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Discussion Starter #1
Hello All,

I'm hoping someone that has gone through my particular ordeal can help shed light on my current situation. I somewhat recently purchased this 90' 190e 2.6(though previous owner states its been swapped with the 3.0 from a 300e). Thing is the car cranks but won't catch on, I've replaced the fuel pumps, fuel filter, spark plugs, ignition coil, distributor cap/rotor and battery along with a new OVP relay. Now, I know the fuel pump relay or MAS unit is the likely culprit as I don't hear the pump priming in the "on" position however I've already went through 5 junkyard MAS units, and two "refurbished" MAS units from two separate vendors who both repaired the device in different methods. None of the MAS relays have yet to power the fuel pumps, the only time I've ever heard the pumps priming is when I jumped pins 1 and 2 with a cable but even with the pumps running the car failed to catch and start. I'm running out of ideas here, next step will be to part ways with the car and I really would like to avoid that if possible. Thanks for the time and suggestions in advance.

-Kevin
 

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89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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Have you done the basic 2 checks?

(1) Measure the system fuel pressure at the Fuel Distributor system port (should be 80 PSI)
(2) Checked the ignition with a spark tester (or just the old fashioned way of checking for spark with one the plugs removed at a time)
(3) It would also help to put a strobe timing light on cylinder-1 spark plug wire to see what the timing is like.

BTW, even with low fuel pressure, when you first crank the engine the car should start right away (like in less than 1 second) assuming you have two things:

(a) ignition spark present and correct timing
(b) Cold start valve operational

If other fuel element are broken (like FD, FPR, etc. etc) the engine would die after a second or two due to fuel starvation but it will certainly start.
 

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What Dolucasi said. My experience was that there was trash in the fuel pump at the strainer and the valves for the fuel accumulator and pump needed to be vatted in parts cleaner and marking off that there is fuel exit in the rail connecting the accumulator, pump, and filter. There is the possibility that some of your fuel hoses are rotted and getting air. You might want to do some bend testing to see if these crumble. I am a big fanatic of di-electric grease taking care not to cross continuity and putting application on the fuel pump, starter, solenoid, coil, plug wires, relay pins, fuses, any and all grounds, battery posts, cold start connector.....basically any and all electrical connectors under the air filter housing and under the engine. Now this is a 1990 so you might have to deal with crumbling connectors like I did. Unless you want to install a new pigtail, then I suggest you get some heat shrink for when the connectors explode. Take pictures of the pin out before you proceed. All that this will cost you is a $7.00 tube of di-electric grease ( next best thing to solder) and maybe $10 00 for heat shrink. I also suggest that you use premium gas and add a good octane booster like Royal Purple. I brought back a 1984 420SEL with this and I went gung ho on rooting out every electrical connection I could find. I did a cylinder compression test and this is relative to how many miles your MB has. Keep putting your results here for feedback!

Charlane
 

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Discussion Starter #4
Have you done the basic 2 checks?

(1) Measure the system fuel pressure at the Fuel Distributor system port (should be 80 PSI)
(2) Checked the ignition with a spark tester (or just the old fashioned way of checking for spark with one the plugs removed at a time)
(3) It would also help to put a strobe timing light on cylinder-1 spark plug wire to see what the timing is like.

BTW, even with low fuel pressure, when you first crank the engine the car should start right away (like in less than 1 second) assuming you have two things:

(a) ignition spark present and correct timing
(b) Cold start valve operational

I other fuel element are broken (like FD, FPR, etc. etc) the engine would die after a second or two due to fule starvation but it will certainly start.

Hey Dolucasi, thanks for the reply. I've checked the spark using an inline spark tester already, everything looks fine there though I went ahead and replaced the plugs/distributor/ignition coil components anyway. I think testing the FD for fuel pressure is something I'll look to do this afternoon. Don't think I've seen a test port on the fuel distributor however, is there a schrader valve to plug into or am I disconnecting a line to get a reading from?
As for the timing light, I have the tools however I don't know how I'd adjust the timing on this particular engine so I'm really hoping the issue isn't of a timing related variety.

The cold start valve sounds really promising to me actually. I've on occasion got the car to turn on after cranking and pumping the throttle pedal for a couple tries, while having the FPR pins jumped. It starts but refuses to idle and as soon as I stop kicking the throttle, gives out and won't start again. So maybe the cold start valve is not supplying enough fuel to get her going? Originally I blamed the inability to idle as a consequence of having the MAS control unit removed since I believe the idle control function is embedded into the MAS unit.
 

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Discussion Starter #5
What Dolucasi said. My experience was that there was trash in the fuel pump at the strainer and the valves for the fuel accumulator and pump needed to be vatted in parts cleaner and marking off that there is fuel exit in the rail connecting the accumulator, pump, and filter. There is the possibility that some of your fuel hoses are rotted and getting air. You might want to do some bend testing to see if these crumble. I am a big fanatic of di-electric grease taking care not to cross continuity and putting application on the fuel pump, starter, solenoid, coil, plug wires, relay pins, fuses, any and all grounds, battery posts, cold start connector.....basically any and all electrical connectors under the air filter housing and under the engine. Now this is a 1990 so you might have to deal with crumbling connectors like I did. Unless you want to install a new pigtail, then I suggest you get some heat shrink for when the connectors explode. Take pictures of the pin out before you proceed. All that this will cost you is a $7.00 tube of di-electric grease ( next best thing to solder) and maybe $10 00 for heat shrink. I also suggest that you use premium gas and add a good octane booster like Royal Purple. I brought back a 1984 420SEL with this and I went gung ho on rooting out every electrical connection I could find. I did a cylinder compression test and this is relative to how many miles your MB has. Keep putting your results here for feedback!

Charlane
Hey Charlane, I've actually replaced both fuel pumps and the fuel filter on this car when I first purchased it(I was hoping the hard start issue would be solved with new pumps), so I'm fairly certain those should be clean assuming there wasn't too much crude lingering in the fuel tank. You bring an interesting point however with the di-electric grease, definitely something worth looking into.
A compression test is definitely in order as well as I think my fears of a timing issue is becoming more and more apparent.
 

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I urge you to consider using octane booster, adding a little at a time and even with premium gas, for a good, strong, and controlled, combustion at start. There is still the possibility of weak wires yielding resistance, FYI, that I am finding this out myself. You can check the fuse capacity for the connection and discern if the amperage is close to that limit for a good contact with wherever you are tracing.

Charlane
 

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89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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Hey Dolucasi, thanks for the reply. I've checked the spark using an inline spark tester already, everything looks fine there though I went ahead and replaced the plugs/distributor/ignition coil components anyway. I think testing the FD for fuel pressure is something I'll look to do this afternoon. Don't think I've seen a test port on the fuel distributor however, is there a schrader valve to plug into or am I disconnecting a line to get a reading from?
As for the timing light, I have the tools however I don't know how I'd adjust the timing on this particular engine so I'm really hoping the issue isn't of a timing related variety.

The cold start valve sounds really promising to me actually. I've on occasion got the car to turn on after cranking and pumping the throttle pedal for a couple tries, while having the FPR pins jumped. It starts but refuses to idle and as soon as I stop kicking the throttle, gives out and won't start again. So maybe the cold start valve is not supplying enough fuel to get her going? Originally I blamed the inability to idle as a consequence of having the MAS control unit removed since I believe the idle control function is embedded into the MAS unit.
The problem is not your cold start valve, it only operates for 1 second even if it is working and makes the car start in less than one second as opposed to 5 seconds of cranking before it starts.

Kevin, what I would do in order (ease of operation) are:

(1) Put that strobe light to use and point it at the timing marks as some else is are cranking. You should be seeing about 20-30 degrees and relatively steady.
(2) Timing is not adjustable, the ignition timing control unit (EZL) takes care of that. If timing is off, that is a separate path to diagnose
(3) The FD does have a port on it. Actually two, but you will need a male adapter to use it. Otherwise you can use the Cold Start Valve connection to take a measurement

Let us know how you are progressing....
 

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Discussion Starter #8
Just wanted to give an update, I got the car to fire up finally, turns out when I replaced the ignition coil I botched the install and misconnected a few wires(woops). So now the car turns on but won't idle and dies out if I'm not constantly giving it gas(a couple backfires along the way). Also, I'm still convinced that the MAS control unit is faulty as the car only starts with the 1 and 2 pins jumped. Last week I did a little experimenting with a spare MAS unit I had laying around and soldered a small gauge wire from the 1 pin terminal directly to the pole for the fuel pump relay inside the unit. Surprisingly once the unit was attached to the car the fuel pumps were priming constantly(same as if I jumped the pins 1 and 2) but when the car was cranked the engine wouldn't catch.
I ran out of time last night but tonight I'm planning on jump the 1 and 2 pins again to see if it'll catch again, IF it does, I think that throws me back to my original dilemma with the MAS unit. Can't help but wonder if the wiring harness where the MAS unit attaches to is faulty and is somehow burning out the fuel pump relay inside every time I attach it onto the car, just hard to believe that all of these units I've purchased(refurbished included) are all broken units. Update to follow soon, but if this sounds familiar to anyone please feel free to chime in.

* side note, I noticed last night that the aluminum looking module with three coil springs inside of it was heating up during the time I was cranking the car. Not sure if its something normal, I haven't found any information as to what the part is or does. Its located in the very left corner of the battery area under the hood hinge and to the left of the MAS unit.
 

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Yeah I found that, too, that an area was cut in the metal for the connector to it. All I could think of was that that this heated 2 large electrical control units and the battery in inclement weather. I haven't looked into it much further.

Charlane
 

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89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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Sounds like your OVP is heating up, maybe due to a malfunction in your fuel pump circuitry.
I would stop jumping the fuel pump relay before you do further damage and check out the circuit diagrams for your model and see if the fuel pump relay is powered up by one of the OVP circuits. I do not have a MAS but an ECU so do not want to mislead you, just would like to warn you. Though jumping the relay pins should not cause an OVP issue maybe you are jumping the incorrect pins?

What is the condition of your fuel pumps? They will take ~10A each if running properly. See if they are drawing more than that. Unfortunately you will need a >10A current meter for that, most meters around are fused at 10A.
 

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Discussion Starter #11
Yeah I found that, too, that an area was cut in the metal for the connector to it. All I could think of was that that this heated 2 large electrical control units and the battery in inclement weather. I haven't looked into it much further.

Charlane
That's the one! There's a connector plugging into it at the bottom or ride hand side, I forgot exactly. But hmm interesting, that would reassure my worries if that's indeed its purpose, thanks for sharing your findings. Definitely a hard one to figure out since there's no visible part number printed on it(at least not without removing it from the firewall).
 

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Discussion Starter #12
Sounds like your OVP is heating up, maybe due to a malfunction in your fuel pump circuitry.
I would stop jumping the fuel pump relay before you do further damage and check out the circuit diagrams for your model and see if the fuel pump relay is powered up by one of the OVP circuits. I do not have a MAS but an ECU so do not want to mislead you, just would like to warn you. Though jumping the relay pins should not cause an OVP issue maybe you are jumping the incorrect pins?

What is the condition of your fuel pumps? They will take ~10A each if running properly. See if they are drawing more than that. Unfortunately you will need a >10A current meter for that, most meters around are fused at 10A.
The fuel pumps should be good as they're brand new and recently replaced. The device that's heating up is a unknown module/relay that's mounted on the firewall. The OVP though should be in good working order as I replaced it with the newer two fuse design as well(unless it too has blown out since install). I've taken a look at some circuit diagrams but to be honest I'm completely stumped. The diagrams show the relay where the power entering from pin 1 is supposed to be allowed to exit via pin 2 to the fuel pumps but with the fuel pump relay blocking this flow of power it doesn't allow the pumps to be energized with the MAS installed. I wonder if its even a possibility to convert the car to the older standalone fuel relay units that the pre-90 190e were being designed around.
 

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Discussion Starter #13
By the way this is where I get my diagrams from....

 

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Discussion Starter #14
By the way this is where I get my diagrams from....


Post #11 from this thread as well.
 

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Discussion Starter #15
Update: I recently bought a new OVP relay and got the car to fire up, car now fires up at the first crank. So pumped that the car is at this point now, but there's still an underlying issue. Car turns on but will eventually sputter out and die. Once the car stalls out, I have to pressed down on the throttle plate for a couple seconds before trying to crank it over again. Its leading me to believe that maybe there's not a constant fuel pressure being supplied and the engine is simply starving itself of fuel. I still have the fuel pump relay/MAS unit bypassed so the pumps are constantly running, not sure if that might have something to do with the fuel being cut out or if there might be an issue with the fuel filter or some other component.
 

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Hey Dolucasi, thanks for the reply. I've checked the spark using an inline spark tester already, everything looks fine there though I went ahead and replaced the plugs/distributor/ignition coil components anyway. I think testing the FD for fuel pressure is something I'll look to do this afternoon. Don't think I've seen a test port on the fuel distributor however, is there a schrader valve to plug into or am I disconnecting a line to get a reading from?
As for the timing light, I have the tools however I don't know how I'd adjust the timing on this particular engine so I'm really hoping the issue isn't of a timing related variety.

The cold start valve sounds really promising to me actually. I've on occasion got the car to turn on after cranking and pumping the throttle pedal for a couple tries, while having the FPR pins jumped. It starts but refuses to idle and as soon as I stop kicking the throttle, gives out and won't start again. So maybe the cold start valve is not supplying enough fuel to get her going? Originally I blamed the inability to idle as a consequence of having the MAS control unit removed since I believe the idle control function is embedded into the MAS unit.
Check this guy out if you have not...https://mercedessource.com/history

step by step simple guide for problems and repair.
 

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I would keep the MAS relay plugged in... not sure why you keep having to bypass it. Are you sure the pumps won't engage with the MAS plugged in? Did you listen and just prime the pumps by turning the key to position 2 before cranking?

If you go under the car and stick a multimeter on the fuel pump terminals, have someone else turn the key and prime the pumps, and just in the first instant of priming them voltage should jump to about 11.2 volts then go down.

Also always a good idea to go around the car and clean ground wires of any corrosion if you haven't done so already.

Are you using genuine Bosch pumps???
 

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Discussion Starter #20
SpartanV, I've tried a couple of MAS units in place and none of them get power to the pumps on the 2 position. The only way I've ever had any luck on getting the car to fire up has been with the jumper wire at pins 1 and 2. I was actually thinking of measuring the voltage though, may be mistaken but I'm hoping maybe one pump isn't installed correctly and isn't powering on causing the drop off of fuel pressure.

Plinker17722, Its definitely a M103, previous owner said it was out of a 90' 300E. I wish it had the older standalone fuel pump relay design but unfortunately I have to deal with the MAS control unit.

I'm starting to thinking maybe there's a short or voltage spike in the wiring that killing off these MAS units the moment I install them onto the car and power it up. Don't know what else would keep power from getting to the fuel pumps at the 2/"on" position but is able to get power over to them when the relay/unit is bypassed.
 
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