103 hard start fixed!! - PeachParts Mercedes-Benz Forum

duxthe1 · #1 11-13-2008, 07:44 PM

Finally, I've fixed the hard starting in my 90 300TE 4-M, 237k mi. Ever since I bought it a few months back it has been an absolute bear to get started except when stone cold. Once warm it would take anywhere between 10 and 20 seconds of cranking with the pedal on the floor to get running. I had it in the shop to change the oil today and decided to beat my head against it a little more to try and figure it out. With the key on, engine off, and fuel pumps bridged to run, I noticed that the injectors were delivering a fair bit of fuel. Knowing that it shouldn't be doing that I checked a bit further and found the air flow sensor plate just a tad off center and catching the bottom of the air horn instead of returning to the "0" position. I loosened the screw that holds the plate and centered it in the air horn. It now comes up into the air horn about 6-8mm further than before the adjustment. Having addressed everything else that could cause a starting problem previously, it now starts easily within just a couple of revolutions from the starter.

Typically the air flow sensor plate never needs adjustment. Mine was out because someone had previously messed with it when they had no business doing so. Given that the car has near 1/4 million miles my mindset was to find something that had worn out or broken, not find somebody else's screw up.

There are plenty of other things that can cause a hard start in the 103 engine. If you're having problems only when warm/hot it is worth it to check that the air flow sensor plate doesn't bind in the air horn. Especially since the fix is free.

mak · #2 11-13-2008, 08:23 PM

Thanks for sharing the fault rectification . the 103 engine normally causes difficult hot starting when the fuel accumalator located near the fuel pump goes bad . replacing brings a instant cure to hard starts.

In the archives it mentions not to use any resisitor type of plugs in the 103 engine. the resistance is in the leads and another addition of resistor plugs cuses idiling problems.

mak

duxthe1 · #3 11-14-2008, 11:15 AM

Yeah, I had a bad accumulator. Imagine my disappointment when replacing it didn't help one iota

lkchris · #4 11-14-2008, 11:31 AM

A very common cause of hard hot starting on these engines is leaking fuel injectors. You're trying, then, to start a flooded engine.

Not so surprising, really, that they might be worn out in 20 years.

duxthe1 · #5 11-14-2008, 08:54 PM

The air flow plate hanging up on the air horn was acting a lot like leaky injectors. The previous owner had installed new injectors, which I pulled and bench tested and cleaned. Didn't really help. It also had a new fuel pressure regulator which was replaced b/c of a mis-diagnosed failed accumulator. I replaced the fuel distributor, idle air valve, and CIS ecu as well as the MAS unit with my spares, nothing helped. I checked the compression, which wasn't stellar on a 230k engine but not bad enough to cause real problems. I also checked the cam timing which looked fine. Went through the ignition system too, alas no avail. I did find a piece of a paper shop towel in one of the injector nozzle holders. I was hopeful that the other holders would have trash too but after pulling all and checking only the one was clogged with debris. I was at my wits end and was getting close to just accepting my poor starting fate. Needless to say once fixed I was walking around the shop beaming with pride for the rest of the day.