poor acceleration/mpg worse than my Volvo
 

1985 300TDT (wagon) does not accelerate smoothly from a dead start. First "flare" (do you call it a flare?) happens quickly after starting, lasts about 2 to 3 seconds and overrevs approx. 200 to 300 rpm, then continues to pick up speed, next "flare" happens about 20 mph, with much less overrev. Once I get up to about 35 to 40 freeway cruising is okay. Engine seems to rev smoothly with accelerator pushed. I get about 15 mpg. I bought car in Sept 2002. Oil changes (from original maint book) every 5k til 60K, then again at 72K, after that, NOT IN BOOK. I just changed oil and filter, 2 fuel filters, air filter. Current mileage is 120K. Dealer changed trap oxidizer (CA model) to catalyst, and also replaced turbo. Car starts right up (after glow plugs were changed) before that, had to crank about 20 to 30 seconds in the A.M.. Only 3 obvious things (to me, anyway, this is my first MB) door lock plugged at firewall, ALDA cap off - screw has been adjusted - I've tried it a few times 1/4 turn at a time, and oil leaks at turbo connections, valve cover breather, filler cap, oil level does not show consumption. No smoke except on hill trying to keep up with other cars - can see it better at night in rear cars headlights. I have not yet changed transmission fluid or filters/gasket, level is okay. Also, 1 clear fuel line from large fuel filter is "black" the one going towards engine in the direction of the turbo. I would like to get some diesel purge, heard it can help clean up fuel system, but no luck yet in Hawaii. Car idles fine, sounds fine. Before cleaning up engine compartment, very "sooty", is this leaky EGR or was it cracked exhaust pipe at turbo - replaced by Dealer. Any help would be greatly appreciated.

Dear Smartin,
Are you talking about a W123 or a W124?
Anyway, when you say you checked the transmission oil level and found
it OK, do you really know how to verify this?
I can be wrong but given the fact it's your first MB, I doubt about it.
First warm up to normal working temp by driving the car and use the selector
in the other positions to - not only in "Drive".
This is because you can NOT check up the level with a cold tranny. Than it will
always be to high! And when the level is OK when cold, the level is in fact
far to low and will cause that weird behaviour.
In your place the cheapest "tune-up" of the tranny is replacing the oil + filter.
At least the first time, let this be done by a mechanic with MB experience to avoid problems.
For all the other troubles ONE good advise : use the search engine on this
site! It contain tons of information about virtually every MB item!
You will enjoy it and at least learn a lot about your TD.
Have fun!
Danny.

I under stand you have a 85 300 TD Calif.. I have one too.. I am unsure what you mean by flair.. They are not fast cars but I have to wonder if you may not have other problems..

1.. Remove hollow screw at back of intake that has plastic tube that runs over to fire wall behind vacume brake on fire wall.. Clean screw out.. and be sure intake is clean inside where screw goes.. Go to ALDA and unhook plastic line that attaches there.. blow into it.. and be sure air comes out end that you unhooked at intake.. Its common to have bad rubber at the valve that it runs to at the fire wall.. If you can not blow thru or have a leak fix it... Then rehook line.. as a test you can bypass valve at firewall with a rubber hose if you question it.. however if its a problem I would replace it.. It must be clean thru and not leak when blowing thru..

2. Be sure all lines are hooked.. For some strange reason the Calif cars run better with every thing hooked up.. Unlike others that some feel run better with every thing unhooked..


3. Be sure the themrostat is OK.. If the car is not getting up to 80 or above it will not run well ... They tend to dump the turbo air into the cat. to make it start working when cold.. If it does not get up to temp that does not stop.. However once warmed up they run well..

Does the Tac work???? Please answer as it tells us lots more if it does not..



Ken

95300YDT-A: Its a 123. I will check the transmission per your instruct. Thanks.

Ken, Ihave cleaned bolt, but have not checked hole in intake where it screws in. Also have not checked other lines to ALDA, or (overboost?) valve on firewall near brake. Will valve allow air thru with engine off? Tac does work - idle about 500 rpm, highway cruising - about 2500 to 300 (55mph to 65mph). Ken, do you know anything about Mercedes Benz putting older service manual info online. (I called 1-800-for-merc) twice - last Sept, and Jan 03 was told that it may be up in Spring 2003? I do not know if this information would include ALL manuals - Transmission, Engine, etc.,. OH- as far as temperature I do see about 80 to 85 - had to change sender in engine - last week.

The valve will let air thru with engine off... Also the rubber hoses that hook the plastic lines to it will often crack.. If they are cracked and the pressure from the intake does not get to the ALDA it will only develop non turbo power.. The valve is really an over pressure so the engine does not make to much power in lower gears.. For guys like me that live in the high country and pull a trailer with their Wagons... Keeps it from making to much power in the lower gears off the line so you do not wipe out the Trans in low gear.. If you live in the flat lands it would most likley never work.. However leaving it in just in case is good.. A little power loss under a hard load in lower gears is better than replacing the trans.. It should just let air thru and not vent with engine off..

You can pick up a CD manuel at E-Bay for about 14s or 16 Bucks..

Hope this helps..

Ken

KEN - I stand corrected on the thermostat issue. I barely see 80 degrees even after climbing (pretty steep - 1 mile? long) hill going home. Even on the freeway - the temp is UNDER 80, CLEARLY. Will this affect MPG that much? What about EGR? (If it's stuck open? I have to check to see if it is - I have capped vac line to EGR.) Do you know if fuel injection pump could be wasting fuel somehow? - I'm still trying to understand the bad MPG. Without compression test (yet), don't know if that would be the culprit. Again, and maybe this is of NO consequence, but the car does do highway speeds nicely, but again my other car is a Volvo, and this is my first MB. Thanks again!

The 85 300 Calif is set up so that it will not develop power until the temp gets up to about 80 or above... It has a computer of sorts behind the kick panel on the passenger side.. If it does not get up to temp it will have very low power.. Poor fuel mileage.. The Thermostate on Mercedes fails open but as it does it just keeps giving lower temp.. So you need to deal with that.. Get the replacement thermostate at the right temp.. On this model I always get them from Mercedes as they seem to help the car more than many after market ones do as the temp is critical on the California cars..

Mercedes says the EGR on a Diesel does not affect how it runs.. But my 85 300 TDT will climb the same hill at 5 mph better with the EGR Hooked than with out.. Also if you did unhook the EGR be sure to cap the vac line as if you do not you will cause lots of other problems...

Also again.. If the line from the intake to the ALDA has a leak the turbo does no good..

Ken

Ken, Could the EGR be stuck open? If so what would this do to performance/mpg? Also, if thermostat is stuck open, mpg will suffer - how much? I mity-vac'd the EGR, it did not sound like the piston inside was sliding very much - could not get a good look inside "slot" - but if it was functioning correctly, should'nt I be able to easily see the mechanism moving up/down? Again, as far as mpg suffering due to thermostat, is this a phenomenon familar to California diesel, or ALL diesels?

As far as the EGR Valve.. You are just wasting your time.. Hook it up and forget it..
All Cars with Computers including your diesel that do not get up to temp remain in a start up mode until they reach temp.. That means they will not develop power and use extra fuel.. I really do not think the thermostat is stuck open.. It fails open.. Its junk and needs to be replaced..

Also you need to turn the ALDA back down 1/2 turn at a time until you have a large loss of power in the lower rpm.. Then turn it back up about 1/2 or so turns.. As it had been fussed with before.. You have no idea where it is.. If its to rich the soot will clog the CAT and that will keep the turbo from getting enough exhaust to work.. as the turbo is after the CAT... You may need to run it a bit lean for a while to burn the junk out of the CAT..

You really need to start dealing with these things or just shut the hood and forget it..

Ken

smartin,

From what you describe, the "flare" could be a transmission or torque converter problem. It's hard to troubleshoot without more information. There should be no "overrev" as you describe. First thing to do is change the fluid & filter though.

The power loss is very likely due to a blockage SOMEWHERE between the banjo bolt on the intake manifold and the ALDA. It's also possible the ALDA is leaking, which also reduces power, but requires a MityVac to test with pressure. Check all the lines, you can bypass the overboost protection switchover valve (temporarily) and see if that helps. (I left mine permanently bypassed on my '84 as it was plugged and the max boost I measured was ~12.5psi with the wastegate hose blocked, and the circuit doesn't trigger until 16-18psi!)

About the EGR. I politely disagree with Ken. Most, if not all, Mercedes diesels will run significantly better - AND get better MPG - with the EGR disabled. If not, something is wrong. You can plug the line, but that only works if the valve physically seals inside. A more permanent method is to insert a piece of sheet metal between two gaskets at the intake manifold side. This will kill the EGR regardless of the valve condition. Dumping sooty exhaust back into the intake never helps, even on CA cars. I have the valve removed totally on my one CA model 1987, it runs GREAT, and it's disabled on both of my other cars.

Also disconnect and plug the vacuum line to the ARV (air recirculation valve) on the turbo. This is a big power & MPG killer as well. It existed to help the trap oxidizer, which is gone, so you sure don't need the ARV bleeding off boost and hurting part-throttle power. It's disconnected on all my cars, works great.

FYI, 15mpg is REALLY REALLY bad. I've never seen one worse than 18mpg, and 20-22 is the typical bottom end for W123 diesels. I'd check for a fuel leak somewhere - seriously. Also, the factory spec for acceleration is 15.2 (?) seconds from 0-100kmh (0-62.4mph), with two occupants, +/- 7%. Yours should be in the 15-17 second range, on flat roads, near sea level. MPG can be affected significantly by the ALDA adjustment, try messing with it like Ken said (turn CW until power drops, then back 1/2 turn or so). Ignore any smoke seen at night in headlights - please! That's normal even on good running cars, like my 30-32mpg 87's! Look for smoke in bright sunlight under full throttle, high RPM, should be just a wisp - any black clouds and either it's too rich OR you have carbon being burned out. Drive it like you stole it and this should improve in a few weeks or months.

It would also be a very good idea to check timing chain stretch, do a valve adjustment (required every 15kmi), and if possible check the injection pump timing (easy with a $30 tool from the dealer).

Good luck,

Oh yeah - engine temp. Your car either has a bad thermostat, or a bad temp sender in the cylinder head (near cylinder number 2 glow plug, approximately.) A new sender is ~$10, ditto a new t-stat. I'd change both. When I bought my '84 it ran around 60C all the time, with a new t-stat & sender it stays parked at 87C almost all the time (never seen it above 90C, ever).

And yes, the engine running cold can reduce MPG. You should fix this ASAP as it will also increase engine wear!


Regards,

gsxr and Ken - thank you for ALL the help. I just got thermostat from Rusty. ALso, filter and gasket for trans - will have a mechanic do it. Lastly - "leaking ALDA" ? Do I Mity Vac any of the vac ports? How much vac should it hold? I have 2 spares from junk yard - with tamperproof cap still on - if original leaks - can I install one of spares without adjustment? Just so you know - this shall be secondary to thermostat and trans.

The chance of your ALDA leaking is slim, and may not affect performance drastically. What happens is the lower shaft seal doesn't always seal properly. The way to test is with a MityVac that can produce pressure (like the Silverline Plus 4050 kit from thetoolwarehouse.net). You connect the pump to the ALDA and pressurize. It should hold pressure, and only leak down very slowly at pressures below ~10psi. Above 10psi it should hold pressure quite steadily. If the needle drops rapidly, or you can't get it to hold pressure at all, it's leaking. You can just swap on another good ALDA, however it may not be calibrated quite right - you'd have to drive it and see. Photos of the ALDA internals are here:

http://www.meimann.com/images/mercedes/OM603_intake/

I still this this is NOT your problem though, I'd start with the other things mentioned - especially the ARV disconnection, pressure line to ALDA cleaning, valve adjustment, and checking timing chain stretch. Looks like you have your work cut out for you! :cool: :cool:


Regards,

Check to make sure you have boost. A pressure gauge can be simply connected to the ALDA line with a "T" and zip-tied to your windshield wiper. Go for a ride and make sure you get at least 10psi on hard acceleration. Your turbo also has an air recirculation valve on the outlet of the turbo compressor housing. This valve has a rubber diaphram. It is possible this valve is faulty and either leaking boost or "recirculating" it so no boost is achieved. I modified my valve by dropping a 5/16" nut in the spring housing to increase the seat pressure on the valve. Also disconnected the line. I see no reason to "dump" boost other than some silly CARB law. The EGR is easy to disable as suggested. Make a block-off plate by copying the egr gasket and bolt it underneath the EGR, viola! No EGR but it is still in place to keep the Smog Nazis at bay. When is the last time you had a valve adjustment done? What does the tranny fluid smell like? If it smells like burnt brake/clutch lining you may have problems. RT