Is it the fuel pump? for sure?

[austinite]

Car: 1987 300e w124 (automatic)

Problem: Starter cranks, but won't turn over.

The assumption would be it's the fuel pump. I can't afford money or time to buy and replace parts trial and error, so I'm hoping your collective expertise will help narrow down the problem.

Everytime I try to start the car the starter cranks normally. The extent I push down the accelerator is directionally proportional to the the rpms reached on the tachometer. The problem is the rpms immediately free fall to 0 and the engine doesn't turn over. It's like watching the single swing of pendulum on that tachometer.


I've done all the affordable stuff:

Replaced sparkplugs
Checked Spark
Compression test
Starter fluid test
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Spark check: My friend held one of the sparkplugs to check and got a good shock: good spark but bad boot, but would this stop the car from running?

Compression test: good, range 159psi - 178psi

Starter fluid: Had someone spray starter fluid, while I started the car. Engine ran as long as both the fluid was being sprayed and the accelerator pedal was being pushed down.
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If it means anything, the the car stopped working when I tried starting it, not while driving. I also thought I heard a small single thud coming from under the hood at the moment the problem started.

Thanks for any help,
david

PS: What is the small red wire that attaches to the battery?

[Don350SDL]

Your car has a fuel pump relay, located on the false firewall near the battery. It is a black box about the size of a pack of cigarettes, which will say "6 ZYL" on it - Not "KLIMA".

It is not unusual for this relay to fail.

The simple check is to open the driver door, put your head low near the rocker panel and switch the key to the second position (just BEFORE starting). the fuel pump will come on for 1 second (it makes a hissing sound) to pressureize the system - if it does not, the fuel pump is not operating (and that's possible because of the relay).

OK, lpull out the relay, there is a terminal number "87" which is the output to the fuel pump, and a terminal "15", which is battery power switched by ignition. Temporarily bridge these two sockets in the relay holder and try the test above again - the fuel pump will come on and stay on whenever the ignition is on.

(This is dangerous to leave this way! OK for testing though)

If the relay is at fault, then break the seal (silicone rubber) and open the relay (two small screwdrivers to pry it open), you may see a failed part of the printed circuit - bridge it with solder and wire (find someone who can solder if necessary) and that might repair it. Seal it up again! If not, buy a used or new one.

Good luck,

Don

[austinite]

Wow!

Thank you Don, for the clear and precise guidance.

I checked for the sound you suggested. I believe I heard it. I put my ear under the rocker panel with arm stretched to the key. I heard about .9 sec of a buzz that sounded similar to a small mechanical lift.

Does that mean that the fuel pump, fuel filter, and filter relay are all OK?

If so, where do I go from there?

Thank you again,
david

[lkchris]

Starter fluid: Had someone spray starter fluid, while I started the car. Engine ran as long as both the fluid was being sprayed and the accelerator pedal was being pushed down.


pretty clear sign engine not getting fuel or mixture is too rich to fire.

if your fuel pump works, then it's fuel distributor problem

You are talking about 19-year old systems

Fuel distributors are ostensibly repairable, but practically speaking they're all replaced with new ones. ~$2k I think.

My friend held one of the sparkplugs to check and got a good shock

Guess the yellow decal with the red lightning bolt originally stuck to air cleaner that says "caution, this ignition system can kill you" is now missing.

It's just totally amazing how much advice is given regarding spark plugs, etc. Fact is this system is essentially bulletproof and is almost NEVER the problem.

Lots of rubber seals in the fuel system. Plus lots of opportunity for the less knowledgeable to make things worse.

BTW, "turn over" is a term commonly used to describe turning the engine with the starter. You can. Your problem is engine won't start and run.

[cth350]

check out my reply to a similar thread just now. Eyeball your fuel pump setup and see if it's a single pump or a pair of them. If only one dies, you won't know it w/o testing pressure. -CTH

[borj]

Hi!

Just wanted to ask you guys something related on the topic if you dont mind. I just wanted to know how strong should the fuel pump be? I've been having starting problems as well. I hear the hissing sound that you guys mentioned to look for, but i feel that the pressure is not that strong. My suspect is that the fuel pump is not pumping good enough.

Is there a spec for the fuel pump as to how much fuel should it pump over a period of time? Any troubleshooting advice? Thanks :)

Enrique Borja
Manila Philippines
'88 260E w124

[austinite]

Sen~or Borja,

100 psi , is the pressure I was told. Convert for metric, possibly.

[borj]

Thank you very much David :D

[DarkHand]

Hello All! Enjoy being on the forums and a newbie in the MB world...

Also with a question...I am concerned if it is the fuel pump or the electrics on my car. I have a 94 E320. The engine has shut down repeatedly during operation. Case in point doing 65 to 70 mph and then engine shutdown with no warning, no strange grinding sound at all. Also when turning a corner or at slow speeds. This has happened intermittedly about 6 times, even twice at a stoplight.

I have checked the disgnostic block under the hood and have recived a "Code 17" which I do not know how to proceed from there. Also in the rear of the car I hear an intermittent whine (I expected this to be the fuel pump and filter but have put my hand on the components and felt no vibration). The vehicle will start after about a minute or two from shutdown but I find this disconcerting while in the middle of traffic or at speed down the highway.

Any and all advice or direction will be much appreciated.

Thanks

[lkchris]

Any and all advice or direction will be much appreciated.

Get a factory service manual.

[bill streep]

David,

Check the inside of the distributor. I had a cast metal mount for the rotor that fractured once on mine. Going down the highway at 70 and all of a sudden... nothing!