Intermittent Electircal Problem (maybe)?

[expat]

I posted this in the ENGINE section thinking I had a fuel delivery or vacuum problem. Then it struck me that possibly this is an intermittent electrical problem so I thought possibly one of you electrical gurus might help me see the light. So here's what I wrote:

I have a '94 C250 4-door diesel non-turbo (W202), automatic transmission. I think I have a fuel delivery problem, or possibly some kind of vacuum problem, and hoping you wiser MB hands can help me diagnose the problem.

I bought the car with 159k miles and now have about 175km (in the last 10 months). Initially the car ran like a top but then about 3 months ago it started having intermittent problems.

Sometimes it runs like a top, sometimes not. Sometimes the problem stays for a week and then disappears for two weeks, and sometimes it is here one day, gone the next, and back again later that afternoon.

I have not been able to find a patter to the problem's comings and goings.

To me it seems like a fuel delivery problem but I'd think the fuel pump either pumps or it doesn't. Ditto with the injector pump.

What is happening is that the car surges while driving (when not running like a top). Sometimes you start the car and it drives fine for awhile and then starts some "light" surging. Other times you press the gas pedal down and nothing happens, absolutely nothing. Then you press it again, and again, and again, and finally the engine revs and the car takes off like a rabbit, like it has found a new lower gear, and zooms along so quickly you have to back off on the accelerator (and possibly start the process over again).

Sometimes on the highway I'm doing good to make 100k-120k. A slight uphill grade brings the speed down as there is no reserve power. You may or may not be able to feel the car is surging in this situation. Other times, when everything seems to be working correctly, cruising at 120k with reserve power under foot is just as it should be. Since the car does not have cruise control I'm having to bring it back down from 130k-140k.

But then then that evening, or the next day, or the next week, the surging problem returns.

Oh, if the problem is especially bad the car won't shift easily from 1st to 2nd. It shifts out of 1st, then there is a pause as the engine revs up for a second or two, and then the transmission shifts to 2nd, the rpms drop down to normal and we continue surging along our merry way

So any suggestions -- fuel supply?, vacuum?, something else entirely?

 

[w204]

if you rev the engine idle ( In P or N position) how it revs.

 

[expat]

When the car is running good it revs like a champ.

Even when it is in the "surging mode" it revs fine. And those times when the gas pedal isn't working until about the 3rd or 4th depression it revs good then too.

 

[w204]

http://www.mbclub.co.uk/forums/engine/3480-w202-throttle-response.html

Have a look at this post

 

[grober]

http://www.mbclub.co.uk/forums/engine/3480-w202-throttle-response.html

Have a look at this post

Don't think the electronic throttle arguement applies to diesels? My guess you got a tank full of contaminated fuel [ water?] at some point. I would try a complete tank drain and flush---- possibly renew the tank outlet filter-- followed by a complete flushing of the fuel line and associated filters.

 

[expat]

I've thought about the bad fuel solution but I've run the car down to where it is just running on fumes, more than once, so I've got to think whatever that was bad in there, if it was bad fuel, has been burnt off.

Additionally since this problem started I've also run a couple of cans of Bardhal fuel injector cleaner through the system so an thinking that would have helped if I'd gotten a bad batch of fuel.

 

[expat]

Thanks for the help!!

A few months back some of you told me my fuel delivery problem was caused by a solenoid that MB calls the 'pedal value sensor'. They wanted 700Euro for it here in the Republic of Ireland. Since I didn't pay much more than that for the car I started looking around and calling junk yards and people who were parting-out old MBs of my class.

It took some looking but yesterday I got fitted with a new PVS and my total outlay, except the gas for the the 100 mile round trip, was 10 Euro (yes TEN, not a typo), and the mechanic installed it as well!

So for those unsung heroes out there in cyberspace a very big THANK YOU!