Weird idle after changing fuel injection pump rings - PeachParts Mercedes-Benz Forum

invisik · #1 04-04-2006, 07:10 PM

Hey all,

Here's my long story this time! 1992 300D 2.5 Turbo, 217k.

So we were going to take it on a long weekend road trip from Mpls to Chicago and back. A small fuel leak from the injection pump appeared about a week before, but the car was running fine otherwise. So we decided to get the O-rings changed the day before we left. I was running out of time so I took it to a local MB dealer which I don't really like, but they are really close to my house. I talked with the service manager and a tech who is an old-time dieselhead and he said he'd bring in the spline socket to change it out tomorrow.

So I left the car with them, and picked it up the next day, work completed. The IP was dry as a bone (and still is to this day) but the idle was a bit funny, almost like it was missing on one cylinder. I thought there might be some dirt stuck in the lines, so I gave it an italian tune up on the way to a quick appointment. Power and acceleration was good. Still idling funny.

So I took it back and talked with the tech. He said that either the IP pump timing (and thus the engine timing, he said the IP was driven by the main timing chain so if the engine timing was off the IP timing would be off) or else my injector(s) were dirty/clogged.

I said ok, and we went to Chicago and came back without incident (and without a new car, which was part of the trip, doh!). 36mpg, best economy ever in that car.

So now I've driven it for a couple of weeks and it's been exactally the same, funny idle, good power, 28-30mpg aroud town.

I decided to purge it, as that should really clean out any gunk in the system, so I did that this afternoon. The engine is quieter (as usual when purging) but still idle's weird.

The IP is dry, no leaks. The metal fuel hoses coming off the top of it and to the injectors are straight, not twisted or anything. No fuel leakage at the injectors. Idle is good at aobut 750rpm. Car never dies or hesitates. Idle was smooth (relatively for a diesel) with a good rythmn before the service was done.

Fuel filters are pretty new, but I want to change at least the inline since I purged. Will do that this week sometime.

How do you recommend I proceed from here? Any testing I can do on my own that can help narrow down the problem? I don't want to bring it back to this same dealer for "general diagnosis" as I don't really want to bring the car to them at all. It's my fault for bringing it there in the hurry in the first place, I admit that.

Thanks for any help...........

-m

Hatterasguy · #2 04-04-2006, 07:20 PM

I assume your are talking about the delivery valves O rings? When doing this job it is possible that it will be botched. Either they were not torqued properly or didn't seat properly it happens.

If it were my car I would re do that job and see if the problem goes away.

Also it maybe a good idea to remove the injectors for testing.

If that engine is anything like my 603 you need an the RIV tool to check IP timing. But with the tool this is a very quick procedure. If the dealer thinks its timing then have them check it, at their expense. Although timing would not be affected by changing delivery valve seals. I don't see what checking timing will prove.

psfred · #3 04-04-2006, 09:53 PM

Leaking pressure valve holder copper seal on one or more elements.

Take it back and have them re-torque the pressure valve holders (i.e. repeat the job and do it right this time).

Timing is not an issue, it's not touched when replacing a pressure valve holder o-ring.

Your good milage is a result of not injecting as much fuel in one or two cylinders as in the others -- causes rough idle and sometimes rather nasty injector knock.

We replaced them on my brother's SDL last week hoping to cure a rough idle. It helped, but I think it's really injector nozzle time.

Peter

dieseldiehard · #4 04-05-2006, 02:25 AM

Peter, is it possible to have a loss of pressure but no fuel coming out of the delivery ports (valve holders)? As invisik said, there is no fuel leaking on his IP.
The reason I ask, I have been having a nailing type of noise, its in cyl 5 as determined by loosening the lines at the Injectors but I have no leaks anywhere. At least nothing visible at all, not even a film of fuel anywhere.
And I swapped injectors around with no change. I was about to think its my IP, but if you say it is possible that a leak can occur to drop pressure, why doesn't some fuel leak out?

I would still agree that he should take the car back to the dealer and have them retorque the ports to the procedure that I use 30 NM then loosen, then back to 30, again loosen the third time go to 35 NM and its done. Right?

barry123400 · #5 04-05-2006, 10:27 AM

First I would do the retorquing thing first. If no improvement then a volume flow test from each injector into a calibrated container to establish if injector flow is about equal from each injector over the same time period. If accumulated volume over time works out the same for each injector than it gets interesting. The mechanic did nothing to effect pump to engine timing so I would forget that test for now.

dieseldiehard · #6 04-05-2006, 06:12 PM

I've seen the volumetric flow test done at the Bosch service center, they lash the IP up to basically an engine lathe. It uses pipettes for individual ports, tiny pipes carrying the fuel (after purging air) and they read the RPM accurately and run for a specified time, all spelled out in some Bosch publication. Can one do this on the engine? I never thought of trying it but it would be easier (and cheaper) than yanking the IP and carrying it to the Bosch repair shop.
Incidentally the Bosch man (Gus) tells me that a nailing is from too much fuel. Or an open injector nozzle.