7.4 MPI no fuel pump operation,***FIXED***

[Bt Doctur]

2006 7.4 MPI last run 3 years ago. Fresh batteries. Electric fuel pump does not turn on nor does it have the 2-3 prime mode when key is turned to "On".
All connectors pulled and sprayed. No corrosion issues.Main ign and fuel pump relays swapped and changed. No improvement. Main ign relay clicks. Power indicated using a test light on the Red leads of fuel pump relay.Jumping connectors does run the pump. Checked for any missing grounds in the harness. Green /White from ECM does not indicate a ground to trip fuel pump relay.There is spark coming from the coil.
Suggestions?

 

[Don S]

Re: 7.4 MPI no fuel pump operation, Stumped?

Re: 7.4 MPI no fuel pump operation, Stumped?

Do you have a SN ? I don't think Merc even used a 7.4 in 06.

 

[Bt Doctur]

Re: 7.4 MPI no fuel pump operation, Stumped?

Re: 7.4 MPI no fuel pump operation, Stumped?

S/N tags on the aircleaner are non readable
Sorry , 99 270 Sundancer
There is spark coming from the coil,

 

[Fun Times]

Re: 7.4 MPI no fuel pump operation, Stumped?

Re: 7.4 MPI no fuel pump operation, Stumped?

Do you have a scan tool to hook up to the engine?

Have you checked the fuses on the engine?

Do you have power and a good ground going into the ecm?

 

[Don S]

Re: 7.4 MPI no fuel pump operation, Stumped?

Re: 7.4 MPI no fuel pump operation, Stumped?

Did you look on the tag above the starter?

 

[Bt Doctur]

Re: 7.4 MPI no fuel pump operation, Stumped?

Re: 7.4 MPI no fuel pump operation, Stumped?

Working on the tag soon, not the easiest with the motor stuffed down there. Looks like 12 inch riser extentions on it. inspection of all grounding and bonding found nothing.

 

[Don S]

Re: 7.4 MPI no fuel pump operation, Stumped?

Re: 7.4 MPI no fuel pump operation, Stumped?

Working on the tag soon, not the easiest with the motor stuffed down there.

Think digital camera. Works better than a mirror sometimes.

 

[Bt Doctur]

Re: 7.4 MPI no fuel pump operation, Stumped?

Re: 7.4 MPI no fuel pump operation, Stumped?

so far continuity on the green/ white from ECM to fuel pump relay.Flow chart mentions PCM (propulsion control module), what and where is it? Engine number is L 354028 or L 854028
Would appreciate any history PM`d to me.
Thanks

 

[Don S]

Re: 7.4 MPI no fuel pump operation, Stumped?

Re: 7.4 MPI no fuel pump operation, Stumped?

Flow chart mentions PCM (propulsion control module),

What flow chart are you looking at? Never heard of a PCM. Is that the OEM manual?
If not, download manual #23. Then go to page 5E-78. There is a wiring diagram and explantion of the system. Then on the following 2 pages is the flow chart. Follow it, and you will know why the pumps don't run.
So far, it sounds like you may have lost the ground on the 86 terminal on the relay. The green/white wire is power not ground.

 

[Bt Doctur]

Re: 7.4 MPI no fuel pump operation, Stumped?

Re: 7.4 MPI no fuel pump operation, Stumped?

After review of that manual I`m just a bit confused.Will double check my findings and report back with results. There is one thing that confusing.The wire colors in the manual dont match the boat.Main ign and fuel pump relays only have 4 wires.Fuel pump relay wires are 2 reds(14Ga), green /white(16-18Ga) and tan (16-18Ga).No visable ground wire. Manual states it`s part of the harness. one red is constant 12V, other red is switched 12V, green/white to ECM, tan to fuel pump.
Thanks for the help Don.
PCM (man #33)= ECM

 

[Don S]

Re: 7.4 MPI no fuel pump operation, Stumped?

Re: 7.4 MPI no fuel pump operation, Stumped?

The 33 manual is for the 555 ECU, not your MEFI 3 setup you have. Check the 23 manual, I may have gotten the wrong page. But you really don't want manual 33.
PS, the 0L354028 is the correct number, the 0L8 is for an Alpha I stern drive. Not even an engine.

Just checked. There is no tan wire in ANY fuel pump relay ciruit. I don't care what EMU/M you have. There is no tan wires. The only tan wire is in the IAC ciruit and has nothing to do with the fuel pumps.
Has someone been rewiring that engine ????????

 

[Don S]

Re: 7.4 MPI no fuel pump operation, Stumped?

Re: 7.4 MPI no fuel pump operation, Stumped?

Does your ECM look like this

 

[Bt Doctur]

Re: 7.4 MPI no fuel pump operation, Stumped?

Re: 7.4 MPI no fuel pump operation, Stumped?

Thats not the ECM on the boat. MEFI-3 is more like it.
The relay wiring has me confused.
5E-16 shows a ground lead that I dont.
5E-22 shows the main ign relay that I do have .
5E-45 is what i have on the boat for the fuel pump relay..
If fuel pump power is supplied from 439 PNK, then the green /white should supply a ground to trip the relay.But according to the flow chart , the green/white should supply 12V for 2 seconds.Relay cant trip with 12V on both sides of the coil??
Or am I missing something ?

 

[Don S]

Re: 7.4 MPI no fuel pump operation, Stumped?

Re: 7.4 MPI no fuel pump operation, Stumped?

I am seeing conflicting information in the 23 manual. At this point, if I was a dealer, I would be on the phone to Merc Tech to find out what the deal is. But it may be such a thing as it's an old manual and has been updated. May have been service bulletins (although I don't remember any) or manual changes that come through the mail to dealers. Who know.
BUT, if you have power coming out of the ECM, and can confirm that by DVM checkes, then the other side has to be a grournd or the above reversed. As you say, you can't have 2 positives and make it work.

 

[Fun Times]

Re: 7.4 MPI no fuel pump operation, Stumped?

Re: 7.4 MPI no fuel pump operation, Stumped?

You should start with the system diagnostics on page 5E-66, of service manual number 23, That should help walk you through this easier, Stay with the diagnostics tree, it will lead you all the way down to page 5E-78, That is where your main test will be, But start at the top of page 5E-66, Trust me you will only be shorting your self if you jump ahead of the gun.

Keep in mind there is a resistor inline of the pink wire that goes between the distributor ignition control module and the coil, You will want to ohms check it in both directions if I remember correctly. If the resistor goes bad it will not start.

Good luck with it.

 

[Don S]

Re: 7.4 MPI no fuel pump operation, Stumped?

Re: 7.4 MPI no fuel pump operation, Stumped?

I think one thing that may help you is to stop going by wire color on the fuel pump relay.
Go to the section I posted in reply #9 and go by relay pin numbers, not wire color. Here is how those relays and connectors are numbered.

PS: I would bet steps 4 and 5 on page 5E-79 locates your problem. since you already jumped 30 and 87 and the pump runs.

 

[Bt Doctur]

Re: 7.4 MPI no fuel pump operation,***FIXED***

The ECM used in this system appears to supply the ground needed for pump operation and other systems. A scan tool was hooked up and could not comminicate with the ECM . This suggested a no power condition to the ECM. Upon opening the wire harness is was discovered that a previous person used some type of needle point to puncture the insualtion of a orange power wire numerous times in the past. This led to a corroded open in the orange wire that supplied power to the ECM module. Motor is now running properly.
A suggestion to future testers is to NOT PUNCTURE and wires for testing. Obtain a old harness, plugs from a junk yard, etc .to use for testing purposes.
DO NOT PUNCTURE THE INSULATION ON THE WIRE
And a special THANKS to DON S

 

[Don S]

Re: 7.4 MPI no fuel pump operation,***FIXED***

Glad you got it fixed. Guess it wasn't your relay wiring as I was going to bet on.
Poking holes in the insulation of a wire is a HUGE No-No on any EFI engine, or any engine wiring for that matter. I've actully found a couple connectors destroyed due to corrosion from puncured wires and the insulation around the connecter. One was the ECM, had a pin corroded off. 1500 bucks for the ECM, several hundred for the wiring harness and all the labor to find and fix it all.

 

[Fun Times]

Re: 7.4 MPI no fuel pump operation,***FIXED***

Glad you got it fixed. Guess it wasn't your relay wiring as I was going to bet on.

I was going to bet on either a backed out wire at the ECM or an over looked bad fuse going to the ECM, Or worse a bad ECM.

Glad you found it also.