Fuel pressure / regulator problem ??? - Mercedes-Benz Forum
 
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#1 (permalink) Old 05-05-2013, 08:40 AM
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Fuel pressure / regulator problem ???

Hi, I've been having some fuel delivery issues in my 95 C220.

Short story:

Is the regulator bad AND if I keep the tank full will it quit dying on me?

Long story:

It died on me about 2 weeks ago or so while I was on the freeway. Fuel just quit being supplied. I traced it down to find no fuel was coming out of the pump anymore, and I could hear the pump running and verified 12V to it. So I bought a new (aftermarket) fuel pump and filter. I had trouble getting it going because those numbnuts at the cheap fuel pump factory soldered the wires onto the wrong terminals, which was hidden under the plastic cap, and it took me a little while to figure out what was going on. At some point I went to the gas station for 5 gallons of gas, just in case it needed more. So anyway, with the wires swapped now, the car started. The pump was a little loud and buzzy but it worked.

Ok now....I drove it for a day, and I guess with all my trouble shooting and taking hoses on and off, I didn't get a hose clamp back on tight enough and it died on me while driving---but this time it was only because the hose came off the outlet side of the filter. It only drained the fuel in the filter and then stopped. But then after I reconnected the hose I could not get it started again. Then I think I flooded it from pumping so much. I kept waiting and trying again but it wouldn't start. Finally I decided to get some gas, even though I had 1/8th of a tank, right about where the yellow light would start to come on. Usually I could go 40 miles or more at this point, but maybe it needed gas... So I got gas and Viola! It ran fine again.

Now, it is a week and a half later, and the car just died on the freeway again. I jumpered the relay and pulled the hose off the outlet of the fuel pump....definitely getting power and it sounds like its running but no gas is coming out. This time I had more than 1/4 tank of gas, almost 3/8 when it died. I figured this crappy fuel pump already died on me but before having it towed, I had to try one more thing...I went and got a gas can and put 5 gallons more of gas in it now (well, actually i think I put in just over 3 gallons and left some in the can)...this put my fuel gauge just above the 1/2 tank line. And then, for some strange reason, it STARTED!!

I drove it home but it was giving me some acceleration issues. It had no pep, was really slow, and when I punched it, no matter what gear I was in, it did not accelerate quickly as it normally would. I felt I was lucky to make it home.

I did some reading on the forums, and I am going to check the fuel pressure regulator by pulling off the vacuum hose and seeing if has comes out. But that is in the engine compartment, right? Why would I be getting no gas coming out of the pump at the back right behind/under the tank? Could the weight of the gas in the tank be critical right now to help push the fuel through the pump? I think I will rent an inline pressure gauge too but want to check the regulator first.

Thanks for your help!
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#2 (permalink) Old 05-05-2013, 10:44 AM
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Wild guess, but does your car have CPS?
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#3 (permalink) Old 05-05-2013, 11:08 AM
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Yes it does, but I pulled it and visually inspected it and it "looked" fine, no cracking, pretty clean. I don't feel like this has anything to do with heat because this morning I went to fill up about 8 blocks away...it was not doing good at all on the way there but once filled up it ran good on the way home.
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#4 (permalink) Old 05-05-2013, 03:23 PM
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There is no DIY way to test CPS, other than get a new one.
You also might have dirty tank "sock" and still have more possibilities for the problem.
I think hooking up pressure gauge to the fuel system is in order.
Easy test would be clogged tank ventilation. Open the gas cap when engine hesitate and see if it makes a difference.
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