Knock sensor for a 108 4.5?

[Rackne]

Did this motor ever come with a factory knock sensor?

[Litton]

I don't think they used a knock sensor until the later years/models when they went to more stringent emmisions.

[Tomguy]

No, there isn't a knock sensor - the vehicle would have to have automatic timing adjustment (not manual via a timing light) for this feature.

[Rackne]

I'm aware of my vehicle not possessing a knock sensor, I'm looking for a knock sensor to install and wondered if any later variants of the 4.5 utilized one.

[psfred]

Well, that depends on whether you consider the M119 a variant of the M117!

The simple answer is no, the iron block V8s never had a knock sensor. No use, as the ignition timing isn't computer controlled, and the D-jet injection wasn't "smart" enough anyway. Probably not the K-jet either, too slow to react.

No knock sensor on anything prior to about 1990, I don't think, and the iron M117 was "retired" in 1981. It was replaced with the M119 block (I think), which is VERY similar, but made of aluminum with silicon "liners". Also uses KE-Jetronic or LH-Jet, and I think only the LH Jet has a knock sensor.

Peter

[autozen]

Why do you want a knock sensor? That car doesn't even require supreme. It is low compression and designed to run on regular.

Peter

[Rackne]

I'm toying with the idea of water/alcohol injection ala messerschmitt in order to safely advance the timing without pre-ignition. The Holley Commander 950 w/ a crank trigger is the direction I'm inclined towards, as I'll be able to retard the timing if I run out of juice and it has a knock sensor option.

[Tomguy]

Originally posted by autozen
Why do you want a knock sensor? That car doesn't even require supreme. It is low compression and designed to run on regular.

Peter

Absolutely incorrect. It will BARELY run on regular (pinging like a SOB). It REQUIRES a minimum of 91 octane and I PERSONALLY would never use 92 unless I had to (I use 93 when I fill up).

[autozen]

Tomguy,
If you have a U.S. version 4.5, it was designed to run on regular. If you are having a problem, you need to take a look at your advance mechanism or the computer or something. I was new car prepping these cars at the dealership at the time they were introduced. I even run a 560SEL and a 90 300SEL on mid grade without problems. I also run a 90 300E on mid grade. Admittedly if I really wanted to work these suckers, I'd fuel them with Chevron premium. The 4.5 is a low compression engine and should run fine on regular.

Peter

[wbain5280]

I think it would be nice to run a modern fuel injection system on the car with a knock senssor and an O2 sensor. The distributor would have to be replaced. I'd like to dump the CIS on my 300SE and put in a Motronic system.

[Tomguy]

Originally posted by autozen
Tomguy,
If you have a U.S. version 4.5, it was designed to run on regular. If you are having a problem, you need to take a look at your advance mechanism or the computer or something. I was new car prepping these cars at the dealership at the time they were introduced. I even run a 560SEL and a 90 300SEL on mid grade without problems. I also run a 90 300E on mid grade. Admittedly if I really wanted to work these suckers, I'd fuel them with Chevron premium. The 4.5 is a low compression engine and should run fine on regular.

Peter

I don't consider 10:1 (IIRC) low compression, really.
And the manual states that you need 91 minimum in it. I would put no less in.

Not to mention the fact that EVERYONE says that their 4.5 pings with low octane. Plus I'm running ~3° more aggressive with my timing. PERHAPS the 450 version of the 4.5 (117.985/6), with its less agressive cams and stricter emmissions followings doesn't need it, but the 117.984 surely does.

[autozen]

Tomguy,
When I go down to my hobby shop today, I'll check my 1973 MB Technical Data Manual and check the compression. I believe it is somewhere around 7 or 8. You may have a 3.5 engine in there which is high compression and was only sold for the year of 1971 in the U.S. Lean over the left front fender with the hood up of course and with a flashlight read the engine # off the bell housing below the left bank. If the # starts with 116, you have a 3.5. The year 72 was the first year for low compression for MB. Many people believe that a 72 350SL is 3.5 liter, but it isn't. It has a 4.5 liter engine in it. If you have 71 250 coupe, you have a high compression M130 engine. If you have a 72 250 coupe, you have a low compression M130 engine. I also need to point out that these are American low compression engines not to be confused with the extremely low compression engines produced for countries with very poor fuel.

Peter

[Litton]

I was wondering about this myself. My owners manual for the '72 4.5 call for a minimum octane level of 91 RON. The compression ratio is called out as "8". Is the "8" a MB short-hand for 8:1? That doesn't square with a 91 octane requirement.

[autozen]

Tomguy,

I checked my TDM today, and the Europian 117.982 and 117.983 had a ratio of 8.8:1. The U.S. version had a ratio of 8.0:1. The ratio for countries with poor fuel is 7.5:1. If you are advancing your ignition from 5* atdc you will experience pinging and run the risk of piston damage.

Peter

[autozen]

Warren,

If you are unhappy with the performance of your 300SE, you may be running in open loop. Cosidering where you live I am assuming you have a Federal car which means that your check engine light will only come on if there is a failure in the o2 system. You will need to plug an off ratio meter into the round diagnostic plug at terminal #3 to see if it sweeps. if you get a fixed reading, you need to look that reading up in the DTC code book to determine where the problem is. Your system can't be scanned, because it is analog, and there is no data stream.

Peter