'85 300D very slow revving
 

Hello guys,,
I'm trying to get the '85 300D turbo running decently. It had been sitting for several years before I got it.

After changing crankcase oil and trans filter and fluid, air filter , fuel filters, primer, it would start right up, but the engine had very little power, and it would sputter sometimes.

I drained the tank and removed the strainer- it was a terrible mess. I cleaned and replaced. While apart, I blew compressed air back through the steel fuel line and the return line.

I did the diesel purge thing- 1 can lasted about 23 minutes.
At this point, it is definitely better, but it is still pretty slow to rev when you goose the throttle- it seems like it takes a a second before it gets up to high rpms. I also have a 240D and I think it may rev a bit quicker.

My next step is to adjust the valves. I've done this and I made custom 14mm offset wrenches for this purpose.

So at this point, it is close to driveable, but it doesn't acellerate like I think it should, especially being a turbo.

What else can I try? I'm pretty sure I'm not getting air incursion. I put on yet another primary filter and hoses and the primer pump feel right.

Maybe I need to open up the turbo and make sure it is good shape. Kent Bergsma discusses this.

Maybe I should change the large fuel filter again since I did the diesel purge and maybe it clogged up. Or maybe I should do a 2nd can of diesel purge. By the way, I'm running off-road red diesel fuel while doing my testing, since I have a big tank of it for tractors.

I do have at least some sort of vacuum leak- it takes a few seconds before it shuts off. There are several more vacuum lines and gizmos in there as compared to my 240. I guess some of it is related to the EGR and other pollution devices.

Re Awakening
 

Just keep on doing the many little niggly things you're doing and drive it, it should get better .

No need to take the turbo apart, simply see it if twirls easily by your fingers .

If not it's time to try running MMO or other <magic> elixir through it directly .

If there's no exhaust smoke and the turbo doesn't drag it's likely the catalytic converter and you're in luck ~ once you've cleaned everything up and fixed the fiddly bits your Mercedes dealer will replace the clogged cat. for FREE ~ a kid I know got an '85 300D for $300 from a used car lot and did all this, sold it for $3,500, it ran like a scalded cat after replacing the clogged cat. .

Start with the basics. Check the ALDA lines, overboost switchover valve, banjo connections, and banjo bolts leading to the ALDA. If you have a clogged or broken ALDA line, you get no boost fuel enrichment. Car will be a SLUG.

Since the Turbo Boost kind of is not noticed till around 2000 rpms if you are slow before that it is not the Turbo or the overpressure relay nor a clogged fitting although all that should be checked anyway.

If you put the new Fuel Filters own and ran like that before you drained the tank and the cleaned the Tank Screen there is a chance you clogged your filters.

When mine was scary slow at acceleration on the low end it was due to the throttle linkages not being adjusted correctly. Too much play in them and the Throttle Lever on the IP was not being moved far enough.

The Bell Crank on the Fire Wall between the Accelerator Pedal Linkages and the throttle linkages has parts that deteriorate with age. However, in my case I think some former owner fooled with the linkages. There is specific lengths for the linkage rods in the Manual.

With the Engine cold and shut off grab and hold the Throttle Arm on the Fuel Injection Pump and keep it from moving. Have someone slowly depress the accelerator pedal and while that are doing that watch to see how much play is in the throttle linkages.

Drive without the Fuel Tank Fill Cap on. If things improve then your Fuel Tank Vent is clogged or restricted.

I would second checking all linkages. Cured similar problem on my 85 300D. Also make sure intake and filter are clear and clean.

It may depend on whether the engine has been warmed up or not. Especially in winter.

Back when I was working from my home office, my wife would use the 300D. I would hear the usual clatter clatter as she started the car and then moved slowly up our long driveway. Then once at the highway, she would floor the pedal - the engine would whine as revs increased. I would cringe.

I tried to get her to start off a little more sedately, at least until the old girl reached operating temperature.

My 82 300SD has a low mile, factory engine implant but it sat 7 years. Similar symptoms of yours, that steadily improved over time as I found and fixed or adjusted things. Saw improvement from: Replaced cracked "U" boot, repaired broken connector to sensor on boost pipe, lube/adjust linkage.

Also changed fuel filters, glow plugs. Didn't see signs of fuel contamination or start problems, so saw no improvement from this. Fuel gauge initially topped out just above 1/2 full, but slowly improved. Now sits at F on fill-ups. As power improved over time, saw slight decrease in MPG. Car has more power, but less MPG now than I remember in an 81 that I had in 90's. MPG is 22-24 in mixed driving, depending on amount of stop/go city driving. Best highway so far about 26 mpg. Planned on couple trips this Summer, but things are different now. Don

To Rev .Or -Not- To Rev. ?
 

Yes, run them well but no, revving the piss out of them isn't good .

Each one is different, it depends on where yours shifts .

My '82 240D shifts later than I'd like so I never need to floor it, I just give it 1/3 ~ 3/4 throttle and it marches right out, if I don't let up on the throttle the up shifts occur way too late .

One day I need to address this but .

My '84 300CD shifts sooner and so I drive it harder and much faster too .

Missing Message
 

This was posted 1.21.21 then removed :

Here is the message that has just been posted:
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There is not much more you can do than change the fluid and filter and pray. The smell of burnt fluid indicates high levels of clutch wear and friction leading to high heat buildup. Evidence of metallic dust in the bottom of the pan usually means excess gear or bearing wear. These indicators do not necessarily mean your transmission will fail next week or even next month. By keeping the fluid clean and using a transmission additive you can push more life out of a dying transmission. You will need an additive with a viscosity enhancer. I like the Lucas brand. This can reduce some of the clutch slippage and friction thus reducing heat.
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A few thoughts .

Slow revving doesn't necessarily mean poor acceleration .

When I used to encounter fleet vehicles that revved freely in neutral but were very slow off the mark it turned out that the sprag clutch in the torque converter was often bad .

We're lucky in that our Mercedes have a torque converter drain plug (5M hex) and more ATF is retained in the T.C. than anywhere else so it's critical to always drain it too, just doing a pan drop, clean and replace the filter is nice but no where near an actual ATF change .

As mentioned, various snake oils are available , I know and trust Lucas Products for engine oil but my go to for slushbox woes is TRANS-X in the yellow bottle, thanx to a tip here some years back .

It's important to discern the problem before throwing parts / repairs at it .

Unless the ATF is clear, bright red and sweet smelling it needs changing, NOW in every case even though it may not fix the basic complaint .