Why do I have to warm up even in summer? - PeachParts Mercedes-Benz Forum

Bill()C · #1 07-10-2008, 01:31 PM

87 300SDL

This winter I was highly annoyed at my Benz for taking soooo long to warm up to a smooth idle, took it into the shop even, which was a waste of $600 and no resolution.

Basically by Summer I figured this would be long gone, but it takes a good 10 minutes of driving to get rid of the rough idle.

I don't know where to start. Even after the coolant is up to full temp it still has rough idle. I just ran some Diesel Purge thru with no real affect. I'm guessing this is an injector issue?

Where do I start?

Thanks for any pointers,
Bill

79Mercy · #2 07-10-2008, 01:35 PM

What all did the mechanic replace for 600 bucks?

Hatterasguy · #3 07-10-2008, 01:36 PM

What did the shop do for $600? What did they say?

A 603 should start just like a fuel injected gas car unless its zero out. The idle should smooth right out by the time the oil pressure rises.

Bill()C · #4 07-10-2008, 01:53 PM

I led the mechanic at the time to think the glow plugs weren't working right and I couldn't figure it out... did all the normal tests. In the end, after he replaced the GPC (which I found working properly, but he insisted they were "tempermental") it turned out only to be a faulty dash indicator ground, but I was still left with the really rough idle

... I can't quite remember what else he did... Oh, OK, Nuetral safety switch which I told him to do and had nothing to do with the problem. OK. So he only screwed me for $300.

Anyway...

I do have good oil pressure. I actually installed an aftermarket gauge and I get 60+PSI when driving highway down to 17PSI when warm and idling.

In the winter it feels like it's running on just one or two cylinders until fully warmed... in the summer it feels like it's just missing two perhaps. This goes away at higher revs and goes away completely after say 10 minutes of highway driving... bring her back down to idle and she's fine.

I would say minimal to moderate smoke out the tailpipe.

Bill

Hatterasguy · #5 07-10-2008, 02:15 PM

Start cracking the injector lines and see if you can narrow it down.

If you can narrow down the cylinders it's most likely an injector, if not it could be the IP. But before messing with the IP I would pull the injectors and have them tested and repaired if they need it.

vstech · #6 07-10-2008, 02:24 PM

it COULD be GP's but my bet is on injectors. cost on those relay's is around 250, so you at least have that in there for the 600.000.... assuming he put in a new relay. also it's now going to continue glowing after start for 3 minutes... so you have that going for you.
follow Hattie's advice and figure out which injector is giving you problems and pull them and drop them off at a injector shop. best 10.00 per injector ever spent!

Hatterasguy · #7 07-10-2008, 06:17 PM

Nah its not GP's, it would smooth out much faster if one or two was out. If only one or two was working it probably wouldn't start.

t walgamuth · #8 07-10-2008, 07:17 PM

could it be air in the fuel lines?

Tom W

carnut · #9 07-10-2008, 09:14 PM

Isolate the roughness to its cylinder by cracking loose each metal line at each injector, much like pulling a plug wire off a gas car. With it running, crack the line loose, a good injector will run much rougher when this is done. A faulty injector will not affect the idle roughness. That way you can confirm an injector issue. Would be good to know compression is even on all cylinders and that the valve adjustment was already done as well.

babymog · #10 07-10-2008, 10:30 PM

Could be collapsed lifters, and 17psi oil pressure its low for that engine.

I'm thinking it might have crap in the oil system, at least part of the problem, PO might have been 240Joe.

85chedeng300D · #11 07-10-2008, 11:54 PM

How is your water temp reading? You mentioned that it's taking a long time to warm up, but smooths out after a 10 min highway drive even in the summer, right? Have you thought about a thermostat sticking open? Most of the t-stats are fail-safe to fail in the open position.

...just a thought

pawoSD · #12 07-11-2008, 12:12 AM

Injectors/Timing/Lifters....could all be a culprit in the issue. Glow plug roughness smooths out after maybe 20-25 seconds tops. Even our 617's all start up and idle smooth all the way down to about 25F....below that they are "less smooth" for maybe 1-2 mins at most if idling, less if you drive away right away.

Bill()C · #13 07-11-2008, 12:31 AM

I'm gonna see if I can remember each point...

The engine doesn't really take THAT long to warm up, but the roughness doesn't seem to correspond to coolant temp. So when I was saying it warms up I meant sufficiently for the roughness to go away. The coolant temp has been warm for a while at that point.

I've checked, rechecked, ad nuseum the glow plugs. This problem persists well beyond the time GP's would affect. (as noted by others here)

I disagree on the oil pressure. 17 PSI on a warm engine at idle is what I've read many times on this forum. That's over 1 Bar.

I will admit I'm skeptical of cracking injectors open to use as a diagnosis of anything other than bleeding air. (I'm confident I don't have an air issue, but that was a good point. I have sections of clear line.) I've pretty much got nothing to lose by trying.

So I'm wondering if it's injectors are we saying that they aren't popping at the right time or fully, or bad spray pattern or something? I've seen injectors out of my old 123. They don't look like they'd be hard to rebuild.

Bill

pawoSD · #14 07-11-2008, 12:34 AM

I bet ongoing roughness could be the injector nozzles....or they may be out of balance....or the timing may even be off a bit (timing chain stretch perhaps?)

My dad's 300SD was very rough until he had the injector nozzles replaced and all of them balanced/tested. Its still a little bit rough, but way less than before, and performance is way better.

vstech · #15 07-11-2008, 09:15 AM

the point made about valves got me thinking... while you cannot adjust valves on the 603, you could have a dirty oil passage in the valve train causing the lifters to take longer to pump up... how long have you had the car? how clean is the cam looking through the oil fill area? do you drain oil at 3K? 5K 7K 15K longer? ever?
if oil change is in the 5K dino 10K syn range and you have had the car for at least 2 or more changes, that's probably not it, but something to think about.

cracking the lines on the injectors is not a bad thing, and you can do it at the IP if it makes it easier for you. you're not bleeding them (although if there is any air, it will show up!) you are preventing fuel from going in each cylinder to kill roughness in that pot to see if you can find which pot is making the roughness. after you locate the pots that don't make it worse, or quiet it down even, swap adjacent injectors and see if the problem moves to the previously good pot. that will say weather it's an injector problem or a problem with the cylinder/valves.... (if it doesn't move with the injector do a compression test on it, and then do a bleed down test or take it in to a shop)