M42 running rough but pulls strong SOLVED

[5Toes]

okay heres some videos:





the second video shows the brick wall the car hit between 5 and 6000 (its hard to tell though)

the car has good power (and a very rusty muffler) as seen but not sure if that misfire noise is pinging???. the car has many new parts including:

-new bmw oe crank sensor
-mess under intake done
-rebuilt head
-180psi compression 1-4
-new spark plugs ngkbkr6ek
-new fuel filter
-rebuilt fuel injectors - s52 pink tops (same flow as stock ones at 3bar)
-fuel pressure never dips below 3bar even when problem happens (gauge confirmed)
-all new intake seals and intake boot
-ICV bypassed with hole drilled in coin and unplugged
-swapped old AFM for new unit from picknpull off e36 m42 - car runs better with new AFM but still has artificial redline

DME throws code 1262 for ICV not plugged in.

installed brand new plugs and did a plug chop and 1-4 are running lean. I also noticed that the intake manifold was very cold compared to the valve cover, not sure if normal.

the car WILL NOT IDLE on its own unless you rev it up, probably due to ICV being unplugged, I get that. but the artificially low redline problem cant be related can it?

not sure if it is AFM related or faulty fuel injector from my guy. have always had good experiences with the 4+ injectors Ive had from him so I am kinda ruling out fuel. the car bucks very hard when on/off throttle (possibly due to broken gas pedal at bottom mount). misfires at small throttle inputs and up until 3500rpm till it clears up.

there MIGHT be a vac leak but I highly doubt it, everything is torqued down good and all the lines hooked up properly

anything helps :) thinking about getting AFM rebuilt by bavrest and going from there. I believe you need a 5v power source to bench test the AFM properly and I dont know how to do that.

so TL/DR:

1. is my engine pinging or what???
2. what could be the cause? cam sensor, bad AFM's bad or what?

[5Toes]

new cam sensor installed, car runs better but still bad. each thing Ive done the car's drivability has gotten better, but the artificially low redline and misfiring at small engine loads are still the main problems.

still leaning towards AFM since my fuel pressure checked out good.

[bmwman91]

Hmmm...what condition are your ignition cables in? How about the coils? I had a coil go bad on me once and it would cause ignition cut at certain RPM ranges. It could also be the AFM, as you note. Pop the cover off and take a look at the carbon track. It is relatively easy to adjust the copper wiper spring to contact an unworn section of the track (increase or decrease the radius).

[5Toes]

the ignition coils are very low miles Bosch units I bought a couple years ago and had on my m50nv. also have a brand new m50nv cam sensor on the m42, it is the same sensor just a fyi for future DIYers

ignition cables look old and tired, I was thinking they need replaced, might be doing that next. or AFM rebuild.

going to check out the afm tonight, I have two nwo for this car so I can do a little work on them

[MVincken]

looks to me that your car is running a really low gas mixture.

what do you mean with hole drilled in coin bypassed ICV?

[5Toes]

I took a U.S. dime and drilled a 3/16" hole in the center of it, and placed it over the ICV hose barb and stuck the hose over. it blocks the air and simulates (very poorly simulates) the ICV in operation. I have a new ICV in the mail, hopefully that will allow me to make some progress.

yes the car is running lean. not sure if it is one of my fuel injectors thats the problem, or if both AFMs are bad. I popped the cover off the car's original AFM and it has a pretty worn resistor track.

the rain is relentless today and halting progress, but I have two more rebuilt injectors now to swap out with the ones in there. it may be a fuel problem.

the way I understand motronic the only way the car can be running lean is a bad AFM or bad fuel system. fuel pressure checks out so...

I have also tried driving the car with the o2 sensor unplugged and that made no difference.

[MVincken]

try to fully close your ICV hole, your engine is sucking in air that the ECU isn´t aware of.
the ECU thinks that the air that passes trough the MAF is all the air that comes in the engine, and calculates the injection amount on this value.
but your engine is sucking in more air trough the ICV hole, and this is why your car is running lean

[5Toes]

I agree. my new ICV comes in the mail tomorrow, so am going to install that then! also have a new AFM on the way

[MVincken]

ok, lets hope that fixxes the problem.
i wouldn´t be driving that much, lean mixture isn´t very good for your engine.

[bmwman91]

Yeah I am betting that this is mostly due to the "dime ICV". The Motronic has a hell of a time maintaining the idle without being able to control the air flow into the engine, even if the incoming air is being metered.

[5Toes]

my town has had constant rain, wind and fog the last few days and I dont have a garage... making working on the car pretty sucky.

I tried driving it around yesterday though with different combinations of the AFM and ICV plugged/unplugged. with afm unplugged and ICV plugged in the car ran decent actually, lots of power but LOTS of hiccups in the powerband too. only ran smooth at full throttle.

the car also idled on its own!!! would almost die every time from dipping too low but would hunt from 500rpm to 1000 or so. new ICV came in the mail and it tested good so gonna try to install that when I get a break in the weather.

[5Toes]

issue turned out to be a vac leak from the lower intake manifold. there are two sleeves that align the manifold and I overlooked them when installing it beforehand. the cylinder head had dowel pins and the manifold too, basically crushing all 4 of them and creating a big vac leak. new dowel pins = problem solved! car idles at 800rpm smooth now :)

[mjimport]

Awesome! Great to hear success stories. It's one more bit of info I might need myself!
But I am having a hard time understanding what you mean about crushing the dowels, I have my intake off now and want to make sure I don't get the same vacuum leak. I think it slides on pretty easy and aligns well.

[5Toes]

there are only supposed to be the two sleeves, but my rebuilt cylinder head had the dowels installed AND my intake manifold had them too. so they crushed against eachother.

just got back from test drive with freshly reset DME, and the the car misfires very badly under load. going to swap ignition coils out and go from there tomorrow.

the plugs looked like this basically, probably the cause of this misfire under load.

[bmwman91]

Dowels, or sleeves? I think that the manifold has sleeves around a couple of the studs.

Anyway, glad you fixed it. The busted ICV needed to be replaced anyway. I had a big vac leak between the upper and lower manifolds once. It was because of the steel brackets that connect the upper manifold to the head. They were bolted tightly to the head, and when I put the upper manifold on it was not seated properly because the steel brackets were not in a good position. So, make sure that the brackets are sitting loose until after you tighten all of the nuts down!