I'm going to put my gauge on the supply line and see what it is supplying for pressure. It's just good to have confirmation.

Well, I found two issues. The Accumulator was leaking and has been replaced. Checked the bottom of the EHA, and it was wet with fuel. New "O" rings (green) had been installed so they were not suspect. So it was leaking and has been replaced. No more leaks.

I tried to find a fitting in the pressure gauge kit that would let me tie it to the supply hose to the FD. As I understand the system, pressure from the FP to the FD should be the same whither the supply is connected to the FD or not. Am I missing something? It would seem to me that using the press gauge connected to read the differential pressure would read FP pressure. Am I missing something?

Since the pressure regulator is downstream of the FD, supply pressure must be read with the system intact.

Thank you. That's what I thought.


On to a flow test on the FP.

Installed the brand new EHA and a salvaged Fuel Pressure Regulator. Applied fuel pressure to the system and got 6.3 bar of control pressure. I had no pressure difference, but with an unadjusted EHA, not unexpected.

When I shut the FP down, the pressure dropped to 4.0 bar and held. Starting to see some light at the end of the tunnel.

Got out there this morning and right back to 5.1 bar. Installed a brand new FPR and still only 5.1 bar. As long as the FP delivers enough fuel pressure, the system should hold at least 6.5 to 7.0 bar of pressure.

I don't have fittings to close off the fuel return to the tank. So I clamped the rubber hose with a pair of vise grips to cut off the flow. The pressure did not change one bit.

I'm to the point I suspect the new fuel pump. I'm going to test the flaw rate in the morning.

Well, the second new FP and FF came in and and are installed. Still the fuel pressure low, 5.1 bar.

So far;
The tank has been flushed twice with clean fuel,
Two new Bosch Fuel Pumps,
Two new Bosch Fuel Filters,
New Bosch Fuel Accumulator,
New Inlet Fuel Filter,
Rebuild Fuel Distributor. Build went back together without using the case screws for anything but guides. The only pressure used was light finger pressure to slowly squeeze the two halves together,
New EHA Controller,
New Pressure Control Valve.
From there it returns to the Fuel Tank.

There are three gallons of fresh fuel in the tank. I have the FD just setting over the Plenum with no fuel pipes hooked up. The car is setting level. Start the fuel pump against "0" pressure. Watch pressure steady build to 5.1 bar and hold. I purge the fuel test gauge and hose system to vent any air, and still no change. The system holds 3.0 bar, dropping to 2.0 bar in one hour. There re no visible leaks of fuel

I have had the first fuel pump produce 6.4 bar for a brief time. The second has only produced 5.1.

The only possible thing I can think of that I can think of is the Fuel Tank Cap?

I tried to adjust the DP at the EHA. Turning the adjusting screw in 1/4 turn and testing again went like this
1 QT in, no change
1 QT in, no change
1 QT in, slight resistance felt at the end of the adjustment, no change
1/2 T in, same resistance, no change.
At that point I stopped.

Any ideas would be welcome.

Sounds like you nearly replaced everything, but what's the problem again? Is the car not running? Your best bet would be to leave that 5.1 bar alone and see if the car cranks up. Do the fine tuning after you have it running.

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1990 190E 3.0L

I broke the fuel return line loose and flow tested the pump. I got a liter in less than 30 seconds. 2 liters per minute. While I was there, I installed all three PR and none will hold more than 5.1 bar.

So I mounted the FD and used the original EHA that I had and I got my DP to adjust 0.4 bar. Then I remembered when I started this project that I had wound up with 1/2 gallon of fuel in my crankcase. Come to find out that the Sensor Plate was set so high that the FD Plunger was not bottoming out at engine idle. So reset the SP so that the fuel was not dumping at idle. I now am able to set the DP to 0.4 bar. Press the SP and I get fuel delivery, release SP, and fuel flow stops. There just might be some hope here. Close up for the night as I have raw fuel everywhere and will button everything up in the morning.

So I get ready to finish putting the system together in the morning. Start the FP just to check everything again and all I can get is 2.2 bar out of the fuel pump. What pressure I did get came up very slow. So I'm right back where I started.

What are the chances of getting two bad fuel pumps?
The fuel tank has been flushed twice,
I'm on my second new FP,
Second fuel filter,
new Accumulator,
new FD inlet fuel filter,
new Pressure Regulator.

Any thoughts would be appreciated. This thing is about to drive my buggy.

The system pressure is 5.5bar and the lower chamber pressure is 5.1bar, which is normal. What connection do you use to measure the system pressure and the lower chamber pressure?

I had to take some time off, and do some more reading and pondering.

I put my original EHA back on the FD and I was able to get 0.3 bar DP and left it at that for now. Whoever wrenched on this engine before me, had the Sensor Plate adjusted so that the FD plunger did not set at the bottom of its travel and the FD was dumping fuel into the crank. So I reset the Sensor Plate so that there is about 3 - 4 mm of travel before the SP makes contact with the Plunger.

I can now "ALMOST" get the engine to catch. I have no idea what, if anything, was done at the throttle position potentiometer. Any ideas as to what to check?

EDIT: Went out and tried to fire the engine off again. Normally I turn the key one, depress the throttle to the floor, release the pedal then crank the engine. This time I pushed the pedal to the floor and cranked. Twice I got about three cylinders to fire then the engine died.

Just to add more fat to the fire.

IT"S ALIVE!!!!! I watched a video of Pierre Hedary's again and found the answer.
https://www.youtube.com/watch?v=zXJkvD4rjPI

It was the OVP relay. My '91 350SDL runs the same relay. I pulled the OVP from the 350 and swapped it out to the 300. It took a few cranks, but it caught and run like a scalded dog. It still needs some fine-tuning, but it's up and running.

Thank you to those who replied and put up with the rantings of an old man.

The saga continues. After I swapped out the OVP relay with the one from my 350SDL, the engine cranked and ran. See above.

Went out the next morning and made the final set on the EHA and got the DP to 0.4 bar, per spec. Button everything up and fire the engine off again. Fires right off. Bring it up to 2,000 rpm and let it come to full temp, just under 80c. Back off the throttle to idle and it settles at 800 rpm. Shut engine down, crank, and repeat three times. Slept the best I have in a long time.

Got up this morning, go out, and I'm right back where I started. The engine will fire, runs a few seconds then dies. If I really work the throttle just right, I can get it above 400/500 rpm. The engine runs well at 2,000 rpm. Get it to operating temp, back off the throttle and the idle comes back to 400 rpm, sets there and shutters like it just short of shutting down, and the engine will not accelerate. From all of my readings, this indicates a bad OVP relay. Swapping out a suspect one, with an assumed good one, results in a solved problem. What am I missing here?

I expected to have to rebuild/replace most of the fuel system. There is just too much info on the issues on the web to not know. But my research has led me to believe that most, if not all, are just normal maintenance.

I keep reading about the relays having a high failure rate. How much truth do you find in the claim?

So I open up one of the two OVP relays that I have. Touched all of the solder joints. Install it back in the car and the car will crank, but has the same issue, low rpm and not coming off an idle.


I read many comments about the ABS light. This light comes on when the ignition is switched on and

the ABS light goes off when the engine does crank. As I understand this should indicate that the OVP is working.


Just where do you set the idle speed on this engine? The airflow meter adjustment sets your A/F ratio. This engine acts like a carburetor engine would if you had a very lean idle mix and it stumbles off of a standstill.

I pulled the idle air controller this morning. The rotor is stuck at about 30% open/closed. I wonder if that would be an issue?