Author Topic: Is this the correct AFM for 91 318i? (Read 6331 times)

Petebee · « **on:** December 29, 2011, 09:01:03 AM »

This looks like the one in my car:

http://www.pelicanparts.com/cgi-bin/smart/more_info.cgi?pn=13-62-7-558-785-M263&catalog_description=Mass%20Air%20Flow%20Sensor%20without%20Adapter%20Lead%20%28Rebuilt%20%2D%20Core%20Charge%20Applies%29%2C%20E%33%30%20%33%31%38i%20M%34%32%2C%20%33%31%38iC%2C%20Each%20

Pelican has another one with a different connector (wide vs. circular) that is over $600!

I am having some issues and plan to test the airflow meter this weekend.

Weird thing is mine has an extra length of wire that is connected between the main harness and the wire for the AFM plug...essentially the same type of connector that fits on the AFM. Seems weird - was that some type of warranty fix?

DesktopDave · « **Reply #1 on:** December 29, 2011, 11:35:18 AM »

Yep, that was a BMW fix back in the early 90s. It's a set of resistors to improve cold start performance or something like that.

I bought my car not running and it had that extension when I bought it. The car only had a 1215 code when I got it; removing the factory extension cleared it right up. I found the connector wasn't waterproof, seemed like it was missing a seal.

Don't buy a rebuilt AFM. Even if it's bad, you can likely rebuild it. Look for an M20 e34 525i ('89 & '90 only)...I think that is the exact same part and it'll be cheap. The earlier e30 AFMs are very similar but the connector is different.

Petebee · « **Reply #2 on:** December 29, 2011, 02:17:39 PM »

Thanks Dave...seemed like the extra wire was some type of fix.

As for the AFM are you telling me that I can rebuild mine, or just get a junkyard unit from the E34 models you mention.

DesktopDave · « **Reply #3 on:** December 29, 2011, 04:44:58 PM »

Both. I don't know this 100% for sure, but the later M20 units look identical except for the plug. Can't be a coincidence. The M20 e34 is an unloved beast, parts cars are common (M20's were installed before prod. date 8/90). The M20's in e30's tend to have higher demand, and the M30 AFMs are in very high demand.

Best bet is another M42, of course. Your cross-ref was every pre-OBDII M42.

Petebee · « **Reply #4 on:** December 29, 2011, 05:48:57 PM »

Okay so I pulled the AFM and pried off the plastic cover. Per the other "AFM How It Works" threads I've seen it looks like I have the worn grooves under the sweeper arm.

Doesn't look like we can adjust these North/South as the sweeper doesn't have the retaining bolt like the Porsche AFMs...so it is off to the pullapart tomorrow to look for another one.

The E36 M42 OBD1 AFMs work in addition to E34 M20, right?

DesktopDave · « **Reply #5 on:** December 29, 2011, 06:32:44 PM »

I just double checked my old pictures. None of the M20 AFMs use the same connector, not even the 525i. Mostly every car with that round connector uses a MAF instead.

The M42 models seem to be your only straight swap.

I'll bet the circuit board is pretty similar between all these models but I have no proof whatsoever. I wonder if any other AFM boards would be a direct fit?

Petebee · « **Reply #6 on:** December 29, 2011, 08:26:26 PM »

Okay so I searched around some more and a few folks mentioned bending the sweeper arm a bit - I did this and now the arm tracks slightly above the old track marks.

Put the AFM back in and the car was still acting funny - stumbling under throttle, smelling rich.

Figured I would test the continuity on the coolant temp sensor. I couldn't get a consistent reading as each time it would be different. All readings >1000 ohms and <2000 ohms (had the meter set at 2K ohms).

Does this mean the CTS is bad? I started the car with the sensor unplugged. Stumbled a bit on initial start up (about 2-3 seconds) then idled out. Revving the engine would make it bog just slightly at initial application of throttle but would rev okay w/o the stumbling. Threw a 1221 code while running unplugged.

Plugged the CTS back in and it ran about the same as unplugged state.

Any advice?

DesktopDave · « **Reply #7 on:** December 29, 2011, 08:39:36 PM »

Make sure you measure the AFM temp sensor too, should be pins 4 & 5 on the AFM. According to the 3 series repair manual:

Coolant temp sensor @58degF 2300-2700 ohms; at 180degF 300-360 ohms.
Intake air temp sensor @68degF 2200-2700 ohms; at 122degF 760-910 ohms

I usually see pretty stable readings on the sensors, unless I can't get the leads attached pretty well. I'd think if the readings are close, even if they're not rock-solid, your sensor is OK.

However, I did have some similar troubles with my e24 recently. The position sensor controls spark on the older Motronic systems; if it's out of range, no fire. The resistance readings seemed to be in the correct range, but they were not stable. Once I replaced those sensors that problem was resolved.

Petebee · « **Reply #8 on:** December 30, 2011, 10:03:11 AM »

Okay so I did some sensor testing:

Crank Position Sensor (lower plug on wiring harness): 514 ohms
Cam Position Sensor (upper plug on wiring harness): 1221 ohms
Air Flow Meter (pins 1 and 5 on AFM multi-connector): 358 ohms, constant reading throughout opening flap; flap action is smooth
Air Temp Sensor (pins 4 and 5 on AFM multi-connector): 566 ohms
Coolant Temp Sensor (cold): 3550 ohms (had to go to the 20K reading on the multimeter to read this, at 2K reading it was above the 2000 limit)

Note I read the AFM sensors out of the car in order to actuate the flap.

Three things appear problematic.

The Coolant Temp Sensor seems way out of range (very high reading).
The AFM reading stays constant throughout motion of unit.
Air Temp Sensor reading is low.

At a minimum I think a new Coolant Temp Sensor is in order...don't you think?

DesktopDave · « **Reply #9 on:** December 30, 2011, 09:23:23 PM »

Yep, the CTS is reading a little high. The computer will think it's like 30 degrees cooler than it actually is. I'm curious if other BMWs use the same part.

It's been a while since I tested my AFM, but I'm pretty sure it should sweep up then down, then up again. That test is not conclusive from other BMW sources, they insist that you need a 5VDC supply to test it correctly. If I get a chance maybe I'll give mine a little test to see what it does. Maybe the sweep arm isn't properly contacting the board?

Petebee · « **Reply #10 on:** December 31, 2011, 12:18:57 PM »

Retested the CTS at full warm engine and got 280 ohms rating, so it appears to be doing its job...at least when warmed up.

Will an M30 AFM work? I have some buddies that I may be able to barter with to get one.

And oh...I noticed that I have a leak in my radiator. When it rains it pours. At least I was able to get the windshield wipers fixed on my Scirocco so I have a car to drive.

Any experience with the Behr radiators from Pelican? Much cheaper than BMW.

To cap it off my daughter's 940 wagon is running crappy. Suspect it is the fuel line that feeds the in tank pump. It is a Volvo Regina system, so I have a bunch of corroded fuel clamps to deal with...ugh.

DesktopDave · « **Reply #11 on:** December 31, 2011, 02:04:16 PM »

I've heard of a few guys doing an M30/M20 Frankenstein mod. They transplant the M20 board inside the M30 housing. More cross-section, theoretically more air. Sounds like a lot of work to me, especially as the M42 AFM is more than adequate.

I've been tempted to seal a radiator, but at 30psi or so it'd have to be plastic welding to really resolve it. Our nylon & aluminum radiators have a limited lifespan. I've used high-strength Eastwood plastic epoxies in the past for temporary radiator repairs. JB Weld doesn't work well in that situation.

I haven't done the Behr, from what I've heard 'round the campfire most people like them. I do have a leaking heater core by Behr, so I'm not so sure myself.

Those old 940s were great cars. Wish they still made them. Fuel system work is always a smelly mess...I just cracked two clamps patching up my e24's corroded carcass. Damn thing still won't start, I think the overpriced fuel pump has given up the ghost.

Petebee · « **Reply #12 on:** December 31, 2011, 02:06:44 PM »

Okay there's a used M42 AFM on eBay that is $50...I might just go ahead and bite the bullet. It is a 100K car.

Good thing about the Volvo is there are plenty of them in the local pullapart, so I can usually get good, non-rusty stuff for repairs cheap.

Petebee · « **Reply #13 on:** January 05, 2012, 08:55:34 PM »

Okay got the replacement AFM and put it in. Initial impression while car was idling in the garage was okay...it seems to be idling decent. Hand blip of the throttle at the throttle body and the slight bog is not evident.

I took her out for a spin and thrashed her after she warmed up a bit. Rev'd to redline in 1st and 2nd gear without hiccups and no CELs. Stomping throttle on and off in 3rd and seemed to cope with things well.

Fingers crossed this was the problem. Now I have to replace the radiator, upper timing gaskets, oil filter housing gasket and tensioner crush washer to stop the leaks

No rest for the weary.

Petebee · « **Reply #14 on:** January 08, 2012, 09:07:52 PM »

Thanks Dave for all of your help. I think the new/used AFM solved my woes. I replaced the radiator on Friday and have been driving the car all weekend without any issues. Pulls nice and strong to redline just like a well tuned M42 should.

Note that it fires much quicker now...before I'd have to crank it for 5-6 seconds before it would start.

Don't talk to me about the Volvo. It took me all day yesterday to install the in-tank pump and it still doesn't run worth a crap (but I can hear the new pump whirring in there). I am going to pop in new fuel injector and radio suppression relays since I should have started there!