Logo

454bs not turning up

boatofus

New member
"Hello every one. This is my f

"Hello every one. This is my first time posting on this site but have been reading it for a while. All of the info that is posted here has been so very useful to me being that i like to do my own repairs. Recently after a long day of fishing i was headed back to the barn when i had to slow down to let another boat go by and when i went to go back up on plane my port motor wouldn't go past 2000 rpms and was breaking up. Being that I had just filled up that morning i figured it was a fuel problem. So i changed all of my filters including the Oberg, witch was a little cloged, and took it out for another spin. Same issues happened<font face=""arial,helvetica""></font><font face=""courier new,courier""></font><font face=""times new roman,times,roman""></font>}. Changed the cap and rotor, witch seem to have a little corrosion on the terminal(1 year old tune up).As i am changing these parts i noticed a vacumm line running to the TB from I guess would be some kind of ingnition or timing control. Well that tube was laying under the Heat exchanger hoses and was crushed. I went and bought a new hose witch i extended about 7inches so i could run it over the hoses and not risk crushing it again. The Starboard engine was runnnig fine but had the vac hose in the same position. Once I put the new hose on she purred like a kitten. Has anyone had this type of issue before. Sorry for the long post."
 
"chris:

it would help a bit


"chris:

it would help a bit if we had a better idea which engine you had. guessing, a mid 90's TBI setup, probably with a MEFI-1 computer?

The only thing I can think of with a vacuum line would be the fuel pump regulator.

Thanks for the data points."
 
"Makomark,

Sorry for the l


"Makomark,

Sorry for the lack of info. 95'454 XL TBI, velvet drive 5000 trans. The vac line runs from the TB to a black breaker box mounted on the inboard riser. In the box are breakers for the fuel pump, ignition, main 50amp ,etc. Also their are two electronic modules, one has only one plug and is mounted by itself and the other has two plugs and the vac line. Any thoughts?. Also when i bought tune up parts last year the mechanic gave me 7mm wire and this year i went to a different supplier and was given 8mm wires. The boat seems to run better with the 8MM. Is this possible?
I really appreciate the help and respect the people who have all of this knowledge and are willing to help.

Thank you."
 
"Chris:

Memory overflow on


"Chris:

Memory overflow on this end....i forgot about the MAP sensor. It would need a vacuum line to sense what's going on in the manifold. The concerning part is you said the module has TWO plugs & the vac line. All the MAP sensors I've seen only have one plug. No idea what else it would be. If the MAP has a leaky vac line, the ECU will adjust the fuel curve (injector dwell) and rich I believe.

On the wires, any change you noticed probably was NOT due to the insulation jacket diameter increase but due to the core within the wire.

thanks for the missing details, i'm sure somebody will benefit from this in the future."
 
"Makomark,

You are probably


"Makomark,

You are probably right.I didn't unscrew the relay but it looks like two seperate units. Three seperate relays one with the vac. So if I am understanding you correctly the relay with the vac line is the MAP sensor relay. That would make sense on running rich becuase that engine was starting to admit blue smoke witch I believe is unburned fuel from running to rich?
Thanks again."
 
"Not a relay but the actual se

"Not a relay but the actual sensor. To see one, go to the engine parts link and enter "9-33601" in the PART Number box. Functionally, they provide the same info a vacuum gauge would but to the ECU vs a human. MAP = Manifold Absolute Pressure.

On the smoke - i thought black was rich and blue was oil. its usually a bit subjective and always subject to some interpretation due to current light.

I think the only two relays are for the ignition and the fuel pump control. A wiring diagram would resolve that."
 
"Makomark,

You truly have i


"Makomark,

You truly have in depth knowledge and I will take your word on it. Should i replace the MAP sensor being that it probably has been seening some bad conditions having the vac tube restricted?
Thanks for all of your help."
 
"Makomark,
I just looked up t


"Makomark,
I just looked up the part and you hit it on the head. So it looks like there is another sensor mounted behind it. Cool. Thanks again."
 
"Not until you know it is bad

"Not until you know it is bad (or just have a surplus stack of bills). They have no 'memory' so no benefit to replacement.

If you have a hand held vacuum pump and a DVM, they are pretty easy to test."
 
"Makomark,

Yes I do have bo


"Makomark,

Yes I do have both instruments. What does the voltage do when the vac increases and what wires should i be testing. Also, being that this is a MEFI-1 system would a diagnostic program had shown me the problem with the map sensor? I realize it is an early system and is limited to certian information and should i purchase the basic program from Rhinda Tech or the Mercury diagnostics reader?
Thanks."
 
"Rinda makes the Merc scan too

"Rinda makes the Merc scan tool if that's what you are referring to.

Would it had shown you the problem? - that's a tough one. I would say those scan tools will provide you the info you ask for, within the ECU's limits. I doubt that it would have tagged a ruptured hose as a problem - that where the operator "adds value" and justifies the hourly rate. Usually the ECU will set a code if the sensor is "bad"; exactly what bad is is defined within the ECU.

Last time I checked, the MAP sensors behave like throttle position sensors. Three pin connectors. One "end" lead has a fixed reference, usually +5V and the opposite is Ground. the sensor output is in the middle. throttle closed = high vac = low MAP = low sensor voltage (<= 1.0 volts). Throttle WOT = low VAC = high MAP = high sensor voltage (=> 4.0 V). If you get the +5 and the ground backwards, the reading will be opposite. If you are just checking the functionality of the sensor, you just need to see the voltage change when you vary the vac."
 
Back
Top