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I'm having problems with my 88 300E. Lately if I've been driving it for a couple minutes, I get problems with the car starting to sputter and run really rough. Mainly at low speeds, but I can feel that it's not quite right at higher speeds as well. If I let the car sit for awhile, it will be running fine the next time I get in until I've driven it for a little bit. I was living with the problem fine for awhile, but eventually it cut off on me at a stop light and would not crank. It turned over just fine, but would never fire up for more than just a cough. After letting the car sit for a couple hours, it cranked fine and I drove it home. I took it to a mechanic who works on Mercedes and he didn't seem to know what the problem was. He replaced the fuel filter and did a couple other small things, but three days after I got the car back, the same thing happened again. I have noticed that the problem seems to be worse if I let the car sit all day the day before without driving it at all.

I've been pouring over threads on this site and it seems that the mostly likely causes are the OVP or the fuel pump. I do have my ABS light come on regularly, but it doesn't stay on at all times. I'm thinking about getting some used parts and just replacing the OVP and fuel pump both to see if that will fix the problem. Is there anything special to know about replacing the fuel pump? The OVP seems pretty straightforward. Also, is it worth replacing the fuel relay while I'm at it? Any help is appreciated.
 

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190E, SLK350
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67,190 Posts
80% the problem is the OVP. Replace it with a NEW one, don't even bother putting a used one that could be faulty and you will end up chasing the problem for a long time.
The OVP should simply be a maintenance item that needs to be replaced every 5 to 7 years. If your ABS light comes on, this is another indicator that the OVP is toast. Don't just replace its fuse, get a NEW OVP.
 

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190E, SLK350
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67,190 Posts
Replace the fuel relay if you're not getting gasoline to the engine. You seem to get gas but to truly test for fuel delivery, you can remove the fuel relay, bypass it by jumping the two pins that will start the fuel pump. Do that after you replace the OVP, so that you're not dealing with two combined problems.
Next, while you're at it, check your fuel pressure with a CIS tool. That would indicate if your fuel pressure regulator is working fine and if your fuel distributor is doing its job. Next, check the EHA for leaks.
 

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190E, SLK350
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For more tips go the W124 subforum on this site. The guys/gals in there are far more knowledgable and are very helpful.
 

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1987 300e (W124) - 223K miles, 1995 C280 (W202) - 250K miles Sold
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226 Posts
Mine acted like that last year. I replaced everything in the distributor with new parts. I wish I'd had the nerve to tackle the front seal while I was that close, but I didn't have a new seal to put in, so I closed everything up. up. Starts and runs fine now - but still has an oil leak. Parts didn't cost a lot, although I don't recall the total. Maybe $75 altogether? Tip: label the plug wires and distributor cap (by cylinder number) so you don't mix them up when you put it all back together. Also, it's wise to take some good photos before you start and during the job.
 

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1989 W124 260E Saloon. M103 lump.
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The pins to join up are 7+8 on the fuel pump relay this will keep the fuel pump running But remove it right after the test ..If you dont it will pump fuel even with the key in the off possition. You will find the relay by the ovp at the rear of plastic cover or shield at the back of battery .Check the fuses on the top of the OVP relay..at the same time
 

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1989 W124 260E Saloon. M103 lump.
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1,618 Posts
Any news on the problem .Not to good after you help, only to be left with not knowing if it was fixed.
 

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07 E350, 80 240D 4 speed, 90 300SE, 87 260E
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2,823 Posts
If the OVP change does not fix the trouble, I suggest investigating a possible fuel tank venting issue. I am chasing a similar problem now on my 1987 260E.
 
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