Miss at Idle - Page 2 - PeachParts Mercedes-Benz Forum

sailor15015 · #16 08-07-2006, 11:15 PM

rrgrassi,

How is your shaking problem coming along? When hunting down fuel leaks, don't forget that short piece of hose that goes between the primary fuel fitler and the lift pump (the thing the primer pump is bolted to). Its about an inch long and it gets pulled over so it has a bend in it from the weight of the primary fuel filter. I had this hose start to let air in at idle but leave no visible leak. Plus it didn't let enough air in to cause problems at cruising speed so it ran fine down the road.

Blevinsax · #17 08-08-2006, 02:25 AM

Hey thanks for the VERY helpful tips guys...

So I've been thinking - I'm putting my 350SD in the shop this week for the GreaseCar installation (sorry, I wish I could do everything myself, but I'm a professional saxophone player - you can hear my music on my website at www.RustyBlevins.com - so I cannot risk wrecking my hands/fingers, so the installs and repairs, etc. have to be done by a pro!) and I'm thinking of asking my repair tech to replace the original fuel lines all the way through the car from the tank forward. Is that overkill? I'm convinced that my rough idle problem is somewhere in the fuel delivery because the car starts and runs BEAUTIFULLY in the morning and it only acts up intermittently with the rough idle. I'm also thinking of asking him to run a Diesel Purge, too - sounds like that is a great thing for a diesel with lots of miles on it.

Thanks again for all the helpful info - and please keep it coming! I love to read about your experiences!

sailor15015 · #18 08-08-2006, 02:46 AM

Replacing all the rubber fuel lines is not overkill. In fact, its regular maintenance, I believe.

Blevinsax · #19 08-08-2006, 02:53 AM

Perfect!!! Now I won't feel like a complete rookie when I ask him to replace all the fuel lines! Thanks!

DieselAddict · #20 08-08-2006, 02:19 PM

Have you replaced the fuel filters recently? Your problem could be caused by a plugged up fuel filter or the screen in the tank. If you have very dark fuel in the prefilter, there's a good chance the tank screen or the spin-on filter is filthy and causing the engine to starve at idle. To see if it's the tank screen causing the problem, take a look at your prefilter (I assume you have the transparent one) when the car is idling poorly and see if there's enough fuel getting to it.

Blevinsax · #21 08-08-2006, 10:59 PM

I checked the inline filter and it looks pretty clear, but it had a pretty big bubble in it - probably 20% of the filter was full of air - althought I had not started the car overnight. Is that normal?

I am also suspicious of the main fuel filter because some one (idiot) before me painted some of the engine silver and the nuts that hold the top of the fuel filter on are still painted, so obvoisuly they have not been removed in a while - I bet when it comes out it will be filthy! I sort of hope so because maybe that will be the root of my rough idle problem!

Here's another question - let's say, hypothetically, that I decided to try to replace that fuel filter myself (remember, I'm a professional musician and I need my hands and all my fingers working 100% all the time - I don't mean to be a wimp, but I've lost money before 'cause I hurt my hands!) What is involved in priming the fuel line on the 350SD? Is there a primer pump? I have replaced the filter on our GreaseCar kit and it wasn't too much trouble, but it also has the purge funtion that eliminates any air bubble, etc. Any advice???

Blevinsax · #22 08-09-2006, 12:49 AM

Okay, I just checked under the hood again after driving the car a bit this evening and there is still a pretty sizable bubble in the inline pre-filter. Is this normal? Fuel still looks pretty clean and clear, though.

It drove pretty darn nice today - only acted up a little bit with the rough idle, certainly not as bad as it has been before - seems to like the B20 I put in it! Hopefully it will be even more fond of 100% WVO when the GreaseCar is intalled later this week!

DieselAddict · #23 08-09-2006, 02:24 PM

How much fuel is in your tank? If the bubble gets smaller with a full tank, then it's definitely the tank screen that's plugged up. In that case some StarTron added to the tank may clean it up (and fill up the spin-on filter with gunk) but you might still have to remove the tank screen and clean it manually.

Mercedes discontinued installing the hand pumps with the introduction of the OM603. You just use the starter to prime the system. However when replacing the spin-on filter and to avoid putting unnecessary wear and tear on the starter it is advisable to prefill the filter with clean fuel or draw fuel through the filter first by using a hand-held vacuum pump.

You should be able to replace the fuel filter yourself. Do wear gloves though, and I'd say that even if you weren't a musician.

Blevinsax · #24 08-09-2006, 02:27 PM

Right now my tank is a little under half full. Does that bubble sound right?

Thanks for the priming tip - I'll remember that! Good info! Thanks!

DieselAddict · #25 08-09-2006, 02:30 PM

Well just watch the bubble as the amount of fuel in the tank goes down. If the bubble slowly gets bigger, then you know what that means. Take a look at my post above one more time if you haven't already done so because I just added some info...

rrgrassi · #26 08-09-2006, 03:32 PM

Ok, I replaced the primer pump, and I did remove some air at the 2ndary filter. I havenot had a chance to replace mounts and shocks yet. I did break open the fuel lines at each injector, and each time, engine developed a miss, so I think I can rule out the injectors.

I really do need to replace the shocks and mounts, cause I can shake the engine side to side pretty easily, and there is an audible pop, as the engine shakes to a stop at shutdown.

#27 08-09-2006, 04:45 PM

You are well advised to get to a session with Diesel Purge. For the most part, at least so long as there is nothing broke, a smooth idle cold that becomes a rough idle hot is caused by a dirty injector.
The bad mounts don' t help the rough idle at all either, nor would an air leak. From what I have seen the bubble you mention is not the problem. Most of these diesels have the same bubble most of the time. If it were sucking air you would see a stream of small bubbles there at idle.

rrgrassi · #28 08-09-2006, 04:53 PM

My pre filter looks good, no darkening. The bubble remains a constant size at idle, fast idle or faster. I was hoping to eliminate the injectors due to cost.

#29 08-09-2006, 05:17 PM

A can of diesel purge will cost you around ten bucks. Well worth the money, get into the habit of running it through the fuel injectors once a year.
If you can find a Perfomance Parts catalogue they have a simple diagram to hook it up. Not hard to do, you disconnect the incoming fuel line from the pre filter and put a bolt in there to plug it. Then attach a fuel line at least 18" long to it.
Then disconnect the fuel return line from the big filter to the return fuel line that goes back into the tank. Put another 18" fuel line there and get a medium size glass jar and put the fuel feed line into the bottom to pull fuel out and the return line into the top to pump the unused fuel back in.
Then fill it with diesel purge and start the car, let it idle and run up the rpms every so often until the diesel purge is gone.
Then rehook the lines and enjoy the improved fuel delivery you will get.
Should find it here:
http://www.************************/productpage.aspx?pid=103893&name=Lubro+Moly+Diesel+Purge