M10B18 runs very bad

[Roelio]

Hi,

I'm back with another problem.
My m10b18 (injection) recently started running very bad. I drove the car the day before without any problems, the morning after day it ran unstable.

Symptoms:
-fuel comes out of the exhaust
-runs poorly
-slow throttle response
-fuel lines started leaking -> to high pressure?

I already looked for vacuum leaks, the car has spark(and new spark plugs), the impulse Generator has 1100 ohm and gets 12 volts.
Any ideas what it could be ?
Please take a look at the video to see what I mean.
https://www.youtube.com/watch?v=FMpvKyxpz_s

Thanks in advance.
Roel

[Bonymaenjack]

Hi,

I'm back with another problem.
My m10b18 (injection) recently started running very bad. I drove the car the day before without any problems, the morning after day it ran unstable.

Symptoms:
-fuel comes out of the exhaust
-runs poorly
-slow throttle response
-fuel lines started leaking -> to high pressure?

I already looked for vacuum leaks, the car has spark(and new spark plugs), the impulse Generator has 1100 ohm and gets 12 volts.
Any ideas what it could be ?
Please take a look at the video to see what I mean.


Thanks in advance.
Roel

Leaking injectors ?, sorry that's the limit of my expertise .I have a similar problem although not as bad

[Brianmoooore]

Take the spark plugs out and post a pic. of their business ends.

[Roelio]

Thank you for the quick reply
I'll have a look at the injectors .
The spark plugs look very black.

[Brianmoooore]

Those plugs indicate an engine that is running very rich, which fits in with what you describe.
Unfortunately, I've no experience of working on the injected version of the M10 engine at all, although I have owned and worked on a couple of the carburettor version, but it's just an engine, so the principles are the same.
Petrol is a very poor choice of fuel for an internal combustion engine, since these engines need to run on gas, and petrol is a liquid. To get around this, petrol is fed into an engine as a very fine mist, simulating a gas, either by a carb. or an injector system, which works reasonably well when the engine is hot, but causes problems when things are cold, with the mist collecting back into a liquid again.
To deal with this, the fuel mixture needs to be made extremely rich at start up, in the hope that it will be somewhere near correct by the time it reaches the cylinders and spark plug.
Your engine is running very rich when hot, so the first thing to check is whether the ECU thinks the engine is constantly cold, and is continuing to supply the extremely rich mixture long after it should be.
The ECU is fed engine temperature information by the coolant temperature sensor, by a brown/red wire to pin 10 of the ECU plug. Unplug the ECU, measure the resistance between pin 10 of the plug and body earth, then reconnect the ECU, run the engine up to full temperature, then unplug it and measure the pin 10 resistance again.

[Roelio]

Thank you for the very detailed explanation.
I checked the resistance and it went higher with the engine hot, looks like its fine.
After that I checked the fuel pressure , it was a whopping 7 bars. I didn't even know my pump could go that high. The pressure doesn't change when revving so it must be the the fuel pressure regulator and maybe the fuel pump to?

[Brianmoooore]

If the fuel pressure is 7 bar, then you've found why your car is running rich!
Fuel pump is OK and don't write off the pressure regulator just yet. The pump supplies fuel to the injector rail, and the fuel pressure regulator bleeds off excess fuel to keep the pressure in the rail at a constant preset pressure above the pressure inside the inlet manifold. This will be either 2.5 bar or 3.0 bar, depending on which your engine uses, so the measured pressure should be this, less the partial vacuum in the inlet manifold.
The excess fuel is returned to the tank by the larger diameter hose connected to the regulator, and your symptoms will occur if this pipe is blocked, so disconnect the hose, connect a temporary hose with one end in a bucket, and run the engine while you check the pressure again.

[Roelio]

Good idea, I will check if the return hose is blocked as soon as possible Thanks!

[Roelio]

Hi,

Problem still not solved.

The fuel return line is good.
The pressure meter was wrong because my other e30 had the same pressure.
Fuel injector's have a correct spray pattern and aren't leaking.

Any other ideas you guys might have besides testing the fuel pressure with a calibrated meter?

Thanks

[Brianmoooore]

I checked the resistance and it went higher with the engine hot, looks like its fine.

What were the figures?
Does the engine get up to full working temperature OK?

[Roelio]

I believe it was around 5 ohms cold and 25 ohms with the engine running for couple of minutes(not sure anymore tho) . With the engine running this bad I'd rather not get it to operating temperature, I will try to run it for longer if it helps.
The engine runs better cold than hot tho.

[Brianmoooore]

First problem is that I don't know what age your car is
Prior to December '84 the ETK says it used a sensor that I'm unfamiliar with that appears to be listed as 2500 ohms at 20 degrees. After December '84 the sensor changes to the 'blue' sensor, used on all BMWs right up to when it changed to the combined engine/gauge sensor used on the 24 valve engines. This sensor (measured at the ECU plug) should read around 4000 ohms cold, falling to around 300 ohms or less when the engine is at full temp.
Whatever you have measured doesn't appear to be this.

[Roelio]

hmm thanks for the detailed reply, I'll check the sensor as soon as possible again!
The car is from 87
Really appreciate the help, thanks!

[Oseanosea]

So.... What happened? Did you get it sorted?

[Roelio]

Forgot to post the solution...

The problem was the fuel return line that comes directly from the pressure regulator(very close to the engine and hard to see), it got pinched. Because there was fuel coming out and the lines where not clogged everything looked good but when I checked how much fuel came out via the Bentley manual it was clear there was a problem which made the pressure go up to 7 bar . Hope this helps others!

Thanks for the help!

[Oseanosea]

Interesting. A couple months ago I had a gasoline smell in the cabin. It took a while to track it down. My 318i’s fuel return line’s hose clamp was loose, and the metal ridges wouldn’t hold tightening up. I replaced the clamp and all is good again. The early BMW’s have an elegant simplicity to the majority of their design. That’s why I enjoy tinkering with them.