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An M120 that was shutting off on right hand turns is now refusing to start...what now
Hi Guys,
I'm usually working on my w116 as my SL has been (mostly) fault free, but I'm stumped.I hope I can get some advice as I was hoping to get a few more weeks of driving before storing it for the winter!
A week ago my 96 was shutting off on sweeping right hand turns. As soon as the car straightened out, it would turn back on itself and be fine. Then it started shutting off after a hard acceleration run, and restarting just fine. I assumed a bad fuel pump (this has a later style pump), and put one in. Before I did that however, it stopped starting altogether. I was a bit annoyed but just figured the pump was done.
Put the pump in, lowered the car down, filled the tank back up..and nothing. I know I have fuel pressure as I cracked a line up front and got a nice spray.
Here is what I have so far
-It cranks strong, no issues with the battery .
-I can hear the throttle bodies when I turn the key to position two.
-All the cluster lights stay on, not sure if thats normal as I've never really had the car fail.
-The car always started fast, and I am not thinking its the crank position sensors as they shouldn't fail all at once. I would imagine the car would have started taking longer to start, or I would at least get one bank to fire. Right now I have nothing.
-Should I check anything else? Ignition switch??
-I had no check engine lights when the car would shut off.
Guys, I have no idea where to start, but I'm willing to test anything.
My next idea is to test the crank position sensors, but I don't know where the wires lead to. I'd put an oscilloscope on the output and look for a signal...but where do I go?
I am afraid your vehicle is exhibiting the signs of failing wiring harness(es). Just like my '94 sl-600 did. I even had Star Motors MBZ in Houston do a Pre-purchase Inspection and they did change the fuel injector harness (charged some $300 for that in 1997but didnot mention the others). Slit open some black plastic wiring bundles and check for cracking and disintegration of insulation--which MUST be fixed. Far better to replace failed insulation wire sections one at a time on the car. Removing/replacing the harnesses to repair then takes lots more time, and many lenghts/sections are OK. Just splice in new aircraft quality wiring of appropriate size--either by GOOD soldering or pro quality crimp ferules.
Sounds like a wire has worn through its insulation and is now shorting out on the body.
This happened to me where my car would crank but not start.
It turned out to be a sensor in the hood on the driver's side. I followed the wires that run up the hood hinges and found the rubbed through wire.
The car had everything working, but wouldn't start unless I actually fed fuel manually past the throttle blades and then it would only run for a few seconds until the fuel was spent.
This happened after I swapped out my AC evaporator/heater stack which requires the dash and a good chunk of the underhood parts to be removed. The worn wire was a fluke and had nothing to do with the AC repair, it just happened to manifest itself just after the repair.
I had the car flat towed to a very good local independent that knew MB cars very well and downloaded the wiring diagram for the car and traced everything having to do with the ignition circuit. The worn wire was hidden in the hood. I thought it was a miracle they found it, but they are just very good tech.
I am afraid your vehicle is exhibiting the signs of failing wiring harness(es). Just like my '94 sl-600 did. I even had Star Motors MBZ in Houston do a Pre-purchase Inspection and they did change the fuel injector harness (charged some $300 for that in 1997but didnot mention the others). Slit open some black plastic wiring bundles and check for cracking and disintegration of insulation--which MUST be fixed. Far better to replace failed insulation wire sections one at a time on the car. Removing/replacing the harnesses to repair then takes lots more time, and many lenghts/sections are OK. Just splice in new aircraft quality wiring of appropriate size--either by GOOD soldering or pro quality crimp ferules.
Well...i got the car to start. I had an air bubble in the fuel pump and it took a while to prime...but the problem is still her!
The 96 has the updated wiring harness that does not wear with age. I inspected the harness when I was doing the front timing covers and saw nothing worn out.
As far as chafing on the hood hinge...im going to have to look there too.
I feel sad for you--tracing down wiring defects on these MBZ is terribly difficult and time consuming. The error MAY be coming from the ECU, The start allow system. The Run authorize system, a misbehaving switch in a door handle, the ignition authorize system etc.etc. etc. You are going to get a COMPLETE scan which checks and confirms EVERY connection.
I feel sad for you--tracing down wiring defects on these MBZ is terribly difficult and time consuming. The error MAY be coming from the ECU, The start allow system. The Run authorize system, a misbehaving switch in a door handle, the ignition authorize system etc.etc. etc. You are going to get a COMPLETE scan which checks and confirms EVERY connection.
Thats the fear!
Today I will look for vacuum leaks. I also bought a pedal position sensor as it always happens when I quickly let off the accelerator. The tach drops to zero right away, and pulsing the pedal sometimes starts the car back up. Sometimes it doesnt
09-26-2020, 12:18 AM
