Bad Fuel Pump?

[stancel]

My TLDI will run fine as long as you keep pumping the primer bulb. If you quit, it will go about 100 yards and die. And if you let it sit for 10 minutes the fuel filter under the cowl drains to about half full and you have to pump the primer bulb a dozen times to prime the fuel system again. Everything from the fuel connection at the motor back to the tank has been changed or checked. No problems there.

Only thing I can think it could possibly be is the small fuel pump that feeds the FFP. Bad diaphragm or check valve I assume. Am I overlooking something else obvious?

 

[dude11]

Sounds like you got it.Is it a stand alone type pump,using vacuum to function?

 

[stancel]

It is a stand alone pump, but I can't honestly tell you how it is driven.

 

[TOHATSU GURU]

That engine has a self diagnostic feature that you can access using the service manual or you can take it to a TLDI certified dealer or you can randomly replace the parts. The least expensive option is to buy the factory service manual, put the the engine in test mode and let it tell you why it's sick.

 

[Sea Rider]

If being handy remove fuel pump and check internal diaphragm condition. E fuels screws thin rubber diaphragms way faster than non E fuels. Usually balloons, deforms diaphragms very easily including small o'rings that deals with fuel. When an engne springs back to life while primming bulb, it's usually a faulty fuel pump condition..

Happy Boating

 

[stancel]

Thanks for the responses. It should be noted this motor is brand new. It is a warranty replacement for a 2012 that Tohatsu was unable to repair. So yes, this is the second brand new Tohatsu that has problems.

I know the first piece of advice is to bring it in to be looked at, but the dealer in my area is closed weekends, and my taking an afternoon off work to run a boat 30 miles up the road for drop off and pickup is much more expensive than my doing little inexpensive fixes myself. Of course, if those fixes don't work or cost more than a few bucks, I will have to bring it in. But until then I figured I would just pick some brains on here .

I had enough spare boat stuff laying around to change everything from the motor connection back, including the fuel tank, and that made no difference. I also keep a spare fuel pump for every motor I have ever owned, so I changed that out too and it wasn't the problem.

Basically, if I go through the process of "force feeding" the fuel system as per my service manual, it runs until you stop once or twice. But, once you shut it off for 10 minutes or so, then crank back up the motor runs a minute or two then dies. Sometimes you have to stop a few times before that happens. And, when it does happen, the fuel filter under the cowl is half full of air as seen in the photo.

So my question is since the fuel pump is new, and the primer bulb is also new, and both have check valves, doesn't the air in the filter almost have to be getting into the system from between those two components? If that is most likely true, then there isn't much there. A couple o-rings on the filter and a quick connect that I can just eliminate with a splice fitting.

And Guru, the following error codes are present. When the dealer installed this motor they said they couldn't get it cranked and thought the problem as a faulty connection at the fuel tank. That definitely wasn't it because I put a straight fitting on the tank so there is no disconnect. I don't know if these codes are from them installing the motor and not clearing them, or from the fuel system running out of fuel multiple times. But the Faulty FFP code is erroneous in my simple minded opinion, because as long as I pump that primer bulb I have no issues. If the FFP was bad or malfunctioning, it doesn't seem like pumping the primer bulb would make a difference.

Light 1, 2, 3, RPM
off, off, steady, 5500 - Faulty #1 TPS
off, off, steady, 6000 - Faulty #2 TPS
on, off, on, 5000 - #1 TPS Power supply high
off, off, steady, 7000 - Faulty FFP
blinking, off, steady, 5000 - #2 TPS idling position error
off, off, steady, 5000 - Faulty CPS

Thanks guys, and sorry for the lengthy post.

 

[pvanv]

Have you reset the TPS and cleared the codes?

 

[stancel]

Have you reset the TPS and cleared the codes?

No, I haven't. The reason being I don't want to clear codes in the event it does end up at a dealership to be worked on. And, I figure (perhaps wrongly) if I pump a primer bulb and the engine runs fine then it isn't a problem with a sensor or the FFP.

 

[pvanv]

Since you have recorded the codes, clearing them isn't a problem. Standard repairs on TLDI motors require that the TPS initial setting be correct -- it's one of the first things a tech will do. It never hurts, and often helps.

Air is compressible; When the fuel system comes up to pressure, any air bubbles in the pressure side shrink. Once the pressure is off, they re-grow. If they are trapped in a high point, they don't completely bleed out of the system. We see that often in horizontally-oriented in-line filters. In the case of your settling-bowl filter, I would expect air to get purged when priming to the air separator.

Fuel delivery to the air separator (and high-pressure FFP) is identical to the system on a conventional carbed motor, so if you have verified that there aren't any air leaks from the fuel tank pickup to the fuel pump, then if squeezing the primer eliminates the problem, it would appear that your pump is not working well enough for your setup. If the tank is located very low, or if the tank vent is not allowing air in easily enough, the pump must develop a lot of suction to draw fuel up. If that's the case, try setting up a known-good portable tank, at or above the height of the motor. That will help to rule-out a too-much-suction problem.

A minor air leak in the low-pressure section of the fuel system (such as a cracked fuel filter or bad o-ring for the filter bowl, or a similar defect at the water-separator filter) could allow air into the system when the fuel is not being pumped, because it's subject to suction as the fuel tries to go back down into the tank.

What is your model/serial? I'm guessing it's an MD75 or 90.

 

[stancel]

Thanks Paul. I will video record the error codes and clear them. The motor is a MD50B2.

The only thing I haven't eliminated on the low pressure side of the system is the quick connect at the motor, the fuel bowl and associated o-rings, and the fuel lines going to them. I changed the fuel pump, so I am fairly confident it isn't that. Used a spare gas tank I had, a different primer bulb, and bypassed the water knock out filter. Also replaced all those squeeze hose clamps with real screw down clamps, and replaced all the fuel lines b/w the motor and tank.

I am going to eliminate the quick connect at the motor next, then the fuel bowl. Might also put some clear tube in place of the fuel lines temporarily to see if I see bubbles. Beyond that, it will get into stuff that cost money and I will have to try and get it to a repair shop in the near future.

I guess my initial question was whether or not air could bleed backwards through the fuel pumps check valves. If it can't I figured any air being introduced into the system has to come from between the fuel pump and the gas tank.

 

[pvanv]

All check valves can weep back a little. Have you reset the TPS?

 

[stancel]

Thanks Paul. I got in touch with Tohatsu. I am going to clear the codes, check the throttle arm position and reset the TPS. After that if it is still giving me problems I will have to get it to a repair center.

 

[stancel]

I cleared the codes, reset the TPS, put a straight fitting in place of the quick connect at motor and changed orings on fuel bowl.

One thing I did see though was that the vapor line that comes out of the top of the separator and goes to the throttle body had been zip tied to a larger line so tight that it was pinched completely closed. Not sure if that would cause a problem but I fixed it.

Took boat out and couldn't get it to act up. Not calling it fixed yet. Will know for sure after the next couple of outings.

 

[pvanv]

I cleared the codes, reset the TPS, put a straight fitting in place of the quick connect at motor and changed orings on fuel bowl.

One thing I did see though was that the vapor line that comes out of the top of the separator and goes to the throttle body had been zip tied to a larger line so tight that it was pinched completely closed. Not sure if that would cause a problem but I fixed it.

Took boat out and couldn't get it to act up. Not calling it fixed yet. Will know for sure after the next couple of outings.

Sure could. That tube lets the vapor out to atmosphere at the throttle body, where air flow draws it into the motor for burning. If the vapor can't be relieved, it could pressurize in a big bubble inside the separator, and once the low-pressure pump stops, it could refill the entire separator and fuel lines with "air".

 

[stancel]

Thanks for all your help Paul. I am hoping that was it.

If anyone else comes across this thread with a similar issue, check the small vapor hose shown in the picture below. Mine was zip tied to the larger fuel line next to it too tight and was closed off. You can still see the impression from the zip tie it was so tight.