Probably the bloody fuel pump relay but... - Page 2 - PeachParts Mercedes-Benz Forum

Rick76 · #16 11-06-2016, 11:52 AM

Might be a good idea to add a 30 Amp fuse (for dual pump system) in the fuel pump circuit. I added one but it was more to give a convenient way to disable the fuel pump so I could crank the engine after an oil change without it starting.
Yes, definitely check your pump current draw unless you have been doing something recently (your accumulator?) that could have shorted out the pump wires.

puzzler · #17 11-06-2016, 02:47 PM

Interesting to me since I just tore my car apart certain the fuel pumps were good because Id just had them out testing and cleaning, I actually found the car suddenly ran when I disconnected the rear fuel pump..clarifying the middle pump worked fine and then after cleaning the rear pump they both worked fine..Solved..Then a week later they both failed leading me to think it was a bad X connection ...No way it as the pumps!

and in the end it was simply the fuel pumps. They were trying to fail repeatedllly but I kept messing with stuff and they would reactivate..Called for a tow but then before the truck got there..the car ran again..All in all it was about three months of daily driving with about four/five failure episodes..

hope to see the end result in this repair..

(95 E320 with 200K miles..was sitting for about two yrs in a barn..)

Lots of good info on this thread, thanks to the wizards for the good detail..

Diseasel300 · #18 11-06-2016, 05:49 PM

Quote:

Originally Posted by Rick76

Use only electronic grade resin core solder. You don't need an aggressive flux whatever that is.

ROSIN core solder comes in many various grades from totally useless, to capable of bonding corroded wires, and everything in between. Using a weak flux (usually says it's "eco") will not give you a good bond, nor will using "lead-free" solder since the original solder on the card is lead-based. A good rule of thumb for soldering fluxes.....if it smokes and smells bad when it hits the iron and leaves behind a reddish-brown "goo", it's the right stuff to use on these cards. Just clean the card well with rubbing or denatured alcohol when finished to get rid of the leftover rosin.

Stretch · #19 11-08-2016, 10:08 AM

Bit of an update.

I scraped and found this =>

I took it to an electronics shop that does repairs and got someone to solder it for me - I know the soldering iron I have is too crappy to manage something like that - one of these days I'm going to invest in a proper soldering and desoldering station (but not this month)

Chaps seems to have been a bit liberal with the solder - we'll see if it works tomorrow

"He" seemed to think that the pump must have been drawing in excess of 40 amps to burn through that "thick" bit (doesn't look thick to me but hey ho I guess these fairy types see things differently).

To try and stop the next obvious thing from happening I've ordered a new fuel pump. I will measure the current draw on the old one before I rip it out though (just in case it is still kind of OK - probably not)

puzzler · #20 11-08-2016, 10:46 PM

Hey, looks like you got it..! keep us informed and just to comment, doesnt the relay already have a fuse on it so adding one? Possibly your car is different..Correct if Im wrong but the FP and OVP relay and fan relays all have fuses..Wasnt it Rick76 that pointed out that paint over the solder..there is truly some priceless exprrtise floating around here..Now I had repeated FP failure over about six/eight weeks first one and then both worked and then both failed..for a while the car started and died but would not run..Crazy..Never did blow the fuse and the relay is fine..

Diseasel300 · #21 11-08-2016, 10:56 PM

When repairing burned traces like that you can either apply a heavy coat of solder or solder in a wire to reinforce the trace. Personally I like to do both, or just route a new wire from point to point and call it good. The heavy coat of solder helps maintain some structural integrity that was lost when the copper burned through. With the heat applied to melt the trace, it becomes fairly weak and the solder helps reinforce it and keep it from burning again.

Electrical gremlins can be hard to track down. I finally found a wiring short in my SDL this afternoon that turned out to be caused by a hot contact on a relay in the fuse box (melted wiring insulation). Was NOT FUN cutting out the wiring and replacing that, but it works like a champ now. My point is that sometimes the causes and their effects don't seem related and can be maddeningly frustrating to find the root-cause!

In addition to checking the current draw of the pump, I'd suggest following the wiring harness to the pump as well and seeing if it has been chafed or rubbing against something. A short to ground can cause failures like that too. If the fuse doesn't blow first, the trace will act like one!

Rick76 · #22 11-09-2016, 07:07 AM

The fuel pump circuit is unfused until a little later in the 90's when they went to the green cube relay with the 30 amp ATC fuse mounted in its top.
Good to add a 30 amp fuse to those vehicles made before the factory fuse was added (or 15 amp for simgle pump systems).

Stretch · #23 11-09-2016, 10:13 AM

Found the new fuel pump in a sodden box next to my front door today - don't you just love couriers...

...tomorrow is the day - don't expect an update today!

Stretch · #24 11-11-2016, 10:20 AM

Oh deary me - whilst measuring the current draw on the old pump (which was 5 amps by the way - the current was rising but stopped quickly by the operator because =>) the (old) sealing rings on the new fuel filter decided to fail - underside of the car got washed in fuel...

...well I was hoping the rings would do another trip but they just weren't going to "do their effing job"...

...fuel pump current draw went up quite sharply to 4 amps then started to climb higher to 5 amps but was stopped when I heard and smelt that oh so familiar sound and smell.

Bollocks.

You wouldn't believe how difficult it is to get the slightly fatter (correct) sealing rings here. I was almost tempted to go to the dealership and buy them individually for 4 euros a piece (or whatever they are). In the end mail order saved the day but of course the delivery hasn't arrived yet.

So that part of the car is going to be new.

New fuel filter - new accumulator - new pump - new sealing rings

...

Eeek:- How much????

Diseasel300 · #25 11-11-2016, 10:33 AM

Sounds like your car is channeling my SL... Fix one thing, 3 more problems present themselves.

Good news though....you eventually run out of things to fix!

Stretch · #26 11-12-2016, 04:58 AM

Quote:

Originally Posted by Diseasel300

Sounds like your car is channeling my SL... Fix one thing, 3 more problems present themselves.

Good news though....you eventually run out of things to fix!

Well you would hope that would happen wouldn't you.

Perhaps you haven't seen what I've done so far?

Achtung - Das schweinhund baby benz thread

Diseasel300 · #27 11-12-2016, 08:06 AM

I've read all 3 of your long-term builds (including the LR wagon). All of your threads are highly interesting and give me some hope that my own OCD isn't too far out of control! I appreciate that you take the time to photograph and explain what it is you do and why you do it, inquiring minds always want to know.

My point remains valid though....you eventually run out of things to fix! Unless you're me and you break what isn't broken...

Stretch · #28 11-12-2016, 10:31 AM

Quote:

Originally Posted by Diseasel300

I've read all 3 of your long-term builds (including the LR wagon). All of your threads are highly interesting and give me some hope that my own OCD isn't too far out of control! I appreciate that you take the time to photograph and explain what it is you do and why you do it, inquiring minds always want to know.

My point remains valid though....you eventually run out of things to fix! Unless you're me and you break what isn't broken...

I'm always breaking stuff - half the fun!

So OCD - eh? D'ya reckon?

Stretch · #29 11-18-2016, 03:09 PM

Bringing it to a close - looks like the soldering fix on the relay did the job.

New fuel pump and relay seem to be getting along.

New pump (made in Denmark I think) is way noisier than the old one.

Just got to change the coolant tomorrow and it should be good to go (until the next problem).

puzzler · #30 11-19-2016, 12:42 PM

Thanks for the follow up! I just replaced FPs on 95 e320 with bosch and they were far more quiet than the old worn ones before failure..Great detail on all of this..