Merc TBI

[boat doc]

I have a Merc. TBI that is giving me fits. This thing hestates, and stumbles for about 2-5 seconds when you shower down on it. The problem gets worse the longer you run the boat. <br /><br />350 mag tbi gen+<br />tournament ski<br />sn: 0k147324<br />engine temp 155<br />fuel pres 29<br />injecter pulse 8.33 <br />timing (out of service mode) 10-14 deg <br /><br />I am leaning towards the fuel pressure regulator, because the fuel presure is out of spec. This system has the merc. cool fuel system on it, with the fuel pressure regulator in that cool fuel box. I have replaced the fuel pump, because it was making an awful racket, and the fuel pressure was a little low. I guess, has anyone had a problem with the regulators? Does anyone have any suggestions before I pull my hair out?<br /><br />Thanks for the help

 

[snapperbait]

Re: Merc TBI

29 psi on TBI.. woah! supprised it even runs.. Spark plugs must surely be fouled...<br /><br /> Sure you used the correct pump? I'd double check the part #'s...<br /><br />If the pump part #'s jive, look to the regulator or a restriction in the fuel return line..

 

[vinney]

Re: Merc TBI

I would look at the map sensor first on the TBI make sure the hose is hooked up and watch on the scan tool that its working. Next look at the temp thru the scan tool that the ecm is seeing(ecm temp). You said you changed fuel pump there are many different fuel pumps and hi and low pressure. The fuel pumps look the same from the outside. I have install new fuel pumps that where junk out of the box. Whats your fuel pressure? Always change the spark plugs if the engine been over fueling. If the ecm thinks the engine cold it will stay in warm up mode and over fuel the engine. The map sensor will act the same way poor idle and over fuel and then foul the spark plugs. I would run the engine under load with the fuel pressure gauge hooked up and see what the fuel pressure does.

 

[boat doc]

Re: Merc TBI

snapperbait, yes 29 psi, and the book states 35 plus, that is what I was getting at the regulator for. Here is my call at the moment, a bad regulator, killed the original pump. If there was a restriction in the return line, the fuel pressure should increase. If there was a restriction in the feed line, the fuel pressure would decrease. <br /><br />vinney, I checked the map thinking the same thing, but typically a failed map with give you poping through the carb, essentially, the engine is getting more air than it needs, and you get a lean pop effect.

 

[snapperbait]

Re: Merc TBI

TBI runs at 13-15psi, sometimes even less... 35psi, or more, is for MPI....

 

[boat doc]

Re: Merc TBI

oh, maybe I read the wrong book. I will have to check that

 

[boat doc]

Re: Merc TBI

no, I read it right, 30 psi with cool fuel system, 43 psi with with vst system, all gen + engines. That is unless there is an update that I have not gotten. I have not been a merc dealer in about 3 years.

 

[nms1991]

Re: Merc TBI

check your throttle position sensor. If the map fails it could also go completly rich no popping though the thottle body. Also check your intake manifold torque possible vacumme leak, only 8 bolts holding the the intake instead of 12 like the old style intake manifold, also only at the end of the end of the intake.

 

[boat doc]

Re: Merc TBI

i'll check, but I should hope not only haveing less than 200 hrs.

 

[anesthes]

Re: Merc TBI

8 bolts? What are the TBI setups vortec ?<br /><br />I know all the automotive tbi setups are 55# saturated injectors that run at 15psi. The police package uses a 60# injector, and good for around 210hp. Maybe the marine stuff uses higher fuel pressure to lower the DC of the injector?<br /><br />Do the marine applications run a 122747/122746 ECM like the automotive, or is it marine specific?<br /><br />-- Joe

 

[anesthes]

Re: Merc TBI

The inj PW you posted.. is that 8.33ms at idle??<br /><br />-- Joe

 

[boat doc]

Re: Merc TBI

yes

 

[outboardguy]

Re: Merc TBI

As per your spec you gave,you show idle timing to be 10-14 deg at idle.Have you put it into service mode? Does the engine raise rpm when put into service mode? The reason I ask these is that I had an engine today that would idle slow and showed the timing at 10-12 at idle. Turns out the Iac Motor is getting stuck so the engine is bumping timing to try to keep the engine running.