Fuel Pumps Getting tired ???

[tpenfield]

This season I have noticed that my twin 7.4 MPI engines are requiring a bit more cranking when they are first started. In the past years it was typically 5-10 seconds of cranking with the starter and then they would fire right up. This year it is more like 10-15 seconds until they fire and sometimes a bit longer.

Once they have been running, they will re-start just fine, it is that initial 'cold' start when the engine has not been run in a day or so.

I had this issue with my carb'ed 7.4L and attributed it to the fuel siphoning down into the fuel tank. So the extra cranking would be required to re-prime the fuel line.

I am wondering if the same sort of thing would/could be happening with the MPI engines :noidea: They have the VST fuel pump for the fuel rail and the combo sea water pump/fuel pump that runs off the v-belt on the engine. (serial #'s in my sig below)

My initial thinking is that the VST tank should hold a residual amount of fuel up at the engine that would facilitate a cold start, but just wondering if the VST pumps are susceptible to siphoning down if the engine fuel pump is doing the same.

I have read through the trouble shooting guide, which has numerous recommendations on checking the sensors. My Diacom software shows no codes and that everything is looking normal. As long as they continue to start, I should be fine, but also want to tip a potential problem in the bud in case it gets worse.

T. I. A. for thoughts and advice.

 

[alldodge]

Mine does the same thing and I have the Gen II cool fuel. I have even tried to turn the ken ON, then OFF, then back ON a few times to see if there is a difference, but to my surprise there was none. My thought is when dead cold the ECM makes sure it gets signals from most all sensors before allowing fuel to start.

Since I replaced the starter with a permanent magnet one it cranks over much fast, but still does the same thing. Might actually be a good thing, the motor requires oil pressure to build up before it allows it to start, don't know just a guess

 

[tpenfield]

Good info AD. I'm not sure if the ECM (MEFI1) looks for certain things like oil pressure or a certain number of revolutions before it fires. There is a sensor on the fuel rail, which tells the ECM it has got fuel pressure. It seems like it is fuel starved as the engine may start to catch after about 10 seconds, but still requires a few more seconds of cranking until I can feel it kick in.

It is hard to say what the ECM is deciding, verses what may be an engine condition.

I just don't want to be killing batteries this summer but as long as it starts in a reasonable timeframe, I guess I'll live with it.

 

[alldodge]

Thought about it a bit more and paid more attention to the time your talking about (10-15 seconds). Mine cranks first time for maybe 5 seconds or tad less, once fired up it fires up in a second or less.

Would be nice to know is it spark or fuel that is keeping it to crank so long. Could hook up a fuel pressure gauge and find out if the pressure is there on cold start times.

If it wasn't so hard to change, I would suggest trying a PM starter.

 

[tpenfield]

Maybe I could stick the timing light on the engine to see if I am getting spark during cranking. The schrader valve on the fuel rail is buried under some closed cooling components, so ignition would be an easier thing to check first.

 

[tpenfield]

Wondering if I can get the timing light to trigger off of an injector pulse :noidea:

 

[alldodge]

Wondering if I can get the timing light to trigger off of an injector pulse :noidea:

I doubt it, not enough voltage to trigger, but code use a Noid light to see if it is pulsing.

 

[Silverbullet555]

I highly doubt the ecm is blocking spark for a certain amount of time on a cold engine. However, I've been surprised before.

I wouldn't think it would take 15 seconds to get it to fire though. It sounds like it is without fuel from the injectors, all the way back to the tank. The question is why.

1 tank or 2? 1 fuel pick up or 2?

Perhaps anti siphon valve is hung up letting gas go back into the tank. It's not what they are designed to do, but their inherent design can act as an anti drain back valve is I understand them. Couple that with fuel pressure regulator letting the fuel system bleed off all pressure and maybe you are starting empty of fuel each time.

Of course, the likelihood of 2 engines having the same issue at the same time is pretty rare unless tjey are pulling fuel through the same pickup.

Fuel pressure gauge will tell you how they are doing.

I have mefi-scan if you want to borrow it. Mine is for mefi 4 so I'm not sure if it will work on mefi 1.

 

[tpenfield]

Thanks, James.

I have the Diacom software, so I think that is the same as the MEFI-scan (which I considered when buying the Diacom). There is a single 160 gallon tank, but individual pick-ups in the tank and separate fuel lines for each engine.

I noticed the symptoms from the initial start of the season while 'on the hard' this spring. I didn't think much of it when doing the initial start-up of the engines, because that is fairly typical after a long winter rest. But then, the problem has persisted, - these puppies do not want to wake up even after a couple days rest - so that kind of raises a flag in my mind.

I ran the engines a few times during the weeks of prep work and each time they took a while to start. I replaced the fuel filters just before launch day. Fortunately, right before my boat hauler came, I started the engines and ran them for 5 minutes each, so that they were 'primed and ready' when we got to the launch ramp. Just did not want to be YouTube fodder at the ramp They fired right up.

Next time out is Saturday, so I'll try to set up the timing light and see if I am getting ignition throughout the cranking cycle. Maybe I can figure out a way to reach the schrader valve on the fuel rail to check the fuel rail pressure at start-up.

It's funny that both engines are showing the same symptoms at the same time, but they are close together in the engine bay, so maybe they talk . . .

 

[tpenfield]

OK, real time update. I started the engines after a one week rest. The port engine started in five seconds, the starboard engine started in six seconds.

So I guess the engines are ready for the season. I will have to just keep an eye on them .

 

[Silverbullet555]

They were hitting the snooze button.

 

[achris]

....... but they are close together in the engine bay, so maybe they talk . . .

Yes, they talk. It's the Master/slave connection between the ECMs. ... :lol:

Chris. ....

 

[tpenfield]

Yes, they talk. It's the Master/slave connection between the ECMs. ... :lol:

Chris. ....

Yes, and I think the engines were saying to each other this past week . . . "we better shape up . . . remember what he did to us all last summer "

Anyway, we had a good outing today. My brother picked up a new (to him) boat in Chatham today and met up with us out in the bay for some celebratory beverages



It is a Grady 305 with twin 350 HP four strokes.

 

[alldodge]

It is a Grady 305 with twin 350 HP four strokes.

Nice boat, but its OB

 

[tpenfield]

Nice boat, but its OB

Salt water . . . gotta love outboards for that

 

[tpenfield]

Back on the topic of the fuel pumps . . . I think I will check the cam oil on them since I have not checked them in a long time. Then, I'll just see if the engines start as they should as the summer proceeds.

Not sure why they were so 'sleepy' during my prep work. I ran them 4-5 times and each time they were tough to start. I wonder if it was because there was not much fuel in the tank then (maybe 5 gallons) :noidea:

I put 45 gallons in the tank for launching and added another 60 gallons yesterday. (160 gallon tank)

I also got the trim pump on the Port engine that is acting up . . . but that is a story for another time :facepalm: