Urgent help needed, engine running poorly

[Touge Hack]

Hi guys,

This is a complicated post but I guess all details are necessary so here goes.
My E30 M20B23 gets around 220km to a 55L tank of petrol, or around 11 miles per gallon in American terms.

On a cold start only, it appears to be running so rich that black fuel is spat out the exhaust all over the ground and wall. It also sounds like it has a misfire, again, only when it is cold. Once the car warms up it usually idles ok, apart from slight 50-100rpm variances.

I took the car to a BMW mech who knows his stuff. We tested the CO2 reading at idle, and it was within factory specs.

We also tested the A/F ratio. Now here is where it gets weird. We hook it up in the tailpipe, go for a drive, and the display was maxed out at 19.9! So the mechanic reckons perhaps the sensor was busted, so went went back and it did it again! Got another sensor, and it did it again. So under full load, it was always maxed out, and would only drop slightly in between gear changes. We even put the sensor on the other exhaust tip, still got the same reading.

So we get back to the workshop and check the plugs. All plugs were replaced about a month ago, by the way. Low and behold, the back end of the spark plugs were absolutely coated in fuel, practically dripping, yet the electrode end was totally white, where it had been burnt off!

So, what the fudge is going on?!?

My mechanic has a couple of ballpark theories:

1. Perhaps one of the fuel pumps doesn't work at all or is very lazy and that the fuel flow/delivery rate has dropped substantially, hence why the car is running so lean.

2. The coolant temp sensor is f-ed, so when the car starts it thinks the temperature is not what the atmosphere is, and is overfuelling to compensate. However, if this is the case, why does it then run lean? And why am I getting only 220km to a tank?

Does anyone have any other ideas? Please, this is absolutely shitting me up the wall, and burning a hole in my wallet too...

[gixerdave1983]

well if the plugs are dripping its not running lean is it, and a bad fuel pump wouldnt make fuel come out the exhaust!! i thought you said your mechanic knew his stuff!

[Touge Hack]

Perhaps you misinterpreted my post...

The back of the plugs (towards the nut end) are dripping, but towards the electrode end all the fuel is burnt off, all of it...which might indicate it is running incredibly rich on start up, and then lean after that.

[slawler]

have you made sure that all of the plugs are fireing? if those plugs you put in are new maybe that is whats causing it to run the way it is. check your entire ignition system. If you think its the fuel pump, IF its going bad it will make a loud buzzing sound and will have to replace it. just check those things at and tell me whats up.

[j.amrol]

I think the afm is at fault. Pull/ or drill out the plastic covering the hex head screw towards the engine side of the afm (usually blue), and turn the screw inside counter clockwise to make it run leaner or clock wise to make it run richer (at idle). In SMALL increments.

[j.amrol]

Also do you have the air temp sensor hooked up? I once bought an E30 with an afm adapter & cone air filter it only got 15 mpg.

[StarkeyT22489]

well i dont know alot about E30s because im very new to them but i know that a fuel pump will not dump that much fuel into your motor to make it pour out the muffler. because that means that its not being compusted. i would check your fuel injectors and your fuel filter. i would start from that back and work your way forward. i mean i came from the world of building 10 second camaros so im very good with them and im trying to transfer what i knew to what i can learn. and for a motor to run lean thats all in the fuel. system a computer can only do so much.

[j.amrol]

Did you buy the car like this, or did it occur after something?

These cars do run a little on the lean side up top anyway. Your definitely getting too much fuel, so the fuel pump is out.

If your spark plugs aren't firing in the right order, did you take all the plug wires off at the same time or change them one by one?

There is a air temp sensor on your airbox, make sure it's hooked up.

I still blame the AFM, it meters the amount of air coming in via a barn door style flap. The spring inside loses tension after say 20 yrs, or somebody fiddled with it before. If your running rich at idle it's because the afm isn't allowing enough air to bypass. Turning the screw I described will change that. You could always go pull one off a junk yard.

Do you have any "flat" spots in your rpm range while driving?

[kylelauffer]

it could possibly be your cold start valve. because it idles fine when warmed up. or try oxygen sensor.