1997 Mariner 150HP Magnum EFI surging

[futech]

Hey guys,
Right i have a problem here. At 3,000 rpm engine seems to be fine but as soon as i go over this and get up around 4000 rpm the engine starts surging. Was out in it today and it was doing it at 3100 rpm and after i got to location and left again it ran fine, then started to slowly do it again when i was up at 4000 rpm. This problem has really got me baffled as i have been working through the workshop manual and have replaced a whole lot of parts that i feel like were not the problem.

Parts replaced so far.

H.T Leads
Spark plugs
Stator
Both switchboxes
Trigger
All new reed valves.
Fuel Pump
Fuel lines, hoses, bulb, filters
Flywheel as one of the magnets had come off
removed and cleaned injectors/tested ok

Any advice on where i could look next would be much appreciated as i have run out of ideas. Im hoping there isnt a ECU issue but don't know how to test it. I have looked through these forums and some other threads sound like the same sort of problem but no one has had a resolution.

 

[Faztbullet]

Re: 1997 Mariner 150HP Magnum EFI surging

Check fuel pressure and mechanical fuel pump diaphram as sounds like high pressure pump may be starving in VST,

 

[futech]

Re: 1997 Mariner 150HP Magnum EFI surging

I have checked these and they look ok to me. Went out in it today and the problem was way worse, turned around and put boat back on trailer. Im just going to take it into a workshop and get them to sort it, ive spent to much time and money on it now.

 

[futech]

Re: 1997 Mariner 150HP Magnum EFI surging

Ok so i have taken another look at this (havent totally given up yet) I found the timing was incorrect. So i adjusted that and took it out again. No surge but only could get up to 3800 rpm then nothing after that. Just another question, i tested the low speed circuit of the new stator i fitted and the readings were around 60 volts which is way off the minimum. Could i possibly have a fautly new stator also?

 

[futech]

Re: 1997 Mariner 150HP Magnum EFI surging

Right so i finally worked this issue out. Thought id come back and explain. The loss of power at high rev's was a big drop in fuel pressure. So the new fuel pump i installed was faulty out of the box. Engine is running good again.