W126, 300 SE fuel pump (?)
 

Hi all, I am in North San Diego with my 300SE ,1989, and a little while ago I lost power on the freeway.
All the dash dummy lights went on and the car would not
accelerate. Off to the side of the freeway, the engine died.
It would not crank over (head lights did not dim as ignition was turned) and the dummy lights remained on.
I checked all bands etc. I hoped it was not a timing chain(belt).
Did not seem like it.
i recalled reading in other posts (see how great this site is!!)
about tapping on the fuel pump in order to get it going.
Well, I tapped on the fuel pump and I gave one or two light taps on the fuel filter.
Car started up and I just arrived home.
The pump does not seem to make noise ((correction-it buzzes like a bee )) and i did not experience
poor acceleration before.
I plan to call Phil at fastlane on Monday to see how fast I can get a pump. or else I'll have to resort to the dealer.

Anybody have any opinions??
Could it have been just the fuel filter (this is still in maintainance spec time- below midway) or is it better to change the pump.
is there another part of the pump like the check valve that may be
going bad? I don't know where the check valve is.

Thanks for opinions!!

p.s. car has new distributor cap and wires,plugs. acceleration is still smooth, idle is o.k., battery is newer.

yeah the pump buzzes like a bee.

I'm may be going out on a limb here. Pro techs correct me if I'm wrong.

The fuel pump relay on the 88-89 300SEL's in setup pretty much like the 300E W124 with the 103 motor - fuel pump relay somewhere near the battery. Don't recall the acronym or name of the gadget it lives behind, but it's in this general vicinity - much has been said about it here - check archives.

I'm not saying that tapping the fuel pump didn't help, but on the 88-89 300SEL's, the fuel pump relay is notorious for causing the sort of problem posted.

I wonder if there was enough of a cooling off period and tapping the fuel pump was merely a coincidence?

Do your homework on the relay. I experienced a few episodes as you described and through diagnostics was able to determine that it was indeed the relay. Replacing the relay is much less expensive than replacing the pump. Prior to ordering a new one, I took the cover off of mine and found some bad solder joints. 2 minutes with the soldering iron and my problem was fixed. Getting the cover on and off was a pain, but it was already a problem part so if I ruined it, no biggie. I did reseal my cover with silicone sealer during reassembly.

thanks for the info on the relay. I did check the archives prior to
posting and found some info on the relay however with many, poor acceleration episodes were a symptom that seemed associated with the relay.
not more than five minutes passed between the engine dying
on the freeway shoulder and my tapping the fuel pump
with a tool resulting in the car starting up again.

the fuel pump does make a rather high pitch 'buzz' which i
don't think is normal. Audible from outside the car's rear.

Any further opinions are appreciated.

I won't discount the relay.

THANKS

Hi unkl300d,

the check valve is screwed into the fuel pump on the exit side and the banjo fitting is connected to it (at least on a W126). I guess it is there to keep the pressure up in the line once the car stops, i.e a one way valve that blocks the return of the fuel. I don't think it has anything to do with your problem.
Regards
Reinhard Kreutzer

Thanks
 

Thanks for that info.

Anybody else have opinions?

unkl300d,

My car would cut out without any prior indication that anything was wrong. Sometimes, I could restart it immediately as though nothing was wrong at all. On occasion, it would stumble a bit under heavy acceleration. I did find that my problem was accentuated by cooler moist conditions. In fact, I went over a month with no symptoms at all. First cold rain after that, I couldn't get her started again without the relay out and circuit jumpered. The diagnosis on the relay was VERY easy for my model (85 380SE). Pulled the relay and jumpered the correct pair of pins with a short piece of wire with the key in the on position and the pump started running as it should.

By the way, my pump has been noisy since I bought the car 6 years ago and it runs great. I do have a problem with the pressure leaking down when shut off, and I am hoping that the pump check valve is the cause for that problem and the noise. I'll let you know, as I have one on order and it should be here in a day or so.

Thanks Q and all that have responded.
I spoke to my mechanic back home this morning and he was not
alerted by the symptom of noise from the pump. He said that noise as I described did not indicate a failing fuel pump.
However, he asked if it had back fired when restarted after the shut down (no), and whether it was surging or had lousy acceleration. I don't experience this other than the normal
uneven idle with the trans in Park.
He advised me to drive it around before deciding on service.
i.e. pump replacement.
So, I have driven it about 23 miles on freeway averaging 75 MPH
on the night after I got it started up to get home and today I drove it for about 25 miles averaging 55 MPH. Total drive time so far about 1 hour and 15 minutes. Successfully.
So, I plan to continue using the car and observing.
I'll put some Red Line Total fuel treatment in tomorrow before freeway testing.
It may have passed some blockage debri temporaneously or perhaps was some bad gas, i.e. water globule or other.

I'll post outcomes.
If I make it back next week to San Francisco, I will have the mechanic check it out.
When it failed Sat. night, the ambient temp was about 60 F
or a bit less. It is about 63F during the day right now.
I will keep an eye on the relay as well, so I appreciate the
relay jump tip in case I need to resort to that on the way home later.
I'll pack some wire but I don't really know the jump sequence. Q?

Shaken but not stirred!

Your car is probably different from mine. I wouldn't want to misguide you into damaging your car.

My relay was in the fuse box. It was black and simply pulled out of the socket. My service manual stated two particular pins to jumper to engage the pump. Be aware that you bypass control circuits by jumpering, so it is not a means to continue driving the car without the relay for certain. It is merely a way to test the system. If I had to jumper to get home though, I would.

Made it with no problems
 

Thanks to all who replied.
You saved me from changing out a fuel pump!!!

I drove back to San Francisco with no problem.
I did add a full bottle of Red Line total fuel treatment before the trip and the car performed well.
So, perhaps my problem stemmed from a momentary debri or bad fuel

Thanks again !!!:D

Dealer sez...........I need your help
 

Well 4 months later and the car cuts out again twice. The dealer diagnosed it as follows:
"Road test verified complaint,basic engine test, fuel pressure test; diagnosis revealed fuel filter dirty, fuel pump, fuel pump relay, switch over relay faulty/compromised;replacement recommended for correction. No correction performed. Customer advised of vehicle condition. $140."


So, the fuel filter was changed about a year ago and less than
5000 miles ago. But I can accept that the filter is dirty due to some contaminant.
However, I figure my fuel pump is OK (original pump) but perhaps the relays may be bad.

I ask for opinions.
Which relay should I replace first? Both?, then also replace the filter and cross fingers that pump is OK??
OR is it about time to replace the pump also??? (112K miles).

I just wonder whether this apparent shot gun approach to replacing all items listed is genuine or malarky.

Your opinions are appreciated.
THANKS.

Denis

Hi Denis,

it's not only the miles, it's also the age. That pump is 13 years old...
I hate to break down on the side of the road. So I rather spend the money on the parts and install them myself (if I feel confident that I can do it) than paying a tow truck or pushing the car over a busy intersection.

However, if you don't mind the hassle, then you start with the cheapest and work your way up. (Again, with my kind of luck, it would be the last part that I replace that will fix the problem, so I replace them together.)

Good luck

Reinhard Kreutzer

Thanks
 

Thanks Reinhard, that sounds like the right thing to do.

It would ave been nice to spare the fuel pump, but like you say, it is more hassle later if it reoccurs...even worsr if it fails completely.
At least now, a tap on the filter gets the car going again.

I'll order from fast lane and get it on.

Denis

Opened up the ump relay and found it good.
Had the pump and filter changed today.
Good ol Bosch fuel pump..........made in Chech republic...can't wait for the peoples' BOSCH (china)

Old pump sounded the same and car runs no diferent. But now 2 variables have been eliminated and I hope there will be no more stalls.

Reinhardt, thanks for the rely information. I cleaned up the prongs
before re-installing the relays.