M103 starting poorly still: Fuel pumps not priming?
 

I have been chasing the starting issues on my 190E for several months now and haven't driven the car in a couple of weeks because it is an inconvenience to have to take 2 minutes to get it to start and run well enough to pull out of the driveway. I have tried so many things but had an idea last night: maybe the fuel pumps aren't priming.

It takes about 15-20 seconds of cranking to get it to sputter to a start and idle at 450rpm then has to run for about a minute before I can move it without it stalling. Once it warms up, it runs like a M103 typically does, like a slouch in the low end and better in the upper end. I tried to hear the pumps priming last night as I cycled the key on and off but couldn't hear them though I could hear them on my parts car back when that still had the engine in it. Is it possible that the pumps are not priming in the "run" position of the ignition but starting to pump once I put it into the crank position? Is there a good way to test this theory?

Method I -
Hook up a test light to the pumps, with leads that are long enough for you to see the light when you are seated in the car. Then cycle the key; the light should be on for 2-3 seconds per cycle.

Method II -
Have another person cycle the key while you listen under the car close to the pump location.

I listened to it, it was extremely quiet and only cycled for about 1/4 second. I'm assuming that's not right?

Not right, indeed. Look to the fuel pump relay as the most likely culprit. If you are so inclined, after removing the relay from its socket, pop off the cover, and carefully examine all the solder joints and traces. Cracked and/or cold solder joints occur quite frequently.

When the relay is out, jumper circuit 30 to circuit 87 (typically pins 7 & 8). The pump should run continuously, and the engine should start promptly.

does this car have a cold start injector?

Link number 7 and 8 on the fuel pump relay with copper wire , it will then run all the time .So remove the wire after you have done it .If you dont it will flood the engine...

Search for a thread stated by me: Fuel accumulator failure analysis and run the simple on-the-car test. This component is often overlooked, but given you symptoms, it's the number one suspect.

Duke

Yes it does. I have been trying to find out information on how to test it but still not sure what to do.

Your symptoms sound a lot like mine though it has to have been sitting at least a few hours before it has problems starting again.

That's typical. A small crack in the diaphragm as in the photo attached to the thread I recommended you review will cause the accumulator to bleed down slowly and take time to fill up the leaking accumulator to build fuel pressure during cranking.

It sounds like do didn't look up the thread I recommended... your choice.

Duke

I did, which is why I said your symptoms sound similar but not the same. I'm going to test it later this week.

I removed the rubber line from the outside side of the fuel accumulator and pulled vacuum on it and got 40ml of gas in my catch can. It then held vacuum fine. I think it is probably fine. Next, I'll test the cold start injector.


I also tried the clear line plus priming the system, didn't seem to do anything but I had already pulled all of the residual fuel out of the accumulator.

Injector tested at 10.6 ohm, did not fire with the engine cold but it's about 70F out here. Should it fire when it is this warm?

Injector sprayed when jumped. The plug was only giving it about 2 volts. I have ordered a rebuilt MAS relay that was on ebay for $40, ordering an OVP relay since it's cheap insurance, and a new CIS coolant temp sensor.

[QUOTE=w123fanman;3647697]I removed the rubber line from the outside side of the fuel accumulator and pulled vacuum on it and got 40ml of gas in my catch can. It then held vacuum fine. I think it is probably fine. QUOTE]

Your test is not clear to me, but it's not the test I recommended to check for a leaky fuel accumulator diaphragm.

Duke