Follow-up thread: High altitude starting, pinging problems - PeachParts Mercedes-Benz Forum

rgnprof · #1 06-30-2008, 11:42 AM

This is a follow-up to 2 previous threads - one on checking cam timing and one on engine knocking and injection pump timing. Anyway, we are in Colorado and car ran great until we hit about 5000-6000 ft and then it started pinging again on me - especially under any kind of load. We are staying right now at 8000+ and the car is a real bear to start in the morning - lots of cranking and LOTS of gray smoke. Once I get it running, it smokes about the way it did in OKC - very little - but still pings and knocks.

Since this is the NA '78 300D, there is no ALDA, and the FSM says that there is supposed to be some kind of built-in altitude adjustment - in the injection pump itself. I am also having trouble with the vacuum locks and the cruise (also vacuum controlled) does not operate as well holding the speed - both of which I know are altitude related. I know there is a vacuum connection on the injection pump - is that related to my problems as well???

I'm thinking of checking my pump timing again - any suggestions, or am I just stuck with these kinds of problems until I get back down?

Also, an interesting observation is that I am getting BETTER gas mileage when the car pings and knocks - I got 22-23 early in our trip and now I am getting above 25??? Maybe it was running too rich before...pump timing too far advanced (see my previous thread).

ryan

#2 06-30-2008, 02:34 PM

Quote:

Originally Posted by rgnprof

This is a follow-up to 2 previous threads

You should keep all the threads together. Splitting them up makes searching for answers much more difficult for everyone when they find only those two threads without an end result or an incomplete answer.

Anyways, its pump timing at this altitude. Advance it to 26-28*BTDC. The vacuum system is not related to the engine except that pressing the throttle for more power means less vacuum is available to charge the system.

rgnprof · #3 06-30-2008, 07:34 PM

Thanks for the advice - I didn't know whether or not it was best to start a new thread or not...

I think the other 2 threads had reached some resolution, so I decided to just start a new one.

So I want to advance the timing - and if I do that, I will have to adjust it again when we get closer to sea level??

I thought this pump would make this adjustment...

Thanks, ryan

DieselAddict · #4 06-30-2008, 07:46 PM

In my experience with diesels and living at a high altitude, the thinner air brings out the worst in diesels which as you know primarily rely on compression. If you have lower than optimal compression or injector spray pattern, you may not notice anything at lower altitudes but you probably will higher up. Sometimes all you can do is live with it. I would not recommend adjusting the timing just for temporary changes in altitude.

For the record I didn't read or even see your previous 2 threads.

rgnprof · #5 07-02-2008, 11:01 AM

I can live with the pinging and knocking - it's the getting it started in the morning that's the real problem. Once I get it started, I generally don't have any more problems the rest of the day.

Went out this morning and tried to get it going and I finally wore the battery down. Had a friend give me a jump and the car started right up on the second try. Checked the alternator and it is only putting out 13.7 volts +/-...

I am wondering if at this altitude - which clearly strains my car - if I have a slightly less than optimal charging system that that could be part of the problem? Maybe an alternator belt that is a little loose and not charging the system optimally (I guess 14.5 volts, +/-), or a slightly weak battery would be exacerbating my problems?

ryan

bustedbenz · #6 07-02-2008, 11:27 AM

Quote:

Originally Posted by rgnprof

I can live with the pinging and knocking - it's the getting it started in the morning that's the real problem. Once I get it started, I generally don't have any more problems the rest of the day.

Went out this morning and tried to get it going and I finally wore the battery down. Had a friend give me a jump and the car started right up on the second try. Checked the alternator and it is only putting out 13.7 volts +/-...

I am wondering if at this altitude - which clearly strains my car - if I have a slightly less than optimal charging system that that could be part of the problem? Maybe an alternator belt that is a little loose and not charging the system optimally (I guess 14.5 volts, +/-), or a slightly weak battery would be exacerbating my problems?

ryan

I'm not accustomed to thinking of alternators in terms of more than 14.0 volts. I'm not saying I'm correct in this, but most of the ones I mess with put out somewhere between 13.6 and 14.0 and rarely more. I haven't got any troubles that I know of.

DieselAddict · #7 07-02-2008, 12:37 PM

Quote:

Originally Posted by rgnprof

I can live with the pinging and knocking - it's the getting it started in the morning that's the real problem. Once I get it started, I generally don't have any more problems the rest of the day.

Went out this morning and tried to get it going and I finally wore the battery down. Had a friend give me a jump and the car started right up on the second try. Checked the alternator and it is only putting out 13.7 volts +/-...

I am wondering if at this altitude - which clearly strains my car - if I have a slightly less than optimal charging system that that could be part of the problem? Maybe an alternator belt that is a little loose and not charging the system optimally (I guess 14.5 volts, +/-), or a slightly weak battery would be exacerbating my problems?

ryan

When was the last time you adjusted the valves and checked your glow plugs?

rgnprof · #8 07-04-2008, 04:30 AM

The glow plugs are new - within the past coupe of months and the valves were adjusted right before I left for this trip.

I drove the car 730 miles today - from South Fork, CO to Twin Falls, ID and got great gas mileage - with the car occasionally pinging until we got below about 5000 feet. I got 29 mpg - driving from east of Durango, CO to just north of Salt Lake City. I know that's just one tank, and I'll look at the average, but it doesn't seem like the pinging is hurting performance???

The only trouble was getting it started this morning at 8200 feet! Once I jumped it, it started on the 2nd crank.

ryan

nhdoc · #9 07-04-2008, 05:49 AM

How old is your battery and have you had it tested? If the battery is marginal it won't spin the engine fast enough and just like in the winter it just won't start. Does it seem to crank as fast as it used to or should? That may be contributing to the trouble you have starting it at high altitudes.

There is a compensator on the IP, it is on the back and looks like a can with an open port (I believe the port is right on top). Often times people assume there is supposed to be a vacuum hose attached to it and add one but it is supposed to be open to the atmosphere to sense pressure and adjust fuel accordingly. Make sure yours has the port open and there is no dirt or crud in it too.

rgnprof · #10 07-04-2008, 03:45 PM

The battery came with the car - so it's at least 3 years old. I have not had it tested, other than putting my voltmeter on it... It clearly cranks the engine faster when I am jumping the car.

I know the port you are talking about on the IP and there is no hose connected, but I've never checked it to see if it is clear or not - I'll take a look. Is there any thing else to do to check out this part of the IP?

ryan

nhdoc · #11 07-04-2008, 04:46 PM

Checking volts with a meter will not tell you what the voltage is under load - are you checking it when just sitting or while cranking?

If you are saying that it cranks faster when you jump it than when you are just trying to start it normally, but before you have drained it down to the point of needing a jump then the battery is weak. Maybe it is not even the right kind as these cars use a BIG battery. Just the fact that you got it started with a jump tells me it is probably contributing to your problems.

I bought a Bosch battery at Pep Boys for my '79 and I think it was 1000 CCAmps. Is your battery bigger than any other car battery you have ever seen? I'd suggest you get a new one and make sure it is one of those big mommas. They are only around $100 and if yours is already 3+ years old you will need one sooner or later.

If that port on the IP is open and clear I think you could probably test it but I don't recall how...for now just make sure it isn't clogged with dirt and take care of the battery.

rgnprof · #12 07-04-2008, 11:03 PM

I just checked my battery - it's an EverStart from Wal-Mart and it's only 780 cranking and 650 cold cranking. I'm sure this is part of my problem...

ryan

nhdoc · #13 07-05-2008, 08:03 AM

Quote:

Originally Posted by rgnprof

I just checked my battery - it's an EverStart from Wal-Mart and it's only 780 cranking and 650 cold cranking. I'm sure this is part of my problem...

ryan

Yeah, get a new one and a bigger one. If you are on a budget then go to autozone, they have decent ones for about $60-$70 that are around 1000 CCA. Next step up is Interstate and Bosch at around $100 and the gold standard is the M-B OE battery from the dealer...it's probably around twice that by now. Change the battery and see how you do starting it at altitude. You need to be able to spin that engine faster to generate heat and compression under extreme conditions...a small battery just won't cut it.