E30 316i cat and o2 info

[Gwyllgi]

Hi everyone. I am searching internet for a long time and i cant find the answer. I have e30 316i, 1990, 2seat, EU. M40 engine, LPG installed. I have an bad consumption (15l per 100km) and i'm trying to resolve this problem. Most of ppl say that i need to check my o2 sensor but i cant find it on my car!
On VIN decoder i can see that my car is bought without CAT. So, does e30 316i without cat have o2 sensor??
Is there any pictures of exhaoust system with and without cat so i can compare it with my system? If i dont have cat, may the problem be in airflow meter?
When it run on lpg, revs are constantly goes up and down while on gas it works fine (with that i assume idle valve is working fine?).
Pls help

[MarcoZandrini]

Great question! The O2 sensor provides feedback to the engine computer (DME). The DME uses that data to determine the fuel/air mixture. So, technically the car can have an O2 sensor and not have a cat. Did you check www.realoem.com?

[Gwyllgi]

Yeah, i know purpose of O2 sensor, but i was killing myself finding it. I have checked page that you have provided, it says i dont have O2 sensor:
So i can conclude that i dont have 02 sensor. So, if i'm correct, only relevant info for "DME" is AirFlow meter?

[dworthy]

Sorry lad, but the 316i E-30 will not have an oxygen sensor.

Now what you do need to do is check the timing belt, for if it snaps, you just as well get a new motor.

So besides the above, this is what I would check:
1) Distributor and rotor
2) Spark plugs and leads/wires
3) AFM, test it and make sure the swing is easy
4) Vacuum lines and leaks.

[Gwyllgi]

Well, i think motor and timing belt are ok. Car is driving fine, I dont have any problem driving it. After buying it it was running irregularly/shaking in idle, both on gas and lpg. Few ppl told me that i might have problem with spark plugs and SP wires. I have changed that and now is all ok, on gas. On lpg it constantly goes up and down with revs, lets say from 500rpm to 900rpm.. Few seconds on low then one second on higher. Beside that, low fuel ecenomy is problem.

i will definetly check vacuum lines, and now after i know i dont have O2 sensor, I will change MAF.. Only problem is to find it, under normal price ofc..

[dworthy]

Yes with the idle going up/down that can be caused by a vacuum leak or the idle stabilizer valve (ISV). Most of the time you can just clean the valve and it will work fine.

Don't change the AFM, for that would be just throwing parts at the car, test it first.

BTW you have a Air Flow Meter on the M-40 motor. A MAF is a Mass Air Flow and that is on the newer cars.

[Gwyllgi]

Oh, i tought thats the same, thnx for info.
Apart from idling problem, changing AFM could resolve my fuel economy problem? Since I dont have O2 sensor..

How I can test AFM?

[dworthy]

Start at about 3:00 on this video:https://www.youtube.com/watch?v=hQYRep6K15k

Yes, it is for a 84' 733i, however yours will be very similar. Now, I don't think you would need to pop off the black cover as that would be only needed if you notice a drop in the resistance test.

Also you should test the throttle body sensor aka Throttle position sensor too.

[Gwyllgi]

Ok, thnx for help!

[Gwyllgi]

None of the above was problem. Cylinder head gasket broke and now whole engine head is on inspection, maybe itself broke. :S

[dworthy]

Well it is what we call diagnosing. You start with a known system and go from there, we would have made it to Compression and leakdown test later, but would have helped to come back and tell us that those sensors were good.