Pressure testing the fuel pump on a 2007 Mercruiser 3.0 TKS Mercarb

[flyman219]

I want to run a pressure test on my fuel pump to see if that is what's breaking down after running for a bit on plane,

( http://forums.iboats.com/forum/engin...s-at-3000-rpms )

From what I can see it would require me to remove the rigid steel fuel line and add couple of barbed fittings and some rubber fuel line to plumb in the pressure gage. To save me a trip to the marina does anyone by chance know the exact type ( size and type ) of fittings I'd need to use on the carb and fuel pump? At a glance the pump would need a female barb adapter type and the carb would need a male barb adapter

Thanks

Mike

 

[Bondo]

Ayuh,.... Welcome Aboard,..... I think you'll find that 3/8" steel automotive brake lines are the same size, 'n same fittin's,....

 

[alldodge]

add couple of barbed fittings and some rubber fuel line

Will add, most of the barbed brass fittings are NPT (pipe thread), this is not the same a 3/8 brake line thread. Since your fuel pump will only be putting out 4 to 7 psi you don't need a lot to keep it sealed. You can put the fuel line directly over the end of the fuel line flare fitting on one end. Now you only need a fitting for the carb or fuel pump end. The fuel pump end in most cases has a 1/4 NPT fitting (1/4 NPT barbed fitting from hardware store) that is connected to the 3/8 line fitting

 

[Fun Times]

I want to run a pressure test on my fuel pump to see if that is what's breaking down after running for a bit on plane,

Depending on the fuel tester gauge design you own, you have two easier options available to test pressure at the carb.

1) Merc part number 91-18078, http://www.ebay.co.uk/itm/NIB-Fuel-...78-Outboard-/301474905771?hash=item46314dfeab

2) Merc part number 91-806901, http://www.ebay.co.uk/itm/NIB-Fuel-...l-91-806901-/121537263383?hash=item1c4c2f7717

 

[flyman219]

Thanks for the help guys, that should do the trick!

Mike

 

[flyman219]

On a closer inspection (we duh why didn't 'I do that before) I see that the fuel line has two 3/8" steel tubes with flares and nuts or caps and a rubber hose in between the fittings under a heat protector. What I decided to do was cut the rubber hose section and add a T fitting to put the pressure gage into the circuit. The motor runs at 8 PSI plus on the carb side of the fuel pump at full speed. At idle it will drop to about 5psi. We tested the performance again and once again after about 5-10 minutes of running at about 4K RPMs with the motor was making noise like detonation or pre ignition knock again and loosing power! I put the timing light on the motor again and I see I'm getting what looks to be the full advance on the timing. We were loosing power so we slowed it down to a idle for a while. After about 5 minutes of slow trolling we kicked it again and hit planning for another 5-10 minutes at about 4K RPMS and started to hear the detonation again!

I'm really getting to be at a loss as to what to check next. If you look at the link and all that we have tested and replaced there is not much left (other than the weak link LOL), any help or thoughts would be appreciated

Mike

 

[alldodge]

I think you have an air leak in the fuel line/pump. While the fuel pressure gauges are not that accurate, you shouldn't be reading 8 psi. In my opinion its either the pump, filter or line which is causing problems. Try this, get a piece of clear hose and install between pump and carb

 

[Scott Danforth]

check the carb inlet filter if you have high pressure.

detonation is most likely poor fuel quality or ignition too far advanced.

detonation is bad

 

[flyman219]

" While the fuel pressure gauges are not that accurate, you shouldn't be reading 8 psi. In my opinion its either the pump, filter or line which is causing problems. Try this, get a piece of clear hose and install between pump and carb "

The carb is rebuilt with a new filter. We have got the same results as the original carb that we replaced ands the filter under the fuel pump has been replaced.

" check the carb inlet filter if you have high pressure.

detonation is most likely poor fuel quality or ignition too far advanced. "

We have been running Boat gas from Yarrow Bay who is known for providing great fuel quality. I have checked and re checked the timing in "base mode" to be at 2 degrees ATDC like the motor requires.


So I think that what is going on is something out of the ordinary, I'm pretty handy around motors especially a simple 4 banger with a 2 BBL carb, but that being said this has got me stumped!

What would a cracked intake exhaust manifold act like?

Mike

 

[alldodge]

My understanding your having a high rpm miss, and it only happens at high rpm

What would a cracked intake exhaust manifold act like?

Cracked exhaust would allow water to enter the cylinders and this would also happen at lower rpms. If there was a crack or vacuum leak on the intake it would idle rough and lack power

I'm back to using clear tubing

 

[flyman219]

Thanks Alldodge,

It's not what I'd call a miss at high speeds, it starts as a slight ping at high rpm's (3500-4000) then the motor begins to loose power without sputtering, coughing or spark plug misfire after about ten minutes of running time. I think the power loss would be described best as similar to driving a car at high elevations (9000 ' above sea level) and stepping on the gas to pass someone. You notice there is not the normal power you had at sea level.

If I pull back on the throttle the motor will fall back to idle speed and run smooth as normal. I can putt around just above idle with no problem, but if I try to put the rpms up to 3000 plus rpms there is no t much power being created. Similar to lack of timing advance. I have checked the timing and see that at those rpms when the motor is not producing power the advance appears to be normal at about 25 degrees. The advance is off the scale and I don't have a adjustable timing light to be able to call the exact number of degrees, but it is well above the idle advance of about 12 degrees. (I did set the timing to 2 degrees ATDC in base mode per the specs for the boat) (2007 3.0 mercruiser TKS carb)

I'm wondering what type of clear line might be safe for a quick test to see if I am getting air in the fuel line to the carb. The hardware store has some soft vinyl type of stuff on spools that might work for a short test.

 

[flyman219]

After thinking about the symptoms again maybe I am having too much fuel pressure forcing fuel past the float valve and giving me a rich mix at higher rpms, (like running a car in thin air at high altitude). What would the maximum fuel pressure the float could resist?

Mike

 

[alldodge]

Hoping Fun Times would come back in, but there is a knock sensor used with the Bravo drives that I found, don't know if Alphas use them or not. If you have a knock sensor and the module is picking up a knock it will retard the timing. If this happens you loose power

 

[flyman219]

I am looking for fun times too, the Admiral is starting to put the pressure on me to get this right once and for all :blue:

I don't believe the 3.0 Alpha one Gen II have a knock sensor on them. The ignition system and the carburation is pretty basic....................... of course that doesn't say much for my ability to diagnose this issue such a simple motor

 

[Scott Danforth]

there is no knock sensor on the 3.0.

my concern is you state there is a slight ping. that could be detonation.

Have you checked the distributor cap and rotor? I have had a fouled distributor cap cause it to not want to run at load, and periodically backfire because it was firing multiple cylinders at a time.

 

[flyman219]

I gave it a full tune up about 10-15 "motor" hours ago. At the time I installed the new parts the performance didn't change or improve much. Since then the performance has not got worse or better other than the day I changed out the prop from a 14.25X21 to a 14.5 X17. The boat ran pretty close to what I would expect to be normal for about 5 hours before slipping back into the situation I'm in now again. Very strange to have the performance change so dramatic with a prop pitch drop and then slip back into the lack of power at 3-4000 RPMs.

Mike

 

[alldodge]

In manual 41 (TKS supplement) there is a knock sensor listed for the bravo drive, that's why I brought it up. Figured FT could clarify. Things don't add up, trying a bit of spit balling

 

[Fun Times]

The motor runs at 8 PSI plus on the carb side of the fuel pump at full speed. At idle it will drop to about 5psi.

While 8 psi is the highest max number that you should see on an accurate gauge, the "plus" could be concerning depending on what it really is getting up to. There's really no known definite max fuel pressure number that would send the carb into full flood mode per say but on basic average, typically when you see or hear of someone noticing excessive carb flooding while running, it usually seems to be somewhere in the 12-15 psi range. How due your spark plugs look? < if you really suspect a over fueling problem during the event.....If in a safe area, shut the engine down and pull a plug on each side of the engine and see if it looks fuel fouled.

We tested the performance again and once again after about 5-10 minutes of running at about 4K RPMs with the motor was making noise like detonation or pre ignition knock again and loosing power! I put the timing light on the motor again and I see I'm getting what looks to be the full advance on the timing. We were loosing power so we slowed it down to a idle for a while. After about 5 minutes of slow trolling we kicked it again and hit planning for another 5-10 minutes at about 4K RPMS and started to hear the detonation again!

When you're installing the new ignition module under the distributor, are you applying heat transfer compound/Thermal Conductive Grease merc number 92-805701 to help keep the module cool? http://www.michiganmotorz.com/mercruiser-quicksilver-compoundheat-p-857.html

Reading your other topic, the fix kept on seeming to be a new module possibly due to heat it seemed.

You may as well have a look to see if your exhaust shutter has fallen off the top of the exhaust pipe as an exhaust blockage could have an effect on the engine performance after a little while. http://www.mercruiserparts.com/Show....png&inbr=12824&bnbr=190&bdesc=Exhaust+System

As mentioned by everyone, This engine doesn't offer a knock sensor.
Check the alternator voltage while the problem is occurring and check the heat of the alternator as well....Should typically be around 170 or less degrees on average.
Try running an external fuel tank if you haven't already.
http://www.bing.com/images/search?q...rm=QBIR&pq=fuel+clear+hose+&sc=8-16&sp=-1&sk=

 

[flyman219]

While 8 psi is the highest max number that you should see on an accurate gauge, the "plus" could be concerning depending on what it really is getting up to. There's really no known definite max fuel pressure number that would send the carb into full flood mode per say but on basic average, typically when you see or hear of someone noticing excessive carb flooding while running, it usually seems to be somewhere in the 12-15 psi range. How due your spark plugs look? < if you really suspect a over fueling problem during the event.....If in a safe area, shut the engine down and pull a plug on each side of the engine and see if it looks fuel fouled.

While we are not near those pressures I'll need to pull a plug and check it. Would I be able to notice a change in appearance in just having the motor run with the power loss condition for just a few minutes?

When you're installing the new ignition module under the distributor, are you applying heat transfer compound/Thermal Conductive Grease merc number 92-805701 to help keep the module cool? http://www.michiganmotorz.com/mercru...eat-p-857.html

I do have the heat transfer paste applied to the module to keep it cooler. We did have a module failure, the module would not advance above 12 degrees no matter what RPM we ran the motor up to. When the motor starts to act up and loose power at 3-4K RPMs I have checked the timing while my son in-law drives and we are getting what looks to be full advance. About double of what we have at idle, about 12-14 degrees.

Reading your other topic, the fix kept on seeming to be a new module possibly due to heat it seemed.

I agree, we felt that the module's were the problem, the symptom of lack of power and not missing or sputtering just a smooth powerless performance was pointing to lack of full advance. We have replaced the OEM module with a NAPA (TP59) replacement and a Delco (D1965A) replacement and another same NAPA (TP59)where we are now,

You may as well have a look to see if your exhaust shutter has fallen off the top of the exhaust pipe as an exhaust blockage could have an effect on the engine performance after a little while. http://www.mercruiserparts.com/Show_...Exhaust+System

I think that will have to be on a to do this week to make sure we're not dealing with a exhaust blockage limiting the breathing ability of the motor.

As mentioned by everyone, This engine doesn't offer a knock sensor.
Check the alternator voltage while the problem is occurring and check the heat of the alternator as well....Should typically be around 170 or less degrees on average.
Try running an external fuel tank if you haven't already.
http://www.bing.com/images/search?q=...8-16&sp=-1&sk=

I haven't noticed a spike in output of the alternator but I'll check that again and take a infra red temperature on the alternator during the event.

Thanks for your thoughts Funtimes!

Mike

 

[dingdongs]

do you have access to the fuel mixture screw on the carb or has it been sealed over as it was on my friends Volvo 3 litre.once I reset it his boat ran fine again as the mixture screw had moved.may be worth putting a fuel cleaner in the tank or strip the carb and service it.