really weird issue

[ThatOneEuroE30]

So i tested for continuity on the afm harness. It get continuity on all wires from dme to connector. However my car has the afm adapter harness and on pin 41 or the grey/yellow wire i only get continuity up to the the little black box in the adapter after that its nothing. So I unplugged the adapter and put the main harness connector straight into the AFM but the car still runs the same. It really seems like a misfire/fueling issue. Here is diagram im following

[ThatOneEuroE30]

Buddy came over and we tinkered for a bit. We got the car to want to idle some what normal its just it seems to be low enough of an idle that the lights kick on but it seems to be an intermittent problem any more. It still runs way lean and has like no throttle response it seems like it doesn't realize its getting input and then wakes up and does what its supposed to. We are wondering if it just doesn't need a basic tune up like plugs, coils, wires and and maybe a sensor or two like TPS or crank sensor hopefully the oscilloscope can let me know.

[ThatOneEuroE30]

Looks like im making some progress.

Here is a picture of the plugs when i started they all looked like this one




Just threw a set in today for shits and giggles since they are cheap enough and this is what they looked like




Im 70% positive its got something to do with the crank sensor and TPS. The lights will go off if i start the car with the e brake down but with it pulled up they stay on until i give it some juice then go off. The car idles decent now just must be low enough to kick the lights on some how and the cluster with the ebrake pulled thinks its in the aux position but not sure how it could he a short if they only stay on until it get throttle input. Also the throttle input is next to none existent. You can put it all the way to the floor and after a few seconds it will finally decide to rev.

[ThatOneEuroE30]

Went and shot a video of what its doing now. With e brake up and lights are on all i gotta do is touch the gas to get some increase in revs and they go off

https://www.youtube.com/watch?v=lEmwM417eOY

[bmwman91]

Watched the video. Weird! I have nothing for why the e-brake would have any effect whatsoever. There is zero electrical connection between the e-brake light and the ECU (other than being on the same 12V and ground system as the rest of the car). It is also strange that the dash lights are only on if the car is started with the e-brake engaged, but not if it is engaged after starting with it disengaged. So unless there is some sort of insane fault in the instrument cluster that is affecting the DME, I do not see how else this could be a factor.

Connections between the cluster and DME are:
1) Engine RPM (pulses from the ignition system, one per ignition event), DME to cluster
2) Fuel injection rate (pulses from the fuel system, one per injection event), DME to cluster
3) Vehicle speed pulses, cluster to DME

I can't recall if there are others, but those are the main ones. As far as I can tell, even a pooped cluster shouldn't be able to cause poor running via the RPM and fuel signals since, while they do come from the DME outputs to the coils and injectors, there is buffering circuitry in there. One of the 3 plugs in the back of the cluster links it to the DME, so maybe try unplugging that one just in case? I can't remember if that one also has the connection to the alternator which enables charging (yes, the battery indicator lamp is a functional part of the charging system lol), so maybe don't run it too long lest you kill the battery!

All I have to say is that this one is a real pickle. I thought I was pretty good with the M42 engine electronics since I have reverse-engineered the entire DME's electronics and am building a custom harness for an MS3-Pro install...but still no dice with your problem! But, at least because of that I have scope captures of what a number of the DME output signals should look like, so once you get yours we can compare.

I have a feeling that this is going to end up being a real head-slapper. Like, something painfully obvious that never would have been thought of as a possibility. I think we'll all learn something from this!

[gespinal0301]

Are you sure it's getting fuel?

And could it possible that you mixed CPS and CAM sensors when reinstalling them or they aren't properly gapped?

[ThatOneEuroE30]

Are you sure it's getting fuel?

And could it possible that you mixed CPS and CAM sensors when reinstalling them or they aren't properly gapped?

Positive its getting fuel and from my understanding the cam sensor goes into the top plug on the harness box under intake and crank goes in the bottom and thats how I have it.

[cunninglinguist]

Did you test your coils?

[ThatOneEuroE30]

Did you test your coils?

Yep tested perfectly

[ThatOneEuroE30]

Got my scope in and did some testing from what i can tell everything seems to be alright. Only thing that concerns me is the crank sensor isnt as tight as the on BMWman91's in his scoping thread

here is the crank sensor data

IMAGE080 by Brandon Simonson, on Flickr

IMAGE079 by Brandon Simonson, on Flickr

Notice the dip in the second pic. This happens when the engine kind of stutters for a split second almost seems like a quick idle surge that last like for maybe 1/4 of a second

This next image is of the TPS the wave form is me giving throttle input and letting off the no longer has the severe throttle lag its pretty instantaneous. maybe off by half a second after throttle is pressed if that. Once you give it input the wave pattern evens out until you let off so it gets to the peak of the signal and then flat lines until input is taken away.

IMAGE076 by Brandon Simonson, on Flickr


I also scoped the AFM and it seems to be good. Although i didnt seem to get any signal from the IAT sensor but we have pretty much ruled the AFM out when i swapped them and got same results

[gespinal0301]

I would check the gap between the CPS and the block, I know it has a certain spec besides the torque value.

Also, just to completely rule out the AFM I would check pins 4 & 5 (Intake Air Temp Sensor) and check continuity to the ECU pins 14 and 77. Pin 4 of the AFM should be pin 77 on the ecu and pin 5 on the AFM should be a common gnd on the ECU pin 14.

[ThatOneEuroE30]

I would check the gap between the CPS and the block, I know it has a certain spec besides the torque value.

Also, just to completely rule out the AFM I would check pins 4 & 5 (Intake Air Temp Sensor) and check continuity to the ECU pins 14 and 77. Pin 4 of the AFM should be pin 77 on the ecu and pin 5 on the AFM should be a common gnd on the ECU pin 14.

Not sure how the gap could of changed with out removing the sensor bracket or sensor it self but its possible i guess. I have check continuity with all wires from dme to their respective part. they all check out. I'm really leaning toward a short to ground at this point.

[bmwman91]

The CPS is probably fine. My plot looks tight because I captured more than an entire revolution, and I was doing it at varying RPM's (also I was using a $25000 scope I borrowed and it allows for pretty long duration captures).

[ThatOneEuroE30]

The CPS is probably fine. My plot looks tight because I captured more than an entire revolution, and I was doing it at varying RPM's (also I was using a $25000 scope I borrowed and it allows for pretty long duration captures).

Yea I was kind of wondering if you weren't using a high end scope similar to picoscope or somthing. BTW i just ordered the dme you sent me a link to. thanks for that

[bmwman91]

It was an Agilent/Keysight MSO7104B...sitting on the passenger seat with an AC inverter and probes running all over lol. It would have been a bit of a "conversation piece" if I had been pulled over.