So here's the scam.....solved...maybe.

[DesktopDave]

Sorry to hear about your troubles. If you decide to trash the M42, make sure you post some pics of the M21 swap. Always wanted to try that myself.

I know it sucks to track stuff like this down, but I'd be going through the system and methodically checking it part by part. Get a fuel pressure tester on it to verify fuel pressure at the rail, maybe do a volume test too to check the fuel filter.

Did you test the resistance of the CLT, cam & crank sensors? I'd be surprised if your AFM was working at 100%. Most of the ones I've seen are close, but a few were way off. A few have been worn resistor tracks, some have had clock springs loosened up too much. I'll see if I can track down the testing guide for those AFMs, it's not an obvious thing.

You replaced the crank sensor, the TPS and the injectors so far, right?

[bigskyis]

Hi Dave: Thanks for weighing in. The M21 diesel swap is really rather easy. Did one a few years ago on an M10 318. With little exception it is more or less a bolt in. I can walk you through it if need be.  But...back to the M42. Since I posted a few hours ago I have been researching failed catalytic convertors. I think the conventional way to test is to drill a hole in front of cat and insert pressure sensor and measure back pressure. Well...not going to do that today. Another suggestion was to use an IR temp gauge, measure temps at cat inlet and outlet. According to the site, assuming you have a functioning cat, the temp at the outlet should be HIGHER than that of the inlet. Well...after running my POS I measured the temps...clearly, the temp on my cat, at the inlet, is HIGHER, than at the outlet, by approximately 100 degree's F. If this is correct, it would appear (at face value) that I have a convertor that may have failed. The website I referenced said the temperature at the outlet should be higher than that of the inlet and be within 400 degrees F of each other. One thing I have noticed is that when the car is cold (especially today with an overnite low of 9 above) the car seems to run better, but after running up and down the road it just seems to get worse. Maybe the convertor is not completely plugged but is failing. Next weekend I am going to unbolt the exhaust behind the cat a take a look. I will most likely ream out the convertor.  And that is this weekends installment. 

[keflaman]

You can also check for a plugged cat using a vacuum gauge. I started a thread on that a few years ago.

[bigskyis]

Keflaman: Thank you you for the tip. I read up and yes, you can use engine vacuum to aid in diagnosing bad cat. At this point, I am going to pull the cat and have a direct visual on the core. Based on what the PO told me when I bought the vehicle a couple of years ago (wish I had listened to her and asked her a few more questions) I am beginning to think the cat is shot. Would not be surprised if it is original to the car.
If it  is...well...a 22-23 year old cat has probably out outlived its useful lifespan. No complaints. Believe it or not, I am hoping that it is the problem. Will know more on Saturday, Sunday at the latest.

[bigskyis]

Time for the weekend update...I would like to thank the BMW engineers as it was rather easy to pull the catalytic convertor but...that was/is not the problem. Pulled the cat and was looking into from the outlet of the cat. Took me a few minutes...(little slow on the uptake) and then I realized...the cat had been cored already. Put it back together. Fired it up. No change/improvement. Different O2 sensor...no change/improvement. No CEL. No idea. Perplexing to say the least. At least I figured out why it sounded like one of the many rice grinders with a fart can that run around town. Oh well...there you have it. 

[colin86325]

One of the gurus on the S14 SIG mailing list posted something interesting last week where the ceramic insulator on a spark plug was slightly loose and was causing the electrode to be shielded when the plug was installed.  Have you moved the plugs around to see if the misfire follows it to a new cylinder?
Obscure, but might be worth a shot.

[Warsteiner]

Yeah that was Don Fields at MrMCar posting that. When he showed me the plug I couldn't believe it. That's where I built my motors/cars and keep my track car. He taught me everything I know about BMW's. He came up with the S50/52 cam tray idea for me about 7 years ago. I would go the spark plug route and then go directly to the AFM like Dave had mentioned.

Cheers,
~Ralph

[bigskyis]

Colin: New spark plugs were installed a couple of weeks ago.

Warsteiner: I hear you about AFM. Have a "new" (to me one on its way). But...I am not sold that this is the problem

new spark plugs. New BavAuto upgrade coils. Different O2 sensor. Different fuel pump. New blue top Coolant temp sensor. New crank position sensor. No catalytic convertor. None of which has made any difference in how the engine runs.

This weekend, I am going back to basics. Pull the plugs and inspect and re-accomplish compression check. Recheck all my vacuum lines. Recheck the IAC.

The latest fly in the ointment is that my oil pressure light comes on after running for a while. Engine makes no bad noises whatsoever and has not changed one bit in how "bad" it runs. I can rev it up to redline (in neutral) and it goes just fine. I can drive the car...I am able to do 60 in 3rd...slip it into 4th and it slows down. Try 5th and the car goes "backwards". Head for a mild incline/grade in the road and the car is a moving road hazard. Going downhill you would never know anything is wrong.

So...as for the AFM...I jump pins 1 and 2 (fluke DVOM)...with the flapper closed it shows 347ohms. Open the door and the resistance increases to 950 ohms but past a certain point it heads back to 347. At wide open it shows 347 ohms. Not certain as to what to make of it but it does parallel another forum members observations. Does this mean AFM bad? Dunno...won't have my replacement until next week.

So it is a back to basics weekend. 

[Boris3]

Dave asked above if you had replaced/checked the injectors? Could be I missed it but have you pulled these to see if one or more is clogged?

[Boris3]

Sorry for my last, just looked at the first page on the thread on the injector saga.

[bigskyis]

Boris: yes I did swap the stock injectors out for some Ford injectors. No difference in how the engine runs. It is just perplexing the crap out of me. That is why I am going to start at square one this weekend and try to check every thing one more time.

[Boris3]

Car sat for three years. You've replaced fuel pump, injectors, checked lines etc. What about the gas itself. Full tank when the car sat? Added any Stabil before you let it sit? Have you drained the tank or added a bottle or three of gasline dryer?

Other: valve bent, crack in main intake boot, timing off somehow (new to m42s so not sure what to look at here)...

[bigskyis]

Since the Packers were taking it in the shorts today, I went out and started checking everything. Dc'd the fuel pump and checked compression..
187-195 across all 4 cylinders. Not great but at least uniform. I check all the electrical things and everything pretty much is in line with
the Bentley manual specs. Find the vacuum gauge...well...note to self...intake manifold vacuum should be one of the 1st tests one does. Period.
I have 10-11 inches of vacuum at idle. Snap throttle and it drops. Let throttle close...back to 10-11. Should be sitting in the 20" range.
If I have a vacuum leak one would think I should be able to hear it, loud and clear. But I have not heard one. I replaced all the hoses under the intake and used clamps on each one. Should be good there. The only place I have not checked is the intake gasket between the lower intake and the cylinder head. That is pretty much going to be the last thing I can check unless somebody else has any thoughts. I think what I really have is a
tired M42. Most likely in need of a rebuild. Wish I had the gauges to do a leakdown test but I will bet it would show tired rings.  Not a big deal. When I bought the car I knew it was going to be work in progress. And I did buy it with the intent of doing an engine swap. No loss there. Looks like I will be doing the engine swap sooner than later. I will pull the M42 and set in on the engine stand and tear it down as time permits. But in the meantime...project "dwiesel" will be getting teed up. Will order the new clutch and get that ready to stab in. Thank you to everybody here.
I haven't used the vacuum gauge in a month of Sundays (years and years).  A useful tool. And I knew this. Oh well....I had hoped it was something simple but in the back of my mind....

[DesktopDave]

Sorry to hear about that. I've been caught in the "has to be something simple" loop with some cars and bikes when I should have known better.

Fingers crossed you'll find the reason though.