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my 1992 190e Sportline and my wife's 1993 300e
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34 Posts
Discussion Starter #1
i'm a decent mechanic. i suck at diagnostics.

daily driver in decent shape.
been slightly harder to start for a month or so - has to turn over for a couple seconds and when it catches, it staggers to life, barely enough rpms to get running for a few moments. after that, seems to be normal as far as i can tell.
only warning symptom i noticed.

driving home yesterday, stalls dead at a light.
battery fine, starter fine - it would try to start no problem.
caught 3 maybe 4 times, turned over once and then stalled again - no difference with throttle wide open.
towed home.

i can fix most any problem once it's found. i suck at the finding. help me think through:

car needs air, fuel, spark.
missing one.

where is the most basic way to check i'm getting fuel? spark? air? where start? thanks
 

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W201 Moderator
89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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2,269 Posts
Not Air - It would start easily with throttle , so rule that out
Spark - Most likely not from your symptoms, generally will have other types of symptoms like backfiring from intake etc during cranking. But you can check that with a strobe light during cranking.
Fuel - Most likely. How many years/miles on the fuel pumps. That is the fastest wear item in the fuel system followed by Fuel Pump relay.

Don't replace them, first test them. Make sure there is proper voltage at the terminals. If you can measure current draw (will need a 20-Amp meter though) measure the current draw on each)
If you are not good with electrical diagnosys, you can also measure the fuel system pressure, I'm guessing it takes some time to build up to the desired 80 psi, which is probably a sign of weak pump(s)
 

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89 190E 2.6 x2
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1,396 Posts
Dolucasi covered all the important places to check. I always start w/ the fuel pump relay since the solder joints break down.
Pull the relay and jump pins 7 and 8 which will get the fuel pumps running.
 

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Registered
my 1992 190e Sportline and my wife's 1993 300e
Joined
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34 Posts
Discussion Starter #5
thank you internet friends!

i replaced OVP sometime in the last couple years.

i replaced fuel filter and pumps a year and a half ago.

pulled battery. muscled the MAS sensor (not FPR on a '92) out - didn't realize that knob on top was the release haha.
jumpered pins 1 and 2 with a bent wire.
tossed battery back in. fuel pump whizzing away. started right up.

so assumption is bad relay in MAS unit.
 
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