GB300E

Hey guys,

So I went out to my 1987 300E on Tuesday after a big rain the day before and the old girl refused to fire over. I tried and tried, but to no avail. I did the pumping the pedal 3 times thing, and I tried letting it sit in the sun all day yesterday to hopefully dry out the moisture from the rain - still no good.

Can anyone provide me with some assistance? I would like to know where to start on this as I have limited time before I need it operational again.

Cheers

RBYCC

First thing to do is to check the fuse(s) on top of the over voltage protection relay.
It's located behind a panel in to the rear of the battery.
You'll recognize it by the red top with a clear plastic lid covering the fuse(s).
Original relays had one fuse, subsequent replacement relays have two fuses.

GB300E

It's definitely a one-fuse relay, so pull the fuse and check for breakage?

I was looking through the haynes manual and it said spark-plugs were the #1 contributor. Mine are definitely old, and the usual stumble at idle and poor performance at low RPM were both present. As a fairly cheap solution, replace if the fuse is found to be good?

GB300E

Just took a look at it, and the fuse on the relay is intact, next option?

dall89115a

You might try pulling the distributer cap and drying the insides and rotor. Moisture can collect under any cap and cause shorting problems.

Also pull the plug and coil wires from the cap dry them and reseat them. (one by one to avoid any oops later from putting them back wrong, as I've done on more than one occasion.)

If you can watch under the hood in the dark as someone else cranks the engine, watch for any sparks from cracked plug wires.

If you have a timing light available, connect it to see if the coil is actually working and giving good spark. (This can also be done by pulling a plug wire from a plug, sticking a small screw driver in the plug end of the cable and holding the exposed metal of the screw driver close to grounded metal to see if a spark arcs to ground. Be careful doing this as it is easy to get burned if you become the ground point!)

The last idea I have is to listen for air being sucked in around the injectors. (while some one else cranks the engine over) The rubber injector seals and heat spacers are a well know 300 series weak spot.

Argus Panoptes

All these other suggestions are great. Once you rule them out, try the crank position sennsor. Almost the exact same situation happened to me after I got done with the water pump.

GB300E

Found this helpful bit of advice:
http://www.peachparts.com/shopforum/tech-help/194878-91-300e-problems-because-rain.html

So I'm going to WD the coil and see what happens. I pulled off the cap and rotor yesterday, no sign if moisture at all, very dry and no white halo on the rotor either.

Plutoe

Are you getting spark to the plugs!!!

GB300E

Yeah, getting spark at the plugs.
My mechanic buddy took a look at it and ended up having to rewire the fuel pump - using my A/C and windows fuses. The car starts and runs perfectly normal

Any ideas why this would have been (caused by rain)?

BlackStar Stig

You mean you had to jump the fuel pump to make it run? Then I would guess the fuelpump-relay is the problem. A black relay about size of a 20 pack of sigarettes located behind the relay with the fuses ontop.. These relays can fail due to moist combined with age.

GB300E

No,

Here's what I was told happened - when the key was turned, no fuel pump sound. Wire to the fuel pump had shorted, so he ran a new one. Now the fuel pump is wired in with the starter so that when the key is turned to "on" the fuel pump too is "on".

Bought a couple of fuses from MB yesterday to replace the ones' he swapped out - got my windows back now, haha.

GB300E

Update for all of you spark-plug lovers

I ordered a set of NGK BP5EFS (3712) from UK and they came in yesterday - so I went out to install them and pulled the old plugs. Guess what?

Freaking NGK TR5 Vpowers with.... resistors.
(http://www.sparkplugauto.com/ngk/v-p...park-plug.html)
Check out all the carbon buildup on these suckers from the poor burning:



New Plugs ftw!


Here's hoping for some noticeable improvement! Will update when I take it out to drive. I'm expecting better idle, better low-end and top-end response. Thanks RBYCC for the helpful info you've disseminated throughout this website!

GB300E

Impressions:

Man this thing is SMOOOOOOOTH!!
Spins up much nicer, no hesitation like before, and butter smooth idle.
Love it