190E won't start

[Dan Cassaro]

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

[Tiger]

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.

[Dan Cassaro]

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

Post by Tiger
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.

[Dan Cassaro]

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....

[Tiger]

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.

[Wan-ning Tan]

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.

Post by Dan Cassaro
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....

[T.G. Lambach]

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!

[Wan-ning Tan]

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.

Post by T.G. Lambach
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!

[Dan Cassaro]

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

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
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.

Post by Dan Cassaro
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....

[Tiger]

That's great you got it resolved.

[Rah962]

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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