No Start, Erratic Fuel Pump - PeachParts Mercedes-Benz Forum

tvpierce · #1 01-20-2011, 05:42 PM

'92 201 w/ 102 engine.

Car is driven 66 miles daily for my commute without incident. The engine will occasionally stall within the first 60 seconds of operation when it's very cold. But this has only happened twice -- and most recently about a week ago.

Last night, the car sat for about an hour while I was at a doctor's appointment. I came out and it started fine. Drove for about 100 yards, then just stalled and wouldn't re-start. The fuel pump normally cycles for 1-2 seconds prior to start up. During the no-start situation, it would cycle 1-2 seconds, three consecutive times. It did this repeatedly. I let it sit for about 15 minutes, then upon turning the key, the pump cycled once and the engine started.

I drove home without incident. Even stopped along the way... let it sit for about 20 minutes, and it restarted fine.

The next morning (today) it started fine for the 33 mile commute to work. This afternoon, I had to run out to pick up a part. The engine started fine when I left work. I drove about a quarter of a mile, and went in to pick up my part (took about 15 minutes). Came out, and no start again. And once again, the pump was cycling 3 consecutive times.

Let it sit for 10 - 15 minutes... the pump cycled normally, and the engine started.

The one commonality I see is that both times it was a cold re-start. But the pump cycling consecutively seems to me to indicate something other than cold carburation.

Any thoughts?

Thanks in advance.

#2 01-20-2011, 08:58 PM

What kind of maintenance has been done on the car like in the last year or so? That kind of helps narrow down and eliminate a few things. Ignition is the kind of basic starting point on them. Pull the distributor cap and take a look at it in the light check the contact. Also, look at the rotor real well. Has the fuel filter been changed on it very recently & the spark plugs. Have you tried pulling codes on it? It's easy to guess, but guessing gets expensive when it doesn't help the problem. I noticed you have 207K on it. Has all the maintenance been followed pretty well?

tvpierce · #3 01-20-2011, 10:21 PM

Thanks for the response.

I need to update my signature. The car now has 247k miles.

I've had the car for the last 11 years and have kept up on the maintenance. All suspension components have been replaced, plugs/wires/cap/rotor within the last 20K miles, all the brakes, exhaust... in a word, the maintenance is and has always been current. I haven't checked the codes -- I need to build the code reader first. In the last 6 month I had a problem with the OVP Relay. I replaced it and all was well.

The fuel pump behavior makes fuel deliver a suspect. How is the pump pressure regulated at start up? Does it reach a set pressure or is it timed? Where is it regulated? Internally or is power cut to it by a pressure switch at the fuel rail?

Thanks in advance.

mpolli · #4 01-20-2011, 11:50 PM

Bad fuel pump relays are pretty common. Did you try a search?

porkface · #5 01-21-2011, 12:40 AM

the only "regulation" for the fuel pump is the MAS relay, which controls the pumps, ac compressor and has other functions. there is no pressure switch to shut off the pumps. the shutoff is because of a timer built into the relay to prime the system. the pumps stop until an ignition signal is received by the relay and then the pumps run again.

you do need to know what the fuel system pressure is when the car doesn't start. needs a special set of gauges to test. i can't relate to WHY the pumps are cycling 3 times and then no start. sound like a relay and/or another problem. keep in mind, you need to know if there is spark when it won't start. the MAS relay has no control over the ignition. good luck, chuck.

Ferdman · #6 01-21-2011, 03:55 AM

Jeff, the stumbling/stalling upon driving a short distance after a cold start could be due to the Oxygen Sensor. When was it replaced last?

I had similar symptoms on our 1991 300CE that a new Oxygen Sensor resolved. Best to check codes before throwing parts at the problem.

tvpierce · #7 01-21-2011, 09:52 AM

Quote:

Originally Posted by mpolli

Bad fuel pump relays are pretty common. Did you try a search?

It would seem if the Fuel Pump Relay were going, it the pump would intermittently not activate. In this case it activates every time, and when I'm experiencing the no-start, it activates multiple times.

Does that seem logical?

tvpierce · #8 01-21-2011, 10:11 AM

Quote:

Originally Posted by porkface

the only "regulation" for the fuel pump is the MAS relay, which controls the pumps, ac compressor and has other functions. there is no pressure switch to shut off the pumps. the shutoff is because of a timer built into the relay to prime the system. the pumps stop until an ignition signal is received by the relay and then the pumps run again.

you do need to know what the fuel system pressure is when the car doesn't start. needs a special set of gauges to test. i can't relate to WHY the pumps are cycling 3 times and then no start. sound like a relay and/or another problem. keep in mind, you need to know if there is spark when it won't start. the MAS relay has no control over the ignition. good luck, chuck.

OK, the fact that the pump is timed by the relay helps me understand the system a little better. So as mpolli indicated above, I need to at least take a look at that relay.

I haven't been able to troubleshoot spark and/or fuel delivery because of the intermittent nature of the failure. When I'm at home -- where I have a fuel pressure gauge, and an assistant to turn the key while I work under the hood -- the problem doesn't present itself.

tvpierce · #9 01-21-2011, 10:12 AM

Quote:

Originally Posted by Ferdman

Jeff, the stumbling/stalling upon driving a short distance after a cold start could be due to the Oxygen Sensor. When was it replaced last?

I had similar symptoms on our 1991 300CE that a new Oxygen Sensor resolved. Best to check codes before throwing parts at the problem.

O2 sensor was replaced within the last 20K miles... so that should be OK.

Mike Murrell · #10 01-21-2011, 11:07 AM

Had to replace my fuel pump a few years ago - situation different - warm/hot weather.

When it warmed up - temps over 80 degress - car would shut down after 15 miles of driving and that was after starting out cold in the A.M.

Let the car sit for an hr. or so and it would restart and drive for 3-5 miles B4 dying again. Let it side overnight and again - 15 miles B4 croaking

Not saying fuel pumps only die in warm weather - just making a comment.

I had a situation similar to the OPs - turned out to be the OVP.

#11 01-21-2011, 01:57 PM

You could check the coolant temperature sensor. Yours should be a 4 pin I believe. You do a 2x on them. 1&3 & 2&4. +20C 2.28-2.72koms, +80C 290-364Koms. If it's out of range it could cause you trouble when cold there. It's a quick easy check with a vom. You could also check the intake air sensor 2&3 for a reading. Both up front on the 2.3.

SD300 · #12 01-21-2011, 06:59 PM

On the similar topic, I have a 87 190e 2.3, it takes a few cranks inorder to start, so as once warmed up.
Some say is the accumulator leak gas back into the return system so the fuel pressure dropped when stopped,
would the system still work if I block off the return line of the accumulator?
The leak could be due to some hole in the diaphragm of the accumulator?
At present the cold start valve is not hooked up since it can flood the engine, I fidn not much difference in cranking time between hooking up cold start valve or not.
TIA.

tvpierce · #13 02-14-2011, 01:50 PM

With the help of others here, it seems I may have solved the problem. The erratic cycling of the pump seemed to point squarely at the Fuel Pump Relay. I replaced it and have not had the problem since. But because of the intermittent nature of the failure, I'm reserving judgement until I have a few more miles behind me.

Thanks for the help. I'll report back with further results.

mak · #14 02-15-2011, 11:44 PM

Faults with fuel pump relay starts off as intermittent with quick re-starts. Most likely the problem stands rectified with the new relay.

Typical fault with the Fuel pump relay; Internally cold solder joints which can be re-soldered and the relay will work again for some time again.Best replaced along with the OVP and the fuel accumulator .
regards
mak