I have 'new' heads on the engine. engine runs/ valve timing is great (cams lining up almost perfectly) ...well but the problem is that car is very sluggish and I believe it is not well adjusted.
Can someone guide me through proper adjustment in terms of ignition (distributor) and A/F ratio (fuel air mixture) or what else.
I think I adjusted dist. at 5 degrees after TDC yesterday (with vacuum) and I am running fuel pressure at 2.9bar.
Engine is too sluggish and doesn't want to jump when I press the pedal.
Martin

5 degrees after TDC? Unless MB is verrrry different from every other car, timing is usually adjusted to Before TDC (~5-10-12 degrees). Can you see it advance as you rev the engine?

Csaba

This might have been affecting it a little:

http://www.peachparts.com/shopforum/vintage-mercedes/333737-broken-distributor-my-3-5-a.html

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Looking for Early 108 windshield surround wood in decent-to-good condition.

Csaba,
it is my information that with the vacuum hose connected the timing is 6 degrees after TDC! without the vacuum this is a different picture, I think 10 degrees before TDC.

My rotor broke and I am trying to get replacement.
Is there a better method to adjust timing with the light? someone told me he does it according best vacuum and dial backs some degrees? ANyone?

or would you start adjusting without vacuum (10 degrees before TDC...should be around 6 degrees after w/vacuum)..then
check value at 3000 rpm - should be at 30-38? degrees before TDC....

How the heck do you know how to get and hold 3000 rpm when there is no meter in the dash?

Idle is at 750rpm - 800 rpm per definition?

Is this the M116 V-8 engine?

Timing data is in manual which is available on-line (for W116 and 107). Depending on which distributor you have, you probably want to be at about TDC at idle and at 30deg BTDC at 3000rpm. I would set at TDC, then check at 1500 and 3000rpm. If you can't get it to advance tp about 30 BTDC, then your centrifugal advance in the distributor could be sticking and causing the lack of oomph!

Even for M117 NA D-Jet engines, this is best setting. Manual says otherwise, but that is because of emission reasons.

Fuel pressure should be 2bar but lightly more is OK - say 2.2bar. This helps with hot start problems. At 2.9 bar, you are way high for the standard injectors and your mixture will be very very rich! I have thought about going higher, but would have to find higher pressure injectors.

To get mixture right, reduce fuel pressure to 2.2 bar, then adjust idle and load mixtures. You have to do idle with ECU knob, and load mixture with MPS. These are completely separate adjustments. As soon as you touch pedal, you switch from idle mixture to load mixture - provided linkages are set up correctly.

I could give more detail on mixture adjustment, but you will need a %CO meter, a wide band AFR meter or one of the expensive 5-gas exhaust analyzers that some shops have. Without one of those you really can't do it except by trial and error.

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

Thanks Graham.... very interesting

Yes my engine is the 3.5 - M116.981

I have the Bosch # 0231 302 002 distributor and I'll get a new rotor soon.
I'll set dwell at 30 degrees.

"TDC at idle and at 30deg BTDC at 3000rpm" is this with vacuum attached I guess? (The manual says something about 6 degrees after TDC at idle but you say this is a political emmission issue not best performance- correct?
Can I do idle at 0 degrees TDC with fuel quality in Oman?

Idle being 750 -800?
I have the trouble to adjust measure 300 rpm? I have no gauge in the dash (I have old school dwell meter but it doesn't do 3000 rpm). So how can I rev the engine at 3000 and check advance?


Sorry, I was wrong.. I am running 29psi fuel pressure (not 2.9 bar)...close to 2 bar. Some people recommend against higher pressure but I'll try your 2.2bar (I do have the hot start issue sometimes... I flushed the radiator for 2 weeks and I tweaked my fan clutch in order to avoid overheating)

I have still a Innovate Motorsports LM-2 A/F meter in a box... never used it.
Do you think I can use it? I'd need to weld a bung into the exhaust for the oxygen sensor but I am unsure where to place the bung...?.

"You have to do idle with ECU knob, and load mixture with MPS"
questions:
1) How do I set the ECU knob? highest rpm?
2) What is the MPS adjustment for load mixture? How does this work?
I guess I am doing this adjustment with the LM-2

W:
Re: Ignition timing
When you get a new rotor, the question to be answered is: does vacuum applied to the distributor cause advance or retard?

The proceedure that I would suggest is to set idle timing to ~8 deg. BTDC without vacuum. Then, with the engine idling, connect the vacuum line. Did the timing advance or retard?

If, as I suspect, the timing advances with vacuum, set the total advance w/vacuum at over 3500 RPM to ~ 43 deg. BTDC.

Frank,
I am a bit puzzled by your question.

On my 72 D-Jet and from what I have read, on early D-Jets vacuum retards the ignition. Advance is handled by the centrifugal weights. Some later D-jets had both retard and advance, but not in 1971.

Is there something about this particular model that prompted your question?

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

I agree with Graham
If I set timing at let's say 10 degrees before TDC (w/o vacuum) then w/vacuum I am reading maybe 5 degrees after TDC meaning a retard NOT an advance.

Hi Graham,

I think I understand the principle vaguely from what you are saying about higher fuel pressure and ignition timing.
Do you know the Innovate Motorsports LM-2 instrument?
And do you think I can use the LM-2 to dial in the MPS sensor?
If I know the condition I can do the adjustment here in Oman I guess?
Would you help me?

Same happens on mine (72 W108 4.5L M117)

Graham, where can I read how to check/adjust fuel pressure?
Is there any aprox setting for mixture adjustment without the instruments?

sorry for the Hijack

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1972 W108 280SE 4.5
1977 W116 450SEL
1981 E12 528i BMW

So you have US spec car but you are in Oman! The USA specs do say at idle you should be at 6deg ATDC with vacuum. Maybe stay with that at least initially. Make sure you have A/C off. Later you can try more advance.

What fuel does your owner's manual specify? If your fuel in Oman is lower octane, then it would probably be just as well to be on the low end of the 3000rpm advance range. Manual says this can be 30-38deg BTDC, so perhaps 30 would still be good?

Check you manifold vacuum - should be about 15-17" HG at idle. Very important not to have vacuum leaks.

You can get cheap rev counters. But maybe a Digital timing lights with rpm? or a multimeter with tach?.

Even with tach on my car, it is not easy to check at 3000rpm (need two people) I usually set timing at idle (800rpm for your car) first. Then rev car and check at 1500 and then a burst and see where it goes to at 3000rpm. If distributor centrifugal advance is working, according to the specs, your car with vac connected should go from 6ATDC to +/-1TDC at 1500rpm and then to 30-38BTDC at 3000rpm. But they also say vacuum adjustment after retard is 12-18deg retard at idle. That I don't understand. It makes sense on my 1972 (figure below yours in manual), because the vacuum causes the timing at idle to retard by 10-14deg. Take vac off when at 5 ATDC, and it advances to say 5-8 BTDC. But on 116, those numbers don't jive. So I would set at 6ATDC at 800rpm, then rev up and see where timing goes at 1500rpm and at 3000rpm.

Re fuel pressure - 29psi is per spec. 2.2 bar is about 32psig. Car will run richer but still OK if mixtures have not been messed with.

Re Innovate Motorsports LM-2 A/F - That would be great! I have an AEM AFR permanently installed. I put the bung on one side just before the first muffler and after the crossover pipe. Not 100%, but should be OK. Seeing your connection is temporary, you could put one on each side!

Re ECU idle mixture. First make sure throttle position switch is set to signal ECU that engine is at idle.(There is a write up I did on TPS adjustment here somewhere). Set knob on ECU in centre of it's range. 9 clicks from either side, I think!) With warmed up engine, check %CO or AFR on meter. At first adjust by ear until engine sounds OK, then fine tune. %CO should be about 2% (AFR 13.8) but I find that having it richer helps with hot starts. I am at about 4% (AFR 13) Rev car in between and do it a few times and let meter settle out.

For load conditions, you need to adjust MPS. You do it with a 4mm allen wrench - There is an adjustment on one end of MPS. Sometimes it is sealed with wax? if never adjusted.

If you can drive with the meter connected, you can check on say a steep hill (in Oman?) or maybe with brakes partly on and engine loaded up. %CO should be in 2-5% range. (13.7-12.64). If you can't drive with meter, after setting up idle mixture, pull the plug off the Throttle Posn sw. Then adjust MPS so you get about 1% at say 1000rpm. Rev car in between and do it a few times and let meter settle out.

Sorry for the information overload. I am leaving soon for 2 month trip and won't have my books with me, so just wrote down everything that came to mind!

Good Luck with it!

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

http://handbook.w116.org/Engine%5C107%5CM117_45%5C074-120.pdf

No way to really adjust mixture without meter. Except, idle can be done by ear. Just get it run nice! For load mixture, pull the plugs and see if they depict rich or lean running (some plug manufacturers have picture charts). Then make very small adjustments on MPS (1/8 turn at time) and check plugs after a good long run. I forget which way is rich and lean on MPS!

PS: Full engine manual here - just chose a 73 and it should be close.

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

Thanks

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1972 W108 280SE 4.5
1977 W116 450SEL
1981 E12 528i BMW