Help, car dies while driving
 

I've been searching for the same problem but didn't see any. So any help is appreciated.

Cars been running fine, had hard brake problem but fix it. Then soon after that, while I'm driving, it will lose it's oil pressure then die out on the street. It's been happening more often now. Call the shop and they mention it's probably due to vaccum regulator needs to be replaced.

Any ideas that might be correct? Only dealers carry the part and the 3 closest dealer don't have it in stock. Would love to be able to know that's the problem before replacing it.

Thank you.

Michelle

Model and year?

while driving or while slowing down?

the car is a 86 420 sel. I also want to add that when I start the car at temperture below 80 the fuse for the ac unit blows. The engines dies on the road most of the time at night or the day when radio or ac is on. I drove it tonight with both off and had no problems. Since this problem has started the rpms are very low even at 65 mph. Engine will die at any speed. Any ideas of what could be the problem or problems.

My first thought was to wonder how anyone could diagnose a faulty vacuum regulator (whatever that is) over the phone, but I guess its only slightly less bizarre than trying to figure this out over the internet. anyway, even though I have absolutely no familiarity with the 420SEL and you're not giving much away but I'd suggest you start with some logical assumptions to try and get on the right track.

Is this engine temperature or outdoors temp? I'm guessing its engine temp, so what you're saying is when you start the car cold, presumably with the AC on, the fuse blows. What happens then? you change the fuse? will the car start anyway?

Since you're having problems with the AC fuse, try driving with the AC off and radio on and see if that has any effect. I think its unlikely the radio's going to have anything to do with this. You can at least rule it out.

Now we might be getting somewhere. Are you saying the engine has lost power? Does it go as fast as it used to? How is the acceleration away from a stop? Does the engine pull smoothly like it used to?

How does it die? Cough and splutter or completely cuts out? the former would suggest a fuel problem, the latter an electrical fault. If it completely cuts out, what happens with the cars electrics? Do the lights go off? Do the dash warning lights come on? Can you start the car immediately or wait for it to cool down?

I think the first thing you have to do is decide if this is an electrical issue - the engine isn't getting spark in one form or other - or mechanical/combustion, in that it isn't getting fuel. However, depending on the fuel system used on your engine, it could be a combination of both.

If its electrical, it could be a bad connection in the ignition circuit. It could be related to the fuel pump relay and AC circuit but you'd need help from someone more familiar with your model of car for that. I'm not sure which components are used on that model.

Decide if the cutting out is related to engine/car temp. If it only happens when the car is hot, this would suggest a connection is breaking down due to heat, either in a resistor or coil. If it happens whether the car is hot or cold, this would suggest an intermittent component failure, like a relay or wiring.

How long have you had this car? Who normally services it? If its a bad cable or relay, you may need to get your hands dirty trying to replicate the problem in the driveway.

Hope this helps.

The problem with the ac fuse is whenever I start the car when the engine temp is below 80. AC is "not" on, just when the car crank over the ac fuse will blow. If I let the car sit for a while then it will blow the fuse also if it's in there. I just switch the fuse out after the temp is up over 80 then the ac runs fine.

By the way, it's the vaccum modulator. Not regulator. The reason several person mention that is because they said they had a replace quit a few on this body style of mecedes before. With similar symtons.

Car drives normal, except when it dies (or shut off). It felt like it has the kill switch in there. Oil pressure drops and all the lights came on. It's getting harder and harder to restart the car once it dies. I will probably wait about 2-3 minutes and the car will start up normal again. When the problem first occur I can start it back up again right after.

I've had this car for 5 month now. The ac probably occur 2-3 month ago. The previous owner took pretty good care of it.

Michelle

Fuel issues maybe? Like a fuel filter gunked up and/or fuel pump going south?

The thing with the A/C fuse is weird. Is there any foreign wiring in there? (besides the German - I mean, wiring that somebody other than the factory installed)

Does the stalling happen at anytime, or do you get to drive it for 10 or 20 minutes before it dies? When it does die, can you hear the fuel pump hissing when you try to restart?

Keep giving us feedback....eventually somebody will figure it out!

I'm not too sure if the fuse problem is related to this issue. It's more annoying than anything else. I don't know if the wire has been done by someone else.

Car dies anytime, totally unpredictable. I don't hear the fuel pump hissing when I try to restart.

This is driving me nuts. I just want to pin point the problem to see if we could fix it or if it's a lost cause.

Michelle

Well....the fact that you don't hear the pump hissing when you try to restart, makes me think the pump isn't working - which makes me wonder if there is a relay that has mind of its own, or even simpler than that, a loose connection, that with the right bump in the road, looses contact.

I dont have shop manual for this car so I am not sure where the fuel pump or relay is located. Is it in the back by the gas tank or up by the engine.

I also talked to a shop and they thought it might be the 02 sensor, but I have no check light on. Very confused.

Car was find yesterday until about 4:30 then died at about 8 times, each time harder to restart. I not sure I might have been little hard on the battery.
I want to add, dont know if this will help, but since this problem started I have a loss in power. I cant red line the car, even at 80 mph ( foot on the floor) still only 4000 rpms then drops quickly. Could this be fuel problem or electrical?