Mercury 1996 150 EFI Serial number OG361151

[Daretofish]

Hello gentlemen, thank you for all of the advice given on this forum! I have read all I can find regarding this motor.

It's a Pre-Mix, 20" and the water is about an inch from the lower cowl at rest. it has the 5 relief holes in the bottom of the exhaust housing. The boat is a 18' May Craft skiff center console. Propeller is a Mercury Vengeance 21 pitch. The boat handles great and is a really nice set-up! 4000 - 5900 RPM, 53 MPH top end.

Now for my issues;

Erratic warm idle, slows and dies occasionally and requires some throttle to re-start.

Holeshot poor with missing/shaking until around 3000rpm.


New parts:
-Marine starting battery, 800CCA
-Water pump
-Poppet assembly
-Thermostats
-Fuel Filter
-Voltage regulators
-Bleed Valves
-Bleed filter
-Spark plugs NGK BU8H, changed twice
-Stator

Motor has had the following checks completed:

-Compression-hot, all cylinders 128-135
-Leakdown all cylinders 4-6%
-Charging Output 14.5 V
-Ignition output at coils 160-170
-Fuel pressure key on 35psi, idle 34psi, 3000 rpm 32psi key of 34 psi no change for 1 minute
-TPI .28 range .20-.30
-MAP 15
-Timing 3deg ATDC set per procedure
-Fuel injectors serviced at Southern Performance
-Cleaned MAP sensor orifice per JMO on this site
-Fuel water seperator on boat changed and checked
-Bulb is firm at all times

I tried to give as much info as possible, thanks in advance for advice!

[leonreno]

You’ve been thorough but wasn’t mentioned, have you checked the reeds?

[Daretofish]

I have not checked reeds, most of those tests were performed by mechanic, which I'm not!
Does the pulsing from the bleed valve hose give any indication of reed health?

thanks!

[JOE54]

yes it can, pulse pump ,air temp sensor , cyl head sensor ??????? relief holes

[Daretofish]

Is that a thumbs down on the relief holes?

[JOE54]

YUP, heavier boats don't like that, 3 deg may be lil rich low speed back it up lil more and adjust idle up may clean it up some , got remember its premix already lots of oil at low speed

[Daretofish]

After putting Simon rebuilt ECU back on, motor runs better but main problem remains. Poor idle and occasion al cutting off. So I think the problem gets worse the lower the motor goes in the water. It seems as uf the exhaust cant escape other than by the holes in the foot. Is it possible that it has a baffle or other issue that prevents exaust fron escaping through prop or the relief hole?

[JOE54]

I think the problem gets worse the lower the motor goes in the water. It seems as uf the exhaust cant escape other than by the holes in the foot.

very likely most all of the problem tuner is buried in water now

[Daretofish]

Thanks Joe, some observations: the exhaust does escape from the prop when in gear and idling, also the relief on the back of motor at all times. t does not seem to be too rich, just erratic idle, the bleed line has pulses with a little fuel, it's worse when fully warmed up, WOT is 5900-6000

Advancing the throttle slowly the motor seems like it's missing and rough, if you go full throttle it does ok. It just doesn't run well at low rpm's.

Can/should the relief holes I the foot be plugged?

I plan to try the tips provided such as timing and throttle adjustments but this is more than a tweak. It s very frustrating!

[EuropeanAM]

I suspect you may have injectors that are high flow or flooding. "Even" flow is (unfortunately) what most facilities watch for and consider "good".

CORRECT flow (ie: The correct amount of fuel delivered under specific parameters) is what you really need.

Check the items Joe recommended- if that doesn't solve the problem, try backing the TPS setting down to .23-.24 VDC for ONE run and see if it makes any IMPROVEMENT.

[Daretofish]

Some good news! a shop that came highly recommended diagnosed 4 bad reed valves, they replace and did some other tweaks. so Leon nailed it in the 1st reply!
I have been out two days and can report great holeshot, low RPM smooth, top end still great, Idle in gear fine, idle in neutral still cut off a couple times. Still a finicky cold start.
Overall much better running motor!

thanks for replies!

[Daretofish]

Update: I rebuilt pulse pump, found one of the check valves torn. Ran it all over for the last few days, never cut off and ran great! Now just trying to figure mileage. Hope this helps someone.

[EuropeanAM]