poor gas milage and lack of power please help - PeachParts Mercedes-Benz Forum

Victor300E · #1 04-06-2005, 03:53 PM

Hi everyone. I bought 1990 300E with 179k miles. Car is in good shape but Im wondering. My gas milage is aroung 13mpg combined city/highway. And car kinda
slow at pickup. Sometimes it moves very slowly then suddenly 1st gear kicks in and it jumps forward. I had 420sel before and it used to be slow off the start. But I heard that 300E should be quicker. Also when you change from reverse to drive RPM drop down to 350 and car almost stalls then RPM goes back up to 500. When cold its better to pick up speed and RPM will not drop down that much. Im in NYC and gas prices are high in here well I guess all across US now but 13mpg is too low I think. Apreciate any ideas. Thanks

A264172 · #2 04-06-2005, 04:17 PM

Did you get any records with the car?

It could be a lot of things... from a colapsed Cat

to just a new O2 sensor and a tune up.

Based on your symptoms you might want to start with the cat... by disconecting it or the pre cats from the exaust manifold and straping the pipes to something... then test drive and see if it solves your power problem.

Victor300E · #3 04-06-2005, 08:08 PM

I got dealer book with oil changes recorded until 120k miles but nothing major like timing chain or other repairs are not listed. I have some receipts from various shops stating brakes,oil changes,ball joint. Ive changed 1 motor mount(it was collapsed).I changed spark plugs and they looked original. I opened distributor cap and cleaned terminals because they also looked original. I dont think its a great idea of grinding terminals since theyre should be gaped I believe. well after cleaning car became a tiny bit smoother. Thanks for cat tip. Ill try to unbolt pre-cats off exhaust manifold and drive around (maybe Ill like the noise and leave them hanging "dragster wanna be"

I want to check for vacuum leaks around idle air valve. How do I do that? Is there a place I can connect a vacuum gage to check for specific vacuum number and what will that number be? Thanks for help

G-Benz · #4 04-06-2005, 09:12 PM

Without a proper and thorough diagnosis, it's a crap shoot trying to get a definitive solution to your problem. A proper approach is to start by checking ignition components, followed by emission equipment, then fuel system related items.

But since you are getting all sorts of advice thrown at you, I would venture a guess that your MAS (mass air sensor) is bad.

Victor300E · #5 04-07-2005, 07:52 PM

I ordered rubber hoses for idle air control valve. There must be leak there when I checked spraying carb cleaner on them. I also cleaned distributor cap and rotor for now until I get new one. Ill check how strong the spark is tonight. Its getting dark outsie so it will be visible better than on sunny day. I would really like to check compression but have no time I come home late and shops are closed by the time. Also I think gutting out my cat. car has 180kml so Im thinking to gut out my cat would not hurt it

My cat is very loud comparing to my Olds minivan. Mufflers were replaced 6 months ago by previous owner ( I have receipt) so there is a chance of cat being cloged or broken inside not lettign exhaust gasses to pass freely. And of course since I dont know if fuel filer was changed Ill change it as well. It would be nice to diagnose all suspecious components with speacial tools but I cant. Im street type mechanic. I have basic tools and some jack stands and jack. It might sound little but I took off my old 420sel transmission off on the street, rebuilt it down the basement and pt it back, drove the car with no problems for a year then sold it

I loved that car. I had 2 tone interior in it in mint condition but car developed some rust in rear. I dont do body work so I had to sell it. Sorry for long post but if you guys think I should check something elso or I overlooked something that applies to my above stated proiblem please let me know. Thanks
Victor

A264172 · #6 04-07-2005, 11:04 PM

Sounds like your doing pretty well so far... like G Benz says no point sealing up your window if there is a hole in the wall. You might want to look into a few diagnostic tools like a $30.00 multi meter with duty cycle if your vacuum leaks
and spark clean up dont help. It will pay for it self after you don't through one $40.00 dollar sensor at it that you don't need.
Report back on your results... that vac leak sounds promising... 179,000 miles is brittle time for those hoses.

Victor300E · #7 05-02-2005, 08:43 PM

Installed new rubber hoses for idle air valve. Hoses were cracked and most likely were leaking vacuum. I also found that EGR valve membrane didn't hold vacuum as well. I disconected EGR solenoid to eliminate vacuum leak. Found no more vacuum leaks. I have exhaust pipes disconnected of manifold but It was insainly loud to drive around. Im thinking to get free flow cat and make shop weld it on to eliminate possible clogged cat problem since car has 180,000miles on it anyway. Adjusted my duty cycle to 45% on idle BUT when I rev engine to 2500 duty cycle goes to around 36 to 39%. As Ive seen on this forum average should be around 50%. When I average 50% at 2500rpm, Idle cycle goes to 60% to 65%. I read on this forum one member has his duty cycle 45% Idle,50% 2500rpm. Car feels much better with vacuum leaks eliminated but still has poor gas mileage around 14mpg city. Im not heavy on gas pedal so there must be another problem. Any ideas?
Thanks

r_p_ryan · #8 05-02-2005, 09:56 PM

Check out my article in the DIY section on isolating vacuum leaks. It's actually a pretty simple procedure and works wickedly well. I would try wd-40 instead of carb cleaner, but that's discussed in the article.

I also found a huge difference by setting the camshaft timing to spec.

tvpierce · #9 05-02-2005, 11:08 PM

RP,

Did you document the proceedure for adjusting valve timing?

Jeff

Victor300E · #10 05-02-2005, 11:11 PM

R P Ryan
Ive tryed wd40 as well and Im look like that I have no more vacuum leaks. How did you adjust your cam timing? Is it DIY and what tools needed to do it?
Thank

r_p_ryan · #11 05-03-2005, 12:25 AM

Checking it and adjusting it are two different things. Checking it requires only removing the valve cover. After you get the valve cover off set the engine to TDC by looking at the crankshaft at the front of the engine. There are markings that go -30, -20, -10, 0T, 10, 20, 30 on the crank pully (aka harmonic balancer). TDC is 0T. It takes a 27MM socket to rotate the engine on the crank pully. I replaced my spark plugs at the same time and had them out, which simplified turning the engine. Once you get the engine to TDC look up on the head, just behind the camshaft sprocket. There's a cast raised ridge on the #1 rocker arm carrier that aligns with a small hole (1mm?) on the camshaft. Now that you've identified the alignment markings, rotate the engine clockwise one full turn until the markings on the cam line up. Completely ignore the setting at the cranshaft pully until the cam is perfectly aligned. Only rotate the engine clockwise because there's a small amount of slack in the chain and you want to keep the correct side under tension. Once you're happy with the cam alignment take a look down at the crankshaft pully. Between each of the 10 degree marks is a 5 degree separator. I set mine to exactly TDC and it was about 10 degress off. It made a huge difference in the lower-end power.

Adjusting it requires removing the top timing cover. Check out my article on resealing the top timing cover on the M103 engine. After you've got the top timing cover off you need to remove the chain tensioner. This is the large allen plug (10mm?) on the right side of the engine (passenger side in the US). It's spring loaded, and then you need a huge allen wrench (17mm?) to remove an internal collar. The tensioner is extracted by coaxing it out with a scrap bolt. The tensioner is telescopic with a ratcheting mechanism. Once it is out you need to reset it by pushing the inner piece all the way through and then restarting it at the other end. Hard to describe without pics. This is pretty straight forward but it needs to be reset correctly prior to reinstalling it.

Now you're ready to make the adjustment. I'm not sure where the breakpoint is, but in the earlier M103 there's a half-moon key on the cam that can be replaced with one that has a set amount of offset, and they come in 2 degree increments. The later M103 is adjusted by removing the three torx bolts that secure the camshaft sprocket and flipping the sprocket around to have the other side facing the front. This changes the alignment by 3 degrees. I moved the chain by a single tooth and then back 3 degrees to get mine set properly.

A264172 · #12 05-03-2005, 04:32 PM

Quote:

Originally Posted by Victor300E

...Adjusted my duty cycle to 45% on idle BUT when I rev engine to 2500 duty cycle goes to around 36 to 39%. As Ive seen on this forum average should be around 50%. When I average 50% at 2500rpm, Idle cycle goes to 60% to 65%. I read on this forum one member has his duty cycle 45% Idle,50% 2500rpm...

How are you measuring?

... Red Banana should be in pin #2... Black Banana in pin #3... Mercedes uses inverse duty cycle. This confused me a lot when I first measured duty cycle.

If your doing it the other way (reverse pins) that would make your reading 55% at idle and 64-61% at 2500rpm, or 50% at 2500rpm and 40-35% at idle.

90mbenz · #13 05-03-2005, 09:08 PM

When my '90 300 SEL was doggin', I decided to replace the plugs. I couldn't believe how worn the old ones were and how much improved fuel economy and performance became. Start with the simple and inexpensive stuff.