Emergency!...Road trip in 2 days! - PeachParts Mercedes-Benz Forum

MercyBenz63 · #1 07-19-2006, 10:18 AM

Hello all,

Wow, my '92 300E w 130k is really killing me. The car saga started about about three weeks ago when the transmission pump gave up the ghost. Since then it has been constant repair.

My current problem goes something like this...

After replacing the transmission with a used 84k number I drove the car around for about three days without trouble including one journey around 200 miles. Two days ago I was driving the car and went around a corner and the car stalled and would not restart immediately. After allowing the car to sit for 5 minutes it restarted. As it was low on gas I filled it up and took it home. It drove fine the whole way.

Yesterday I tried to drive it but it made it about one block before it died. I was going to pull out from a stop sign when it choked out and died. Again, after letting sit for a few minutes it enough to limp home.

I have noticed that the can sometimes idel but when the thottle is cracked it dies out. Sometimes it won't start at all, just galloping like it wants to start. I should also mention that there have been times in the past in extreme cold temperatures where this car has exhibited these same symptoms.

The car has had good maintenance while in my keep. Recent plugs, wires, cap rotor, synthetic oil etc etc.
I have a strong white spark both at the coil wire and the #1 cylinder. I can hear fuel pumps running but don't know if both are running or what the pressure is.

Extensive search of the forum for this problem points to OVP relay, MAS/Fuel Pump relay, and throttle microswitch.

The fuse in the OVP is good and it does not "rattle" when shaken. I pulled the MAS and resoldered all the connections on the board, no help. I have not yet checked the microswitch, but it seems unlikely that it would prevent the car from starting. My overwhelming feeling is that this problem is fuel related, specifically fuel management.

Does anyone have some diagnostic advice? I am going to check the deadhead pressure from the fuel pumps but I do not know the accepted values.

Please help, I am supposed to leave on a month long road trip in this car on Friday morning.

Thanks in advance.

Obnoxio · #2 07-19-2006, 10:41 AM

Drive your 6.3.

MercyBenz63 · #3 07-19-2006, 11:30 AM

Obnoxio lives up to his name.

Dead head fuel npressure from the pumps is strong, pegs my gauge at over 70 psi.

Jumpered pins 1 and 2 on the MAS Relay connector, I can hear a buzzing fron the fuel distributor area when I do this (EHA?), but the car does not start.

Right now, with everything connected, the car tries to start when turned over but just gallops.

Any ideas?

mctwin2kman · #4 07-19-2006, 12:57 PM

Check all the vacuum lines and connections. Sounds like a nice leak developed somewhere. When was the last fuel filter replacement? Sounds like you let it run low on petrol and maybe you sucked some crap from the tank into the filter and clogged it a hair, I see you tested but pressure and flow are two diferent beasts. You can have pressure, but what you need is flow as well.

mad1 · #5 07-19-2006, 12:57 PM

Quote:

Originally Posted by MercyBenz63

Obnoxio lives up to his name.

Dead head fuel npressure from the pumps is strong, pegs my gauge at over 70 psi.

Jumpered pins 1 and 2 on the MAS Relay connector, I can hear a buzzing fron the fuel distributor area when I do this (EHA?), but the car does not start.

Right now, with everything connected, the car tries to start when turned over but just gallops.

Any ideas?

I had a similar issue with my '88 2.6 - Idling was ok, but as soon as I cracked the throttle it died. I had to have it towed to a mech, who shorted out two connectors in the fuel pump relay area and it worked. Basically, it needed a new fuel pump relay and ran fine after that

MercyBenz63 · #6 07-19-2006, 01:08 PM

Thanks for all the suggestions.

Good point about the difference between flow and pressure, I will check that next.

Also, I checked vacuum connection at the engine side, I'll check at the trans next.
Fuel filter was replaced about 10k ago, both pumps were backflushed at the time...seemed OK.

Pulled the plugs...wet. I have cleaned them and am currently letting the cylinders breathe.

Checked the throttle micro switch...it's switching.
Checked the potentiometer...got several readings from the pins including a fuul open and closed signal.
Checked the idle speed motor...it jumps with the application of 7V.
Haven't checked the EHA...don't even know what I would be looking for.

Does anyone know if the MAS can fail AND have the fuel pumps operate?
Is the MAS a common replacement part at this mileage? It seems it is frequently mentioned but rarely the cause of problems.
Is there a definitive test for the OVP and the MAS relay?

Thanks again, I'm convinced that with your help I'll be on the road in no time.

Obnoxio · #7 07-19-2006, 01:32 PM

Quote:

Originally Posted by MercyBenz63

Obnoxio lives up to his name.

?

Sorry, hadnt had my second cup yet.

MercyBenz63 · #8 07-19-2006, 01:47 PM

Well, before I did anything else I looked again for vacuum leaks, there don't appear to be any. Maybe I'll hook up a vac gauge and crank it a little.

Put the plugs back in and with everything hooked up...no start.

Checked for fuel pump delivery, in the initial squirt and subsequent 1-2 sec crank there were roughly 7 oz delivered.

Thinking about switching the coil out...I have a spare.

Still wondering about the MAS relay.

MercyBenz63 · #9 07-19-2006, 05:48 PM

Alrighty, after reading this post...

1992 300E mostly no start prob

I went back and rechecked for spark. The coil gave a white hot spark SOME of the time.

Replaced the ignition coil and the car is running great so far.

Thanks to all the helpful responders, wish me luck.

~K