having engine trouble with my 5.7 Mercruiser Horizon MPI.

[snatchy]

Hi All,

just wanted to check in and give an update to this long standing issue.

Over the last four weeks or so ive been tinkering around changing a few things.

1) Fuel system pressure is fine.
2) New distributor cap and rotor button
3) Rewired all wires to distributor (very corroded)
4) cleaned injectors.

I took it out on the water the other weekend, and the good news is the surging (which I suspect was the corroded wires to the coil), and the pinging, are both gone. This is great news.

However, the lack of RPM on takeoff is still persistent.

On the boat I have myself, my wife and our three young kids. I have a days worth of food and fishing gear along with a full water tank, and full fuel tank (about 150 and 250 respectively I think). However I still only manage 2900 at WOT.,

Engine is 5.7 MPI Horizon with about 400 hours. Bravo three the dual 20P props and a 2.00 ratio on the drive.

Compression on each cylinder is about 190 PSI, with the exception of one which is down at around 160

Im looking for any suggestions as to why I may be having issues hitting a good RPM on takeoff. I feel as though im starting to break the back of all these issues, but this one is really bugging me. With another family on the boat I need ot ask people to move down the front for launch........................a little embarrassing.

Look forward to any replies.

Dave

Good luck working through the issues. You will get there eventually.

We once had one sparkplug that was partly broken internally and caused intermittent power and surging issues on our V6 MPI. Took a while to find it. If you haven't already (I couldn't see this in your posts), you could change all the plugs to eliminate them as an issue.
Corrosion in the distributor cap is common, but you have changed the cap I see.

Do you have smartcraft info displayed from your engine? It could help with diagnosing the issues. 2nd hand stuff is available these days

Have you had the engine computer hooked up to a Rinda scan tool to see if it has anything useful to say?

[scottar]

As above - make sure it is firing on all cylinders. Also make sure that the throttle is actually being actuated fully by the cable.

[juggernaut]

I had something similar happen to one of the 8.1S Mercruisers in my SeaRay a month back. Was doing a 70klm trip up the coast - dropped the revs back to pull in behind an island for a look - as I went to get back on the plane, my starboard engine would only rev to 3500 rpm and the ZF transmission on this engine sounded like it had blown. Engine idled fine and free revved fine. Did the next 50klms on the remaining motor as I thought the transmission had failed for some reason.

Even the Mercruiser tech couldn't find the problem when I got to my destination. With the suggestions from the ClubSeaRay forum I sorted the problem out - it turned out to be an ignition lead had some cracks in the insulation and was arcing across to the exhaust manifold when the motor was under load in gear and would drop a cylinder and therefore power and rpm and made the transmission sounded like it had a bag of marbles inside.

So my suggestion is to replace your spark plugs and ignition leads and hopefully watch the rpm come back.

[newbienewb]

Hi Guys,

I did buy a second hand rinda scan tool, however the software was so old in it that it wouldn't read my MEFI3, and the seller wouldn't help, so I logged a claim with ebay and returned it.

I have checked the throttle cable and butterfly on the throttle body, and indeed the butterfly does open all the way at WOT.

I changed the leads and plugs about 6 months ago for brand new ones, but didn't gap the plugs. I didn't think you even needed to do that these days.

Pulling my hair out pretty bad over this.

Dave

[Robg]

Have you checked for air leaks on the inlet manifold or any cracked vacuum lines if there are any, just a thought.

[Seppo BNE]

Certainly a tricky one! -- When replacing the distributor cap etc, was the timing checked to be OK?
Not sure on the design of risers/intakes on these, but, is there any chance of a restriction in the inlet/exhaust manifold?
Blocked air filter?, loose crap partially blocking the intake?, part of riser or something in the exhaust blocking the exhaust?
Does it rev up similarly with no load, and under load?

[MyWay]

did you had boat looked by any qualified mechanic yet ?
at least it could point you in the right direction to fix this problem

[newbienewb]

Hi Guys,

Sorry its taken me so long to get back to you. Busy time of year!.

Im quite sure there are no intake / exhaust blockages. I have had risers and manifolds off and checked. I have had exhaust Y pipe out fully and have confirmed no blockages.

There are also very few air hoses into the intake, and i have checked them all and confirmed no leaks.

Tomorrow i will be taking the boat out for a few baseline RPM tests, and i have a question about my timing before i do.

I'm not sure if i have my base timing set correctly. I put the engine into service mode by connecting a paperclip to points A and B on the DLC (this is the same thing that the mercruiser timing tool does). However neither my balancer or my timing cover have indicators to show 8 degrees. I have taken a video of my timing and post the youtube video below.



Can anyone tell me how to correctly find 8 degrees here????

Thanks guys.

Dave

[Gon Fishun]

Dial back timing light.

Dial back timing light..jpg

[newbienewb]

Hi Gon Fishun,

Unfortunately my timing light is not that sophistimacated!

I dont have the ability to dial the timing on my light.

I measured the circumference of the balancer at 637mm.

From there i know that 637/360 = 1.769.

IE: Each 1.769mm is equal to 1 degree.

I got a piece of masking tape, drew TDC on it, and then measured 1.769 * 8 (degrees) = 14.155mm

IE: The 14.155mm mark on my tape equals 8 degrees.

In other words - i made my own timing tape - LOL.

The big assumption I have made is that the one single mark on the balancer is the TDC mark. A gent on another forum has suggested that this is infact the 8 degree mark, but i have to say im not convinced. Every motor ive ever worked on has a TDC mark on the balancer.

Thoughts?

Dave

[Gon Fishun]

Hi Gon Fishun,

Unfortunately my timing light is not that sophistimacated!

I dont have the ability to dial the timing on my light.

I measured the circumference of the balancer at 637mm.

From there i know that 637/360 = 1.769.

IE: Each 1.769mm is equal to 1 degree.

I got a piece of masking tape, drew TDC on it, and then measured 1.769 * 8 (degrees) = 14.155mm

IE: The 14.155mm mark on my tape equals 8 degrees.

In other words - i made my own timing tape - LOL.

The big assumption I have made is that the one single mark on the balancer is the TDC mark. A gent on another forum has suggested that this is infact the 8 degree mark, but i have to say im not convinced. Every motor ive ever worked on has a TDC mark on the balancer.

Thoughts?

Dave

All my experiences have been the line is TDC. We had dial back lights back then. I would take it as TDC and you can check after removing the no 1 spark plug. I think you have done this. The setting you now, by the video, looks good to me. I would not retard it all, if any thing advance it and listen to the motor. But don't go to far. Does the distributor have vacuum or mechanical advance or is it all electronic. If vac or mech and not working this will affect the power.

[newbienewb]

Hi Gon Fishun, i think ill take the mark to be zero. Based on that I have set the timing to 8 degrees using some home made timing tape. The dizzy has no vac advance. Id suggest all electronic.

So this morning we popped down to the bay and went for a squirt. Perfect morning for it. barely a breath of wind.

I did 6 runs with the 20P props, and then 6 runs with the 22P props.

Each run with the 20P props were within a poofteenth of each other.
TakeOff WOT = 2950 RPM
Cruising WOT (with boat trimmed up) = 5000 RPM
Top Speed was about 50 knots give or take.

Likewise each run with the 22P props were almost identical.
TakeOff WOT = 2750
Cruising WOT - 4900
Top Speed was about 55 knots give or take

No pinging at all, and great throttle response once up.

Top end seems fine, and im certainly reaching the 5000 RPM mark. I just seem to be lacking a few RPM's on takeoff. This video is as light as the boat will get. No water, half fuel and two people. Thats about it.

Youtube video of boat taking off and cruising at WOT.

https://www.youtube.com/watch?v=wuJVcmjo3JE

What are your thoughts?

Dave

[scottar]

If it's supposed to only hit 5000 RPM then there probably isn't that much wrong with it apart from being a big heavy boat. It simply means your props aren't slipping a whole lot during take off and the engine is having to wind up. IMO the take off looked normal.

[juggernaut]

Looks fine to me for a boat of that size. In relation to prop choice just make sure you choose the one to give you the required rpm at WOT.

[brett62]

Hi Gon Fishun, i think ill take the mark to be zero. Based on that I have set the timing to 8 degrees using some home made timing tape. The dizzy has no vac advance. Id suggest all electronic.

So this morning we popped down to the bay and went for a squirt. Perfect morning for it. barely a breath of wind.

I did 6 runs with the 20P props, and then 6 runs with the 22P props.

Each run with the 20P props were within a poofteenth of each other.
TakeOff WOT = 2950 RPM
Cruising WOT (with boat trimmed up) = 5000 RPM
Top Speed was about 50 knots give or take.

Likewise each run with the 22P props were almost identical.
TakeOff WOT = 2750
Cruising WOT - 4900
Top Speed was about 55 knots give or take

No pinging at all, and great throttle response once up.

Top end seems fine, and im certainly reaching the 5000 RPM mark. I just seem to be lacking a few RPM's on takeoff. This video is as light as the boat will get. No water, half fuel and two people. Thats about it.

Youtube video of boat taking off and cruising at WOT.

https://www.youtube.com/watch?v=wuJVcmjo3JE

What are your thoughts?

Dave

Hi Dave,

You are doing 50-55 knots ? Mate if you are pulling that speed there is nothing wrong with that. I get 35 knots WOT and we have the same boat with a 5.7l 300hp. Yours must be super charged. What speed are you doing at cruise which would be 3500 - 3800 RPM.

certainly agree with Scott as to the video, all looks good.