2001 MC 5.0 EFI Throttle Body-appear to be running rich. Trying to help a friend

[rothfm]

Hi All again,

Got some numbers, so I thought I'd update for some addtl input.

Someone told me to check vRef 5volts at several sensors, as only TPS, IAC, MAP, and Coolant Temp signal the ECU for fuel trim....So today, I probed each sensor wires, and found 5.19v at each sensor, EXCEPT the IAC. On that one there were 4 wires. 2 were .9v , the other 2 were 10v.

Question 1) Is this 5v theory correct? and are those values for the IAC 4 wires ok?

Question 2) Can the "sensing" wire on these sensors be measured for proper state at idle? Meaning the normal sensor state must present a voltage on the sense
wire for that should be a particular value, or range for that condition. Is it possible to get a ballpark base reading on these lines with a voltmeter?

I located a couple grounds, and they will be cleaned up for sure. But had solid continuity from Batt ground, to lots of areas on the block-So I'm lead to believe grounds seem ok.

Then per Alldodge, We jumped into Base Timing, and put a LED into E/F to inspect for codes...It blew the first LED, another one started to flash, then got hot and quit. My friend had a pack of LED's but unknown type. Maybe those were not "Resistor" type and blew each time. I guess we will have to locate some new ones and ensure they are resistor type.


Question 3) Lastely, we just had "key-on" when doing the jumpers for codes? Is it ok and preffered to be engine running?-dont want to blow anything.

Still pending an actual Fuel pressure test.

Thanks for all the help already-appreciated.

 

[achris]

1) Yes. 5 volts is the driver voltage for the sensors. IAC is not a sensor, it is a valve that responds to ECU input. Those lines are coil drives, and voltage 'anywhere' is to be expected.

2) Sensors that have a 5v and ground connection are voltage dividers, and yes, you can read the voltage on the 'sense' line, but you will have no idea what the 'right' voltage will look like. If you see either hard 5v or hard gound, maybe that sensor is faulty, maybe.

LEDs are 2 volt devices. You need a current limiter in the line or they become an audio device (but only ever once ). Limit the currrent to 20mA, so use a 560ohm or 630ohm resistor.

3) Key ON is fine.

Chris........

 

[rothfm]

Thanks, will get resistor, or proper LED, and hopefully a Fuel pressure reading. Been a tuff one.

 

[rothfm]

Opened up and cleaned all the grounds we could find today. No difference.

Also did some testing with the 4 newly installed sensors, connectors off one-by one, listening for any difference, and there is..We can deduce that the new IAC, TPS, Map, CTS are working ok.

Anyone know offhand what fuel pressures should be?...I thought I read there's a idle range, and another for higher rpm? We will be installing a valve to test that shortly! And getting a resistor, or proper LED for a good code readout.

How does this fuel pump work? does it cycle on/off at all or is it always on (probably a dumb question). Is there any possibility that the Fuel pump can over-produce fuel? I would think it would be the opposite, a pump issue would not produce enough fuel etc...But had to ask those more knowledge

Pending the fuel pressure test and looking for codes, and if the pump itself cannot cause over-pressure, I believe we are getting to the point of looking toward the computer...."IF" we are confident all the 4 sensors are working correctly, and I believe that are.

From the forums, I have the place (california I believe) that can Test them and reprogam etc. That would potentially happen this winter.

Thanks everyone. Big help.

 

[achris]

Spec on fuel pressure is 30psi (at all revs), and yes, the pump can produce too much pressure. There is a fuel pressure regulator (item b in the diagram below) in the fuel system. If it fails then it's quite possible to have considerably more pressure than required. The same pump is used on the MPI engines, and they regulate at 43psi, so the pump is quite capable of producing at least that.

 

[TLC SeaRay]

I am new to the forum but am chasing a similar problem. I have my 2001 Sea Ray 5.0 Mercruiser out of the water doing maintenance. I was getting ready to do a fuel pump pressure test but could not find the spec. The posted diagram really helps to better understand the system. Oh, and my problem is not getting max RPM's at WOT. Problem starts after about five minutes run time.

 

[alldodge]

Howdy TLC

Its best to start your own post so everyone can get involed if needed. Its not nice to hijack another's thread. If you would just start another and we will help. You can reference this thread but make sure to let us know everything about your issue and motor

 

[rothfm]

All dodge is always watchin... Yes, that is a good Diagram.

Alldodge....Would you mind explaining how this "return" path works?....My buddy is going to pull a manifold so he can get to that Cool Fuel/Pump and regulator and see down there. Still pending a pressure test.

He and I discussed that Diagram at length and not understanding that return path, and that "Rupture" line.

Form some reason we believed the item that is on the throttle body was a regulator (the part with the diaphragm and spring)- but now realize it is a sort of Dampener.
So time to get access to that low mounted cool fuel unit.

Thanks again

 

[achris]

The rupture line goes up to the flame arrestor atop the throttle body. If the diaphram in the regulator ruptures, fuel goes up the rupture line and floods out the engine, stopping it, and the ECU shuts down the fuel pump.

Return path is quite simple.

Any fuel that is 'relieved' by the pressure regulator is sent back to the fuel filter. Those filters have an INLET and an OUTLET on each side of the housing. That's so it doesn't matter how the housing is mounted, or which side the fuel tank line and engine line come in from, it's the 'right' side. Each INLET and OUTLET are drilled through, ie connected to the other, so the return path goes back to one of the INLET ports on the filter housing, but could just as easily go back to tank, it's effectively the same thing, but doesn't require an extra line to the fuel tank. Makes the engine more 'self-contained'....

See the arrows on the top of the filter.....

 

[rothfm]

Okie dokie,

Got manifold off and got out the cool fuel assm. Was easier to take it out with all the lines attached(undid lines up top) and remove everything, due to space restriction

Is there any way to test this? Wasnt able to blow back on return line, not sure if it will or not normally

He will replace the regulator and pump, just wondering if anything to look for/try whil its on the bench


Thanks

 

[achris]

Replacing the pump is an expensive path. Getting a fuel rail pressure reading would have been better, and a lot cheaper. Have you managed to read any codes yet?

 

[alldodge]

Is there any way to test this?

You can test the regulator with air pressure and a gauge. Adjust the air pressure tank regulator to below spec (43 psi), then with a rubber tipped air nozzle apply air and slowly increase air pressure. When regulator opens this will tell you what its set at and working pressure.

If you run the fuel pump and block off the output side the pump should be able to get to 60 psi.

Wasnt able to blow back on return line, not sure if it will or not normally

The antisiphon vale keeps from being able to blow back toward the tank

 

[achris]

Set the air pressure at less than 30 psi for that test. ..

 

[rothfm]

UPDATE: Issue is Resolved...Wanted to be one of the few that finished thier posts

Our over fueling issues is solved. My Friends motor is humming along nicely. This took awhile, some trial and error, some education, AND the nice help here on the forums. THANKS ACHRIS AND ALLDODGE.

Fuel Pressure Regulator on the cool fuel unit solved the ongoing mystery!!

Quick recap to help others.

Sympton: Bogging, smoking, hard starting, unable to plane off, visibly too much fuel bieng sprayed.

We initially did all sorts of things including tune-up, fuel injectors, Throttle body work, filters etc, etc... The Pic Achris sent of the fuel path and return path, got us thinking! What threw us off was rebuilding the unit we "thought" was a pressure Regulator, mounted on the throttle body (diaphram/spring). Realizing later this isnt really a regulator. Something was going on inside the Reg on the cool-fuel unit. Its not serviceable. Its hard to reach, but can be swapped.

Immediately noticed the difference in the driveway...and the water-test proved the fix. Running really well. I bet my friend will experience much better mileage/economy now as this started slowely last year and got progressively worse. Last official time on the water he used a TON of fuel.

Thanks again all

 

[pwrplay]

Thanks for posting the fix. I?ve been following this thread from the beginning in case I ever experience the same symptoms as I have the same motor.

 

[rothfm]

Of course, if my Pal had installed a schrader valve and got a proper reading on day one......It Might have helped our cause. All good its working nicely.