Q: Car running sluggish then dies - 1988 Mercedes-Benz 420SEL

asked by on September 07, 2016

My car has been running extremely slow lately. It hasn’t had much power. It idles very well most of the time. Sometimes it idles high from 200 – 900, and it doesn’t stall while driving. But when I accelerate, it clatters, and it doesn’t go higher than 2550 rmps. I finally got it up to 4500 rmps today driving around the block but it was very sluggish on the way home. The car wouldn’t drive over 30 mph at the most and wouldn’t go over 2 mph on the last leg of the block.

It shook and died into the driveway. It seems like it’s not getting enough fuel or maybe too much, but I’m not sure. I have put in new plugs, wires, caps, rotors, coil pack. I pulled the fuel injectors and cleaned them with an ultrasonic cleaner. I put in new injector sleeves, o-rings, new injector air distribution hoses. I replaced some vacuum lines that didn’t look right and brittle hose connectors.

The fuel regulator checks are working with no fuel leaks even when running for long periods of time. I pulled out the fuel pump relay and OVP relay. I found hairline cracks in solder components on the motherboards, so I soldered over all the solder points. I replaced the OVP fuses which take 2. The idle air motor works and hums normally. The fuel pumps hum and work normally. But there was a little improvement after doing all of this. Could it be the fuel distributor? Do you know and have any ideas? Thank you.

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Hello. I would check the fuel filter first. If the filter is clogged then this will occur. If the fuel filter is fine then the air flow meter needs to be checked. This is the most common part to fail on this vehicle. Though there are other parts that can cause this these are by far the most common. If you need to have this repaired, consider YourMechanic, as a certified mechanic can come to your home or office to diagnose your vehicle and repair this.

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