If you have a MAS relay, then the fuel pump relay is incorporated into that. You should be able to hear the fuel pump when the key is turned, especially if you have someone else turn the key while you listen near the fuel pump. What # is on your MAS relay? The two pins to jump on mine are numbers 1 and 2. I don't know if yours is the same. I have a 1990 300SE with the M103 engine. Perhaps someone else can tell you for sure which pins to jump on yours.

Behind your battery compartment is a plastic shield ( just gently squeeze and pull pull the cover towards you) it hide's the relay as well as a number of other items. The relay is about the size of fat deck of cards. Wiggle it back and forth while pulling it up and it should pop right out. If memory serves me right it has seven pins. You can first try a little emery cloth on each of the the pins (the idea being to just score the surface a little not remove material). To expose the circuit board you need to gently pry the housing back on both sides of the unit while pulling the unit apart. Take your soldering iron to all of the contact points on the board.

Hope this is of some help

The problem is fuel delivery. Removed the air filter and poured a small amount of gas down the intake - she started right up, then died.

Since there is apparently no fuel pump relay, is there a simple way to test the fuel pump?

__________________
Neil.


1991 190E 2.6 170k
1995 E320CA 57k
1999 Chevy Tahoe 98k
2000 R1150GS 45k
1983 300CD 178k - sold, but not forgotten

If there is no fpr, then the problem more than likely is the MAS unit. You can simply either get a vom on the pump (there might be 2 pumps), turn the key to on and see if you are getting voltage when the key is turned to the on position. You could also do this with a test light.
OR you can try jumping power and ground to the pump and see if the engine starts, or hell even if the pumps run!
Gilly

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Removed the MAS unit and jumpered two large pins near the passenger fender (two large pins on the other side of the connector operate the a/c compressor clutch) - the fuel pump ran and the car started
Will be ordering a replacement MAS unit.

__________________
Neil.


1991 190E 2.6 170k
1995 E320CA 57k
1999 Chevy Tahoe 98k
2000 R1150GS 45k
1983 300CD 178k - sold, but not forgotten

My $0.02...
This is ignition related, the biggest clue was the loss of Tach signal... and the instant shut off.
I always use the way the car died as a good clue... a slow die off with spluttering and a bit of surging is loss of fuel, and an instant switch-off most likely ignition related.
If it was FPR the electrical side of the engine would have read the tach signal, as the ignition would have not "seen" any loss of fuel pressure or fuel. and the Tach would have just followed engine speed back to stall.
I am calling it ignition related.

__________________
2009 Mercedes ML320 Bluetec

Well, he seems to be happy with the diagnosis.
On an automatic, when the engine stalls, I would expect to see the rpm drop to zero if the engine stalls as the engine is no longer running.
Gilly

__________________
Click here to see the items I have up for auction at EBay

Click here to see a photo album of my '62 Sprite Project Moneypit (Now Sold)

The ‘tested’ replacement MAS unit did not solve the issue. So I decided to dig a little deeper.

First, some important additional background info. About 4 months ago the car started to cut out - once every few days - for no apparent reason. About 3 months ago I found a length of wire in the harness behind the battery that had melted insulation. The wire color was white with red stripe. None of the surrounding wires were damaged.


So I replaced the damaged wire from the MAS unit plug..


.. to near where it goes around the back of the engine - under the vent box. This appeared to stop the intermittent cut-outs.
Note; the above picture shows how the area where I joined the new-to-original wires looks now. But it was fine when I did the repair.

This evening it became abundantly clear the rest of the original wire – which goes across to the drivers side front fender - is bad. It got hot at some point in the past and melted the insulation.





I would like to obtain a good harness if anyone has one available. Car is a 1991 190e 2.6.
Alternatively, I will have to rebuild the old harness.

__________________
Neil.


1991 190E 2.6 170k
1995 E320CA 57k
1999 Chevy Tahoe 98k
2000 R1150GS 45k
1983 300CD 178k - sold, but not forgotten

Something bad happened to make that happen to that wire.....I'd try to figure that out too....

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

Agreed.

Most of the exposed wire is green from oxidation. So it appears this happened some time ago. Could have been much worse and caused a fire!

The bad wire appears to go under the fuse box. I'm also checking for other damaged wires and shorts before making any repairs.

__________________
Neil.


1991 190E 2.6 170k
1995 E320CA 57k
1999 Chevy Tahoe 98k
2000 R1150GS 45k
1983 300CD 178k - sold, but not forgotten

The bad (white + red stripe) wire broke apart right where it enters the underside of the fuse box.



I cannot move the fuse box enough to see how to unplug the wire bundles from the underside of the fuse box. Any ideas how these plugs lock in place?

__________________
Neil.


1991 190E 2.6 170k
1995 E320CA 57k
1999 Chevy Tahoe 98k
2000 R1150GS 45k
1983 300CD 178k - sold, but not forgotten

Discovered that the plugs on the underside of the fuse box simply pull out with a bit of leverage.

After removing the wiper assy, blower box cover and various other parts, I gained access to the harness and cut away the protective cover to check if any other wires were damaged. Fortunately they are not, just bits of melted plastic here and there from the bad wire.

Have now run a new wire from the fuse box to the MAS & OVP sockets and recovered the harness with Split Flex Tubing (1" diameter).

Also discovered that Pin 15 of the OVP got fried. So will need to order a replacement before seeing if these repairs are good.

__________________
Neil.


1991 190E 2.6 170k
1995 E320CA 57k
1999 Chevy Tahoe 98k
2000 R1150GS 45k
1983 300CD 178k - sold, but not forgotten

Replaced the OVP relay and all is well. Have now driven approx 500 miles with no bad signs from the replacement wire, MAS unit or OVP relay.

In conclusion, the OVP relay did it's job by shutting down the MAS unit when the white + red stripe wire with melted insulation finally came apart under the fuse box. I was fortunate that this burnt wire did not damage any other wires in the harness.

As mentioned previously, the melted wire appeared to be very old damage. Probably caused by a temporary short many years ago - perhaps when the alarm system was fitted.

I now have a spare MAS unit (the original was fine) - although the plastic cover is cracked.

__________________
Neil.


1991 190E 2.6 170k
1995 E320CA 57k
1999 Chevy Tahoe 98k
2000 R1150GS 45k
1983 300CD 178k - sold, but not forgotten

You might be able to get the old OVP and resolder it if it's not the fuse that blew. That way you have a spare OVP.

Hopefully you can also get to fix the wiring.

__________________
http://farm8.staticflickr.com/7271/7...144c3fc1dc.jpg

Anyone know if the MAS can be R&Red without damage with the battery still connected?

p.s. MAS sends output signals to:
-fuel pumps (pin 2)
-start valve (pin 8)
-AC comp cut-in (KE) (pin 9)
-AC comp coupling (pin 22)
-TDA engine speed (Tach?) (pin 11)
-Air Pump (pin 19)
-O2 heater (pin 20)

You can check to see if MAS is getting 12 volts at pin 1.