'95 E320 lost fuel pressure, pumps okay and new OVP relay.. - Page 2 - PeachParts Mercedes-Benz Forum

Frank Reiner · #16 10-28-2016, 12:40 PM

Quote:

Originally Posted by puzzler

CONCLUSION: Okay the pumpss were failing progressively..I was mistaken in concluding there was no power to the pumps because I removed a pump and it tested solidly just a few days before....couldnt imagine both failing at once but its likely I was running on just one pump..The x36/3 connection does not appear to exist in my car but the vacuum pump conatined a mouse nest and some of the wires were chewed..Thank god I pulled it all apart and taped up the wires..they ate a little space in the foam box..

fuel pump wires come right through the well in the chassis opposite the pump where one can check and test..

So Ive got to order another fuel pump..possibly will now have full pressure operating since I purchased the car, its always felt weak by comparison to my previous E320, 94 sedan and the mileage is low which also may result from weak pressure..

Are the pumps plumbed in parallel or in series? Plumbed for increased volume or for increased pressure?

puzzler · #17 10-28-2016, 05:14 PM

oh I see the question..Yes. The electrical is in parallel so either/both will run if they have a ground and they work..I suppose a short could kill the circuit or blow a fuse..And the gas line is in series, one pump feeding the other..so I suppose the pressure is accumulative so with one pump you could be undersupplied or else its a backup feature..redundancy. I find the car will run fne on one pump and likely it has been for some time..At one point I found the car would start/die and not run, then when I disconnected the undertank pump it would run continuously just fine..

At that point I conjectured there was a clog in the check valve blocking the flow as a result of pressure..cleaned the check valve and I was good again..

Ive not done a pressure test other than just checking for fuel at the pressure valve..psst test..

Looking forward to the two pump system with new pumps both working.

Frank Reiner · #18 10-28-2016, 05:50 PM

Quote:

Originally Posted by Frank Reiner

Are the pumps plumbed in parallel or in series? Plumbed for increased volume or for increased pressure?

Once free of the excesses of the following, the simple answers to the simple questions are: a) in series, hence the result, b) increased pressure.

Quote:

Originally Posted by puzzler

oh I see the question..Yes. The electrical is in parallel so either/both will run if they have a ground and they work..I suppose a short could kill the circuit or blow a fuse..And the gas line is in series, one pump feeding the other..so I suppose the pressure is accumulative so with one pump you could be undersupplied or else its a backup feature..redundancy. I find the car will run fne on one pump and likely it has been for some time..At one point I found the car would start/die and not run, then when I disconnected the undertank pump it would run continuously just fine..

At that point I conjectured there was a clog in the check valve blocking the flow as a result of pressure..cleaned the check valve and I was good again..

Ive not done a pressure test other than just checking for fuel at the pressure valve..psst test..

Looking forward to the two pump system with new pumps both working.

puzzler · #19 10-29-2016, 06:26 PM

Im a puxxle solver and wish to include the side tracks as well as the straight line..which may be useful to those asking other questions than yours. One could edit down to minimal essence but its far more work...the long letter that one doesnt have time to make shorter..

Not only did you get your answer but others asking other issues may also get theirs. But thanks for the edit..

I might point out you assumed the pressure was accumulative since the pumps are in series..Could be its merely a reduncancy feature and either pump supplies adequate pressure..If thats not to much information

puzzler · #20 11-10-2016, 08:41 PM

So now with one fuel pump replaced the car runs fine again..the other ordered..And then to follow up after getting both new pumps installed and running a tank of gas Im getting 29 MPG in town which is awesome..Fresh cylinder head rebuild and lots of tune up work but its looking like the perfrmance I hoped for!

As a note, the car runs fine on one pump but Im assuming my fluctuations in mileage were due to fuel pump issues and that two good new pumps are primarily responsible for this great mileage Im now seeing..That is if its consistent now repeatedly..

No other noticable problems running with only one pump, acceleration and top speed just fine..but possibly the low pressure provided weak atomization at the injectors..