My Benz hates Hills - PeachParts Mercedes-Benz Forum

bigfredb · #1 10-07-2009, 07:51 PM

OK, so as the title says, my benz hates hills.

My 83 300SD has plenty of power on the flatland. Plenty of power and acceleration. However, going up hills it is a total dog. I get around 40-45mph. On the Freeway, I have to pull over into the "truck" lane with my hazard lights on.

What I have done:
- I cleaned out my Banjo bolt and vacuum lines.
- I have a Vacuum pressure gauge mounted above my dash and it is reading 6 to 8 psi going up the hill.
- I recently replaced the fuel filter(s) to see if that would help. No luck.

What else can I look into?

johnathan1 · #2 10-07-2009, 07:56 PM

I've always thought that it should boost anywhere from 10 to 12 psi? I could be wrong, but maybe you are having issues with your turbo or boost control system?

79Mercy · #3 10-07-2009, 07:57 PM

when was your last valve adjustment performed?

Skippy · #4 10-07-2009, 07:58 PM

I'm guessing that the ALDA still isn't getting boost signal. I think the 126 has some sort of overboost protection valve that sometimes goes bad. That may be your problem.

bigfredb · #5 10-07-2009, 07:58 PM

Quote:

Originally Posted by 79Mercy

when was your last valve adjustment performed?

Its been over a year since the last valve adj.

Skippy · #6 10-07-2009, 07:59 PM

If it's been over 15,000 miles, do a valve adjustment and tell us if that helps.

barry123400 · #7 10-07-2009, 09:10 PM

I assume the vacuum pressure gauge is on the vaccum system? The turbo makes pressure. If so what negative pressure is present on the flat? I may be wrong so if you could clarify.

The gauge reading you really should have is the fuel pressure present in the base of the injection pump. Under high load conditions going uphill the engine may be fuel volume starved. Or some sneaky vendor put a 300d trunk label on a 240d.

winmutt · #8 10-07-2009, 09:12 PM

6-8 psi is to low. You should hit 11psi minimally. Also certainly valve job.

pawoSD · #9 10-07-2009, 11:06 PM

I'm betting it is shifting into 4th gear and lugging up the hill. If you manually shift the gear selector down to 3rd or 2nd gear on the hill does that help?

How big/steep are these hills? A 300SD running properly can easily hold 80ish+ mph up most hills....at least mine can.

kerry · #10 10-07-2009, 11:48 PM

What is your vacuum pressure gauge reading?
Could be a plugged tank strainer. Switching inlet and return hoses would confirm/deny this.

NH82W123 · #11 10-13-2009, 12:55 PM

Kerry, do you have any experience switching the fuel lines to check for a clogged tank strainer on a 300D? I'm having similar problems as the OP (fine performance until getting to highway speeds, then the car feels fuel-starved accelerating over about 50 MPH or so). Do you mean to switch the lines under the hood where the metal lines meet the rubber ones? I tried this morning and the return ("cigar") hose wouldn't reach the metal line that carries the fuel from the tank. Should I get a length of fuel hose and temporarily replace the cigar hose?

Thanks!

Charlie

Phil · #12 10-13-2009, 01:22 PM

You are definitely running low turbo pressure. I would first check the line from the back of the intake manifold to the over boost valve and then to the alda. If you remove the line from the over boost valve and then try it you can see if you now have good pressure (don’t leave it this way buy just do it to test). If that is good you need to adjust the waste gate to get 7 to 8 bar or 10 to 11.5 PSI. Adjust your valve also.

The picture shows the waste gate on my car

sd300td · #13 10-13-2009, 02:11 PM

Quote:

Originally Posted by pawoSD

How big/steep are these hills? A 300SD running properly can easily hold 80ish+ mph up most hills....at least mine can.

MI doesn't have hills like Socal. The OP is likely talking about mountain passes since he mentions truck lanes, 45mph, etc.. 5% grades or more for 2-3 miles, etc. Most of these cars can get over the top at 55-60mph when in proper tune, but not 80mph.

bigfredb · #14 10-26-2009, 04:32 PM

Thanks all,

A friend helped me do the valve adjustment over the weekend. All of the valves were badly in need.

After the adjustment, there was a considerable increase in power available. I haven't taken it up the big hills yet, but so far so good.

One question, is it typical that after a valve adjustment that I would need to adjust the transmission shifting as well? It seems to rev pretty high between each of the gears. If this is the case, how do you make the adjustment?

bsmuwk · #15 10-26-2009, 06:45 PM

It's possible that during the valve adjustment, you've inadvertently tightened the bowden cable from the transmission. Check and recheck the bowden cable for slackness or tightness. To make it shift just a tad bit earlier, slacken. To increase time spent in a gear, tighten.