250 Optimax DFI Serial Number oe410070 having issues (no fuel no power to fuel pumps)

[jeremyholmes]

What I've learned thus far. All 3 fuel pumps work when powered directly. Power at the relay (Four Wires that work the main circuit relay Red to Selonoid has power, Red White has power, Red Purple has no power leaving relay. The yellow purple wire from ECM is doing nothing) My best guess is the relay is faulty and bought a new one and it doesn't work either. The fuses are all good. If I jump power to the fuel pump circuit it powers all the pumps. Its acting as though the ecm is in shut down mode. If I spray some starter fluid in the air handler the motor will fire right up. Its as if the fuel injectors are disconnected. I replaced the fuel water separator filter and the sensor. The wire looks like crap to the sensor. I'm also getting one long beep when placing key in on position. Any suggestions???? How can I test the relay?

 

[Dr Honda]

Pop the top cover off, and make sure the air compressor is spinning, and putting out pressure. If there's fuel pressure... but no air... It won't start either.

 

[jeremyholmes]

Update: Compressor is fine. Power is not staying on at the pumps the engine will run just fine if I hook up a lift pump directly to the battery. Doesn't make any sense to me. Seems as though the ECM is just turns the pump circuit off. Gotta be a bad sensor somewhere. It's a chase at this point.

 

[Dr Honda]

OK... let me look over the diagram on that engine. The 3.0L is a lot different than mine.

 

[Dr Honda]

Did you check the fuses in the holder on the side of the engine. The holder with 4 fuses (starboard side) has the main fuel pump, and a smaller one (port side) has a fuse to the lift pump.

 

[jeremyholmes]

All the fuses are good on the four. the accessories have power and both the the circuit. However the pumps run for about 5 seconds and ecm is shutting the relay off which is cutting the power on the fuel side. Tony, Thanks a million. I have been looking over the schematic trying to make sense of it. I've never seen this before. The alternator wire is good, the selonoid seems fine, the wires on the battery and switch are good, It seems like an ecm issue. Wish I had a scanner to read it.

 

[Dr Honda]

OK.... as convoluted as the 250 Di engine is... we are in luck.


Almost ALL of the positive power for the engine (fuel pumps, injectors, boosters, oil pump... and so on) all comes from 4-gang fuse block. It will be the red/blue wires on the out side.

It gets it's power from the "Main Power Relay". The relay gets it's power from the junction on the starter solenoid.


************ Edit **********

I just saw your post come in, as I was typing.

OK... the ECU is turning it on for a few seconds... then nothing. Well... it's priming. Then it won't start spinning again until it see's fire.


SO... if you put 12v on the pumps... it will continue to run? (not just for a few seconds)


If that's the case... unfortunately, you need to put your hands on DDT, or a Rinda tool, and read the ECU out. With the Di engines... sometimes that's the only way to find out what the ECU is seeing.

 

[Dr Honda]

how's the battery?? This engine is VERY sensitive to voltage, and it will "Crank" with a weak battery, but the ECU will basically shut down. SO... put a meter on the battery terminals, and crank. if it drops below 10.5v... that could be the issue.

 

[Dr Honda]

The other thing to check, is a ground on the Black/yellow wire, at the engine. It's the kill line, and if you have a short, or bad lanyard... it will crank, but not start.

 

[jeremyholmes]

What would happen if I just bypassed the relay and hooked the fuel pumps up to a toggle switch direct to the battery???

 

[Dr Honda]

I assume nothing bad. Heck... hook it to key power, and that way they will just turn on and off with the key. BUT... you will want a relay, and fuse in the system.

But, as above... you really need to see what the computer is seeing. It may be something simple, once a computer is hooked up to the ECU. If you have a Merc dealer around you... they may be able to help.

 

[RiverPro]

I'd like to go back to the good Doctor's question about cranking volts. Depending upon the length, size, and condition of the batt cables, 10.5 at the battery may not be enough for it to fire off.
As stated, the SJ Opti's are super sensitive to cranking voltage. Keep in mind the Opti Sport Jet has to build air and fuel pressure, spin the rotating crank assembly, spin the jet pump "L" drive, AND the impeller spins, thus moving water. I cannot count the times I've had customers bring in no starts and a strong battery cured the fault.