I have searched and searched but cannot find a good diagram of how the fuel tank internals work on a 97c230. Am I understanding correctly that the fuel is actually being pulled from the driver's side (u.s.version)? When I knock on the bottom of the tanks the drivers side is empty and the passenger side sounds full. It will only let me put in about 2 gallons and runs out of gas at about thirty miles. I bought the car wholesale and have no idea what the history is. I have found enough to know the tanks are a common problem, but very little in how they actually work.

I was determined to let the car run out of gas since I have no idea how much is actually in there. I started it and let it idle in the driveway for about two hours. It started to stumble so I thought it was empty. However, when i opened the gas cap some sort of pressurization has taken place and forced gas up the filler neck. I had changed the charcoal canister and blown through all of the lines to and from. I just cant understand why it would send gas out of the filler neck and then starve for fuel. I took a large pipe and blew into the filler neck and it forced the gas back down and must have expelled the air somewhere. It started right back up and ran for another hour before I gave up and shut it off, I know others have had problems with this fuel tank setup. Wont someone please chime in.

What ever happens, please update the thread with results, there are many threads without a final result.

The tanks use a venturi pump fed by return fuel to move fuel from the left sump to the right, it is a pretty wanky system. Take a look how a mid depth well water pump works and you will get the idea how it works. ( This would be the kind that sits in the basement and the venturi is dropped into the well, not the pump / motor type that is dropped down the well. )

A transfer tube below the drive shaft would have been better in addition to the existing transfer above the drive shaft.

The actual venturi pump has no moving parts so there isn't anything to wear out. There is a chance that someone replaced the fuel senders ( the wiper corrodes giving an inaccurate reading. ) but didn't rehook the piping properly. If the fuel filter is clogged / pump failing to the point there isn't enough return fuel volume, it could leave the right side fuel pickup dry.

Not sure why you get hard fuel spray when the cap is removed. From what I recall there "might" be a expansion tank in the filer area and I'm wondering if someone got creative with replumbing the system. There is a 1/2" vent and two 5/16" breather hoses in the area of the fill neck.

These cars use 2 fuel senders to calculate fuel, pull the covers on left and right of the tank to access. I'd ohm out the senders to get an estimate on how much fuel is on each side. Rather than running the engine, I'd bridge the fuel pump relay ( in the trunk ) and pump fuel into a can. ( don't catch fire )

The tank on these can't be removed unless you pull the rear sub frame. The senders can be removed buy you need to make a tool to turn the locking ring. Make sure you drain fuel from both sides, the senders are on the bottom of the tank and all the fuel will fallout.

Thank you for responding. Yes, there are a million threads talking about the problem and I have yet to find anyone with any kind of solution. I have all three common problems. Fuel guage is not functioning, it will not let me fill up the tank with gas without shutting the pump off, and finally I believe it is not making the transfer between tanks. I know the proper solution would be to replace the fuel senders and Venturi, but this is a backup car and my primary car is having a transmission replacement. I can hardly justify having both cars apart at once. Just looking for a solution that can get me through. I did replace the fuel filter but have not put a guage on the fuel rail to verify pressure.

It's more that just pressure, you need volume. A weak pump bypasses internally making just enough volume to run the engine but not much more so little fuel bypasses the regulator and heads back to the tank.

Replacing the senders won't fix your fuel transfer problem. My 97 C280 was siting 4 + years before I got it and the sender wipers were corroded. They can be taken apart and wiper cleaned. The resistor is thick film so don't scrub it too hard and damage the resistive surface.

Also, the senders are wired in series to give proper fuel level and there isn't any sort of monitoring done to transfer fuel.

A filling issue may be a collapsed vent hose near the filler, if this has roll over check valves that might cause a problem as well.

roll over check valve? what and where would those be.

A roll over check valve is a ping pong ball in the filler neck that prevents fuel from poring out of the tank should the car become inverted and cap damaged. I'm not sure if the C had this or not.

I'd have a close look at all the hoses to make sure someone didn't get creative with replumbing the system.

Someone had replaced the vent hoses with standard hose which caused a visible restriction. I replaced with oem. Later that day it wouldn't start at all. The fuel pump had been loud and I had a brand new auto best (cheap) fuel pump so I put that on. Still cranks but no start. Jumped relay ect. Anybody had problems with cheap pumps? There must be a difference in the Bosch for 180 and the auto best for 40.

The car still start and run with a generic pump. Do a pressure test and also look for flow from the return line.

I must have gotten a defective pump. Put the old one on and it started. Ordered a Bosch pump. I will update when I get it on as to weather it helps with the whole problem.

new fuel pump installed and it performed flawlessly yesterday. About 45 miles of stop and go errands. Plenty of shutting off and cranking. This morning, back to the same problem. When I jump the relay I can hear the pump and if you press the valve on the fuel rail fuel shoots out past the fender. As soon as you turn the pump off and go back to the valve, there is no pressure. It will not start even with the relay jumped. I am beginning to believe that the reason no one has given a sufficient solution is that they gave up and had the car crushed out of spite.

anybody ever rewire the plug going to the crankshaft position sensor? I am having second thoughts on this being completely fuel related. I replaced the cps recently, but sometimes if you move the wire it will cure the no starting issue. Could there be a short or break? in a late 96 production of a 97 model would I have to worry about the biodegradable wiring?

95 should have been the end of bio wire. Had to change the engine harness on my 97 C280 when I got it. Mice ( irate husband of the cars actual owner ) chewed through ( used pruning shears to cut ) the engine harness. The insulation was standard plastic in good condition.

You really need to use a fuel pressure gauge.

Pressure tester is ordered and on the way. In the mean time I went to the salvage yard and cut the wire from the cps to the brain out of a wiring harness. I installed it into my car and have put 150 miles on it since without any problems. All of the symptoms pointed toward fuel this whole time but I do believe it was the wire that had caused so much frustration. I will keep updating as I go along.