Strange idle warm start behavior 603 engine
 

My 350SDL runs great when ice cold, anytime when driving and when well warmed up. If I start it cold it fires up in 1 crank revolution but if I just let it idle and warm it it will start to blow strokes, intermittent and not alarming, but noticeable. If I drive it, this goes away almost immediately like fuel is building up in a sticky injector or delivery valve.

It also puffs smoke at the 41-75C range at idle like it's not fully combusting the fuel. Again, if it's driven and warmed up while driving, this doesn't occur.

Next, if the car sits long enough to cool down to say 60C and I start it again, it shakes a lot on startup and clears up to smooth running in about 5-10 seconds

None of these symptoms affect driving the car, purely at idle and mid-temp warm starts. Otherwise great power, smooth acceleration that is expected from the 603.

Any thoughts? Are the delivery valves and injectors the place to start and the likely problem?

One bad glow plug will give you exactly the symptoms that you have.

At first thought that, but initial startup is smooth as could be without a missed stroke. It's almost as if it starts missing strokes after the after-glow has turned off. And once it gets to this point (say 1-2 minutes into running from cold) it's like I said, random about every say 10 seconds, 15 seconds that there's a miss.

Can't help but think that all the problems I explained are related to the same "sticky/fouling" component. Just going on gut feel though.

Still think glow plugs? Will a simple resistance test find the bad one?

I can only go by what you tell me:


I read this as an instant start followed by the usual 603 banging and missing for 15-20 seconds.

However, you now counter that statement with:



So, I really don't know what to think at this point.........other than operator error.:o

arg..i wish i could blame it on operator error :stupid: .

The car has had this problem for ages..and it's not really a functional problem, more an aesthetic one that is getting to me. Timing is spot on at 15 degrees ATDC, just verified a few days ago when i had the IP off.

How about we start at the beginning.

On a dead cold start, is it smooth for the first 15-30 seconds.........or not?

If it is dead smooth........at what point in time does the idle deteriorate?

If it does deteriorate........at what point in time does it return to "smooth"?

I don't think any of us have a clear understanding of the issue.

yes. perfect when starting from cold, no nailing no nothing

about 1-2 minutes in, I'm guessing when after glow shuts off. Nailing starts up too. Not excessive, but it's there.

well, I've never waited until it idles its way up to 80C but once driven seems to correct the problem. If not at 80C yet and I stop driving and let it idle for say 30 seconds to a minute (say waiting at a light) the random misses will come back. At 80C runs great, no misses, no smoke, still nails a bit.


Us? You're the only one replying to me right now :silly:

Thanks!

How long is the afterglow relay set for on the later cars?

How rough does it run? Does it skip like a gasser with a plug wire off?

After 1-2 minutes I'm thinking maybe a delivery valve seal, but thats a WAG.

I retract my statements regarding a glow plug. It's not the issue at the stated point in time.

Additionally, I don't see how it can be a delivery valve if it's temperature related.

The possibility exists for a defective injector, but connecting the problem with temperature change is difficult. I would visualize the possibility of the higher temperature resulting in better atomization from a marginal injector. Apparently, the problem still exists at operating temperature........slightly.......since the nailing is still present.

What I would recommend.........immediately when the problem surfaces at the 2 minute point.........is to crack each injector in sequence and see if you can narrow it down to one cylinder. This won't be easy because the 603 will run rough on five cylinders but it won't miss if you take out the one with the problem.

If you find it, then you can swap injectors to see if the problem moves with the injector.

Not sure. I heard up to 3 minutes I think depending on temperature.

Not rough at all, just a single blown stroke every few seconds, so several (say 20-30, maybe more than 50) full revolutions between each miss. Definitely not on each full cycle of the cam/IP.

I can get a rough start (like there's a bad glow plug) if i do the following

1. Drive car around up to and at operating temp
2. Let car sit for an hour or two to let temp drop to around 60C
3. Restart - here it shakes a lot for about 5-10 seconds...like an injector isn't squirting or a glow plug is dead.

You're running regular old diesel in there, right? Ever put veggie in the tank? Heat would definitely have an effect on how that is injected. Anyway, filters in good shape? I realize I'm way out of my league with you fancy Benz owners (mine's a 617, 85 vintage), but does that thing have a rack damper?

Prior to head replacement (yeah, I know, this story is starting off bad) my 617 would crank up well in 32F+ and idle better cold and hot as opposed to mid temp. My theory, cold is when the oil is thicker and gives a little extra compression. Hot is when the rings are expanding and add better atomization with heat, and you've got a little higher compression and smoother idle. Mid temp, neither one is helping.

Like Brian suggested, starting with injectors is a good idea. But maybe you've got slightly low compression, possibly due to a valve not seating properly. Again, I'm way out of my league here speaking to an SDL owner, so I don't even know if your valves require adjustment. But I wish you luck. There ain't nothing better than a good running diesel Benz.

BTW, I'm from the Crescent City. How's the weather? Hot as hell yet? I really miss drinking beer and sucking crawfish heads at Cooter Browns!

It's B20 in there right now. Head is a #22 and just resurfaced and ground (well about 500 miles ago).

I'll go with Brian's suggestion. I think I've identified one faulty injector from the nailing standpoint and will have it tested soon. Would be nice if all the problems went away at once.

As for weather, it's 80 about every day now, fair amount of sun, risk of the odd thundershower. The usual ;)

Infrared thermometer time
 

Time for a temp check on the exhaust manifold with a thermometer. Check right after running for 30sec and then again after it idles poorly. That is the fastest way to determine if it is an injector. Saves a lot of time looking for the bad hole.:D
Bud

The afterglow on this model is up to 60 seconds in very cold temps, probably 5-30 seconds in more normal temps. When warm, afterglow is near zero. I don't think this is a glow issue. Sounds fuel related to me, either injector, or delivery valve seals. Preferred timing spec is 14° but one degree off won't make much difference. I'm assuming that cam timing is ok and the chain isn't stretched (you have checked this, right?).

Or.... I hate to go here, but... what's the oil consumption rate? A good 60x engine should be 4000 miles per quart or better.

:wacko:

Cam timing and IP were spot on...the FSM says to put the motor at 15 deg. ATDC when pulling the IP but I don't see how you can do this without pulling the valve cover to see if it's the exhaust or the compression stroke...so needless to say I saw that the cam and crank were lined up when I went past TDC.

Last time I checked, before I rebuilt the turbo it was about 1 quart at about 2K miles...but I drive it like I stole it and at about 85mph on the highway.

I can't help but lean toward the delivery valves and one bad injector. I'm almost positive it had this miss/shake behavior before I replaced with the bosio nozzles several thousand miles ago.