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UltratechOne
UltratechOne, ASE Certified Technician
Category: Car
Satisfied Customers: 46
Experience:  General Automotive technician for 39 years. ASE certified. Shop Owner and MBA.
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Hello. I have a 1990 mercedes 190e which I recently purchased

Resolved Question:

Hello. I have a 1990 mercedes 190e which I recently purchased with 106k miles on it. It sat for a few years, and I've been trying to get it back on the road. I need a car TOMORROW, so this is now an immediate problem. I have replaced the wires and plugs, cap and rotor, fuel pump, and battery. I have filled the tank to dilute the old, bad gas (not much in there to start with). The car runs beautifully, but when it drives it has an intermitent loss of power, which happens especially when I turn right. Sometimes it fully stalls, other times the RPMs just drop and pick up again after a second or two. Either way, it doesn't lose power for long. But it happens frequently enough that it's not safe to drive. I need to know what else it can be, and what to try next. I have to try to fix it by tomorrow, so hopefully it's not a part I need to special order. Your advice will be greatly appreciated!
Submitted: 1 year ago.
Category: Car
Expert:  UltratechOne replied 1 year ago.

UltratechOne :

hello my name is XXXXX XXXXX i'll be helping you today. welcome to just answer!


 

UltratechOne :

from reading your description it sounds like you have a fuel problem.


 

UltratechOne :

how many miles have you driven the car since putting in the new gas to dilute the old that was remaining?


 

Customer:

We put about $20 to dilute the old gas (car was on E, but had some remaining) when we got the car, and drove it around the block (about a mile) a few times. Then yesterday, after the cap and rotor didn't fix it, we drove all the way to branford and back, about 5 miles each way. It's still doing it.

UltratechOne :

ok, did you also change the fuel filter? it wasn't shown on your list of things you changed.


 

Customer:

Yes, new fuel filter with the new fuel pump

Customer:

We've been trying to decide if it's a fuel or ignition problem, and now I have no idea what's next to try.

Customer:

Fuel gage is also wonky--we filled it up yesterday to be sure old gas was diluted, and it jumps around a little spastically. Probably not related, but thought I should mention it.

UltratechOne :

i still think we are looking at a fuel delivery problem. the main reason i think that is because of the bad gas. that stuff turns into turpentine and just becomes nasty after about a year or so. it will play havoc with trying to get a car to run properly. in this case i would look at the fuel pressure regulator. since it happens on and off i would guess that at the time it is exhibiting the problem you will notice low fuel pressure at the rail. this will require you install a gauge where you can see it (kind of tricky) and then driving it until it is doing its thing.


 

UltratechOne :

also, after about 50-100 miles i would again change the filter because now that bad gas was pulled through it as well and could easily plug it up in just a short time.


 

Customer:

I thought about the fuel pressure regulator, but I'm wondering why it only seems to happen when I turn right. I can turn left all day, with literally no problem. But 1 or 2 times out of 3, it happens when I turns right. Would the fuel pressure indicator cause that type of symptom?

UltratechOne :

also, in order to check to see if it is a faulty fuel regulator, you can for a short time plug off the return line to the tank or pinch it off while you observe the pressure. it should go up.


 

UltratechOne :

it certainly can since it's a mechanical device after all. and perhaps in turning right the momentum does not favor it and thus leads to your problem.


 

UltratechOne :

but really, the best way (and really the only) to verify is to hook up a pressure gauge to the rail and observe the pressure in several different circumstances.


 

Customer:

So if I get a gage and test the fuel pressure and see it drop, is it def. the fuel pressure regulator?

UltratechOne :

that is by far most likely since you have changed to pump already. you know what i would do first however is change the filter again. you are going to have to change it anyway and it just might lead to a fix. you'd be surprised how quickly that bad gas can plug things up. next, if you can do it fairly easily, i would try plugging off the return line to the tank, thereby effectively bypassing the regulator. don't drive too far like this since the pump will be providing pretty much full pressure to the injectors, but it would certainly tell you if you have a fuel pressure drop psituation if it stops doing the problem after plugging it up.


 

Customer:

My fuel pressure regulator has soft hoses, so I can clip off the return line in a few minutes and see if it's still doing it.

UltratechOne :

that's a very good way to approach it. but just remember not to drive too far that way. :)


 

Customer:

My brother has come in in the meantime while I'm chatting with you, and he says he really thinks it's an electical problem because of how suddenly the RPMs drop and how quickly it jumps back to life. It doesn't cough or anything first. He wonders if we're getting power to the fuel system. Is this another possibility?

UltratechOne :

certainly it is. if the pump is being supplied only intermittently with voltage to run, that would cause the same kind of problem. however, remember that with fuel injected cars, fuel delivery problems can seem to be very knife-edge and thus lead someone away from the true problem towards ignition or other electrical problems. the way we would diagnose it here it to first install that gauge like i described and then go drive it. this really is the only way to be sure to look at the fuel delivery system.


 

Customer:

If voltage is no longer supplied to the fuel system, it won't still show a drop in fuel pressure?

UltratechOne :

and plugging the return line or pinching it off will go a long way in telling you what the problem is. if it goes away for instance you know that it can't be an electrical problem or the pump.


 

UltratechOne :

absolutely it will. hence the gauge connected. basically what you need to do is verify fuel pressure through a variety of driving conditions: idling, accelerating, turning right, etc.


 

Customer:

Thank you for your help, Bill. I'm going to go punch off the line and drive to autozone down the street for a gage. You accept follow up questions, right?

Customer:

*pinch

UltratechOne :

absolutely, please go ahead and rate my service (highly i hope! :) and then feel free to ask any followup. just because you've paid for my answers doesn't mean we are done! i want you to have a fixed car ultimately.


 

UltratechOne :

also, when you get it fixed please let me know that too! sometimes customers will just go away and i never know if i helped them or not.


 

Customer:

Thank you Bill!

UltratechOne, ASE Certified Technician
Category: Car
Satisfied Customers: 46
Experience: General Automotive technician for 39 years. ASE certified. Shop Owner and MBA.
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