Significant but strange engine problems. 5.7L Mercruiser MPI Horizon.

[davus]

Thanks Guys,

Alldodge, ive just been looking through the mercruiser #24 manual I have, and am a little confused about which timing procedure to follow.

Your post indicates to follow the process outlined on page 4B-5 "Thunderbolt V Models", however I was under the impression that my motor was an MPI motor with a MEFI3(?) system, which would mean I should follow the process on page 4B-6 "EFI / MPI Models".

Can you help me understand which process I should be following.?

Irishbrannan - Ive got my eye on a code reader on ebay at the moment. With any luck I might win it.

Thanks again guys.

Dave

 

[alldodge]

Your correct, for a MEFI 3 you need a scan tool, a Merc timing 91-805747A2 or jumper these points on your DLC

 

[davus]

thanks Alldodge. Once ive bridged these points, I then go ahead and check timing with standard automotive timing light?.

Hook into onto spark lead #1, and away I go

Dave

 

[davus]

hi guys,

so when I got home tonight I did a few tests on the engine before I was instructed to pack it in for kid duties.

1) I bridged points A and B on the DLC, and checked the timing on the engine. Whilst it doesn't actually have any BDC or ADC marks, it looked pretty good to me. Youtube video attached. Interestingly, as I ever so slightly advanced and retarded the timing, the engine stayed at a pretty consistent 1100 rpm.

https://www.youtube.com/watch?v=6taMfWtgOvo

2) I took the return fuel line off the system, and hooked up my fuel pressure gauge to it. I switched on the accessories just for a second and instantly the gauge shot up to almost 90 PSI, proving to me that the pump does in fact have the capacity to pump high pressure.



3) I removed the airline from the fuel pressure regulator, and the pressure seemed to increase fairly consistently by about 8-9 PSI each time I removed it.

4) As I was playing around with the timing, my hand was at the rear of the motor moving the dizzy, and the engine was hesitating a little. I kept moving my hand around the rear of the motor until I found what was causing it, and it turned out to be an very corroded positive lead to the coil. And when I say badly corroded...as soon as I toughed it it came off in my hand. I wonder if this had something to do with the surging I was feeling out on the water. It was still connected (my moving it around broke the last strand of wire it was hanging by), but I wander if it was just having trouble passing current through one strand of wire.

So that's what ive come up with so far tonight. Really all I think i've proven is that the pump is still healthy enough, and the timing is fairly close to the mark.

I *may* have found the source of the surging I felt the other day, but not convinced.

Further input and advice greatly appreciated.

Dave

 

[Fun Times]

Hi again Dave, By chance have you taken another look at our past conversation as a quick reminder of all the things you've checked and changed back in February of this year...It was a long topic we all had going on there. Here is a link to it if you needed a quick reminder. http://forums.iboats.com/forum/engi...-5-7-mercruiser-horizon-mpi-only-just-started

I'd merge the two topics together but being how long they are, it might get confusing as this one is getting long as well.

Let's hope you've stumbled upon the repair as a bad wire connection to a coil could easily be causing the symptoms you seem to be having. You've done a lot of testing and all seems to be checking out "ok" on the fuel system. I thinking it is time to go for a quick water test to see if the wire repair has helped at all.

Also take your timing light, fuel PSI gauge, and an external fuel tank with an outboard primer ball so you can add additional fuel pressure while under load to see if that helps any with the performance.

Also continue to carefully remove, inspect every wire connector you can fine for any sort of damage especially since you found the one bad one.

The best way to clean fuel injectors is to send them out so they can be flow tested properly for accuracy due to ultrasonic fuel injector cleaning machine is the best way to clean the injectors. You could search fuel injector cleaning online as there are many videos showing you how to clean them but again for accuracy purposes, the do it yourself way using a battery with a cleaning solution isn't really the best way to know for sure if they are flowing, spraying equally.

Good luck.

 

[davus]

Hi Fun Times,

Hope you are well!. I do remember the thread from earlier on this year, but with the introduction of engine pinging and hesitation i decided to start a new thread rather than rehash an old one that everyone would have to re-read. I hope this is OK?.

I did read it, and found a lot of similarities. However I really cant get my head past the fact that even though the fuel pressure is a little low, it has been running like the almost all of last summer without pinging or hesitation, so im really not sure that my 8 or so PSI that im missing is causing my hesitation / pinging / low horsepower.

I also unfortunately dont see a dodgy coil lead causing pinging. If anything this is going to deliver more fuel into the cylinder before it burned, and cause the opposite to pinging.

I havent found any real evidence to suggest that the injectors are blocked, so i think that might be a wasted effort. But the logic adds up that if they are blocked, fuel will be limited, possibly causing pinging and low power.

I agree that doing repairs on boats on land, then taking it out for a water test, only to find that what you did didnt fix the issue is a very inefficient way of troubleshooting. Almost need plenty of tools and spares while out on the water.

Dave

 

[Fun Times]

Hi Fun Times,

Hope you are well!. I do remember the thread from earlier on this year, but with the introduction of engine pinging and hesitation i decided to start a new thread rather than rehash an old one that everyone would have to re-read. I hope this is OK?.

Doing pretty well thanks. Typically iboats likes to keep just one subject going but it shouldn't' be a problem having this one here as the other one is now linked above. In this case, Mixing the two could become one big headache to read it all twice basically. Hope the fellow Moderators agree.

I did read it, and found a lot of similarities. However I really cant get my head past the fact that even though the fuel pressure is a little low, it has been running like the almost all of last summer without pinging or hesitation, so im really not sure that my 8 or so PSI that im missing is causing my hesitation / pinging / low horsepower.

So you are seeing a steady 20 psi this time around when you had fluctuation in February? But physically removing the vacuum hose gives you around 8 psi more? If so first follow the vacuum line up to the intake manifold looking for a damaged/melted line as that's happened in the past to a few members. Then on your next water test, remove the hose to see if it helps with the performance/pinging any.

I also unfortunately dont see a dodgy coil lead causing pinging. If anything this is going to deliver more fuel into the cylinder before it burned, and cause the opposite to pinging.

You can't put anything past a possible failing coil. When it come to marine power, always expect the unexpected until proven other wise.

I havent found any real evidence to suggest that the injectors are blocked, so i think that might be a wasted effort. But the logic adds up that if they are blocked, fuel will be limited, possibly causing pinging and low power.

Had you have the test equipment which I believe is no longer available from Rinda technologies, one test would be to perform an injector balance test to see how much fuel is being sprayed in a set timeframe. Page 5C-34, http://www.boatfix.com/merc/Servmanl/16/16C5R2.PDF

 

[alldodge]

At 90psi I agree there is nothing wrong with your pump, but the regulator is getting my attention.

 

[davus]

So you are seeing a steady 20 psi this time around when you had fluctuation in February? But physically removing the vacuum hose gives you around 8 psi more? If so first follow the vacuum line up to the intake manifold looking for a damaged/melted line as that's happened in the past to a few members. Then on your next water test, remove the hose to see if it helps with the performance/pinging any.

I have checked the air line leading up to the TB and it has no restrictions or holes that I can see. In fact I took the air line for the regulator off at the TB end (was easier to get to than the regulator itself).

Good idea to remove the regulator air line on a water test. This will obviously help to identify if higher fuel pressure will help the pinging.

Had you have the test equipment which I believe is no longer available from Rinda technologies, one test would be to perform an injector balance test to see how much fuel is being sprayed in a set timeframe. Page 5C-34, http://www.boatfix.com/merc/Servmanl/16/16C5R2.PDF

I have my eye on a second hand Rinda Mercruiser Scan Tool on ebay. I think it would be a good thing to have handy at all times, and they seem to be the best bang for buck? Unless any other suggestions.

Dave

 

[davus]

At 90psi I agree there is nothing wrong with your pump, but the regulator is getting my attention.

Is it normal behaviour for the fuel to go up slightly in pressure when the regulator air line is removed?. If so, then it seems the behaviour of my regulator is somewhat normal?.

The low pressure could be:

1) A blockage somewhere on the inlet side
2) A faulty regulator causing a complete shift down the pressure scale across the board.
3) Of course it still could be a faulty fuel pressure tester.

 

[alldodge]

Is it normal behaviour for the fuel to go up slightly in pressure when the regulator air line is removed?. If so, then it seems the behaviour of my regulator is somewhat normal?.

It is normal for the pressure to increase when vacuum is removed. The issue I'm leaning toward is your number (2) fault below.

The low pressure could be:

1) A blockage somewhere on the inlet side
2) A faulty regulator causing a complete shift down the pressure scale across the board.
3) Of course it still could be a faulty fuel pressure tester.

 

[davus]

Thanks AllDodge,

So at this stage we are looking at either dodgy Rotor Button/Cap, or dodgy fuel pressure regulator.?

Would you agree with that?

Cheers

Dave

 

[alldodge]

I'm worried about the pinging you mentioned. If you didn't have the ping I would lean more toward dist cap or rotor, but ping is another ball game for me. I'm still thinking fuel related, only thing that does not go with it, is your knock sensor should be retarding timing (lack of power), unless your getting a code 44 which is the ECM is unable to read the knock sensor.

 

[davus]

ill admit I had the same thought. I would have thought the knock sensor would help.

Having said that, by retarding the timing, I may stop the pinging, but ill lose even more power!

Ive got a guy coming around next week (apparently) who is going to plug in an see if there are any codes.

Any other ideas to try in between now and then?

Dave

 

[alldodge]

Don't think its the gauge but would be worth a try, other then that need more info

 

[davus]

next step is to get a code reader on it. Im going to try and buy a mercruiser scan tool.

 

[davus]

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.

I did win the auction on ebay for a second hand mercruiser scan tool - but unfortunately the seller gave me a bum steer and im seinding it back for a refund. Anyone got a mercruiser scan tool they want to sell?????

Look forward to any replies.

Dave

 

[tpenfield]

Would the water and fuel numbers be in liters or gallons? If gallons sounds like a lot of weight.

 

[harleyman1975]

I agree sounds like an awful lot of weight. how does it perform with just 2 people and minimum gear?

 

[davus]

hey guys. The fuel and water is in litres, not gallons. With just my brother in law and myself (minimum weight) it performs better.

That having been said, it should be able to handle the weight.