Besides a massive vacuum leak, what could cause a timing retardation of eight degrees? Assume that the front of the engine is all lined up, i.e. distributor at TDC as well as the timing chain sprockets...

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Henry Bofinger
1989 560 SEL (black/black)
2001 Audi TT Roadster (silver/grey)

How can a vacuum leak cause valve timing to retard?

Valve timing does change slightly with timing chain wear, and IIRC it causes timing to retard slightly, and I recall that the wear limit on my M103 is about 1.5 degrees. The V-8s are probably more due to the much longer chain, but 8 degrees seems like a helluva lot.

Do you know the age/mileage of the chain?

Duke

Is the subject valve timing, or ignition timing?

Ignition timing. The way I understand it the EZL senses vacuum, and advances the timing as determined via the R16/1 resistor.

I've got severe hesitation at first, then, as the car speeds up, it becomes more responsive. Which must be because the vacuum is advancing the ignition timing.

Mechanic (I don't trust this outfit) said that the timing was retarded by about 8 degrees, which he attributed to a potential vacuum leak.

Timing chain has about 30,000 miles on it. New guides/rails, so I don't suspect it has jumped.

__________________
Henry Bofinger
1989 560 SEL (black/black)
2001 Audi TT Roadster (silver/grey)

hb:

Do you have a timing light, and if so is its use familiar?
At idle, with the vacuum line connected to the EZL timing should be 10-14 degrees BTC.
With vacuum line disconnected from EZL timing should be 3-7 BTC.

The vacuum connection to the EZL functions to provide a small retard of the firing point at sudden, and large throttle openings.

Frank,

How much should my vacuum read at idle at the EZL? I get about 15 Hg, which seems healthy to me.

__________________
Henry Bofinger
1989 560 SEL (black/black)
2001 Audi TT Roadster (silver/grey)

Will do timing light test today, thanks for that very helpful reply.

__________________
Henry Bofinger
1989 560 SEL (black/black)
2001 Audi TT Roadster (silver/grey)

Okay, I understand, now. I believe the ignition system in your V-8 is essentially the same architecture as my '88 M103 inline six.

There is a switch on the KE throttle body shaft that sends a signal to the EZL that the throttle is closed, and under this condition, initial timing is fixed (and not adjustable) and vacuum advance is disabled. This fixed timing is 9 deg. on my M103 and it's listed on the emission control decal on the upper radiator support.

From a dead stop as you open the throttle to accelerate vacuum advance is enabled, but at low revs vacuum is very low, and there is initially no added vacuum advance. As you reduce throttle as you approach cruising speed vacuum increases enough for the EZL to add additional advance over what it adds based on engine speed.

In addition to adding advance with increasing manifold vacuum, the EZL adds advance as engine speed increases... the electronic equivalent of the flyweights and springs used on engines up to the eighties when everything went electronic rather than electro-mechanical.

The R16/1 resistor controls the RATE of advance with engine speed. Different R16/1 resistors were used depending on the market, and some models sold in various parts of the globe actually have a rotary switch next to the EZL that allows the user to select various resistances depending on available octane.

I did extensive testing on my M103 about ten years ago. I wanted to retard the spark advance map because HC emissions were near the ragged edge of the cutpoints, and retarding the map will increase EGT, which will heat up the converter making it more efficient. Knowing the initial was not adjustable I found out about the R16/1 resistor here.

The OE R16/1 resistor for my M103 engine is 750 ohms. Removing the resistor resulted in a more aggressive increase in advance with revs, which increased low end torque considerably, and allowed me to shift into fifth gear at about 35 MPH. Prior to that fifth was unusable below about 45 MPH because of the lazy rate of advance increase with revs. The increased low end torque due to the more aggressive spark advance map definitely makes the engine feel more linear and more pleasant to drive. It also signicantly reduced around town fuel consumption.

SHORTING the R16/1 connector yields the slowest rate of advance with engine speed. It won't get out of its own way below about 2000 revs, but I measured higher converter inlet temperature at idle after a short drive and with the addition of blocking the vacuum advance HC emissions were cut in half and NOx was down 90 percent. The lower HC was due to the hotter converter, and the drastically reduced NOx was primarily due to lower peak combustion temperature because of the severely retarded spark advance map.

You can find all the details by searching for threads started by me.

You mechanic's statement that timing is retarded 8 degrees makes no sense to me... retarded from what? You have to have a baseline to compare.

Shorting the R16/1 socket "retards" advance at low to medium engine speeds, but I think the total doesn't change (32 on my M103), it's just not all in until higher revs. Likewise, leaving the R16/1 socket open gets the full 32 degrees all in at lower revs with the more advance at revs below the point of max advance. And if manifold vacuum is high enough at other than closed throttle, vacuum advance is added to the advance with engine revs.

The R16/1 on my '88 190E 2.6 five-speed is located on the inside battery compartment trim panel. I believe it's located somewhere under the master cylinder on a S-Class, but I'm not sure.

It's pretty easy to test SOTP performance and emissions with both the OE resistor and with the plug shorted or open.

Let us know your results.

Duke

OK, today we took the timing light to the thing. At idle, get this, it was 20 degrees ATDC. When accelarating the engine, it advanced to zero. Two conclusions:

(1) Vacuum is working, since timing is being adjusted
(2) EZL must be malfunctioning, because of the shot initial timing.

Awaiting another EZL from eBay... Wish me luck!

__________________
Henry Bofinger
1989 560 SEL (black/black)
2001 Audi TT Roadster (silver/grey)

hb:

Did the lack of power problem occur immediately after the transmission was exchanged, or was there a period of time after the trans change during which power was normal?

No, the problem appeared right after the transmission was replaced, and never happened before.

There is an update: Timinig is not determined to be 20 degrees ATDC, way off. I suspect the flywheel was reinstalled incorrectly after the main seal was replaced, though the mechanic said it was virtually impossible to mis-align the flywheel because of a notch that needs to be matched up with it. But he is willing to pull the tranny to check it out...

__________________
Henry Bofinger
1989 560 SEL (black/black)
2001 Audi TT Roadster (silver/grey)