Frustrated at random stopping!

[lsmalley]

Ok, so this is not a normal everyday occurance, it happens sporadically maybe once a month, sometimes it'll go for several months without happening where I am driving and the coming to a stop and the car engine will randomly shut off. Everything else will still be on though: radio, lights, climate control, etc. Here is my list of what has been done as far as ful and ignition/electrical:
*Battery replaced under warranty with Duralast Gold battery part no. H6-DLG (originally purchased 3/2/12 with 3 yr. free replacement. Warranty expires 3/2/15. 7/24/13 @ 327517 miles.
*Alternator 2 AWG wire replaced 7/24/13 @ 327517 miles.
*Fuel filter replaced with Pentius filter 7/6/13 @ 326193 miles
*Distributor cap replaced with Bosch 6/23/13 @ 325457 miles.
*Ignition rotor replaced 6/23/13 @ 325457 miles.
*Alternator replaced with Duralast 120amp (Lifetime warranty) 6/22/13 @ 325378 miles.
*Alternator wire upgraded to 2 AWG. 6/22/13 @ 325378 miles.
*Spark plug wires replaced with Bosch wires 6/15/13 @ 324843 miles.
*Fuel pressure regulator replaced 6/9/13 @ 324575 miles
*Air filter replaced 3/13/13 @ 318419 miles
*Oxygen sensor replaced with Bosch Premium O2 sensor (part number 13953). 8/3/12 @ 303775 miles
*Bosch EHA replaced 5/20/11
*Overload Protection Relay replaced 7/9/10

When I replaced the fuel filter not too long ago, I inadvertantly test the fuel pumps by not having the banjo bolt and washer on the filter not properly in place and blasting fuel all over the ground. Only other thing I can see is that the OVP ws replaced 3 years ago, I did check the fuses on it which are good. Anyone have any suggestions?

[oldsinner111]

have you checked all engine ground or negative grounds?Is positive cable new?On my S I added 3 extra grounds as grounding thru body aint the best,and ground wire are little from factory

[Elektri]

Monitor things while driving. Do whatever it takes to set up testing gauges to see what is going on.

Start with a fuel pressure gauge. Rig one up it is sticking out from under the hood so you can see it while driving.

And a multimeter wired to the spark control module +12 volts and ground. See if it is losing power.

When the car stalls next time, look at your testing gauges - see where the trouble is.

[JamesDean]

Check your fuel pump relay / MAS relay.

Our 420SEL had a cold solder joint form on the fuel pump relay. Right on the joint that supplied power to the pumps.

[lsmalley]

How do I check the MAS relay?

[JamesDean]

That is a good question.

The MAS unit does quite a few things

See this document, PDF age 29 or so (page on the image is "108/8")
http://www.startekinfo.com/StarTek/outside/11832/Resources/201Create/PDF/01002.pdf

-Oxygen Sensor Heating
-Oxygen Sensor Signal
-Fuel Pump Control
-Air Pump Control

You might find something in here.
Untitled Document

If your problem is like my 420SEL, the control unit was doing its just most of the time so a test likely wouldn't reveal the problem. The cold solder joint would only act up 1% of the time. It likely wont act up during a test. The only way I was able to figure out what was wrong with it was to open up the box and visually inspect the joint.

I have a MAS unit here on my table. I might open it up at some point here and post a thread with pics. It looks like it opens up fairly easily. Looks like you gotta take off the metal surround somehow and then there is just a bead of silicon acting as a seal.

[Gilly]

Sounds like a MAS or FPR to me too. Can verify, as others have mentioned, by either monitoring the fuel pressure or in this case you could also monitor voltage to the fuel pump, there are various ways to connect to the power supply to the pump, I think there is a connector under the back seat, if you don't mind routing wires to that point (easier than going direct to a pump, you can simply mount a test light, no reason to use a meter, either the power is there or it's not. Just pump from B+ to ground with a small inline bulb, if the car quits, see if the light is on. How long after it shuts down until it will restart, immediately or???

[Gilly]

If this is on your 190, I think it has a FPR not a MAS. "I Think" being the operative words, LOL

[JamesDean]

I'm pretty sure the 1990+ 190's were equipped with MAS units. As were the other m103 equipped cars. I know my 93 has one and the 93 at the junkyard had one.

[lsmalley]

mine has a MAS, not relay

[JamesDean]

I took apart the MAS unit that I had here. A little bit of work to do but its do-able as new ones are $200+.

The only "damage" done was the gutting of the silicon on the outer edge. You could easily restore that with a q-tip and a tube of silicon.

I'll post them up in a bit.

[lsmalley]

Ok thanks. I wonder if I could also get a used one at a junk yard, but then again its a 50/50 chance I'm taking......also, it could be possible my MAS is fine. I haven't gotten any CEL codes. and everything seems to be functioning fine.....its just that rare time the car stops

[JamesDean]

You could do that. Taking it apart is relatively straight forward.

http://www.peachparts.com/shopforum/tech-help/342134-inside-box-m103-mas-control-unit.html#post3187110

[lsmalley]

Just looked at the pictures you had posted. Very good, except the whole electrical circuit board thing is foreign to me. Since the MAS controls a host of other functions and I have systematically looked at (paid attention to) all the other components controlled by the MAS, do you think that the MAS could still be the problem?

[Gilly]

Originally Posted by lsmalley

also, it could be possible my MAS is fine.

Which is why you could run some tests to see if you are losing power to the pumps.