Don't quite know how to phrase this message, but here goes:

My '87 300e died on the highway last week. When I tried to start, it'd turn, but wouldn't fire.
I brought it in for diagnostics, and was told a long list of this and that, the top being Distributor and Rotor.
So I changed that.

Now, had that worked, I wouldn't be writing this.

Something that had been suggested from the beginning was the Fuel Pump.
I spoke with someone that suggested that it was likely the Relay that went out.
He suggested I Solder the Relay.
First of all: Has anyone heard of doing that?
Secondly: Is it likely that it was the relay that went out first? Or could it be the actual pump, or even both?

I know a lot of that last question is case-by-case stuff. But I guess I'm just asking on a general basis.

Just trying to figure things out.
Thanks,
-Chase.

 

it depends on what's the syptoms and other parameter effect.

if you suspect fuel pump, confirming it is easy.

just check the delivery rate and pressure.

 

Thanks for the quick response.

I apologize, but you're going to have to keep things real basic for me.
How would I check that?

At this time, there's no fuel moving when I pump the pedal.
(I had a quarter tank when it died on me.)

 

Chase,

Before we start, do you have a really good set of mechanics tools?
Testing the pressure will require a "fuel pressure gage that will fit Mercedes" or a "fuel pressure gage that you can chop-up to make work with Mercedes". since your car is pre-ufsc. This requires a bit of commitment because you will either spend a good bit of money buying the gage or a good bit of time making one, but once you have it, you can check it every month if you feel like it, and your friends cars too. Honestly, I check fuel pressure every time I do a repair because 99% of my repairs on the MBs are fuel related. Are you listening MB?

Blue

 

Blue, thanks for the suggestions.
I don't have those.
I do have some friends that I can ask around for it, but at this point I'm working without it.

-Chase

 

The trick with FI is that its really not enough to simply have "fuel pressure" it has to be within an "exact" range of pressure and volume, as Sleepwalker said.
I mean you could turn the ignition on and off three times to pressurize the system, then take a 12mm wrench and loosen one of the fuel line fiitingson top of the fuel distributor slightly, to see if fuel sprays out. Then quickly tighten it back. This would let you know if the pump is running at all, but doesn't tell you if its clogged or has 70lbs of pressure instead of 80 lbs.
I know in the good old days, "any" amount of fuel would make one go. I actually kept a motor running once on a stand for three or four minutes, that didn't even have a carburator or fuel system attached, by spraying fuel into the intake manifold with a spray bottle! But with modern fuel injection, the fuel is metered-in with medical precision, hence all the exact tolerences and precise tests.

Blue

 

I have soldiered a fuel relay switch on several cars. It works, but not for very long. Even with a good heavy bead of soldier. I'd just suggest replacing the switch. I had to do the same with my '88 300E. Except I replaced it with a 2.6L engine's relay switch. And yes, for those doubters who do no believe me, it works great. In fact, the 2.6L switch delivers more fuel, which gives me a bit more performance. I replied to another persons post in the E-series forum on here as well. I couldn't remember the name of the switch, so thanks for reminding me. I also think I said it was from a 2.8L engine. Thats wrong, its indeed from a 2.6L engine. I was the the same time of replying to that post thinking of the work I need to my '89 Chevy Cavalier z24 which has a 2.8L engine (garbage). I'm getting ready to rip out the 2.8 and drop in a bored and stroked 3.1 "stroker motor." with a turbo charger and such.

Try replacing the relay switch. Its located near the battery box. In fact if I recall, its located IN the battery box location. Its not very expensive. You can try soldiering, but in my opinion, not worth it.

 

checking the fuel pressure without the aid of tools is difficult for a newbee.

all you can do is to push down that air metering plate and feel if it got resistance or no. turn ignition on and off 3 times to build-up pressure.