How many of you run 87 octane fuel?

[Cobra Jet]

After reading over some online Bentley pages - here's a statement directly from the Bentley, page 120-6 (Ignition System):

Crankshaft Position Sensor (CMP)

The camshaft position (CMP) sensor is used by the engine management system for sequential fuel injection and knock control.





"Knock control" - based on the last 2 words of that published statement by the Bentley Authors, would'nt this mean that the CMP does in fact sense engine knock and therefore relays any such knock data back to the DME, which the DME would then take the appropriate actions to control air/fuel/spark?

? - open for discussion, as many are saying that the M42 does not have a "knock sensor" - maybe the CMP does sense engine knock as per the Bentley...

[colin86325]

The E30 M42 doesn't have knock sensors, but the E36 M42 does.  I had knock sensors on the 1992 E36 engine I pulled.

[Cobra Jet]

I understand that everyone says the E30 M42 does not have any actual "knock sensors" - but what I'm saying is, the Bentley is stating that the CMP serves (2) purposes - sequential fuel injection and knock control...  Is the Bentley incorrect?

Just trying to figure out if the CMP does double duty or not, based on the Bentley.

[nomad]

that Bently is for the E36 model right? Because the E30 model doesn't give the detailed M42 specs right?

I'm interested in what it says about the CMP sensor as well.
There are two different numbers for the sensor though.
E30 318is = 12141721861
E36 318is = 12141734813 could be a difference in function as well? They are the same size/location so no need for a new part number unless they are different.

Also, the E36 M42 block (and later M44) is the only M42 that includes item #15 "ping sensor". This is not present on the E30 variant.


could be that the later M42 Ping Sensor works with the later CMP to send a delayed signal to the ignition.

I believe that the confusion is that you have to work with a manual that is made for the later engines. But, this gives me compelling reason to buy a 92+ M42 if my engine breaks.

[Cobra Jet]

that Bently is for the E36 model right? Because the E30 model doesn't give the detailed M42 specs right?

I'm interested in what it says about the CMP sensor as well.
There are two different numbers for the sensor though.
E30 318is = 12141721861
E36 318is = 12141734813 could be a difference in function as well? They are the same size/location so no need for a new part number unless they are different.

Also, the E36 M42 block (and later M44) is the only M42 that includes item #15 "ping sensor". This is not present on the E30 variant.

could be that the later M42 Ping Sensor works with the later CMP to send a delayed signal to the ignition.

I believe that the confusion is that you have to work with a manual that is made for the later engines. But, this gives me compelling reason to buy a 92+ M42 if my engine breaks.

Hmmm... more good info!

[nomad]

Here's even more good info. Nice read on the updates for the E36

http://www.motortraders.net/groups/group.asp?group=1&menu=87

To ensure that knock is reliably identified, BMW installed two knock sensors on its four-cylinder engines (many otherwise comparable systems for four-cylinder engines use only one sensor).

A multiplexer circuit in the engine control module analyzes the signals. This ensures that only the signal from the cylinder in which combusion is actually taking place is transmitted to the adjacent knock sensor. The multiplexer is switched correctly by evaluating the signal from the cylinder identification sensor (on the camshaft). The knock sensor is a piezoelectric conductor-sound microphone with a broadband characteristic. A piezo-ceramic ring is clamped by a spring washer between a seismic mass and the sensor body. If the seismic mass is accelerated, it exerts a force on the piezo-ceramic element. Opposed electrical charges build up on the upper and lower ceramic surfaces, and generate a voltage at the contacts. In this way, acoustic vibrations can be converted into electrical signals. These in turn are transmitted by shielded wires to the engine control module for processing.

1 Shielded wire
2 Cup spring
3 Seismic mass
4 Housing
5 Inner sleeve
6 Piezo-ceramic element

The knock sensors are bolted to cast bases on the intake side of the engine block, between the 1st and 2nd and between the 3rd and 4th cylinders.

These locations ensure that even when knock is only slight that the acoustic vibrations emitted from the combustion chambers are transmitted reliably to the knock sensors.

[tjts1]

I was under the impression that the crank sensor on our engines was on the front of the block reading off the crank pulley.

[nomad]

And if this isn't a page that should be stolen by m42club.com then I DON'T KNOW WHAT IS!:   http://www.motortraders.net/groups/group.asp?group=1&menu=89

Spectacular info

[nomad]

I was under the impression that the crank sensor on our engines was on the front of the block reading off the crank pulley.

It is.


1. Fuel tank with pump
2. Liquid/vapor separator
3. Fuel filter
4. M1.7 control unit
5. Ignition coils
6. Spark plugs
7. Injectors
8. Fuel rail
9. Fuel pressure regulator
10. Coolant temperature sensor
11. Throttle valve potentiometer
12. Idle control valve
13. Active carbon canister
14. Evap. purge valve
15. Airflow meter
16. Air temperature sensor
17. TDC and RPM sensor
18. O2 sensor
19. Cylinder identification sensor
20. Battery
21. Ignition switch
22. Main relay
23. Fuel pump relay

[Cobra Jet]

I was under the impression that the crank sensor on our engines was on the front of the block reading off the crank pulley.

Not to get off topic, but to supply useful info:

CPS & CMP are two totally different sensors (and most online parts catalogs & vendor sites sometimes do differentiate between the two, while 98% of the time do NOT!  Realoem is the ONLY site that lists the correct part #'s for both, so when needing to order one or the other, be sure you go to realoem for the correct sensor part # FIRST before placing your order!)  

CPS is located externally, is down by the crank and is inserted into a small bracket and it reads the crank teeth & spaces in between, relays that info back to the DME.

The CMP is located internally, up by the valve cover (near thermo housing) and is inserted w/ rubber o-ring into head.  If ordering a new CMP, be sure it comes w/ a new o-ring, some do some don't.

The sensors do look similar - the CPS has a longer wire, while the CMP has a short wire.  Both perform completely different functions.

[Cobra Jet]

And if this isn't a page that should be stolen by m42club.com then I DON'T KNOW WHAT IS!:   http://www.motortraders.net/groups/group.asp?group=1&menu=89

Spectacular info

WOW!  I added that one to my "favorites"!  Someone should definitely get that permanently stored & "sticky'd" to this site before it's no longer an available page in the future - EXCELLENT & VALUABLE M42 INFO.

[tjts1]

Ok so it is at the front of the crank

Because the article in #91 (excellent info by the way) says "Locate sensor at left rear side of cylinder block" which would mean it runs off the flywheel. But I guess that only applies to E36 engines. I was confused. All is well now.

[Cobra Jet]

Hmmm...  based on that very informative link, it seems that the DME used in the PRE -1994 E36 M42 would be nearly identical as far as pinouts & functions as used in the prior E30 M42's - because the tech info provided states that both DME's were "1.7's".

The ONLY differences noted between the E30 M42 DME 1.7 and the PRE-1994 E36 M42 DME 1.7 are those in the shaded blocks below:




The DME used AFTER 01/1994 uses DME 1.7.2.  "A new version engine control module (DME 1.7.2) is used due to a final stage output modification for the ignition coil and all programming changes to accommodate the new air shroud injector system. DME pin designations remain the same when compared to DME 1.7."

http://www.motortraders.net/groups/group.asp?group=1&menu=88



(nomad - I started a new thread in the M42 Reference forum on here and pasted the link you found in there.  There so much valuable & detailed tech info in the link you found that it's only appropriate to create a new thread for it).

[sheepdog]

I wish I had my car to try it out today. It was the first day of the year over 100f. Unfortunately my GF has the car while I work on her volvo. So far I have only tested it at WOT up to 90f intake temp.

I don't think this has anything to do with affording a BMW. I started out using low octane fuel out of curiosity. I wanted to see if there was a way to make this car run reliably on 87 octane without any compromises. So far so good. If ever kill it I'll buy another. But I doubt octane will have anything to do with this car's demise. My next experiment involves water injection.

I don't know, you be the judge. My engine is full of bees.
http://farm4.static.flickr.com/3077/2496605756_c1fdd73074_o.jpg
http://farm4.static.flickr.com/3294/2495781545_5235c82284_o.jpg
http://farm3.static.flickr.com/2034/2496605722_4f04604dac_o.jpg
http://farm3.static.flickr.com/2025/2495781499_5a16af3de7_o.jpg
Ok i'll admit it. I cleaned it.

I think it has everything to do with owning a BMW.
If you cannot afford to feed it properly, you should not have it. Plain and simple. You are risking your motor for 20 cents a gallon.

As fro how clean your motor is, how are the pistons? Rings? Other side of the valves? Is there any casting flash?

BMW does leave some leeway in there, specifically for differences among engines, altitudes, wear and tear, etc... The problem is, you do not know if yours is one of the better or worse ones.  How do you know if you did not get a piston with a slightly thinner casting in the top? Slightly deformed or more casting flash...

You can argue all you want about how good your engine is, the only true test is time. The only way to know is when it dies.

Again, all to save 20 cents a gallon.
Do you also run the cheapest oil you can get? How about filters? Tires?
Save that sort of thing for your Honda or Toyota where it will not matter. You drive a high end sports sedan that needs higher end parts.

[tjts1]

Get real. We drive $1000 beaters. This is no "high end sports car". It was the poverty spec bmw when it was new, its a 17 year old beater today that happens to be fun to drive and gets pretty good mileage. I'm sick and tired of all the "get a Honda if you can't afford a bmw" nonsense Have you looked at how much a 92-95 civic costs? If you want to stay on the safe side and use 91 octane all the time go ahead. Theses nothing wrong with that. But this whole theory that we are somehow not deserving of the all mighty BMW because we happen to run 87 octane is just plain BS. I'm willing to bet 90% of the 10+ year old bmws on the road are being fed 87 octane without a second thought. The first owner might have used 91 octane but once the car hits the used car market, all bets are off.
I filled up the tank at lunch today. 31.5 mpg on 87 octane.
cheers
Justin