Ox66 Fuel Issue

[boscoe99]

Faulty wiring, a bad connection or a faulty CDI would be my best guess.

[Oyster Boat 88]

Wiring isn’t showing anything upon inspection of connectors but I’ll bypass one section at a time to make sure. Since I have a second engine on the port side can I swap the CDI unit to see if that is the issue? Only difference I’d prop rotation ?Looks like the 150 and 200 share the same CDI for years . Should be some used ones available, the price for a new one is crazy.

[boscoe99]

Yes to swapping the CDI.

[boscoe99]

I might get a test light and connect one lead of it to a known good battery power source. Then connect the other test light lead to the wire from the CDI that grounds the pump directly. Turn the key on. Does the light illuminate?

[ttles714]

I am interested and following this post ..... Am I right in understanding that the HPFP is grounded thru a resister ?????? Blow 1200 rpm but above that it is grounded by the CDI ???? Why a resister ????

[99yam40]

I would think at low RPMs the pump does not need to run a full RPM

[ttles714]

I would think that the pump would need steady RPM's to maintain pressure to the injectors ....still trying to understand all this

[DennisG01]

I would think at low RPMs the pump does not need to run a full RPM

The pump basically runs or it doesn't - it doesn't change RPM's otherwise the injectors wouldn't fire properly. The control of the amount of fuel being shot into the engine comes from the duration that the injectors are opened (con*****ed by the computer).

Well, I suppose technically a pump could run at lower RPM, but then it would be failing.

[99yam40]

The pump basically runs or it doesn't - it doesn't change RPM's otherwise the injectors wouldn't fire properly. The control of the amount of fuel being shot into the engine comes from the duration that the injectors are opened (con*****ed by the computer).

Well, I suppose technically a pump could run at lower RPM, but then it would be failing.

would the resister not lower the voltage ?

[DennisG01]

would the resister not lower the voltage ?

I may not be the best one to explain this clearly enough - maybe someone else can (most likely!) do a better job.

Yes, a resistor would lower voltage, but that's not "really" what it's being used for. Besides, it is not a "variable" resistor so it can't change it's resistance value.

There should always be full battery voltage at the HP pump.

The "RPM" that was mentioned earlier in the post is in reference to engine RPM, not pump RPM... in case that's where the confusion lies.

[boscoe99]

I am interested and following this post ..... Am I right in understanding that the HPFP is grounded thru a resister ?????? Blow 1200 rpm but above that it is grounded by the CDI ???? Why a resister ????

To reduce the current flow through the pump. Less current results in less temperature rise in the fuel.

To lower the speed of the pump when it is not needed for the pump to provide a greater volume of fuel to the injectors.

[boscoe99]

I would think that the pump would need steady RPM's to maintain pressure to the injectors ....still trying to understand all this

It is the fuel pressure regulator that is con*****ing the fuel pressure to the injectors. Not the speed of the pump. Pressure that varies with the intake manifold pressure.

The fuel pressure from the regulator is higher when the manifold pressure is higher (throttle opened) and lower when the manifold pressure is lower (throttle retarded).

At all times the fuel pump can provide more fuel than is ever needed by the motor. The pressure regulator sends excess fuel that is not needed by the injectors back to the vapor separator tank.

[99yam40]

To reduce the current flow through the pump. Less current results in less temperature rise in the fuel.

To lower the speed of the pump when it is not needed for the pump to provide a greater volume of fuel to the injectors.

OK then I was correct, the resister does lower the voltage and the speed of the pump when the motor is running at low RPM.
thanks Boscoe

[DennisG01]

OK then I was correct, the resister does lower the voltage and the speed of the pump when the motor is running at low RPM.
thanks Boscoe

And I stand corrected... and learned something new that I thought I knew "correctly" for many years!

[boscoe99]

If the resistor was in the power feed wire ahead of the pump it should lower the voltage to the pump. But the resistor, being in the ground line after the pump, may not be doing that.

I will 'spearment tomorrow.