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Matt, Engineer
Category: Mercedes
Satisfied Customers: 21990
Experience:  Mechanical Engineer with 23 years experience in the auto industry, 8 yrs in formula 1 engine testing
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Our 190E sat for 1 year. It ran fine before but when we went

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Our 190E sat for 1 year. It ran fine before but when we went to start it, it seamed to not be getting fuel. We were able to get it to run by pouring gas not the throttle body. I also, noticed the fuel gauge and the oil pressure gauge were mal functioning.The gas showed empty so, we put a few gallons in. no change. So, we replaced the MAS control unit but there is no change. We checked too see if the fuel pump was getting power and it isn't. I read something about a fuel cut off solenoid but can locate it. any ideas? I'm thinking about draining the tank and replacing the filter but, still don't know why the pump isn't getting power. unless we bought a bad MAS control unit.
JA: How many miles are on the vehicle? And when was the last time it was serviced?
Customer: 190,000. I service the vehicle myself. There are no Mercedes mechanics on the island.
JA: What year is your 190E?
Customer: 1991
JA: Are you fixing your 190E yourself? What have you tried so far?
Customer: I just told you what I have tried to fix this problem. I have done a lot of work to the car in the passed
JA: Anything else you want the mechanic to know before I connect you?
Customer: no


you don't say what engine size this is but it should be on the mechanical injection system K-jetronic

this sounds like a lack of fuel and could be a lack of fuel pressure from the electrical pump at the tank.

If the connections to the pump are corroded or damaged then the pump could stop at any time or could notbe running at full speed. Check that its relay switches in and out and the relay contacts are clean and bright – replace the relay if in any doubt and do the same for the fuse,
Ideally measure the pressure at the inlet to the main engine fuel distributor (should be 5 to 5.8bar) and if this is low check the pump as described and also consider changing the fuel filter as if this partially blocked this too will reduce pressure.

If this is OK then remove the rubber intake boot from the fuel distributor and then unscrew on the top of the unit find the central nut , pipe feed into the fuel distributor and push down on the aluminum plate under the rubber boot you should see the main fuel metering pin / needle rise up smoothly as you push down the plate, if its sticky or dirty then its possible this is getting stuck.

If this is OK then remove all the injectors but leave them connected to their fuel lines and put all into a clear container then turn the ignition on and (having replaced the central feed pipe nut) lift up the aluminum plate all the injectors should spray at once and look for ones that aren't spraying as much as the others - and replace or ultrasonically clean as required.

I'd also try setting the mixture as follows:

so run the fuel pump and depress the air flow sensor plate for a couple of seconds to bleed air out of the fuel distributor. Remove one injector line from the top of the fuel distributor, and while looking into the injector port in the top of the fuel distributor turn the mixture adjustment screw clockwise until the port just starts to fill with fuel then turn the mixture screw 1/2 turn counter clockwise. Reinstall the injector line, start the engine and adjust mixture when it reaches operating temperature. This is the Bosch recommended procedure for initial mixture setting and adjustment.

Customer: replied 1 month ago.
It is a 2.6.
As I explained I believe we're not getting fuel because there's no power to the fuel pump and I replace the mas control unit but still no change. please explain to me how to check the relays. Are there any other relays other than the mass control unit? Is there a fuel cut off switch/solenoid?


I've attached the electrical diagram for the fuel control

as you can see that you should have 12V on terminal 2 of the MAS unit during cranking to power up the fuel pump

so I'd get the multimeter out and check that 12V is coming into the MAS as it should and leaving it as it should

Customer: replied 1 month ago.
Will do.

do you still need help?
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Customer: replied 24 days ago.
I double checked the relay and I also checked the Over voltage protector and the connections inside we're not making contact in the top so I fix that got power to the fuel pumps but the fuel pumps are not working it seems going to replace those. Didn't know there were two.