Finally tested compression on my 300D
 

I was worried that this car might have skeletons in the trunk. Only 135K when I got it, near cherry in and out but a wee bit gutless. Not bad for longer trips, will cruise at 65 to 70 but that's about top speed. Also had trouble cold starting in Dec. in Oregon - about 32° and later in WA at about 38°. Lengthy grinding, was getting worried about draining the battery. Or damaging the starter. Would rest about 2 minutes between 10 second spells of grinding.

I had read that poor compression could be a cause of poor cold starting.

The compression test news was surprisingly good: 1 through 4 - 380psi, 5 - 360. I'm thinking to do it again starting with #5. But I'm guessing this means that trying to get it running well is doable w/o breaking the bank. My '81 300SD was much peppier and that model weighs 300 lbs more.

I haven't yet done a lot with it. I feel stupid in admitting it, but I didn't get the title when I bought it. My SDL had blown a radiator the day before, I wanted to buy the 300D at the indie lot I'd been towed to, stayed overnight, got the cash together, basically jumped through hoops to make it happen. I hand him the money and hold out my hand for the title. He said that the garage owner keeps all the titles at his house for safekeeping and he was 20 miles away taking care of his wife at a hospital and they'd mail it to me. I didn't like the sound of it but I needed to be on my way to make a deadline, I wanted the car, and this wasn't just some guy with a sign in the window. The garage had numerous good Yelp reviews.

Long story short, after two stalling episodes by phone over the next two weeks he said the wife was back home and couldn't find the title. He said he would get a replacement, after a few weeks I discovered this was blowing smoke. The lady who sold the car to the garage has been amazingly helpful, we completed the application for new title Dec. 21st. DMV called a few days ago, it all looks good, I might have it by Feb 1. Bought it in mid Oct., purchased two 21 day 'light vehicle trip permits,' you only get two.

So I haven't put a lot into yet. Was reluctant to invest more until I knew I could get it off the 'paperweight' square and actually legally license it.

I'll next take off the intake manifold, inspect and clean. Perhaps trying to weld up the EGR so it looks functional but is actually deleted.

I saw an old post from Diesel911 about things to check/overhaul before rebuilding the turbo but I can't find it. Thought I bookmarked it.

Check fuel injectors. Sounds like my car - got it with 133K. It would barely hit 60. With new injectors, it does 90 with far less oil burn.

Does it smoke? Does it knock after it's warmed up? Those are both indicators. Also check throttle linkage (unrelated to injectors). Make sure you can really open it up when you're on the pedal. It's possible that the hard start is caused from myriad issues - injectors, valve adjustment, and glow plugs.

Henry C.

looking at you compression numbers I would do this:

- rebuild the injectors
- change glow plugs and ream the carbon out
- valve adjustment

do that and it should improve your cold stating

check your overboost protection system.
check the boost pressure at the ALDA and intake (could be a plugged line)

not easy on a om617 because the intake and exhaust manifolds and the turbo/all the drains are on one side of the engine

As suggested by Cleeves, check your throttle linkage goes all the way to the stop on the IP when the accelerator pedal is pressed to the floor. If the rods are out of adjustment or the pivot on the firewall is wasted, you won't have full travel on the IP. If it seems to accelerate ok, it's unlikely to be a turbo issue, steady-state cruising only generates a small PSI boost state anyway, so you should be able to do in excess of 70 even if the turbo were fully non-functional - it would just take a while to get there.

Cold starting is most likely to be glow plug issues as mentioned above. It could be one or more of the plugs or it could be the strip fuse has a crack in it. The compression numbers aren't terrible, but certainly lower than I'd expect for so low of mileage. Definitely adjust valves. My SDL had compression of 360 on one cylinder and 380 on the rest. It still started fine even if sat outside in below freezing temps overnight.

Proper Maintenance
 

Copy post # 3 and follow it, don't touch the intake manifold just yet ~ there are myriad things you need to do first and in the proper order or you'll just be chasing your tail in circles .

Assuming the odometer works (unusual) you prolly have a very good car there once you get it fettled .

If the valves were not adjusted on a cold engine, prior to the compression test, those numbers have basically set the low end but do not really tell you the true compression values. RTFM, which says adjust valves immediately before compression test.

Great advice. I was worried that the manifold job would be tricky and likely difficult. I bought the gasket, that's when I learned that both manifolds were done at the same time.

During my second trip permit - legal driving on street - I needed to go to WA state for family issues, was making major money on a large job - more loose money than time - so I took it to my Vietnamese mechanic buddy's garage. He owns two 350SD , cut his teeth on Mercedes diesels in Vietnam, prevalent there. I know the guy is good, he found the stalling gremlin in my Chev van - I had searched for two years.

He adjusted the valves, he said two were close to tight. Also smoothed out the occasional hard shake at idle, not sure how that was accomplished. He said he tested the injectors and they were good. I could ask him for more details on that. So the compression test was done about 1600 miles after the valve adjustment. I was thinking that would be good enough but I'm still fairly new to some of this.

Glow plugs sounds like a good idea, not an expensive one either.

I think the odo is accurate, the car exibits modest wear and tear. Oregon DMV gave me the PO's Eugene address, I was in the area so I took the bold step of going to the door. The young woman who answered said the names on the title were her grandparents, both deceased - her mother, now in Montana was the one who had signed it over to the garage, didn't sell it, they told her it would cost $6K to get it running, she gave it to them to cover the diagnostic work. Sounds a wee bit crooked. They did have the title at one time.

Anyway, it had been her father's car, he was a VW mechanic, in her words: from the factory in Germany. It was her car for 15 years. When I got it there was too much tranny fluid in it, maybe a pint or more too much. Made me worry that various fluid issues might not have been dealt with well, after all the dad was getting old, maybe long gone, though you'd think she'd had good tutoring.

The acceleration is not good. I hemmed and hawed about buying it, I only did so because it's a cherry with low mileage. I think I'll land on my feet. If it had been sub 300, would have been forehead smack action, so I'm pleased that it's at least what it is.

It was a cold test, so what, would warm be maybe 20 psi higher?

I'll check the throttle linkage and alda.

I saw a vid from Kent saying that bad injectors can lower life - damage compression. Said that if they squirt instead of spray, still runs, but will wash oil off the cylinder walls.

My thought is that low mileage doesn't necessarily mean all components are in great shape. I did the math, 10 miles a day, every day would yield about 135K. Every start up is going to give some wear and tear. Pretty sure that highway mileage will still make for wear and tear but of course the conventional wisdom is that highway miles are less wear and tear than city miles. I think it spent it's entire life in Eugene, not a huge town, no salted roads. So a 10 mile a day average is not unreasonable.

I've not checked comprssion on my SDL. It has 350K, we occasionally have early mornings around here in the high 30s, never any difficulty starting. Much better acceleration than the 300D. Better engine of course, but still. My 300SD was noticeably better than the 300D.

I think you've done very well, these are getting really hard to find in decent condition. Mechanicals can and will get sorted, it's the cosmetic stuff that will eat you alive if you want the car to really look nice.


I'm pretty sure the proper test is cold, done immediately after the valve adjustment, which must be done on a stone cold engine.



I recently fixed a sloppy throttle linkage on a '95 E300 I picked up last fall, added all sorts of power to the right foot. Still sorting other issues, like very poor power after cold start when temps are around freezing or lower.


My advice is always to start with simple / cheap attempts at fixes, and progress to expensive / complex. However, do not ignore what you know to be wrong, even if expensive / complex to fix.

No.

from the fsm: Measure compression pressure at 80C

link to it:
https://www.startekinfo.com/StarTek/outside/12265/disc_2/program/Engine/617/01-010.pdf


yes valve adjustment is done on a cold engine but why IMMEDIATELY ?

I'm tempted to do it again with the engine warm. Will need to move quickly. Not sure if there's a way around it but I had to partially dissasemble the throttle linkage mount to get the socket on the #3 injector, I think it was that one.

OTOH I read one account where a guy said he thought checking it cold had merit, as the engine is often cold when you start it. Certainly the starts you worry about with an aging diesel are when it's cold.

Not much point in checking the engine when it is warm if you are concerned with cold starts. It is a handy comparison aid when you are checking the over-all health of the engine regarding wear.

At 300+ PSI your problem isn't with compression. 275 is considered "minimal". I suggest you borrow another compression gauge to verify the results. I've had gauges lie to me before.

Thanks for that info, I stand corrected!


Compression values depend on proper operation of the valves. Loose valves can prevent a full charge of air (lower compression) and tight valves can allow some of the air charge to escape (lower compression). The test values in the FSM were established on the assumption that the valve clearances were properly set, so if the valve clearances are off, the test results are not valid. A stretched timing chain can also affect compression, that's why a good practice is to check the camshaft timing when the valve cover is off to perform the valve adjustment.



If there is carbon deposited on the valve face or seat, after an adjustment and some vigorous driving, those deposits will probably reduce or disappear, changing the valve clearance. Sometimes a neglected engine will need two or three valve adjustments in a shorter maintenance cycle, for instance 1000 miles between adjustments, until such deposits are gone and the clearances will stabilize a bit.

If the block heater is working, you can plug that in immediately after driving and before you check the compression, that will keep the engine temp up closer to 80 for a longer time.


The late Marshall Booth used to say the best compression test was cold start during winter. If the engine starts immediately and fires evenly on all cylinders, your compression is good. No need to spend time or money on a compression test which will only confirm that your engine is healthy.

Rather than speculate it is probably fuel starvation or very low to no boost. First make sure the line and fittings to the alda are not obstructed.

Too typical of these to ignore. It could also be very late in timing. Smoke out the tailpipe might also indicate that.

Open the return from the injection pump. Fuel flowing out at idle and when you rev it? If there is close that line for a test.

Problem is severe enough cause should be easy to identify. That the car will not go fast is a major clue.

I guess considering glow plugs when having cold starting issues would be no brainer, but this car starts on the first bump at 50 and 60° so it didn't occur to me.

My mechanic buddy thought that was good enough proof of good compression. He didn't have a suggeston about getting more power.

I haven't yet read about rebuilding injectors. I'll look into it. I have experience with improved injectors (gasser) on my E30. I put in the next-gen injectors, rebuilt professionally, 4 ports instead of one, better atomization - wow, noticeable power increase and it was already fast.

Will have glow plugs in the mail soon. Need to read up on reaming the carbon.

Tonight I looked at the ALDA. I'm embarrassed I didn't notice it sooner. I don't think my mechanic buddy saw it either. The line not clogged but broke:

https://i.postimg.cc/zvLKdjSs/IMG-3355.jpg

https://i.postimg.cc/SNMcCgK8/IMG-3364.jpg

Don't think I did it while working on the engine. I was never in that vicinity. The banjo bolt is plenty clean. I'll need new line, not going to slide over this fitting.

I have a mighty vac vacuum pump. Is that useful for checking the ALDA? Or is the pressure the wrong way?

I think greazzer rebuilds them for reasonable money.

that explains your low power problem.

you need a reamer that goes into the glow plug hole

To me, odds are with the new hose it will run a lot better. The car should run 100 mph if things are all working correctly.

The ALDA uses the pressure from the turbo to increase the fuel flow from the injection pump, so using a miti-vac to put pressure into the ALDA is correct, but limit the pressure to 15 PSI. If the ALDA leaks down quickly or won't hold pressure at all, you may be able to take it apart and replace the o-rings to fix that.

So what, just put the mighty vac tube on the banjo bolt lead and apply 15 psi of vacuum? I'm going to need to remove that old bit of plastic tube from the lead anyway.

Many on here including me have had Greazzer rebuild injectors. Reasonable price, fast turn around and much easier than sourcing parts then going through the learning curve.

BASIC ALDA TESTING
 

Yes, exactly that .

If it won't hold vacuum you'll soon know .

Obviously if the car was sluggish from the first time you drove it. You did not create the problem..

Just before you hook up the new hose to the alda. Blow on the end to make sure there is no obstruction in the over boost valve or the manifold connection. That line when functional does not really have constant air flow as such. It relays the air pressure from the manifold to the alda. By just compressing the air.

With that line open there would have been air flow. This might have included some of the egr garbage fed into the manifold going through that line. That increased the chances of soot buildup in the manifold fitting and the over boost protection valve.

So you just make sure that the system is still open by reducing the air pressure applied. Or just take the car for a short drive to make sure the sluggishness is gone. The engine was just simply fuel starved.

I likes me the sound of this.

Does it have the same thread as the glow plugs, sort of like a tap but not as agressive? I've seen the kits you can buy to extract broken glow plugs, it's not that kind of thing is it?

I can't find that hose stock at Pelican. I'll send an email.

It just looks like vinyl hose basically. Sold at most hardware stores. Take the barb with you after removing the piece of old hose to check for fit.

link to a om617a reamer (connect mercedes and source together if I try to post it as one word the link gets blocked): https://mercedes source.com/store/heavy-duty-carbon-reamer-pencil-glow-plug-chambers


more on reamers:
https://www.youtube.com/watch?v=bdsojoTJ0p8

Good stuff. I deleted the part about how to get to the site. Who knows, they don't like to be a platform for a competitor, not that I think they'd search every post.

I've heard of the trouble in getting reamers out. I don't have any Kroll, I have some PB Blaster. Probably wouldn't hurt to spray some on now. I'd hate to need to spring for one of the extractor kits now. IIRC I've read of home made reaming tools.

But yes, I think I'll be getting his reamer and the wrench that goes with it.

I thought about that but the stuff in the car seems thinner walled than the haredware store varieties. Flexible but less flexible than the hareware store variety. I'll cast about a bit, might end up needing to use whatever I can find.

Temporarily, you can use vacuum hose as a connector.
Typically, 12 psi is the max pressure the hose will ever see.

I don't recommend a vinyl hose because when it gets really cold that hose becomes rock solid and can break from vibrations of the engine. Try rubber or something



you mean getting glow plugs out? OM617 don't have problems with plugs seizing in the head.


you don't really need any special wrenches. a small 12mm ratcheting box end wrench can be helpful but if you're doing injectors at the same time and removing the hard lines you don't need that either.

I just had a thought. When I put in new windshield sprayers, pulling the old ones off was a bear and no way did the new ones want to go in to the old tubing. I put my heat gun on the ends of the tubing till it got soft enough to slip over, when it cooled it was on fast. I have enough slack to on the ALDA line to cut off a half inch and reuse. The rest is sound enough.

I can't recall if I had enough extra length on the sprayer tubes to cut off a bit, I think I did.

Yes, I'm sorry, I meant glow plugs. I was reading about glow plugs seizing up, perhaps that was on the OM603.

I haven't looked but you're saying with the injectors out it's easier to get the plugs out? It looked like it would be more roomy. I can't decide if I should get the injectors rebuilt. They don't have the sharp points sticking out, Kent mentioned that, but that's not a real scientific test.

OM603 is not that bad but on the OM606 it's a nightmare



it's easier with the injector HARD LINES removed. I highly recommend rebuilding your injectors on an unknown engine. It will pay for itself and will improve cold starting.

I suspect you’re right. At 135k, unlikely that many of the components have been replaced or rebuilt.

Injector Service
 

Be smart and send them to Greezer (SP) ~ they do need periodic service and he adjusts them to within 5# pop off pressure, you will LOVE the increased power and smoothness this balanced power affords .

if its really only 135k miles the injectors should be like new. I'd check the glow plugs for function and check all my vac lines for leaks and go with it.

You're saying the injectors nozzles should be like new if they've run 135K miles? I don't agree with that. Mine were in deplorable condition at 135K on a 1-owner well maintained example. 3 out of 5 were shooting a straight line of fuel and the remaining two weren't far behind. All had cupped, concave nozzles.



Henry

Did you do all the miles yourself?

No, got it in 2017 with 133K miles. 145K now. Very good original docs, most of the miles were put on in the late 70s and early 80s. Owner died in '01 or so and it went into storage until I got it from a family friend of his - it was in a sealed shipping container until they retrieved it in 2017, drained the gas tank and sold it me. The car is in excellent original condition, and I have no reason to think that poor maintenance caused premature deterioration of the injector nozzles.

-Henry

Sounds like a nice car!

Thanks! I've finally replaced most every rubber bit that I can source on the car - all the light and window seals, suspension, you name it. Parts a bit pricey but labor is just time. All I can think of now is the cruise control and door lock vacuum leaks. It's so very smooth and quiet on the high way, hard to put words to the satisfaction I feel from getting it to run like it does now. 99% Rust-free to boot; maybe it will outlive me too.

Henry

I blew on it, could just barely get air through. Does the union thing on the firewall have any dirctional flow or is all just connected there? I see the one line that goes over to the manifold.

Perhaps I should remove that and see if cleaning is needed.

I gave it 15 psi (would that be correctly referred to as negative PSI?) and it held well. I had to look pretty close to see the needle moving downward. The heat gun method worked pretty well. Warmed the end of the old tube to get it slightly soft and jammed it over. Tight as hell now. The line not really in bad shape after I cut of 1/2 inch.

It's tough call. I called my mechanic, he said he has a machine that tests them, which he did, as I still have them out he invited me to bring them in so he could show me. The nozzles look flat, they all look pretty damned good.

Oh man, I would give a lot to know the maintenance history. The title trouble was almost a blessing in disguise as w/o that I likely wouldn't have interacted with the PO. As I mentioned, she said her father was a VW mechanic, "from the factory in Germany," I can only guess that means either factory trained or previous engineer of some sort at the factory. Their name is indeed German, and much about the car is in pretty good shape. The father owned the car for the first 20 years or so, and only passed away a few years ago. That's one reason she was so helpful with the title renewal issues, and they wanted her to jump through hoops. Wanted her mother's death certificate (they had proof of her father's death), inheritance distribution (she had not titled the car in her name after her mother's death), a letter from her 'personal representative' (poor man's notary, best I can tell) verifying that she releases interest. I sent her photos of my first trip (below). She said she was so happy to see her car having adventures in the world and that her father would be smiling that someone was restoring it.

So who knows, would a guy with the means and knowledge replace injectors at say, 80K? My car sounds a bit like you describe yours. The body has a few tiny marks but the doors all close with that lovely, solid thunk sound. Even the cruise control works.

OTOH, the tach does't work (it's on the list) or the clock, and the climate control is always hot. Vacuum is not good (definitely on the list).

But hey, working cruise control is like a miracle. Works very well, really useful on the long trips.

https://i.postimg.cc/xTQ2TB3Y/IMG-2686-1.jpg

https://i.postimg.cc/L8xbbshr/IMG-2675-1.jpg

https://i.postimg.cc/J7QXkRLh/1-C32-...529-E694-F.jpg

Air normally just gets compressed and decompressed in that line. So there is no signifigant air flow as such. It should be okay. You will know as soon as you drive the car.


It appears that over time some of the soot etc from the egr introduction to the intake manifold lodges in the manifold fitting specifically. Plus sometimes reaches the boost limiter. Since the time the line broke off there would have been air flow in that line with some of the egr gasses and soot etc. Was why I though to blow on it was a good ideal. The boost limiter could be directional. Is a possibility. When there is an obstruction it usually will be in the manifold fitting.

This is a great point, the pressure line fitting at the intake manifold and the over-boost control valve can get plugged up with soot, and then you get a sluggish engine. You said you can barely blow through it, to me that means a fail. I'd recommend you remove the fitting from the manifold and spray it out with brake cleaner and maybe push a bit of wire in / out.

Sounds like a passed test to me. Positive pressure, negative would mean a vacuum.