantically relaxing]

Re: Merc 350 mpi not producing full power

Firing up my way-back machine, I remember 2 separate issues that caused me to lose power--

First, summer of '79 in my new 17' Galaxy bowrider, slant-4 Volvo/270 outdrive. We were at Lake Powell on vacation. Beached on a small island to let the kids play... Even have a pic of the exact day & place!

--- once we left that island, I'd lost 4 mph. This was pretty significant since this hotrod only managed 35 mph top end with a 15x17 prop. 31 was all I could get on the way home. I checked the prop, and 2 of the 3 blade had a nick in them-- a NICK! In rotating the prop I couldn't see any evidence of bent blades. The big nick was about 1/4 in, and the edge of the blade was ever so barely flattened a bit and a little bit of mushroomed edge, for maybe an inch. The small nick was barely noticible, mostly a little mushroom. I filed them as best I could, and picked up ONE mph. I couldn't believe that such tiny damage could cost that boat a 12% drop in top end! But it did, and I've tried to keep my props pristine ever since (tried )

Second power loss issue, water in the outdrive. Nuff said about that, but as QC says, SOMETHING must be causing a loss. Might not be water in the drive, but it could be a bad bearing or mis-adjusted gears, or...?

 

[QC]

Re: Merc 350 mpi not producing full power

I had the boat out yesterday. Still 19p 4 blade aluminum. I trimmed up a bit too high lost speed and rpms went up to 5400 for a second, so I know it's not overpropped and its not hitting the rev limiter.

What was RPM just before she started to rev up? Speed? Did she hit the rev limiter at 5400? This happened below trim limit? Can you make her porpoise? If she blows out before porpoise you need to shift some weight aft and retest. Can make a significant difference.

Please answer each question. All important.

 

[jdubslopro]

Re: Merc 350 mpi not producing full power

Rpm was 5000 before trimmed too high, didn't seem to hit a rev limiter, although I can't be certain. it can porpoise but when it does I drop the drive and slow down to regain, the trim limit switch and sender are both slightly out of adjustment but I have a pretty good feel of where the trim needs to be as I've owned it 4 years (the senders are out of adjustment due to replacing bellows and I had it very close but the shop I brought it to F****ed it up I haven't gotten around to correcting it yet)
There is slightly more weight aft now due to the larger motor so I don't think weight distribution is the answer. I'm going to try some different props on it and hopefully get you guys some better results (well and get myself some better results)

 

[QC]

Re: Merc 350 mpi not producing full power

They are fastest if they will porpoise at full trim and full power. Of course you have to control that, but they are fastest with bow light and up. This is why I ask. If you can't get her to porpoise at full trim and full throttle, then I would keep working with weight. I understand the higher weight of the V8, but what matters is overall balance, not what it seems like. How many people on board when testing? Beer? Stuff? water? Fuel? All matters.

Speed before she blew out?

I am thinking you need more pitch. Try a 21 and get us some more data.

You never gave the source of the speed numbers on the sister ship with the "260". The most important data you have provided is actually your first person account of the 4.3. Why are you saying 105 horsepower more? From what, to what?