Intermittent Rough Idle When Engine Hot - Page 2 - PeachParts Mercedes-Benz Forum

snookwhaler · #16 11-15-2009, 08:15 PM

Quote:

Originally Posted by brainlair

This is solid gold, I've had this precise problem with my car ever since I obtained it a year ago. It also sounds like I took the same backwards journey many of you did, starting with purchasing a gold rack dampener bolt only to find that it didn't help.

Diesel911 and snookwhaler, I was hoping make sure I understand exactly which lines you replaced. Both of you are talking about the two opaque black fuel line segments connecting to barbs and held on with hose clamps (compatible with 5/16" hose) that go between the hard line and pre-filter, then from the pre-filter to the lift pump, correct?

I'm wondering whether you two just replaced these opaque ~5/16" lines, or did you ALSO replace the fuel tank to hard line hose, and the three transparent (at least they were originally) lines that connect to banjo bolts:
1) lift pump to fuel filter
2) fuel filter to injection pump
3) (can't remember precisely) injector return line to fitting on filter housing, leads to cigar hose?

I really hope this does the trick, and am quite excited at the prospect of a calm engine. Thanks a lot!

Brian,

In my case the problem was the rubber hose going from the pre-filter to the lift pump. At some point someone (moron) replaced the factory hose clamps with cheap stainless clamps. These clamps did not clamp the line properly. Using the proper clamps and the correct hose fixed the problem. BUT..... I went wayyy beyond that and replaced just about every hose that has to do with fuel "except" the clear lines that run to and from the injection pump and secondary filter (as you mentioned). I did this because I run B99 from time to time and did not want any more problems with fuel leaks. This includes the lines up under the car near the fuel tank. I replaced those when I pulled the tank screen.

Depending on the mileage. I would recommend replacing the rack dampner pin too at some point (as mentioned above). But, only after the simple/obvious things have been eliminated. When I replaced the rack dampner pin, the tip of the pin (on the old one) was worn down considerably compared to the new one. FYI...The car runs the same with either pin (gold or silver) now that the air leak is fixed.

I also totally agree with what jt20 said about fuel pressure. I'm not really sure how critical it is with the MB. But, we put some miles on this car and it is easy to tell when it is time to change a fuel filter. The car turns into a dog and it just does not run the same. I have never owned a car or truck that was so sensitive to this (I have owned several diesel cars and trucks).

You should check out the "Delivery Valve" thread too (the long one). A good read. Lots of info.

Diesel911 · #17 11-15-2009, 08:42 PM

The Hose I replace were the 2 pieces that attach to the Plastic Primary Filter.

The other hare plastic Fuel Lines are all under pressure so they cannot cause a Vacuum Leak.

The Overflow Valve is the one that controls the Fuel Injection Pump Fuel Supply Pressuer; You have one Delivery Valve (I cannot remember the Mercedes name for the valve) per each Cylinder and they are part of the Fuel Injection part of the Fuel Injection Pump.

snookwhaler · #18 11-15-2009, 08:59 PM

Quote:

Originally Posted by Diesel911

The Hose I replace were the 2 pieces that attach to the Plastic Primary Filter.

The other hare plastic Fuel Lines are all under pressure so they cannot cause a Vacuum Leak.

The Overflow Valve is the one that controls the Fuel Injection Pump Fuel Supply Pressuer; You have one Delivery Valve (I cannot remember the Mercedes name for the valve) per each Cylinder and they are part of the Fuel Injection part of the Fuel Injection Pump.

Correct... Those 2 pieces of hose fixed the shake for me too.

I have not read this particular thread in a while. It is the "fuel pressure relief valve". Sorry for the confusion (funny that someone tagged the link delivery=valve). I forgot what the damn thing was called. On the 85's it is not adjustable as the spring is captive. I pulled mine and checked.

I pulled this component too. I was sure it was something major. 2 pieces of hose and 4 clamps fixed the problem.

Fuel pressure relief valve adjustment

brainlair · #19 11-15-2009, 09:07 PM

Thanks for the quick replies you guys. I also just remembered something that might be a clue. As long as I've had the car, there's always been a visible air bubble in the pre-filter. Is this normal, or does it indicate a leak like the one you two describe? The other possibility that comes to mind is that I didn't properly 'burp' it when I installed the pre-filter. I suppose I'll find out soon... i'm going to get some replacement hose tomorrow, and if the bubble and hot idle shake both go away, then we might have our hands on an easy way for someone to tell if their hoses are leaking.

I'm happy to hear that neither of you messed with the harder plastic lines that connect to banjo bolts- that moves it down my list of possible causes

. If it the problem doesn't go away after I replace the pre-filter hoses, my next step is to replace the two hoses that connect the gas tank to the hard lines. And if THAT doesn't work, I'll check how much pressure the lift pump is giving the IP. If the pressure was low, then I'd re-check that spring and replace my fuel filters, but I currently think they're OK because I replaced them ~15K miles ago. Normally they're good for ~30K, right?

Snookwhaler, do mean the thread entitled "Fuel pressure relief valve adjustment"? I've read part of it, but didn't make it all the way through. I read enough to see that I should check the spring on my relief valve, and I stretched it back to spec. But hey, the only way to be sure is to just measure the pressure, so as I said, if replacing the lines doesn't work that's my next step.

snookwhaler · #20 11-15-2009, 09:12 PM

Quote:

Originally Posted by brainlair

Thanks for the quick replies you guys. I also just remembered something that might be a clue. As long as I've had the car, there's always been a visible air bubble in the pre-filter. Is this normal, or does it indicate a leak like the one you two describe? The other possibility that comes to mind is that I didn't properly 'burp' it when I installed the pre-filter. I suppose I'll find out soon... i'm going to get some replacement hose tomorrow, and if the bubble and hot idle shake both go away, then we might have our hands on an easy way for someone to tell if their hoses are leaking.

I'm happy to hear that neither of you messed with the harder plastic lines that connect to banjo bolts- that moves it down my list of possible causes

. If it the problem doesn't go away after I replace the pre-filter hoses, my next step is to replace the two hoses that connect the gas tank to the hard lines. And if THAT doesn't work, I'll check how much pressure the lift pump is giving the IP. If the pressure was low, then I'd re-check that spring and replace my fuel filters, but I currently think they're OK because I replaced them ~15K miles ago. Normally they're good for ~30K, right?

Snookwhaler, do mean the thread entitled "Fuel pressure relief valve adjustment"? I've read part of it, but didn't make it all the way through. I read enough to see that I should check the spring on my relief valve, and I stretched it back to spec. But hey, the only way to be sure is to just measure the pressure, so as I said, if replacing the lines doesn't work that's my next step.

Sounds like you are "on track". The bubble in the pre filter is normal.

I just changed my secondary filter today. It barely made it 14,000 miles. I could feel a difference when I replaced it. I run a lot of different fuel though. I change the primary every oil change or if I suspect somethings amiss (they are cheap).

Do you have the old or new style primer pump?

brainlair · #21 11-15-2009, 09:13 PM

Quote:

Originally Posted by snookwhaler

I have not read this particular thread in a while. It is the "fuel pressure relief valve". Sorry for the confusion (funny that someone tagged the link delivery=valve). I forgot what the damn thing was called. On the 85's it is not adjustable as the spring is captive. I pulled mine and checked.

I pulled this component too. I was sure it was something major. 2 pieces of hose and 4 clamps fixed the problem.

Fuel pressure relief valve adjustment

I guess that's a 'yes', I was writing my reply when you posted. I seem to remember that when that thread was started, it had a different title, but then the admins changed it to reflect the proper name of the part being discussed. I think you might just be remembering the original title!

Twenty1+1 · #22 11-16-2009, 09:23 PM

Ok, sweet... some other people are having the same prob I am... but ya I went out and got the Gold Rack damper bolt first too... got it pretty cheap tho, only $62.50 off ebay. But that didnt help at all... So I'm really new to Mercedes AND diesels... But what fuel lines are you guys talking about? Is there a diagram somwhere that shows what hoses are what? (Also I have a lovecraft biofuels thingy installed by previous owner.) I dunno if that affects stuff? (aside from heating the diesel b4 the injection pump...

JHZR2 · #23 12-10-2011, 02:48 AM

So if Im reading this right, the only place where an air leak can occur is the line that is on either side of the little plastic prefilter?

So no reason to think about changing the transparent hard plastic lines?

My car (82) has been apart for a while because Im doing door seals and havent had a lot of time... but I want to address this and fix it once and for all. I replaced the lines by the prefilter before, but perhaps Ill just do it again... Ive stretched the spring and messed with the RD bolt and all the other tricks...