Start and Stall 88 300 CE 124

[Sean Juan]

Hi Everyone,

I have an 88 MB 300CE 124 M103.

The vehicle has set in my garage for the past year with only 3 or 4 trips in that time consisting of 5-10 miles each. I did add 5 gallons of new fuel this morning as the tank was somewhat low.

The battery would no longer hold a charge. I replaced the battery with new this morning and the car started right away. After idling for 60-90 seconds it stalled. It would restart after waiting a couple of minutes, but would stall after idling for 3-5 seconds max. If I added throttle, it would stall instantly.

The fuel pumps were replaced two years ago with factory new. I replaced the fuel filter this morning, but only after the symptoms were occuring.

I performed several tests and found the following:

The fuel pumps have 12+ volts when cranking and when idling. The voltage to the pumps remains constant for 2 seconds after the engine stalls. When the relay clicks off, then voltage is lost, which is normal. I have jumped the 30/87 or 7/8 on the Fuel Pump Relay to allow the pump to run constant, but the issue still occurs. At no time does it sound like the pumps stop while the pumps are under voltage.

I have also jumped the Overvoltage Relay and the issue still occurs.

I have tested for spark. I have good spark. At times after it stalls, if I try to restart instantly, it may just crank without firing. During this time, I have good spark. I have also pulled a wire and checked for spark during the times that it will run for a few seconds. After it stalls, I can see one or two more sparks after engine has started to stall, but the engine is still turning over due to the momentum of the engine. For this reason I believe that I have elimitated Ignition as a possible cause.

Back to fuel. After it stalls, I can crack the fuel inlet line at the Fuel Distributor and it sprays under high pressure. I know this is not a scientific method of testing, but it is not running out of fuel due to fuel line supply to the fuel distributor.

Twice (over 50 or so starts) the engine did allow me to rev to approx 3000-4000 RPM's running very smooth for several seconds, then the engine abruptly stalled the same what it had been doing at idle.

The symptoms seem like a classic fuel pump relay, but like I said earlier, the pumps have voltage for a couple of seconds even after the engine has stalled and the symptoms never changed even with the relay bypassed.

I did disconnect the power to the EHA Valve and tried again, It stayed running for approx 20-30 seconds before stalling, but was very rough and I had to give it some gas and also seemed like I had to depress the Air Mass Plate down to allow some airflow.

I could use some help and ideas!

Sean