'94 S124 M104 No Crank - Suspect Fuel Pressure
 

Hi, all.

My '94 E320 wagon won't crank to start.

The fuel pump is running constantly when I turn the key to the run position, and under the hood I hear what sounds like spraying/flowing fuel. This happened previously, and when I gave the intake manifold a whack with the heel of my palm, the flowing/spraying sound stopped, the fuel pump shut off and the car started normally, but that didn't help this time.

I thought maybe the fuel pressure regulator was stuck open, so I swapped one in from my parts car, but it made no difference. Prior to this, the car started immediately and ran strong (except for the ongoing idle problem mentioned in a different post).

Any suggestions would be most appreciated.

Best Regards,
Rob

If the engine isn't cranking, forget about fuel and figure out why the starter motor isn't spinning the engine over.

I'm suspecting that there's a lockout in the system that prohibits the starter from engaging if there's no fuel pressure, but I could be wrong.

The engine should still crank even if there's no fuel pressure. Try starting in Neutral. If the shifter bushings have failed or the NSS is on its way out, attempting to start in another position can rule that out as a possibility.

Shifter bushings are tight, neutral or park makes no difference, NSS was replaced in November, starter is good.

check fuse 5 and 9 remove and inspect those fuses

Fuses 5 and 9 check out fine - I measured them with an Ohmmeter, cleaned the ends with a wire brush and reinstalled them; no difference.

The fuel pressure regulator is a relief type not pressure reducing like one found on an air compressor line. The relief type dumps excess fuel to the tank, this the sound you were hearing when the fuel pump was running.

Hitting the intake won't do anything to solve the pump run problem, you will need to look at the relay that controls the fuel pump / wiring. This should be one of the years that had bio degradable wire correct?

An engine will crank even if fuel pressure is lost.

As an added test, though I doubt this is your problem, pull the engine oil dip stick and smell for fuel / vastly overfilled. I've seen vacuum referenced fuel pressure regulators fail / fill cylinders with fuel and hydralock the engine to the point it won't crank. If the engine is left to sit a while fuel will seep past the piston rings allowing it to crank.

On the false firewall, just in front of the brake reservoir cap , there is a 3 wire connector, disconnect by pressing in the tabs, and pull off the connector and the center wire goes to the starter , jumper only that center pin, (not the female side) to battery + wire either the battery or hot fuse, car should start, remember to do this in park , put the brake on as car can start , your bypassing the neutal safety switch, if the starter starts you have an alarm related issue lockout relay issue etc, or ignition switch issue, report back

M104 Fuel Injection Starter Lockout
 

Assuming that this is in fact some type of safety lockout preventing the car from starting due to some problem in the fuel delivery system, I am reluctant to bypass it and jump the starter directly for fear of damaging the engine or causing injury to myself.

Let me ask the question in a different way:
What would cause the fuel pump to run continuously upon initially turning the key to the run position, with audible flowing of fuel through the regulator and back into the tank?

There is no such lockout for fuel fault, when key initially gets turned on pumps get primed then shut off ,car will crank unless alarm lockout relay dosent allow it to crank, you could have a stuck relay , if you removed the relay it will stop,its the green relay behind battery box, the engine control unit turns pumps on via that green relay k27, the engine control module turns the injectors on or off

Have you checked for degrading wiring harnesses in the engine bay? '94 is a year plagued by the biodegradable wiring problems.

Give that man a cigar!

Even though the upper wiring harness was replaced before I got the car, the lower harness was original and wasn't letting enough voltage get to the starter. Replacing the lower harness has cured the no-start issue.

Thank you all for your help.

Best Regards,
Rob

Ive never seen that, but I know my 94 wagons lower harness is peeling , my new harness is in the bag hanging up in the garage, for the last 4 years, I better hurry up and install that harness!