190E won't start

I could use a bit of help with the wife's 1989 190E 2.6... It died suddenly (in traffic, of course), but we were able to restart it. I got it home, but now it won't restart.
Here's what I've checked: Ignition coil: Spark tester shows an nice white spark, easily jumps 15mm Plugs: Tester shows a white spark, but not nearly as strong. Rotor and cap look mechanically sound. Fuel pump relay: I've bypassed it with a fused jumper, and the pump runs continuously. Cold start injector... Works fine, I've applied 10v DC to it and it clicks away nice and clean... Fuel pressure.. I can't give a PSI value here, but there is fuel at the distributor, so it's getting some gas at least Throttle body plate: Held it open while cranking... made very very faint "I might start" noises, but wouldn't start.....
In desperation, I've even poured a bit of gas down the throttle body, just to make sure it had fuel. Still no start. Once or twice, it makes a very feeble attempt at firing up, but no go...
What else can I check? Could it be just a very weak spark? Any and all advice gladly accepted. Thanks, Dan Cassaro
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How about your overload relay? Is the red fuse intact?
What is the resistance value of your spark plug wires?
Clean the contacts inside the distributor caps and rotors.... sand them down to brass.
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Overload relay fuse is OK Plug wires are 1K ohms Contacts nice and shiny. No start. :^(
The more I fiddle with it, the more I think it's the spark somehow. There's plenty of fuel and air, so all that's missing is the ignition of that mixture.... Dan

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Two more facts...
I disconnected the fuel return line, and jumpered the pump and measured the fuel output. I got 1.2 liters in 40sec. The service manual says 1 L per 40 sec is acceptable, so I guess this rules out a clogged fuel filter or a totally dead pump. It would seem that there's gas up to the fuel distributor. As a test, I poured about a half cup of gas into the throttle body, and it started (sort of) and ran for about 3 seconds. I'm guessing this means that it consumed the fuel I primed it with, and there was no more being supplied. Not sure what to test next....
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I'd try adjusting the fuel mixture... try 90 degree clockwise to see if engine respond better... if not, then lean it out the opposite way.
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Because the no-start seems happening suddenly, and the fuel delivery rate seems OK, I am leaning to control failure, for example, the fuel-pump (kick-down) relay or OVP (over-voltage protection) relay. The fuel pump relay provides voltage to, of course, the fuel pump, while OVP provides voltage to CIS control unit (and ABS too).
The OVP is prone to have internal failure. If yours is still the original, chances are it's dying (or dead already).
By looking in the wiring diagram, I think you may be able to test the fuel-pump relay this way:
1. Remove the relay (behind battery, saying Kickdown on top) 2. Its socket should have number on each hole. Look for 7 and 8 (their matching pins on the relay are marked 87 for 7 and 30 for 8). 3. Hole 8 is hot (12v) all the times. 7 goes to fuel pump. Jump these two holes. Now the fuel pump should run. 4. Crank the engine. Does it start? 5. If yes, either fuel pump relay is bad, or it receives no RPM input from EZL (on left fender, in front of ABS servo) 6. When cranking, look at your tach to see if there is RPM signal. If tach moves, the fuel pump relay is at fault 7. If engine did not start in step 5, CIS is at fault. I would replace OVP first. You did say there is spark so I think CIS is fine.
Dan Cassaro wrote:

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My compliments to you for this very thoughtful and reasoned response.
You must make your living diagnosing automotive electrical problems, if not, you probably could.
Happy Thanksgiving!
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Happy Thanksgiving to you too.
I just happen to have a 190D (84) and a printed electrical troubleshoot manual. Guess how I learn to do this? First is the interest (which was the main reason buying this dying 190D). Second is the necessity (it had so many problems in the beginning). Now I get to the point where the next step is to rebuild its engine (255k miles). Never done engine before. Hope it is fun.
T.G. Lambach wrote:

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I got it started! Here's what happened: The fuel pump relay (the thing I checked first!) was bad AND the OVP relay was loose. So, even when I shorted the pins to engage the pump (mentioned in an earlier post as well as below), it wouldn't start because the relay wasn't connected. The socket for the relay doesn't seem to be attached to anything, it was just floating around back there. I managed to hold it firm while seating the relay, re-jumpered the fuel pump, and it started, although with some difficulty. A few more off-then-start cycles, and it was back to normal. Thanks to all those who posted suggestions! Dan

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That's great you got it resolved.
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replying to Dan Cassaro, Rah962 wrote: My 89 300se was doing the same thing so I replaced the fuel pump and filter ,all kinds of junk came out and it seemed to take care of the problem.
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