M42 puzzle

[roguetoaster]

I assume you checked the plug wires too, and maybe pulled the plugs to see if one of them broke?

Would certainly be worth looking at the fuel pump/wiring for it locally.

[Boris3]

Pulled the plug wires to see if I had pooling oil in the wells but did not test continuity. A friend of mine also asked if I had checked the plugs. Should have already done this but haven't. Will take a look tonight.

[TobyB]

Hmm- this might be a long shot, but I wonder if the o2 sensor's shorted internally or intermittently.
The ECU doesn't use it cold, so that part makes sense, at least. If it's
'wandering' (yes, they do that sometimes when they die) that might be messing up
the ECU's ability to learn.

fwiw,

t

[Boris3]

Done most of the short shots so I'm into long shots. Got home too late to check plugs and wires. Car is outside and the rain has arrived.

[Boris3]

Swapped the plugs. Maybe a bit smoother but still same issues.

Smooth idle cold, after a few minutes stumbles and almost dies. Disconnect O2 sensor and idles smoothly, give it throttle still runs smoothly but cel flashes. No codes stored. Think it's time to try a new O2 sensor.

Checked plug wires. Resistance on wire 1 is 15.33; wire 2 is 5.76; wire 3 is 5.74; wire 4 is 5.98. Meter set at 20k. Not sure what values should be.

[bmwman91]

The plug thing on the AFM is an opamp noise filter. It was retrofitted onto some cars to deal with rough idle issues. I recommend keeping it on there.

[Boris3]

Found a few cracked vacuum hoses I had missed (the one under the ICV, and one of the hoses from the crankcase to the throttle body) and replaced them. Smoothed out the idle a bit but still rough. Replaced the O2 sensor this morning with OEM Bosch unit and now idle is steady both cold and warm engine.

I still get the blinking CEL whenever I hit the throttle, with no stored codes. And I noticed that on the road at speed sometimes I would get the CEL blinking off throttle as well. Though clutch in and coasting and no light (figure I'm back down to idle).

Car runs fine...so I am confused to say the least. Time for smoke test, piece of tape over the light? It does look like I have an oil leak from around the oil filter housing. Would this be enough to cause the problem?

[bmwman91]

Glad you got things working better.

The only thing that I can think of is the TPS itself at this point. It is possible to get it open...maybe try that and clean it out with a Q-tip and some alcohol (don't get any fuzzies in there). Take a macro-mode pic of the carbon track and post it up!

[kwill22]

Yea the only things that really cause cel on our cars is usually some type of electrical problem. Rather it be not enough spark or the air flow metering or running rich because of o2 sensor etc. at least in my experience.

[Boris3]

Speaking of electrical I'm wondering about the reading I was getting on plug wire #1. Three times the resistance that I was seeing on the other wires, I tried it several times and it was either no reading or consistently high. I'll pull the wires out of the loom channel tonight and see if anythings up. Big ticket item to buy though just to see if it's the wires.

Design of the tps on the m42 does not make for easy access. Intake runner right in the way of one of the Phillip screws. How do you get at it?

[bmwman91]

I have used needle nosed pliers to break the bottom screw loose.

[roguetoaster]

That, or take the throttle body off.

[TobyB]

You know, in the 'department of random departments' department.
this kind of sounds like a ground issue. As in, there's a ground bolt somewhere
that's not tight. There are only what, 4 or 5 of them, it might be worth a check.

More evilly, a ground wire that's broken internally...

Something really random that's making the ECU barf momentarily, but not remember
that it's barfed.

t

[Ryann]

Have you checked your battery connections and the engine ground strap at front right?

[Boris3]

Found a used set of wires locally that I'll pick up on Saturday. I'm either getting no reading on the #1 wire or 3x the resistance compared to the others. No cracks in the wires.


Ah random evil. Battery connections are good, battery to ground, right side ground off the motor mount, where else should I be checking? Any quirks compared to the 325i?

TPS access I was guessing throttle body removal.