78 300 harder and harder to start - PeachParts Mercedes-Benz Forum

Cannon · #1 05-12-2002, 10:56 AM

After replacing my battery and glow plugs, my 300D has been harder to start than ever. The only way it starts now is with a battery cable boost and allowing the glow plugw to stay on 60+ seconds. Any cures?

stevebfl · #2 05-12-2002, 12:09 PM

The logical response to your problem as stated is that you did something wrong installing the battery and glow plugs. That is the only conclusion to be drawn from the evidence submitted.

Are we dealing with a problem spinning the motor or does it go beyond that?

Cannon · #3 05-12-2002, 02:55 PM

The battery was installed last week at Western Auto. I installed the glow plugs the next day. When I turn on the key, the wire looms that connect the glow plugs get red hot, and even then the motor won't start. the battery turns over fast enough I believe, but the engine just kind of coughs every revolution until I jump start it.

Cannon · #4 05-12-2002, 09:52 PM

After warming up the engine, the car will start after about 5 seconds of cranking. This will occur even after three or four hours of sitting around cooling off. Is it valves? They haven't been adjusted in 6,000 miles.

MikeTangas · #5 05-13-2002, 12:40 AM

"When I turn on the key, the wire looms that connect the glow plugs get red hot,"

Something doesn't sound right. The wires shouldn't be getting red hot, or at least I don't think they should. Are you sure they are all wired in correctly?

tcane · #6 05-13-2002, 11:43 AM

It's normal for the wire loop resistors connecting the glow plugs to glow red (this can more easily be seen at night). The early 300D's have the "loop" style glow plugs and the connecting wire loops are part of the circuit. The later 300D's have the "pencil" type glow plugs that have individual wires running to each glow plug. The wires running to the pencil type GP are large diameter wire to handle the current flow.

Check list for hard starting problems:

battery (a new battery must be charged up before using since it has been sitting on a shelf for who knows how long);
charging system not working;
starter turning too slow;
glow plugs not working:
fuel system flow impaired (change fuel filters, clogged fuel line, algae in system, etc.);
fuel pump pressure low;
fuel pump check valves and/or springs failing;
bad fuel;
air leaks in fuel system;
water in fuel system;
wrong oil viscosity (too high like a straight 40W);
restricted air intake flow (badly clogged air filter);
injection pump return fuel line check valve spring collapsed (take out and stretch to ~ 25mm);
injector nozzles failing;
injection pump start of delivery is out of spec;
valve adjustment needed (low compression if too tight);
low compression.

Good Luck!
Tom