systematic testing of fuel components - Page 2 - PeachParts Mercedes-Benz Forum

lsmalley · #16 04-20-2014, 12:18 PM

Quote:

Originally Posted by Ferdman

Ismalley, if you get one or both existing fuel pumps running properly you could return one or both new ones. It bothers me to buy a new part when an old part just needs some TLC.

Ferdman, you were right. When I put the new fuel pumps in and tried them out, they both worked. Then when I buttoned everything up, nothing. I put my light back on the fuel pump connectors and got no power. Faulty MAS. I replaced it and they both work again. Took my old fuel pumps to the battery and tested each one....they both work as well! However, the damn car stalled on me again yesterday. It only happens when I am coming to a stop. But it doesn't start right back up, I have to wait a bit. Anyone???

Elektri · #17 04-20-2014, 12:42 PM

Monitor electrical power to the fuel pumps when driving. And/or monitor fuel pressure while driving.

Note: My A/C fan was acting up - not working sometimes, maybe once every 4 days it would briefly go off. So I set up a voltmeter to monitor the power going to it... Well it NEVER did it again! (These things know when you are watching and will then behave...

)

lsmalley · #18 04-20-2014, 03:47 PM

Quote:

Originally Posted by Elektri

Monitor electrical power to the fuel pumps when driving. And/or monitor fuel pressure while driving.

Note: My A/C fan was acting up - not working sometimes, maybe once every 4 days it would briefly go off. So I set up a voltmeter to monitor the power going to it... Well it NEVER did it again! (These things know when you are watching and will then behave...

)

Monitored the power to the fuel pump and though I originally had a faulty fuel pump, turned out to be the MAS unit. I swapped it out with a known good one and still stalled out. So far I have ruled out all electrical ignition components and narrowed it down to a fuel related problem since spraying carb cleaner in the air intake seems to make the car start up after a stall. IF I don't spray the carb cleaner after a stall it will just crank and crank. So this is what I have done/replaced:
1) 2 new fuel pumps (replaced)
2) fuel accumulator (replaced)
3) MAS unit (replaced/tested)
4) ovp (replaced)
5) EHA (tested)
6) fuel pressure regulator (p/n 0438161001) (tested)
7) fuel pump check valves (replaced)
8) IACV + hoses (replaced)

lorainfurniture · #19 04-20-2014, 08:49 PM

Fuel pump relay?

JamesDean · #20 04-20-2014, 08:51 PM

Quote:

Originally Posted by lorainfurniture

Fuel pump relay?

On MY90+ M103 had the fuel pump relay replaced by the MAS relay. I think it pretty much does all the same things.

lorainfurniture · #21 04-20-2014, 10:18 PM

Hook up the mechanical fuel gauge and run it through the hood and lay it on the windshield. You can buy on at harbor freight for $20. Just curious; when was the last time you did an ignition system tune up? Cap, rotor etc?

lsmalley · #22 04-22-2014, 01:32 PM

Quote:

Originally Posted by lorainfurniture

Hook up the mechanical fuel gauge and run it through the hood and lay it on the windshield. You can buy on at harbor freight for $20. Just curious; when was the last time you did an ignition system tune up? Cap, rotor etc?

Cap, rotor, wires, plugs, are all new and have been replaced about 3 times in the past 3 months with more new parts to ensure that they weren't the culprit. But I think I found the stalling problem. I went online and went to the az haus parts site where I checked the fuel/air components and I looked at each individual component they had for sell. I then made a note of all the parts and checked them against the parts I had already replaced. I came across a small 3 port check valve called a purge valve, this valve is located right above the driver side wheel in the engine bay and right below the abs and behind the side marker light. Bingo! One of the valve hoses were disconnected. The 3 hoses that go to the valve are one hose from the ezl, one hose from the throttle body, and a large hose that is connected to something inside the driver side fender. I reconnected the hose and drive for 2 days without stalling. I don't know if you all remember the fire I had under the hood of my car that toasted all the word on the driver side. I guess when I replaced the wiring I inadvertently detached the hose ass it is resting right under all the wiring on the driver side. I will continue to drive and see if the stalling has been remedied, but so far 2 days and no stalling and I was stalling before at least twice a day.

lsmalley · #23 04-22-2014, 05:01 PM

Ha! No sooner then I said I ended up stalling again today. This time twice within an hours time! This is really frustrating. I pull over, remove the air cleaner housing spray carb cleaner on the plate and start the car while giving it gas at the throttle switch and continuing to spray the carb cleaner which is keeping the engine running, as soon as I stop the spraying the engine cuts out. This time I did something that I now thing I figured out the problem...I think. I tapped on the black EHA on the fuel distributor while starting the car and the car started right up. o.O?? I tested the voltage at the EHA and I think I read somewhere it should be 4.5 or something like that which I am getting, but is it possible that even though the voltage is fine that there is some mechanical part malfunctioning? What I did was get the car running, adjusted the mixture back to the appropriate setting, then I unplugged the EHA. I'm not sure if that will stop whatever mechanism inside from functioning, but I want to test it out before I end up buying anymore parts. Is this the correct way to bypass the EHA or is there such a thing? I think I read somewhere that the KE-Jetronic CIS-E system in these cars are mechanical/electrical (via EHA), but disconnecting the EHA will cause the car to still function, but only mechanically. Anyone care to elaborate on this or the possibility that my EHA is bad even though I am getting the correct voltage?

engatwork · #24 04-22-2014, 07:55 PM

Quote:

will randomly shut off while stopped at a light and wont start back up.

Are you having to have it towed everytime after this happens?
Are you able to start it up after it has cooled off?

Quote:

don't know if you all remember the fire I had under the hood of my car that toasted all the word on the driver side.

I did not remember that. I'm wondering if there is some wiring damaged that you have not found yet?

lsmalley · #25 04-22-2014, 08:01 PM

Not heat related and not related to faulty wires. Strictly fuel. As stated in my posts above it starts back when I spray carb cleaner or flammable solvent in the intake. I'm now guessing eha as mentioned above.

Elektri · #26 04-23-2014, 08:59 AM

The EHA just adjusts the fuel mixture to be more lean or more rich based on the computer input from the oxygen sensor. If you disconnect the wire going to the EHA, it will just use the default mechanical lean/rich adjustment and not do any adjusting of the fuel/air mixture.

The EHA is like a tennis racket held out in front of you in the center. If the ball comes to the left, you can swing that way. Or right, swing the other way.

Note these things are all designed to work with the factory specification fuel pressure. If the fuel pressure is something other than what it should be, then I imagine weird things could happen?

Also note that if you try replacing all the parts until the problem is resolved, you can introduce new problems if a defective or wrong specification part is installed. And the problem could be something like wiring, a wiring connector, sludge in the gas tank, etc. And in that case, replacing all the parts would not resolve the problem.

Thus why it is better to use test instruments like a fuel pressure gauge or voltmeter. Then track the problem down to its cause.

lsmalley · #27 04-23-2014, 12:25 PM

I keep hearing something about a test port on the distributor, but I'm not sure which one I need to check. Could someone circle the correct port on a photo for me? The thread by one forum member mentions a lower and upper chamber test port? Its confusing to me as I'm not sure which they are referring to.

JamesDean · #28 04-23-2014, 12:36 PM

Yes.

With the fuel pressure test set that I have.. one ends gets connected in place of the cold start injector and the other is connected to the test port.

The set has a lever in it that will switch between system pressure and upper(or lower--cant recall) chamber pressure.

IIRC you wanted like 0.5 bar difference or something.

I'll have to see if i can find the pictures.

lsmalley · #29 04-25-2014, 07:18 PM

It's been 3 days now since I unplugged the EHA and it has not stalled. So I think I have finally found the culprit. However, the part is so pricey that I tend to drive the car around like this for a bit just to be sure it doesn't stall. then maybe after a week or 2 of no stalling, I'll plug in the EHA again and see if it stalls again, then I'll unplug once more to be sure. Sytematic testing! :-)

JamesDean · #30 04-25-2014, 08:16 PM

This makes me wonder...

If the EHA is unplugged:
1) Is CIS-E aware of this fact?
2) Does CIS-E fault out?
3) When it fault out does it return to open loop control?

If 1,2,3 are true then you are presented with the following:
1) Is the EHA really bad?
2) Or did reverting to open loop control resolve the problem?

Of course if it stalls out again..then none of the above matters..