Engine Straining at Higher Speeds
 

Hi again folks,

It looks like the majority of my vacuum problems have been fixed by rebuilding the pump- thanks for all your help!

Now I am very concerned about the engine being very loud at higher speeds and RPMs. I know diesel engines are inherently louder than gas, and that doesn't bother me. What concerns me is that the engine sounds like it is straining to maintain speeds higher than 45 mph. The engine is operating at 3000 RPMs at about 63 mph, which I have learned from this forum is average. But the engine sounds like there is another gear into which the trans should be shifting, although I can clearly hear it shift through all four gears. It's like I am pushing her to accelerate past 45 and maintain higher speeds. I get worried that it's too much and she's going to break down. :(

Although I've done a lot to the car (replace all filters, oil change, diesel purge), I have not yet done a valve adjustment. Since I bought her only 6 weeks ago, I don't know when one was last done. It's almost winter where I live, so I have garaged the car for the winter. I will be driving her from time to time during the Winter months though. I'd like to have some idea of what might be wrong so I can plan to work on it come Spring. Would a valve adjustment ease this stress on the engine? What else can you suggest?

Thanks,
Avery

'85 MB 300D Turbo, 254K miles

Brakes binding? Or other driveline drag? Check that you coast easily and long if you slip into neutral on level ground. Feel the wheels for heat.

Maybe your pedal linkage to IP is maladjusted or needs lubricant, and it feels like you are pushing hard when in fact the movement at the IP is normal.

Maybe your rad fan is frozen to the clutch, making a lot of air noise.

Check the tranny and diff fluid levels.

Check all your accessories on the fan belt that they are spinning freely / not binding or frozen, check belt alignment.

Find another similar car with a 617 and drive or ride in it to see whether what you are experiencing is normal.

There have been recent reports here about fuel quality problems...

You should adjust your Valves.

Has the condition you describe always been there?

At the rear of you intake Manifold is a Banjo Bolt that can get plugged up with crud. If it gets restricted the Boost pressure from your Turbo Charger will not reach the ALDA on the Fuel Injection Pump and the ALDA will not give it the extra Fuel to match the Boost.

Also if you plugged a Vacuum Line into your ALDA instead of the Correct line the ALDA will not work properly.

Also what is your Boost Pressure? Some have had their Waste Gate opening at low pressures and decreasing the Boost Pressure.

Front brake pads were just replaced- rotors seem to turn properly. Not sure about the rear. No mention of problems during the inspection last month. I have not tried coasting the car- will try that. When I let off the gas, the car doesn't drop speed quickly.

I adjusted and lubed all the throttle linkages with ATF a couple weeks ago. The bushing at the firewall is bad, making the pedal a bit stiff, but I don't see how this would cause the problem I'm experiencing.

Rad fan seems to be moving properly, no abnormal noises. The trans fluid level is good. I know my diff leaks- not sure where to check its fluid level. I'll check the FSM. All belts seem to be moving properly. I tightened them all last week- no squealing now.

I don't think it's a fuel problem. I read some posts about bad diesel, but I'm not getting the other symptoms.

I'm starting to wonder if my tach is inaccurate, that it's revving much higher than it reads. I know the speedo is 3-4 mph off- would the tach be too? Honestly, I don't know if my turbo is working at all, as I never hear the characteristic "whirr" sound when I accelerate. Could this cause the engine to work harder at higher speeds?

You typically don't hear the turbo working over the diesel calamity going on at speed.

Without good turbo boost, you won't get up to speed any time soon and would feel like a total slug and the engine would not be "working hard" 'cause it's not getting the boost.

Typically tachs work or they don't, and wouldn't be slightly off by a factor like a speedo might be due to wrong tire size or diff ratio.

I like the idea someone suggested, get in another similar car and see if you're experiencing "normal" but just have different expectations.

Your description makes it sorta sound like your tranny is not offering up one more gear on the top end. Are you sure you're getting all the shift points happening that should be? Do you get kick-down if you try (press hard)?

I HAVE A NEW CAR!! At least it feels that way now :-)

Diesel911- you were absolutely correct! The banjo bolt in the back was completely clogged. I thoroughly cleaned it and the fitting, as well as the ones at the ALDA. Result: so much more power! She was able to accelerate to 65 with little effort, and maintain it without me holding the pedal almost all the way down. I think the RPMs lowered a bit too- now it's about 2900 @ 65 mph.

I don't know what the boost pressure is. From the looks of the procedure to check it, I'll probably have to wait until the Spring.

As for the trans, it sounds like it is going through all four speeds. And it will downshift when the pedal is floored. The engine still sounds a bit loud, but I think a valve adjustment will help that.

Thanks again everyone for your help and advice. This forum is like having full access to my very own diesel experts! :-) (actually, I'm sure it's exactly that!)