The continuing saga of the random miss

[grumpsjr]

So I followed the advice of one of you gentlemen on the board (I apologize that I can't remember who, and it looks like the latest archive is not posted, so I can't reference the original post) and disassembled the AFM this weekend to try and solve the still random miss on my E12.

At this point, it was only missing on throttle tip-in below 1500 rpm or so. If I GENTLY eased on the throttle, rather than taking off normally, the car would not miss.

Disassembling the AFM showed that the circuit board track was indeed worn through at the first part of the wiper travel. So, I worked on the wiper (nervously, that did not seem like something I wanted to be messing with) to move it to another part of the track. Upon reassembly, the car does not seem to be missing at all.

Famous last words, I know, but wanted to post and get this documented for posterity, and to say thanks for the help. Will keep you all posted as things continue to develop.

[John in Simi Valley]

It makes sense.
When I leaned on the AFM and the trouble cleared up,
it MAY have been distorting the AFM just slightly enough to fix it.

[alotawatts]

Disassembling the AFM showed that the circuit board track was indeed worn through at the first part of the wiper travel. So, I worked on the wiper (nervously, that did not seem like something I wanted to be messing with) to move it to another part of the track. Upon reassembly, the car does not seem to be missing at all.

Has your idle been smooth before and after the AFM tweak ?

[grumpsjr]

The idle fluctuated slightly before, especially when warm. Now the idle is indeed smoother, albeit at a higher rpm. My theory is that now that the ECU is getting a good signal from the AFM, things are acting more as they should and I need to go back and adjust throttle switches, idle speed, etc.

On Mon, Feb 2, 2009 at 10:36 PM, alotawatts <alotawatts@aol.com (alotawatts@aol.com)> wrote:

Has your idle been smooth before and after the AFM tweak ?
thx



Carl in Seattle 3 E12's and 1 R27

Post generated using Mail2Forum (http://www.mail2forum.com)

[Lenny D.]

So I followed the advice of one of you gentlemen on the board (I apologize that I can't remember who, and it looks like the latest archive is not posted, so I can't reference the original post) and disassembled the AFM this weekend to try and solve the still random miss on my E12.

At this point, it was only missing on throttle tip-in below 1500 rpm or so. If I GENTLY eased on the throttle, rather than taking off normally, the car would not miss.

Disassembling the AFM showed that the circuit board track was indeed worn through at the first part of the wiper travel. So, I worked on the wiper (nervously, that did not seem like something I wanted to be messing with) to move it to another part of the track. Upon reassembly, the car does not seem to be missing at all.

Famous last words, I know, but wanted to post and get this documented for posterity, and to say thanks for the help. Will keep you all posted as things continue to develop.

I may have advised you on the old board about the wiper track. Well, congratulations, you did it! It may seem scary but it's not as fragile as it might seem. Just no gorilla-like action... Now, reset the AFM with your digital voltmeter and the O2 sensor. How?

I threatened several months ago to post this, but never got around to it (sorry, Peter!). This is an AFM calibration instruction document I got from Metric Mechanic over ten years ago, and have their permission to post it publicly. It's just a digi-pic of the instructions, so it is what it is. It can be found here (there are three pages):

http://i99.photobucket.com/albums/l309/ ... ion001.jpg

http://i99.photobucket.com/albums/l309/ ... ion002.jpg

http://i99.photobucket.com/albums/l309/ ... ion003.jpg

Perhaps we can add this to the FAQ.

[grumpsjr]

Hi all,

I thought I would provide an update and solicit further advice. I am still trying to troubleshoot this misfire. Currently, it only seems to happen when the car is fully warmed up. The typical behavior is for me to start and drive the car when it's been sitting overnight with no problems. Then, if I shut off the car and re-start, it will idle poorly and misfire consistently.

As a side note, my tachometer is acting up, but it does not seem to indicative or related to the misfire. I believe this is a separate grounding issue with the cluster.

To date, here is everything I've done:
New cap, rotor, plugs, and wires.
Replaced AFM with known good.
Replaced coil, combo relay, ECU, and ICM with known good.
Replaced all questionable vacuum lines
Replaced AFM intake bellows.
Replaced AAV (on valve cover) and Idle Control Valve
Replaced Fuel Regulator
Adjusted valves, though they are probably a little loose.
Replaced distributor and reset timing
Rewired a couple of iffy looking connections.

I am running out of thoughts. I will verify today that the fuel system is holding pressure - this did not appear to be the case before I replaced the fuel pressure regulator yesterday. If it is not, I'll replace the fuel pump.

Other things I haven't attacked - the thermotime switch or vacuum temp. sensor to the distributor. When some of the parts above did not appear to improve the running (most notably ECU, ICM, and combo relay) I put original parts back on.

At this point I'm stumped - to me it feels more like an electrical issue (i.e. something is shorting a signal) but I'm NOT an expert.

A bit of history - this all began when I replaced the cracked and torn AFM intake bellows - which made me think vacuum leak somewhere. The same day, I had the car up in the air to look at the brakes, and I wonder if raising/lowering the car jiggled something loose - but I have not been able to determine what.

My apologies again for the long post - any advice is GREATLY appreciated.

Thanks all,

[Lenny D.]

but I know how frustrating chasing a misfire can be. What exactly do you mean by 'tachometer is acting up'? It is my understanding if the tach. is malfunctioning (or not connected (properly)) the engine will not run. I would chase that first.
Swapping known parts can be tricky, they have to be done one at a time and let time elapse for a good evaluation, or you wind up not knowing what did what. Very time-consuming, but it's the only way to know for sure.
I agree about ignition-related (and heat-related), (and wiring in general, these cars are old) and I would look really hard at the AFM (again), its CONNECTOR, and wiring harness. I had two spades in the AFM connector plastic housing come loose causing the wires not to firmly connect to the pins in the AFM resulting in a terribly rough idle, followed by a start/die condition. See that the spades are 'locked' in the housing. (Bend the little metal 'tang' of each spade if they're not seated so that it 'clicks' into place in the housing).
WAG would be impulse sensor in the distributor, but I'm not sure it fails only sometimes, mine did and the engine would not start, period. Another WAG would be ballast resistors, and come to think of it, remove and clean the spades and pins of the ICU connector, and visually check the wires going into the plastic connector are not touching anything they shouldn't (each other).

My off-idle misfire(s) were due to two separate issues, and displaced by several years. The first was HT wires, particularly the coil lead, it gets beat up five times as bad as the others. A 2yo set of Beru wires failed, and caused me great angst until I replaced them. The second time was the worn track in the AFM, and repositioning the board, per Mike's advice, solved that one.

Good luck, but you must be methodical, if time-consuming.

[grumpsjr]

Thanks Lenny,

It looks like I have some electrical stuff to do to cross your suggestions off the list. I looked at the AFM connector, but wasn't really sure exactly what to examine. Now I have a better idea.

I did adjust the wiper on the circuit board of the AFM, and even switched AFMs with a good known working.

Perhaps I should also try throwing my old plug wires back on.

But - I'll ensure the fuel pump is working properly (I do notice that it runs ALL THE TIME with ignition in ACC or ON position - bad relay?) and then proceed from there with your suggestions.

Will keep you posted,
Brian

[grumpsjr]

My issue sounds real similar to 'under the radar's so I'm going to keep an eye on his posts as well...here's the afternoon update.

When I swapped the fuel pressure regulator yesterday I noticed that the fuel system was not pressurized when I removed/loosened the regulator from the fuel rail. So, I thought I would check today with the known good regulator installed.

Still no fuel pressure. So it looks like my next step will be to change the fuel pump. Does this seem like a logical next step? What else should I be considering?

Thanks all - will keep you posted. Probably won't get to the fuel pump till the weekend.

Brian

[under the radar]

ha ha ha...i'm watching your thread! yeah, it looks like i'll try replacing my main pump also.

[Lenny D.]

Thanks Lenny,

It looks like I have some electrical stuff to do to cross your suggestions off the list. I looked at the AFM connector, but wasn't really sure exactly what to examine. Now I have a better idea.

I did adjust the wiper on the circuit board of the AFM, and even switched AFMs with a good known working.

Perhaps I should also try throwing my old plug wires back on.

But - I'll ensure the fuel pump is working properly (I do notice that it runs ALL THE TIME with ignition in ACC or ON position - bad relay?) and then proceed from there with your suggestions.

Will keep you posted,
Brian

No, the only thing that makes the fuel pump run is a contact switch inside the AFM. I bet you the switch got misadjusted when you were fooling around in there. It should break contact at the rest or engine off position, and make contact as soon as the door moves. Just bend the heavier of the two leads to make that happen. The fuel pump should NOT run with the engine off (safety feature) in any key position but START.
I repeat, do one thing at a time, and evaluate the outcome.

I doubt you have a fuel problem with this complaint, but fuel pressure is controlled by the FPR (fuel pressure regulator). They rarely fail and fail rich when they do. I would check that before the fuel pump which also fails only after extreme mileage, sludge buildup from a car sitting undriven, etc. and even then, the common complaint is 'running outa juice' at high RPMs. This isn't your complaint. A misfire is exactly that, a non-firing.
Additionally, I would examine all your fuel lines (the metal ones under the car for obstructions from something having hit them) and most importantly, all the rubber ones, for good fuel flow. For safety reasons any of them that are questionable should be replaced with BMW fuel line. Pulling off the cold start valve hose and letting it squirt into a container while cranking should show you your flow (SAFETY FIRST!).
Elsewhere on this board Mike has addressed an inexpensive fuel pressure gauge and the acceptable values.

[nerdorama]

Hi Brian,

I know this is just a single point of info and unlikely your problem, but here goes anyway. Couple of years ago my '80 had a rough idle/missing sort of problem and would stumble badly under mild accelleration. I looked at a lot of the things you've been exploring. Somehow I accidentally touched a wire between the AFM body and a grounded point on the engine. Saw a definate spark, but the engine suddenly began idling smoothly. I never quite figured the real cause, but have a wire spanning the rubber duct connecting to the throttle body so I have some ground continuity. It's been running like a champ since.

Good luck,
John

[grumpsjr]

Thanks John,

I'm willing to try anything at this point. Where are the two ends of your wire connected? I'll add this to the list for the weekend.

Appreciate the thought!
Brian

[nerdorama]

To give it try, you don't have to connect them anywhere. Just touch one end to the case of the AFM, the other to the engine block or intake manifold (anywhere that's a good ground). That's how I discovered it by accident. I suspect that the AFM has a marginal ground connection in it's cable, but I coudn't find it.

In the end I just stuck one end of the wire under the edge of the rubber duct so it was in contact with the AFM's case. The other end across to the other end of the duct. If you end up with the same problem, I'll take a picture.

Good luck,
John

[grumpsjr]

Thanks again, John. Will keep you posted.
Brian